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Review

Narrative Review of Production Impacts of Pregnancy Shearing in Pasture-Based Systems

by
Rene A. Corner-Thomas
1,
Kailun Zhang
1,
Fernando J. Roca Fraga
1,
Karina Neimaur
2,
Ignacio De Barbieri
3 and
Paul R. Kenyon
1,*
1
School of Agriculture and Environment, Massey University, Private Bag 11222, Palmerston North 4410, New Zealand
2
Facultad de Veterinaria, Universidad de la República, Route 8, km 18, Montevideo 13000, Uruguay
3
Sistema Ganadero Extensivo, Instituto Nacional de Investigación Agropecuaria, Route 5, km 386, Tacuarembó 45000, Uruguay
*
Author to whom correspondence should be addressed.
Ruminants 2026, 6(3), 61; https://doi.org/10.3390/ruminants6030061
Submission received: 6 May 2026 / Revised: 9 July 2026 / Accepted: 15 July 2026 / Published: 20 July 2026
Versions Notes

Simple Summary

Pregnancy shearing of ewes has been utilised by farmers to increase lamb birth and weaning weight and potentially survival; however, results across studies have been inconsistent. This review identified that shearing ewes during mid-pregnancy is the period most likely to achieve a consistent increase in lamb birth weight; however, outside this window the response is not consistent. Factors that may play a role in the mid-pregnancy birth weight effect include shearing comb type, gestation length, ewe pregnancy nutrition and feed intake, metabolic changes such as glucose and insulin-like growth factor and placental changes, but no single clear mechanism could be identified. Currently data on the links between prenatal, postnatal and long-term outcomes are not available. Further studies, however, are required before the mechanisms that consistently cause the positive birth weight effect from mid-pregnancy shearing can be identified. This review also identified that in some studies, pregnancy shearing increased lamb weaning weight, survival, thermoregulatory capability and improved maternal behaviour and ewe milk production. However, given the inconsistency found, pregnancy shearing is not a management tool farmers should use to get the desired management outcomes with respect to these traits. To maximise the chance of a birth weight response, farmers should focus on twin-bearing ewes with adequate body conditions, shear with a comb that leaves a greater stubble depth, and ensure ewes are offered at least pregnancy maintenance feeding levels and are of a good body condition score.

Abstract

This review used a qualitive approach to help further understand the benefits of pregnancy shearing and its potential mechanisms. A recent meta-analysis showed that pregnancy shearing increased lamb birth weight when conducted between days 42 and 100 of gestation but not after day 100; however, there was no effect on lamb weaning weight. Factors identified as potential mechanisms for the lamb birth weight response include comb type, gestation length, ewe pregnancy nutrition and feed intake, changes in ewe hormones and metabolites and altered placental development. There was, however, no single consistent parameter identified for the birth weight effect and more research is required. Shearing can potentially increase lamb survival, thermoregulatory capability and improve behaviour and ewe milk production but, again, further research is also required to confirm these. In conclusion, to maximise the chance of a birth weight response, farmers should focus on twin-bearing ewes of adequate body condition, shear with a comb that leaves a greater stubble depth and ensure ewes are offered at least pregnancy maintenance feeding levels.

1. Introduction

Perinatal lamb losses are both a significant financial and welfare issue for outdoor pastoral and indoor lamb systems (see review by Bruce et al. [1]). Most lamb deaths occur within the first few days post-birth. Small lambs generally display higher mortality rates and are often associated with being multiple-born and dying of starvation exposure, especially under outdoor pastoral farming conditions. Small lightweight lambs have a greater surface-area-to-bodyweight ratio and in unfavourable environmental conditions display greater cooling than larger heavier lambs [2,3]. Therefore, techniques which can increase the birth weight of otherwise lightweight lambs and/or improve a newborn lamb’s thermoregulatory capacity are likely to result in reduced deaths due to starvation exposure. An additional impact of lamb deaths is the inefficiency of ewes that lose their lamb(s) as those ewes had utilised more feed during pregnancy and produced less wool than if they had not been pregnant [4,5]. Management strategies which reduce lamb losses will not only reduce farmers’ costs but increase their returns as more lambs will be available for sale, but will also increase the numbers of lambs available for selection as replacements, thus improving rates of genetic gain through an increase selection intensity.
Shearing ewes in pregnancy is as a management technique which can improve lamb survival through increased lamb birth weights [6]. In their 2003 narrative review, Kenyon et al. [6] suggested that the birth weight response to pregnancy shearing appeared to be most consistent when ewes were shorn during mid-pregnancy (days 60 to 100), when lambs would be otherwise destined to have had low birth weights, predominantly due to being multiple-born. These authors, however, did not attempt to qualify the effects and since then many additional studies have been published. In addition, newer studies have examined the impacts of pregnancy shearing on additional parameters such as ewe and lamb behaviour and milk production, which were not covered in the previous review. In this new narrative qualitative review more than 80 studies examining the effects of pregnancy shearing have been identified. These studies examined the associations between pregnancy shearing with a range of ewe and lamb parameters and changes in metabolic and placental processes. The review specifically focused on studies undertaken under pastoral conditions and aimed to outline the management conditions farmers could utilise to obtain consistent effects from pregnancy shearing and to identify where further research is still required.

2. Narrative Review

2.1. Lamb Birth Weight

Several studies have shown that shearing during pregnancy can increase lamb birth weight, but not all. Under indoor housed conditions, shearing during early gestation (days 1 to 60) [7,8]; mid- (D60–100) [9,10,11,12,13,14,15,16,17,18,19,20] and late gestation (D100—term) [15,16,17,21,22,23] have been reported to increase birth weight. However, others reported that shearing in early [24], mid- [25] or late gestation [26,27] failed to increase birth weights. Under pastoral outdoor conditions the impact of pregnancy shearing on lamb birth weight has also had contrasting impacts (see Table 1, Table 2 and Table 3), with shearing in early, mid- and late pregnancy not always resulting in a positive impact on lamb birth weight.
Shearing during mid-pregnancy has been suggested to have the greatest chance of enhancing placental development and therefore increasing lamb birth weight [28]. Kenyon et al. [6] in an earlier qualitative review also concluded that shearing in mid-pregnancy was likely to most consistently increase lamb birth weight. More recently using a meta-analysis approach, including indoor and outdoor studies, Zhang [29] reported that shearing between D42 and 100 had a positive impact on lamb birth weight, while shearing in late pregnancy had no effect. Therefore, based on this combined information farmers should target mid-pregnancy if they wish to increase lamb birth weight through pregnancy shearing. The meta-regression model also showed that a moderate-to-large positive effect on lamb birth weight occurred only on those studies where ewes were shorn between days 42 and 100 of pregnancy. After day 100 of pregnancy, shearing yielded a smaller non-significant effect. Both litter size and the presence of additional treatments in the studies resulted in non-significant effects on lamb birth weight.

