On a global scale, the production of small ruminants is carried out in extensive grazing systems, mainly in arid or semi-arid lands where the contribution of grasslands generally does not cover the nutritional demands of the animals [1
]. Based on data from the Food and Agriculture Organization (FAO) [2
] and Iñiguez [3
], it is estimated that more than 30% of the world’s sheep stock is bred in dry regions, where crops or other livestock production is not possible. Arid and semi-arid regions are characterized by low annual rainfall (<400 mm) and poor water-bearing capacity of the prairies, which lead to low primary productivity [4
]. This feed scarcity, mainly during summer and winter, is a major constraint for sheep reared in these regions [5
The Magellan Patagonia region of Chile constitutes a good example of sheep farming on semi-arid extensive grazing systems. In Chile, around 66% of the national sheep stock are raised in arid and semi-arid regions [6
], with more than 50% found in the Magellan cold steppe. The Magellan Steppe has low annual precipitation (200–400 mm) and low average temperatures (around 5 °C), high evaporation, and strong winds. All these factors lead to poor water supply in the prairies and therefore limited pasture and nutrient availability [8
]. This reduced nutrient availability is especially concerning during pregnancy, resulting in a null body weight increase and around a 22% decrease in body condition score in twin-bearing ewes [9
The increase of twin-bearing ewes in the herd is assumed to be a good strategy to improve the productivity of sheep systems, since the additional newborn has a lower energy cost than the maintenance energy of an additional sheep. However, undernutrition of twin-bearing sheep may cause intrauterine growth restriction (IUGR), and therefore low birth weight (LBW) neonates, which suffer from increased morbidity and mortality [9
]. In this case, under adverse climatologic and/or nutritional conditions like in the Magellan Patagonia, twin newborn mortality could reach up to 40% [10
], negatively impacting profitability and animal welfare.
We recently demonstrated that IUGR in twin sheep fetuses is associated with hypoxia and oxidative stress [9
]. Maternal oral supplementation with vitamins C and E during the pregnancy period (days 30 to 140 of gestation) increases these vitamins in the cord blood of near-to-term fetuses, diminishing the oxidative stress and increasing fetal weight [11
]. In the present study, we aimed to evaluate the effects of maternal oral herbal vitamin C and E supplementation on pregnancy outcomes, postnatal viability, and development of lambs, from grazing twin-bearing ewes kept under natural underfed conditions or supplemented with concentrate.
Pregnancy is associated with a significant increase in maternal BW caused by increases in fat deposition during early pregnancy, employed afterwards to support fetal development, and by the increase of fetal weight during late pregnancy [15
]. This pattern is related to an increase in BCS due to fat accumulation during early pregnancy and a later decrease during late pregnancy. In the present experiment, such patterns were clearly observed in sheep supplemented with concentrate but not in non-supplemented ewes, in which BW showed non-significant changes and BCS was always decreasing throughout pregnancy. This finding supports evidence that twin-bearing ewes kept in a natural Magellan Patagonian prairie are normally raised in a state of undernutrition [9
Supplementation with concentrate was adequate to keep maternal BCS above 2.0, a level still considered adequate for optimum lamb birth weight [16
]. To this, it is important to highlight that the increase in BW observed in newborn lambs from mothers with nutritional supplementation is equivalent to the decrease in newborn lamb BW reported when the mothers consume a diet that only covers 70% of the requirements [17
]. This coincides with the level of nutritional restriction suffered by pregnant sheep maintained under extensive grazing conditions in Magellan Patagonia, observed in the present study [18
]. Accordingly, lamb birth weight from ewes supplemented only with concentrate increased around 17% when compared to lambs from non-supplemented mothers. This difference is consistent with what was previously reported as the final effect of maternal nutritional supplementation on fetal growth in underfed twin bearing ewes [9
The results of the current study also confirmed that in underfed twin-bearing ewes kept on a natural prairie during pregnancy, the observed fetal growth restriction is associated with oxidative stress. We have previously shown that maternal undernutrition and twinning led to decreased oxygen supply and increased oxidative stress at the feto-placental unit in near-term pregnancies, which was associated with decreased intrauterine growth [9
]. In this context, it has been demonstrated that maternal administration of antioxidant vitamins C and E results in an adequate placental transfer of both vitamins and improves fetal antioxidant status and growth in twin pregnancies [11
]. The data from the present study are in agreement with the previous one, since supplementation with antioxidant herbal vitamins C and E improved birth weight and antioxidant capacity (in around 15% for both) of the lambs. There are, to the best of our knowledge, no other previous works on supplementation with vitamins C and E during gestation in ewes. There are, conversely, previous studies in sheep with vitamin E supplementation alone or combined with selenium during the last third of gestation. However, there are no conclusive results from these studies, since some show a positive effect on the lamb’s birth weight [19
], while others failed to find any effect [20
]. Such differences may be due to use of different doses of vitamin E, routes of administration, and duration of treatments, in addition to eventual differences in sheep pregnancy rank, breed, or other unspecified.