2.2. Pre-Weaning Lamb Growth Rate and Weaning Weight

Similar to pre-weaning lamb growth rates, varying results have been reported for the impact of pregnancy shearing on lamb weaning weight. While some indoor studies have reported a positive effect on weaning weight [19,20,30,31], others have not [25] and one study reported a negative impact on weaning weight [20]. Similarly, under pastoral conditions some studies have reported a positive impact on weaning weight, while others have not (see Table 1, Table 2 and Table 3). A negative impact on weaning weight under pastoral conditions was observed in only one study (see Table 3).
Combined, these inconsistent individual research findings for both pre-weaning lamb growth and weaning weight support the meta-analysis undertaken by Zhang et al. [29], which found no overall effect of pregnancy shearing on lamb weaning weight, nor was there a significant effect of timing of shearing. This lack of a consistent positive effect supports the suggestion by Kenyon et al. [6] that it may be the nutrition of the ewe and/or her body condition that drives any potential impact on lamb growth and weaning weight, rather than solely a pregnancy shearing effect per se. Overall these studies indicate that shearing ewes in pregnancy is not a technique farmers should utilise to consistently increase weaning weight if that is their aim.
Interestingly there appears to be a lack of studies that have examined the impact of shearing of the ewe on the lifetime live weight or performance of the resulting born lambs. The concept of foetal programming is well established [32] and therefore potential lifetime effects could be possible. Further long-term research is needed to determine if this was indeed the case.
Table 1. Summary of the effect of pregnancy shearing in outdoor pasture-based systems on singleton lamb birth and weaning weights (kg) and survival to weaning (%), including day of pregnancy when ewes were shorn, location of the study, mean (+SEM) of the unshorn group and difference between the shorn and unshorn group if significantly different. Grey areas indicate no values were reported.
Table 1. Summary of the effect of pregnancy shearing in outdoor pasture-based systems on singleton lamb birth and weaning weights (kg) and survival to weaning (%), including day of pregnancy when ewes were shorn, location of the study, mean (+SEM) of the unshorn group and difference between the shorn and unshorn group if significantly different. Grey areas indicate no values were reported.
Day ShornLocation aBirth Weight (kg)Weaning Weight (kg)Survival Ref.
UnshornDiff bUnshornDiff bUnshornDiff c
D50UY5.0 ± 0.10.5 kg (10.0%)20.9 ± 0.52.3 (11.0%)85.3-[33]
D50UY 21.3 ± 0.7- [34]
D50NZ5.1 ± 0.20.7 (13.7%)26.1 ± 1.0- [35]
D705.1 ± 0.20.8 (15.7%)26.1 ± 1.0-
D1005.1 ± 0.20.8 (15.7%)26.1 ± 1.0-
D53UY4.4 ± 0.31.4 (31.8%)23.6 ± 1.44.5 (19.0%) [36]
D69NZ5.8 ± 0.2- [37]
D70NZ4.6 ± 0.20.8 (17.4%)34.2 ± 6.8- [38]
D70NZ4.9 ± 0.20.7 (14.3%)25.5 ± 0.7- [39]
D70NZ6.0 ± 0.07- 85.1-[40]
D70UY4.0 ± 0.11.5 (37.2%)27.2 ± 0.697.5 (27.4%) [41]
D1104.0 ± 0.11.3 (34.2%)27.2 ± 0.699.8 (36.0%)
D70UY4.5 ± 0.17- [42]
D1204.5 ± 0.17-
D70NZ6.2 ± 0.2-25.6 ± 0.9- [28]
D1006.2 ± 0.2-25.6 ± 0.9-
D1306.2 ± 0.2-25.6 ± 0.9-
D74BR4.8 ± 1.20.7 (14.9%)11.2 ± 3.1- [43]
D79NZ5.6 ± 0.1-24.2 ± 0.4- [44]
D79NZ4.8 ± 0.10.3 (6.7%)25.9 ± 0.5-71.1-[45]
D1194.8 ± 0.1-25.9 ± 0.5-71.1-
D85 δUY4.6 ± 0.10.5 (10.9%)15.2 ± 0.3- [46]
D85 δ4.6 ± 0.1-15.2 ± 0.3-
D94 δ4.5 ± 0.10.4 (8.9%)18.3 ± 0.2−1.1 (−6%)
D94 δ4.5 ± 0.10.3 (6.7%)18.3 ± 0.2-
D90NZ4.7 ± 0.11-15.8 ± 0.4- [47]
D100TR *3.2 ± 0.10.6 (18.7%)20.2 ± 1.024.4 (21.7%)8416[30]
D110UY4.3 ± 3.5- [48]
a BR = Brazil, NZ = New Zealand, TR = Turkey, GB = Great Britain, UY = Uruguay. b Difference in live weight between lambs born to ewes in the unshorn and shorn groups with the percentage difference given in parentheses. c Difference in percentage of lambs that survived. Studies with more than one row of data for a given shearing day included either more than one shearing comb type (δ). * Ewes maintained on pasture and housed at night.
Table 2. Summary of the effect of pregnancy shearing in outdoor pasture-based systems on twin lamb birth and weaning weights (kg) and survival to weaning (%), including day of pregnancy when ewes were shorn, location of the study, mean (±SEM) of the unshorn group and difference between the shorn and unshorn group if significantly different. Grey areas indicate no values were reported.
Table 2. Summary of the effect of pregnancy shearing in outdoor pasture-based systems on twin lamb birth and weaning weights (kg) and survival to weaning (%), including day of pregnancy when ewes were shorn, location of the study, mean (±SEM) of the unshorn group and difference between the shorn and unshorn group if significantly different. Grey areas indicate no values were reported.
Day ShornLocation aBirth Weight (kg)Weaning Weight (kg)Survival Ref.
UnshornDiff bUnshornDiff bUnshornDiff c
D50UY3.9 ± 0.10.3 (7.7%)17.3 ± 0.50.3 (3.5%)70.68.30[33]
D50UY 16.8 ± 0.7- [34]
D50NZ4.5 ± 0.2-20.8 ± 0.9- [35]
D704.5 ± 0.2-20.8 ± 0.9-
D1004.5 ± 0.2-20.8 ± 0.9-
D69NZ4.3 ± 0.11.1 (25.6%) [37]
D70NZ4.7 ± 0.050.5 (10.8%)27.31.0 (3.6%) [49]
D70NZ4.2 ± 0.12-27.3 ± 3.80- [38]
D70NZ4.2 ± 0.1-21.6 ± 0.4- [39]
D70NZ4.7 ± 0.10.4 (8.5%) 78.8-[40]
D70UY3.1 ± 0.10.8 (25.8%) [42]
D1203.1 ± 0.10.3 (9.7%)
D70NZ4.3 ± 0.10.7 (16.3%)18.3 ± 0.8- [28]
D1004.3 ± 0.10.4 (9.3%)18.3 ± 0.8-
D1304.3 ± 0.10.3 (7.0%)18.3 ± 0.8-
D76NZ4.8 ± 0.11.1 (22.9%)19.4 ± 0.6- [50]
D79NZ3.5 ± 0.20.4 (10.5%)20.1 ± 0.8-79.2-[45]
D80NZ4.8 ± 0.10.3 (6.3%)20.4 ± 0.5- [51]
D80NZ4.2 ± 0.10.3 (7.1%)18.8 ± 0.6- [52]
D85 δUY3.3 ± 0.1-12.5 ± 0.6- [46]
D85 δ3.3 ± 0.1-12.5 ± 0.6-
D94 δ3.5 ± 0.10.6 (17.1%)18.1 ± 0.8-
D94 δ3.5 ± 0.1-18.1 ± 0.8-
D90NZ3.6 ± 0.10.4 (10.7%)14.3 ± 0.4- [47]
D100TR *3.1 ± 0.1-16.7 ± 1.123.4 (20.4%) [30]
a NZ = New Zealand, TR = Turkey, UY = Uruguay. b Difference in live weight between lambs born to ewes in the unshorn and shorn groups with the percentage difference given in parentheses. c Difference in percentage of lambs that survived. Studies with more than one row of data for a given shearing day included either more than one shearing comb type (δ). * Ewes maintained on pasture and housed at night.
Table 3. Summary of the effect of pregnancy shearing in outdoor pasture-based systems on mixed lamb birth and weaning weights (kg) and survival to weaning (%), including day of pregnancy when ewes were shorn, location of the study, birth rank, mean (±SEM) of the unshorn group, difference between the shorn and unshorn group if significantly different and reference. Grey areas indicate no values were reported.
Table 3. Summary of the effect of pregnancy shearing in outdoor pasture-based systems on mixed lamb birth and weaning weights (kg) and survival to weaning (%), including day of pregnancy when ewes were shorn, location of the study, birth rank, mean (±SEM) of the unshorn group, difference between the shorn and unshorn group if significantly different and reference. Grey areas indicate no values were reported.
Day
Shorn		Location aBirth
Rank b		Birth Weight (kg)Weaning Weight (kg)Survival Ref.
UnshornDiff cUnshornDiff cUnshornDiff d
D5NZ1 + 2+ 34.4 ± 0.1-18.9 ± 1.5- [53]
D301 + 2+ 34.4 ± 0.1-18.9 ± 0.3-
D63 εIEMixed3.8 ± 0.150.7 (17.7%)31.8 ± 0.851.8 (5.7%) [31]
D63 εMixed4.1 ± 0.150.5 (11.2%)31.6 ± 0.852.2 (7.0%)
D63IQMixed8.2 ± 0.20.9 (10.4%) 80.0-[13]
D105Mixed8.2 ± 0.2- 80.0-
D70NZ2 + 34.8 ± 0.1-25.5 ± 0.83- [54]
D70 χNZ2 + 34.3 ± 0.040.4 (10.0%)25.6 ± 0.31.07 (4.2%)75.25.5[55]
D70 χ2 + 34.3 ± 0.040.1 (3.0%)22.5 ± 0.5-76.5-
D70NZ1 + 25.1 ± 0.10.3 (5.9%)21.9 ± 0.4- [56]
D70NZ33.9 ± 0.09- 53.2-[40]
D72 αNZ1 + 26.1 ± 0.1-30.1 ± 0.8- [57]
D72 α1 + 24.6 ± 0.10.6 (13%)23.4 ± 0.7-
D74NZ1 + 24.2 ± 0.10.3 (7.3%)18.9 ± 0.7- [58]
D84–108UY1 + 24.1 ± 0.040.4 (9.9%)13.4 ± 0.10.5 (3.8%)71.09%[59]
D79NZ1 + 2 24.2 ± 0.4- [44]
D90NZ1 + 25.0 ± 0.1-22.9 ± 3.3- [60]
D100 αES1 + 24.6 ± 0.2-12.7 ± 0.6- [61]
D100 α1 + 24.0 ± 0.2-12.3 ± 0.6-
D115 δNZ1 + 24.3 ± 0.10.6 (13.9%)20.4 ± 1.1- [62]
D115 δ1 + 24.3 ± 0.1-20.4 ± 1.1-
D114NZMixed4.3 ± 0.1-17.4 ± 0.5- [63]
D114Mixed4.3 ± 0.1-17.4 ± 0.5-
D118NZ1 + 24.5 ± 0.1-18.4 ± 0.4- [64]
D120ZAMixed3.9 ± 0.1-21.5 ± 0.4-65.66.2[65]
a, ES = Spain, IE = Ireland, IQ = Iraq, NZ = New Zealand, UY = Uruguay, ZA = South Africa. b 1 = singleton, 2 = twin, 3 = triplet, Multiple = twins or more, Mixed = birth rank of the lambs was not specified, 1 + 2 = values reported included singletons and twins. c Differences in live weight between lambs born to unshorn and shorn group ewes with the percentage difference given in parentheses. d Difference in percentage of lambs that survived. Studies with more than one row of data for a given shearing day included either more than one breed (α), experiment (χ), shearing comb type (δ) or nutritional treatment (ε).