The main finding of the present study is that lambs born to ewes suffering significant losses of BCS during pregnancy, but supplemented with antioxidant vitamins, showed a birth weight similar to lambs from ewes with adequate BCS. Such data support results from an earlier study [9
], indicating that the effect of carrying twins, plus its concomitant oxidative stress at the fetal-placental level, is even more limiting for intrauterine development than that of maternal undernutrition in pregnancies developed under the same disadvantageous conditions of Magellan Patagonia. We could infer, from these results, that the antioxidant vitamin supplementation is effective for counteracting placental dysfunctions affecting the nutrition and oxygenation of twin fetuses as a result of the fetal-placental oxidative stress.
These hypotheses are supported by previous data. Firstly, it has been found that the administration of antioxidants directly to sheep fetuses increased umbilical flow, which would favor fetal growth [22
]. Supplementation with vitamin E to pregnant ewes has also been reported to increase angiogenesis, and therefore, would favor placental function and fetal development [23
]. Such positive effects of antioxidant supplementation on placental efficiency and newborn body weight was reported in pregnant undernourished rats [24
]. Similarly, in single ovine pregnancies developed under oxidative stress in a chronically hypoxic environment at high plateaus, supplementation with antioxidant vitamins increased placental efficiency between 10% and 45%, depending on the animal’s altitudinal origin [25
On the other hand, it is widely accepted that postnatal growth is highly dependent on, and positively correlated with, birth weight [26
]. However, we cannot leave aside some influence of compensatory growth; in this way, a former study in sheep showed that, under good nutritional conditions during the postnatal period, LBW lambs equaled the BW of normal birth weight lambs around 50 days of age [28
]. In the present study, there were no differences in BW at 60 days of life among lambs from sheep with and without nutritional or vitamin supplementation.
Notwithstanding, lambs from mothers supplemented with vitamins were heavier (about 5%) at 120 days old than lambs from sheep with no treatment or even with concentrate supplementation. This finding is remarkable from the biological point of view, although this difference should be taken with caution because it was only at the limit of being statistically significant (p
= 0.056). Previous studies on the effects of maternal supplementation with vitamin E in the last third of gestation on developmental patterns show contradictory results, reporting improvements in weaning weight [21
], and no effects in other cases [20
]. These results highlight the need for further studies on causes and significance of these effects, which are not specific of sheep. In this sense, studies in a different species, the pig, have shown that maternal supplementation with antioxidant compounds (polyphenols in this case), improves antioxidant status of the fetuses [30
] and body weight of the neonates [31
]. Afterwards, developmental patterns were positively affected by maternal supplementation independently of birth weight since, comparing individuals with similar weight at birth and weaning, piglets from supplemented sows reached higher average daily weight gain and, therefore, higher body weight and corpulence than their control counterparts [32
Lamb viability was around 10%–12% higher in lambs from vitamin supplemented ewes, both at 60 and 120 days. These results, although differences did not reach statistical significance, have practical importance and support previous data addressing that lambs with higher birth weight have a lower risk of mortality and therefore greater viability in the pre-weaning stage [33
]. These data are also supported by previous studies which showed that pre-weaning survival of twin lambs is around 10% increased by applying weekly injections of 900 IU of vitamin E during pregnancy [21
] and around 70% increased by supplementation with vitamin E and selenium in the last third of gestation [20
]. Hence, maternal supplementation with vitamins C and E in combination can also be a good strategy to improve the pre-weaning survival of lambs in multiple pregnancies. Effects from nutritional supplementation alone were lower than that of vitamins; undoubtedly the combination of both nutritional and vitamin supplementation leads to better postnatal survival.
Finally, it is important to note that the cost of vitamin supplementation per pregnant ewe was marginal in relation to the final benefit. The vitamin administration route used in this study, as a premix included in a commercial concentrate, meant a daily cost per animal of US $0.0195 including vitamins, resulting in a total cost for 113 days of gestation of US $2.20. However, the greatest cost in this form of supplementation is the concentrate, since vitamins represent less than 10% of the total cost. Thus, it is possible to include vitamins in lower amounts of the concentrate, which could significantly decrease the total value of the supplementation. Furthermore, it would be interesting to study eventual time windows during pregnancy in which supplementation for shorter periods could have similar effects to those found in the present study, certainly reducing its cost.
In conclusion, these results highlight the importance of preventing oxidative stress in compromised twin pregnancies from underfed ewes to improve newborn outcomes and later postnatal growth and viability of the lambs. Increases in prolificacy and productivity of the herd under natural rangeland systems by increasing twin-bearing ewes are penalized by a low birth weight and viability of the twins due to maternal undernutrition and increased feto-placental oxidative stress. In addition to nutritional supplementation of the pregnant sheep, administration of herbal antioxidant vitamins C and E during pregnancy may constitute a good nutritional strategy for sheep reared at harsh environmental conditions.