2.3. Lamb Survival

Pregnancy shearing under housed conditions between D58 and D120 has been reported to improve singleton lamb survival [7,9,10,13,15,26]. Similarly, under pastoral outdoor conditions pregnancy shearing has been reported to increase lamb survival in some studies but not all. Kenyon et al. [55] reported higher survival in one of two multiple-born lamb cohorts born to ewes shorn at D70 and López-Mazz et al. [33] reported higher survival in twins but not singletons born to ewes shorn at D50. In a study that included only singleton-bearing ewes, De Barbieri et al. [46] reported higher lamb survival among ewes shorn at D108 compared with those left unshorn. In contrast, Smeaton et al. [66] and Kenyon et al. [45] reported no effect on singleton or twin lamb survival after shearing ewes at either D70 or between D79 and 119, respectively. Cam and Kuran [30] reported that under mixed management conditions of grazing during the day and housing at night, shearing singleton-bearing ewes at ~D100 improved lamb survival, while in a similar study Corner et al. [52] reported no effect of shearing at D80 on the survival of multiple-born lambs. Combined, these data clearly indicate that although a positive impact on lamb survival from pregnancy shearing can occur, it is not consistent and therefore, cannot be advised as a management practice to do so. However, currently there are no studies that suggest a negative impact on lamb survival.
When an increase in lamb survival resulting from mid-pregnancy occurs, the increase among lambs that would otherwise be born with sub-optimal birth weights reduces their risk of starvation or exposure [6,52]. Other factors suggested to contribute to the potential positive effect of pregnancy shearing on lamb survival include increased gestation length, lamb vigour, thermoregulatory capacity and fat reserves (see later sections), along with easier access to the udder. Pregnancy shearing has been suggested to help ewes be more aware of their lambs and removal of fleece from the belly facilitates newborn lambs in locating the teat [7,17,67], while under pastural conditions pregnancy shearing may encourage ewes to seek shelter during lambing [68,69,70].
Any increase in lamb survival may also potentially be due to an increase in the milk yield and quality of colostrum and milk, although the impact of pregnancy shearing differed across studies. To date only one study has examined the impact of shearing on colostrum [42], which reported there was no difference in colostrum yield but there was a tendency for ewes shorn at D70 to have an increased protein percentage in samples collected 1 h post-lambing, compared with unshorn ewes; however, no effect was observed when ewes were shorn at D120. In milk, the effect of shearing on milk yields has been split with increases reported in three studies [20,30,36], and no differences were reported by three others [61,71,72]. The effect of shearing on milk composition has shown somewhat consistent results for protein percentage but variable results for fat, lactose and total solids. Shearing at D110 was reported by Knight et al. [71] to increase milk protein percentage and total solids until weaning at 15 weeks and increase the percentage of fat until week 8 but it made little difference in the percentage of lactose. Sphor et al. [36] also reported a small increase in milk protein after shearing at D53. González-Luna et al. [61] reported that shearing (D100) increased the milk protein percentage of Manchega ewes but did not alter fat or lactose percentages, whereas Lacaune ewes showed an increase in total solids and fat but no effect on protein or lactose. Garcia-Rodriguez et al. [72], however, reported no difference in either milk fat or protein concentrations after shearing at D100.
The inconsistent effects of shearing on milk yield and composition somewhat align with the variability in the effects of pregnancy shearing on lamb survival and growth to weaning. To date, only Sphor et al. [36] have reported positive effects on milk yield and composition along with improved lamb weaning weights. They found that lambs born to ewes shorn at D53 were 4.5 kg heavier at 15 weeks of age than those born to unshorn ewes.

2.4. Newborn Lamb Behaviour

The progression of newborn lamb behaviours include standing, finding the udder, suckling and bleating assist with the development of the ewe–lamb bond and are linked with both lamb milk intake and survival [73,74,75,76]. Pregnancy shearing shows some evidence that it can result in changes in newborn lamb behaviour. In the first hour of life Banchero et al. [42] reported that pregnancy shearing at either D70 or D120 was associated with an increase in the proportion of lambs that successfully stood compared with unshorn ewes, with a greater response seen among twin than singleton lambs. Lambs born to ewes shorn in mid-pregnancy (D50 and D79, respectively) attempted to suckle earlier and were quicker to successfully suckle than those born to unshorn ewes [33,44]. Similarly, within one hour of birth Banchero et al. [42] reported that a greater proportion of lambs born to ewes shorn at D70 or D120 successfully sucked compared with lambs born to unshorn ewes.
Labeur et al. [77] conducted an arena test to observe the behaviour of lambs at 4 h of age and after a cold challenge at 5.5 h of age. They reported that lambs born to ewes shorn at D90, but not D130, took longer to bleat at 4 and 5.5 h of age than lambs born to unshorn ewes. The latency for the lamb to return to their dam, however, was not affected by shearing at D90 but lambs born to ewes shorn at D130 took less time to reunite than lambs born to shorn ewes. Shearing at D90 and D130 had no effect on the latency for the lamb to stand after being placed in lateral recumbency at the start of the test. Combined, these results suggest that mid-to-late pregnancy shearing has the potential to positively impact lamb postnatal behaviours which could improve lamb survival. To date, however, a direct link between lamb behaviour and survival from pregnancy shearing has not been identified as the majority of studies have utilised relatively low numbers of lambs.

2.5. Newborn Lamb Thermoregulation

Infrared thermal imaging after a cold challenge (4 °C for 1 h) and showed that lambs born to ewes shorn in late pregnancy (D125) maintained body surface temperatures better than lambs born to unshorn ewes, although their rectal temperatures were lower [78]. They suggested that this was due to lambs born to shorn ewes relying on enhanced brown adipose tissue (BAT) thermogenesis to maintain homeothermy, whereas those born to unshorn ewes had to constrict blood vessels in their skin. This hypothesis is somewhat supported by the findings which indicate pregnancy shearing of housed ewes between D98 and D133 can increase in heat production of newborn lambs [27,79,80].
Newborn lambs can be exposed to cold, wet and/or windy conditions and therefore their thermoregulatory capability directly influences survival particularly in extensive outdoor lambing systems [81]. Lambs utilise BAT to rapidly generate heat and help maintain their core body temperature [82]. Stott and Slee [27] and Symonds et al. [83] reported that housed ewes shorn at D133 or D119 and exposed to temperatures between 6 and 12 °C gave birth to lambs with enhanced foetal BAT deposition compared with lambs born to unshorn ewes. Interestingly, in two further studies the positive effect of pregnancy shearing at D120 on lamb BAT was only observed when housed ewes were fed below maintenance [84,85]. Late pregnancy shearing (D120) has also been reported to increase BAT mitochondrial protein level and thermogenic synthesis and therefore can increase lamb heat production efficiency and BAT activity [83].
In contrast, few studies in extensive pasture-based conditions have reported the effects of pregnancy shearing on newborn lamb thermoregulation capability. The majority of studies have reported that shearing at D70 had no effect on lamb summit metabolic rate, rectal temperature and/or rate of change in heat production [39,56,86]. Revell et al. [38], however, reported that twin, but not singleton, lambs of shorn ewes (D70) had a higher summit metabolic rate (SMR) than unshorn ewes. The lack of an effect of pregnancy shearing in these outdoor systems, compared to their indoor counterparts, may be due to the earlier stage of pregnancy as no studies have examined late pregnancy shearing.
Overall, these results indicate that pregnancy shearing has the potential to increase lamb survival. It appears that if this is to occur, it is driven by an increase in birth weight and therefore, as multiple-born lambs are most likely to be born below optimum birthweight from a survival perspective, farmers should target the shearing of these ewes in mid-pregnancy. Few studies that have examined the impact of pregnancy shearing on ewe milk production, milk composition or lamb behaviour and thermoregulation. While none of these factors appear to be a driver for increased lamb survival, the studies are few in number and in general suffer from relatively low lamb numbers, making it difficult to statistically test for a survival effect. More studies are required examining these potential drivers and these need to include large number of lambs so that lamb survival effect can be tested before firm conclusions can be drawn.

2.6. Lamb Fibre and Wool Characteristics

Pregnancy shearing effects on lamb wool follicle and wool traits are inconsistent. Revell et al. [38] found that singleton and twin foetuses (between days 140 and 141 of gestation) from Romney-type ewes shorn at D70 had increased secondary-to-primary-follicle ratio and a higher density of secondary follicles than foetuses of unshorn ewes. Similarly, shearing Merino ewes at D141, but not D106, Van Reenen et al. [87] reported an increase in lamb total and secondary follicle density and the number of follicles at ~7 months of age compared to those born to unshorn ewes. In contrast, two studies by Kenyon et al. [45,54] reported that among Romney-type ewes shorn at D70 there was no effect on the ratio of the secondary to primary follicles nor on the secondary follicles of the progeny post-weaning. Sherlock et al. [88], however, reported that mid-pregnancy shearing (D70) resulted in a decrease in the number of secondary follicles in offspring at 6 months of age. There was, however, no effect on the ratio of secondary to primary follicles. The density and number of primary follicles in all studies in which they were measured were unaffected by pregnancy shearing [38,45,54,87,88].
Pregnancy shearing has been reported to inconsistently influence lamb fleece characteristics. Revell et al. [38] reported that shearing Romney ewes at D70 resulted in greater greasy fleece weights among singletons but not twin lambs at three months of age, while in Coopworth-type ewes shorn at D70 [54] and Merino ewes shorn at D106 or D141 [87] there was no effect on greasy fleece weight of the progeny. One study to date has reported an effect of shearing on mean fibre diameter whereby 6-month-old lambs born to Romney ewes shorn at D70 had larger fibre diameters [88]. All other studies reported no influence of either shearing at D70 [45,54] or D106 or D141 [87] on fibre diameter.
Pregnancy shearing has not been reported to influence lamb fibre curvature [45,88], medullation percentage [45,54], yield [38,45,54,87], staple length [45,54,87,88], staple strength [87], loose wool bulk [54,88] or wool brightness [45]. No effect of pregnancy shearing on the whiteness of their progeny’s fleece has been reported in the majority of studies [54,87,88]. Kenyon et al. [45], however, reported that at three months of age, lambs born to ewes shorn in late pregnancy (D119), but not mid-pregnancy (D79), had whiter wool than lambs born to unshorn ewes.
Combined, these studies indicate that shearing ewe in pregnancy is not a management method that farmers could use to consistently alter the fleece characteristics of their offspring.

2.7. Lamb Parasite Resistance

The impact of pregnancy shearing on lamb parasite challenge resistance has been examined in a single study. López-Mazz et al. [33] found that lambs at ~two months of age born to ewes shorn at D50 had lower faecal egg counts, than those born to postpartum-shorn ewes. Furthermore, they also showed a reduced FAMACHA index score, an indicator of anaemia severity, and thus parasite infection. While these results are promising, further work is needed before any conclusions can be drawn.

3. Potential Drivers of Pregnancy Shearing Birth Weight Effect

3.1. Placental Changes

The placenta provides the foetus with nutrition from its dam, and therefore plays an important role in foetal development and growth [89]. Placental size and weight influence foetal growth particularly in late pregnancy [84,90]. Cantou et al. [41] showed that pregnancy shearing at both D70 and D110 increased placental weight; however, Banchero et al. [42] reported increased placental weights after pregnancy shearing at D70, but not D110. In contrast, Revell et al. [38] found no effect of shearing at D70 on placental weight.
Lamb birth weight is positively correlated with cotyledon number, size and weight [91,92]. Pregnancy shearing at D70 and D110 was reported by Cantou et al. [41] to increase the weight of 2–3 cm cotyledons, and shearing at D70, but not D110, increased the total number of cotyledons. In contrast, De Barbieri et al. [59] reported an increase in cotyledon number but not weight after pregnancy shearing between D80 and D108. While pregnancy shearing at D70 was reported by Revell et al. [38] to increase the proportion of occupied caruncles, it did not alter cotyledon weight. The ratio of lamb birth weight to placental weight, or placental efficiency, can be used as a proxy measure of the placenta’s ability to transfer nutrients to the foetus. Placental efficiency has been reported [93,94] to increase after pregnancy shearing at D110 [41]. Combined, these studies suggest that changes in placental size and function could be involved in the increase in lamb birth resulting from pregnancy shearing, but more work is required to identify if there is a direct relationship.

3.2. Ewe Metabolic Changes

Pregnancy shearing has been reported to cause changes in ewe metabolism such as increased glucose metabolism, use of non-esterified fatty acids and formation of ketone bodies such as β-hydroxybutyrate (see review by Freitas-de-Melo et al. [95] and following sections). Within 24 h of shearing between D50 and D120, ewes can show increased circulating glucose concentrations which can persist for up to 10 weeks [14,18,35,96], but not always [97]. Mid-pregnancy shearing was hypothesised by Revell et al. [37] to increase placental glucose transport capacity, improving foetal nutrient supply. It is established that glucose uptake of the foetus increases with greater maternal glucose concentrations [98] which can support increased foetal growth.
In the later stages of gestation, ewes are often in a lipolytic state as tissues become reliant on non-esterified fatty acids (NEFA) as a primary source of energy, sparing glucose for the foetus, even in well-fed ewes [99]. Dabiri et al. [63] suggested that the observed increase in NEFA concentrations post-shearing was to support heat production in the recently shorn ewe. Pregnancy shearing in some studies has been reported to result in an relatively short-term increase in ewe NEFA concentrations post-shearing between D91 and D120 [14,96,100]. Others, however, have reported no differences in NEFA after shearing between D92 and D107 [14,18,101,102].
During fat mobilisation, β-hydroxybutyrate (BHB) is a ketone body that is formed by the liver [103] and blood concentrations are used as an indicator of excessive fat breakdown and ewe energy status [104]. No effect of shearing on BHB concentrations has been reported in the vast majority of studies [14,17,61,83,105]. Some studies, however, have reported that ewes exhibited persistently lower BHB concentrations post-shearing compared to unshorn ewes, when shearing occurred between D91 and D120 [15,96,102]. In a study by Clarke et al. [84] they reported that although both shorn and unshorn ewes showed an increase in plasma BHB concentrations around day 140 of gestation, the rise was greater in shorn ewes. They also reported, however, that there was no difference in BHB levels of the two groups over the course of the entire pregnancy.
Mid-pregnancy-shorn (~D92) ewes were reported by Symonds et al. [14] to have lower insulin concentrations post-shearing than their unshorn counterparts. They hypothesised that a metabolic mechanism triggered by shearing may reduce maternal glucose utilisation and increase foetal glucose supply. Ewes shorn at D69 were reported by Revell et al. [37] to have lower basal insulin levels and a weaker insulin secretion response in late pregnancy compared to unshorn ewes, especially those carrying twins. They suggested that rather than relying on insulin this may have been due to the foetus increasing its glucose uptake capacity through the placenta. In contrast, other studies have reported no differences in insulin concentrations between ewes shorn between D50 and D100 and unshorn ewes [35,61].
Insulin-like growth factor (IGF-I) and IGF binding protein (IGFBP) are key regulators of nutrient partitioning between the ewe and foetus [106]. IGF-I is expressed in many foetal tissues and is required for lamb growth and development [107]. It appears only two studies have reported the effect of pregnancy shearing on IGF-I and IGFBP. Pregnancy shearing at D69 was reported by Revell et al. [37] to result in a 25% reduction in maternal plasma IGF-I concentrations and an increase in maternal IGFBP-1 of two to three fold. Jenkinson et al. [47], however, reported that pregnancy shearing at D90 resulted in an increase in maternal plasma IGF-I at D108 and D136 but no corresponding effect on IGFBP or lamb IGF-I at 100 days of age.
Thyroid hormones play an important role in ewe energy metabolism [108]. They promote the oxidation of glucose and oxygen and, by regulating multiple metabolic links and enzyme activities, improve metabolic efficiency [79,109]. These changes can influence foetal growth and lipid metabolism [108,110] and promote the maturation of tissues, organs and brown adipose tissue (BAT) in the final stages of foetus development [111]. Therefore, the growth and development of the foetus would be altered if thyroid hormone secretion of the ewe was consistently altered by shearing during pregnancy. Ewes shorn between D50 and D100 have been reported to have increased concentrations of plasma tri-iodothyronine (T3) and/or thyroxine (T4) [35,38,96,101,105]. These findings suggest that sustained upregulation of thyroid hormones after pregnancy shearing could be the driver for the birth weight response, although this effect has not always been found [54].
Combined, the above results indicate inconsistent changes in ewe metabolism post-pregnancy shearing. However, it is possible that when changes do occur they contribute to increase foetal growth and lamb birth weight. Further research is required to confirm any link between changes in ewe metabolism post-pregnancy shearing and the birth weight effect.

3.3. Ewe Feed Intake

Pregnancy shearing has reported to modify ewe feed intake. Under housed conditions inconsistent effects of pregnancy shearing on ewe feed intake have been reported. Mousa-Balabel & Salama [112] reported that for three hours after shearing between D70 and 100 or at D130 housed ewes showed an increase in eating frequency and decrease in drinking. Increased feed intakes have also been reported for ewes shorn between D63 to D112 [10,13,15,16,22,26,31,113]; however, others have reported no effect on intake when shearing occurred between D90 and D120 [8,14,17].
It has been suggested that in extensively managed sheep, the magnitude of the increase ewe feed requirements and intake are dependent on ambient temperature, wind velocity, and other environmental factors [67,68,100]. The effect of pregnancy shearing on ewe intake under outdoor conditions has also been inconsistent with most studies reporting no effect of shearing between D90 and D115 [38,60,62,63]. Two studies, however, reported an increase in ewe feed intake. Dabiri et al. [64] reported an increase in feed intake for 20 days after shearing at D118 compared with unshorn ewes, while Kenyon et al. [56] reported an intermittent increase after shearing at D70. Given that many studies have shown an increase in lamb birth weight without an increase in ewe intake [38,39,62], it can be concluded that an increase in ewe intake is not the mechanism for the increase in lamb birth weight.

3.4. Feeding Allowance/Level of Pregnant Ewes

The level of pregnancy nutrition has a direct effect on lamb birth weight [114,115]; however, the relationship between ewe feeding level in both housed and pasture-based ewes prior to and post-shearing on the birth weight response to pregnancy shearing has been inconsistent. Pregnancy shearing between days 70 and 120 under housed conditions has resulted in increased lamb birth weight when ewes were provided either low [19,83,84], maintenance [7,11,14,31,52], high [8] or ad libitum feeding levels [8,9,10,13,15,17,19,22]. Conversely, pregnancy shearing had no effect on lamb birth weight under housed conditions when ewes were offered low [116], maintenance [25,26] or ad libitum feeding levels [23,24].
Under mixed housing and pasture studies, the effect of nutrition on lamb birth weight has also been inconsistent. Cam and Kuran [30] reported that maintenance feeding levels only increased the birth weight of singleton but not twin lambs after pregnancy shearing at D100, whereas both Revell et al. [37] and Banchero et al. [42] reported that ad libitum feeding conditions resulted in heavier twin lambs, but not singletons, after pregnancy shearing at D69 and D120. Further, González-Luna et al. [61] reported that pregnancy shearing had no effect on lamb birth weight when ewes were offered ad libitum feeding levels. Under pastural conditions, the lamb birth weight response to pregnancy shearing based on feeding level has also been somewhat inconsistent. After shearing between D70 and D130 singleton- and twin-bearing ewes fed to gain 75 to 100 g/day variously showed an increase in birth weight among only singleton lambs [35], or only twins [28], or both singletons and twins [56]. Combined, these results make it difficult to draw clear conclusions in relation to the chance of obtaining a birth weight effect from pregnancy shearing. In their review, Kenyon et al. [6] suggested that when nutritional demand of both the ewe and her foetus(es) is greater than feed supply it would be unlikely that a birth weight response would occur following pregnancy shearing. Somewhat in support of this, it is well established that underfeeding ewes during pregnancy limits lamb birth weight as she does not have the capability to help enhance foetal growth [117].

3.5. Gestation Length

Gestation length in sheep has been reported to have a positive relationship with lamb birth weight [118,119] and is related to ewe nutritional status [118,120]. In late gestation foetal growth is rapid [121], so any increase in gestation length could help explain increased lamb birth weights from pregnancy shearing. Several studies have reported increases in gestation length of between 0.5 and 2 days under both indoor and outdoor conditions when ewes were shorn at D30 [30,54], D50 [33], D70 [38,39,42], or ~D80 [15,44,52]. In studies that reported the gestation lengths of singleton- and twin-bearing ewes separately, López-Mazz et al. [33] reported an increase among both singleton- and twin-bearing ewes, while Revell et al. [38] and Cam and Kuran [30] reported increases for only singleton-bearing ewes. However, the relationship between gestation length and the effect of pregnancy shearing on lamb birth weight is unclear. Increases in both gestation length and lamb birth weight following pregnancy shearing have been reported in five studies [15,30,33,38,39,52]. However, one study reported an increase in birth weight without a change in gestation length [44], while two reported an increase in gestation length without an increase in birth weight [26,42].
Given that a birth weight response can occur without a change in gestation length, it is unlikely that an increased gestation length is the sole mechanism for an increase in lamb birth weight, but in some situations, it could be a contributing factor. Further, Kenyon et al. [6] suggested that the increase in gestation length observed in some studies was likely too small to fully explain the increases in lamb birth weight.

3.6. Shearing Stress

Shearing is one of the greatest stresses a sheep experiences [122] and can induce immediate changes in ewe behaviour [112,123]. Pregnancy shearing has been associated with a rise in cortisol in some studies [44,124] but not all [14,105]. Blood cortisol concentrations are used as an indicator of acute stress and increase rapidly when sheep are exposed to stressors [125]. Increased cortisol concentrations may increase ewe metabolism by stimulating gluconeogenesis and storage of glycogen in the liver, which can increase glucose concentrations [126], thus indirectly enhancing foetal growth.
The physiological response to stress has been hypothesised to be the mechanism for the lamb birth weight response to pregnancy shearing [44,127]. Sham-shearing has been used as a method to potentially separate the stress effects of fleece removal (i.e., shearing) and involves all the events of shearing without actual fleece removal [50,52]. It has been suggested that sham-shearing does cause both psychological and physiological stress responses [50,128,129,130]. Similarly, crutching prior to lambing has been used as a stressor, and includes the removal wool from around the udder and britch while leaving the rest of the fleece intact [131]. It has been hypothesised that the stress response to crutching lies somewhere between sham-shearing and shearing [52,132].
In response to full sham-shearing Corner et al. [52] reported that peak plasma cortisol concentrations of ewes at D80 were higher than unshorn ewes, but lower than crutched or shorn ewes. In addition, they reported that crutched ewes showed a similar pattern of cortisol concentrations over time compared to ewes shorn at D80. Neither sham-shearing nor crutching at D50 [133], D70 [38], D80 [52], or D107 [18], however, have been reported to influence lamb birth weight. Similarly, repeated sham-shearing between D74 and D105 had no effect on lamb birth weight [50]. Combined, these results indicate that the shearing event itself is not the driver for increased lamb birth weight post-shearing.
The above factors show some potential to drive the increase in birth weight; however, no one factor appears to be a clear driver. This information, however, may allow for the development of management techniques that farmers can use without the risk of shearing ewes under pastoral condition in winter. Most studies have considered a small number of physiological mechanisms; therefore, future studies should focus on measuring a range of metabolite and hormone changes following shearing in mid-pregnancy to link prenatal, postnatal and long-term outcomes.

3.7. Type of Shearing Comb

Pregnancy shearing in outdoor temperate pastoral systems during winter can impair the ability of the sheep to maintain homeothermy, leading to hypothermia and even death [134]. The use of a comb that leaves a greater wool stubble length can be used by farmers to reduce the risk of winter shearing. For example, a cover, R13 or winter comb which leaves a stubble depth of approximately 9 mm, 11 mm and 7.5 mm compared to a traditional shearing comb which leaves 4 mm [46,59,63] can be used. Dabiri et al. [63] suggested that ewes shorn with a cover comb can withstand 4 to 5 °C lower ambient temperatures before needing to evoke a thermoregulatory heat-production response, due to the extra stubble depth, compared to a ewe shorn with a standard comb.
Cold exposure can potentially increase gestation length [135] and lamb birth weight [136]; therefore, it is possible that a shearing comb that leaves a greater stubble depth could impede the birth weight response from shearing. If, however, a birth weight response can be achieved when using a comb that leaves a greater stubble depth, it can provide a greater level of safety for ewes in outdoor spring lambing systems (i.e., winter-shorn ewes). Greater lamb birth weights have been reported in multiple studies where ewes were shorn with a comb that left a greater residual fleece depth (i.e., cover, winter or R13 comb) compared with unshorn ewes [33,50,52,55,59,136]. In studies comparing the effect of shearing with different comb types the majority of studies have reported an increase in lamb birth weight after shearing between D50 and D115 with either a cover or R13 comb and a standard comb [35,46,62]. Combined, these results indicate that the birth weight response is possible when either a cover, R13 or winter comb is utilised and therefore farmers should use these options when pregnancy winter shearing under outdoor conditions.

4. Maximising the Lamb Birth Weight Response to Pregnancy Shearing—A Focus on Outdoor Pastoral Winter Shearing Systems

Under pastoral grazing spring lambing systems, pregnancy shearing coincides with winter and therefore places ewes at risk of cold stress, hypothermia and death [137]. This review indicates that ewes can be shorn with either the cover, R13 or the winter combs and an increase on lamb birth weight can occur, while the ewes are afforded greater insulation. Therefore, if winter shearing, farmers should utilise one of these comb types rather than the standard comb and monitor weather conditions. Comb type is likely less of an issue in housed conditions as ewes are protected from environmental conditions.
The timing of pregnancy shearing is an important consideration based on the results of the meta-analysis in this review. The optimal time to shear is mid-pregnancy between D42 and D100 in order to generate the birth weight response. To ensure shearing is conducted during this optimal window farmers should consider using tools like mating harnesses or pregnancy scanning to identify the appropriate stage of pregnancy.
It was concluded by Kenyon et al. [56] that the birth weight response is greatest under conditions in which the unshorn dam is destined to give birth to lambs of low birth weight. Furthermore, based on a follow-up study Kenyon et al. [39] suggested there were actually two criteria required to achieve the birth weight response: firstly, the ewe must be likely to give birth to otherwise low birth weight lambs, and secondly, have adequate body reserves and/or feeding during pregnancy in order to respond. Using these principles and the results of this review it is possible to devise a management plan to maximise the chance of obtaining the birth weight effect from pregnancy shearing, while minimising the number of ewes shorn, reducing both costs and the risk to the ewe if she is shorn under poor outdoor weather conditions. To date no studies have reported an increase in birth weight in triplet lambs from pregnancy shearing. Furthermore, increasing the birth weight of singleton lambs has the potential to push their birth weights into the lower survival rate range, driven by a greater risk of dystocia [138]. As twin lambs are lighter than singletons at birth [138] they have a greater potential to display increased foetal growth and heavier birth weight from pregnancy shearing, meeting the first criteria proposed by Kenyon et al. [39]. Therefore, the ewes that should be targeted for pregnancy shearing are twin-bearing ewes. It is well established that to optimise ewe productive and reproductive performance, ewes should have a minimum body condition score (BCS) of 3.0 [139,140]. Ewes with a minimum BCS of 3.0, should have sufficient body reserves available to partition energy towards increased foetal growth and lamb birth weight after pregnancy shearing. Ewes below this minimum, especially those well below this minimum, are less likely to be able to support additional foetal growth. Furthermore, sub-pregnancy maintenance nutrition is known to reduce foetal growth and lamb birth weight [141]. Therefore, based on the second criteria of Kenyon et al. [39] to maximise the chance of increased foetal growth and lamb birth weight from pregnancy shearing, only ewes with a BCS of at least 3.0 that can be offered at least pregnancy maintenance feeding levels should be pregnancy shorn.

5. Conclusions

The review is the first to use meta-analysis to show that pregnancy shearing increases birth weight but has no effect on weaning weight. An important factor in the analysis was the timing of shearing, with shearing being most effective when conducted between 42 and 100 days of pregnancy. Although there is evidence in the literature of increased lamb survival from pregnancy shearing, further studies are still needed to confirm this. Furthermore, the qualitative review shows that pregnancy shearing has other potential advantages including, but not limited to, improved ewe–lamb bonding and improved lamb body reserves at birth. However, more research is still required to confirm these. This review indicates there is still a lack of consistent results to identify the mechanism(s) for the heavier birth weights from pregnancy shearing. Changes in the placenta, ewe metabolism, feed intake and/or gestation length can be associated with the birth weight response but this is not always the case. Overall, the review indicates that to maximise the chance of a birth weight response from pregnancy shearing ewes, farmers should: focus on twin-bearing ewes of adequate body condition, shear with one of the combs which leaves greater stubble depth, and ensure ewes are offered at least pregnancy maintenance levels of feeding post-shearing.

Author Contributions

Conceptualization, P.R.K., F.J.R.F. and R.A.C.-T.; methodology, K.Z., P.R.K., F.J.R.F. and R.A.C.-T.; software, K.Z. and F.J.R.F.; formal analysis, K.Z. and F.J.R.F.; data curation, K.Z.; writing—original draft preparation, R.A.C.-T., K.Z., F.J.R.F., K.N., I.D.B. and P.R.K.; writing—review and editing, R.A.C.-T., K.Z., F.J.R.F., K.N., I.D.B. and P.R.K.; supervision, R.A.C.-T. and P.R.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
DDay of gestation
DICDeviance Information Criterion
VCVariance component

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MDPI and ACS Style

Corner-Thomas, R.A.; Zhang, K.; Roca Fraga, F.J.; Neimaur, K.; De Barbieri, I.; Kenyon, P.R. Narrative Review of Production Impacts of Pregnancy Shearing in Pasture-Based Systems. Ruminants 2026, 6, 61. https://doi.org/10.3390/ruminants6030061

AMA Style

Corner-Thomas RA, Zhang K, Roca Fraga FJ, Neimaur K, De Barbieri I, Kenyon PR. Narrative Review of Production Impacts of Pregnancy Shearing in Pasture-Based Systems. Ruminants. 2026; 6(3):61. https://doi.org/10.3390/ruminants6030061

Chicago/Turabian Style

Corner-Thomas, Rene A., Kailun Zhang, Fernando J. Roca Fraga, Karina Neimaur, Ignacio De Barbieri, and Paul R. Kenyon. 2026. "Narrative Review of Production Impacts of Pregnancy Shearing in Pasture-Based Systems" Ruminants 6, no. 3: 61. https://doi.org/10.3390/ruminants6030061

APA Style

Corner-Thomas, R. A., Zhang, K., Roca Fraga, F. J., Neimaur, K., De Barbieri, I., & Kenyon, P. R. (2026). Narrative Review of Production Impacts of Pregnancy Shearing in Pasture-Based Systems. Ruminants, 6(3), 61. https://doi.org/10.3390/ruminants6030061

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