The effects of transport and related preslaughter operations on the welfare of animals can be measured directly on the individuals through changes in both their behavior and physiological indicators [37
]. However, often the welfare conditions of animals destined for slaughter are also evaluated by determining mortality, weight loss, frequency of sick or injured animals at arrival, and physical and biochemical defects in their carcasses, such as the presence of bruises and alterations of muscle pH, color, and water retention [19
3.2. Weight Loss
From the moment sheep are collected from the fields to be loaded and transported they are, in general, deprived of water and feed; when arriving at the slaughterhouse they are provided with water but continue without feed during lairage. Deprivation of feed and water in animals produce changes in the blood variables related to stress and inanition [38
], and also changes in behavior, due to hunger and thirst. All the aforementioned indicators reflect that animal welfare is compromised, being of ethical concern. In quantitative and economical terms, lambs will reduce their live weight, and if transport and food deprivation is long enough, they may also reduce carcass weight [39
To investigate the weight losses in lambs, four commercial loads transporting 2106 lambs (mean 29 kg live weight), bred and loaded at the same farm were followed and studied; two of these loads of lambs were slaughtered at a local slaughterhouse after a terrestrial journey of 12 h and the other two loads were transported to a slaughterhouse in the central-southern region of the country, after a 46 h of terrestrial plus maritime ferry crossing journey [39
]. In each load, 25 randomly chosen lambs were individualized to measure live weight before and after transport, hot carcass weight, bruising, pH, and muscle glycogen (total 100 lambs). In the lambs transported for 46 h the live weight losses were higher (13.4 vs. 4.8%) and the carcass weights were lower (13.7 vs. 14.9 kg) than in the lambs transported for 12 h. Considering that around 500 lambs are transported in a load (truck with trailer, three floors), and each lamb loses approximately 1 kg of carcass weight, approximately 500 kg of lamb carcasses are being wasted in one of these journeys. Certainly, this cannot be sustainable in economic terms, nor in animal welfare terms.
In sheep, as in cattle, bruises are not visible in the live animal due to the thickness of the skin and wool, hence they can only be detected at postmortem inspection of the carcass [56
]. The presence or absence of bruises on a carcass, as well their severity and extensivity, are indicators of the welfare of the animal preslaughter, because bruises are associated with the process of transport and handling of the animals [56
]. Besides being painful while the animal is alive, the damage produced by bruises on the carcass requires trimming and parts of the carcasses have to be condemned, reducing the weight and value of the product [19
Knowles et al. [55
] found that in lambs, the distance travelled was a poor predictor for bruising, but other studies have found a positive relationship between these variables [6
The percentage of bruised carcasses found in Chilean studies with long transport distance varies between 33% [39
] and 64% [40
], and for lambs transported up to 12 h it varies between 22.7% [63
] and 25% [40
]. Tarumán et al. [63
] found a significant (p
< 0.05) association of transport time and live weight with bruising, with the most exposed animals being those transported for more than 4 h and those that were heavier. The latter could be due to the higher actual stocking density found for lambs of higher weights during transport, because transporters consider number of lambs per pen instead of kg live weight per pen [28
The characteristics of the bruises in lamb carcasses were classified by Tarumán and Gallo [31
] according to severity (or depth in terms of tissues affected: subcutaneous 1, muscular 2, and bone or fracture 3), to extension of the lesion (diameter), and the anatomical region affected.
Due to the small size of lambs, there is a risk of lesions in the transport vehicles as their legs could be easily trapped in floor or wall cracks in the vehicle and also open spaces between the vehicle and the ramps. According to Anderson and Horder [64
], external factors like transport and handling would be responsible for the location of a bruise. For instance, during loading and unloading, lambs are often pulled by the wool or grabbed by different parts of the body when they refuse to move, which also increases the likelihood of bruising [16
]. This handling is in accordance with the small size of most bruises observed (<5 cm) and the tissues affected (mainly subcutaneous). These findings are similar to other international studies that have mostly registered superficial, small bruises: 2–4 cm in lamb carcasses [62
Several authors in Chile [31
] have found that the loin is the predominant anatomical location of the bruises in lambs, which agrees with Cockram and Lee [61
]. The location of the bruises on the loin could be explained by handling, due to handlers pulling the lambs from the wool on their back. In fact Jarvis and Cockram [20
] studied the relationship between potentially traumatic events during loading, unloading, and handling of sheep, and found a relationship between the occurrence of wool pulls by handlers and bruising on the sheep.
Tarumán et al. [63
] found that there is a risk for more bruises when lambs are transported commercially on bad roads, as shown earlier by Ruiz de la Torre et al. [41
] experimentally. Large lesions (diameter) and deep lesions (affecting muscle) are more likely to be produced when lambs fall during transport and are then trampled by other animals standing.
Considering that compared to international studies there is a high prevalence of bruised lamb carcasses but the lesions are mainly small and superficial, it is suggested that handling the animals appropriately by training stockmen and transporters could reduce this problem.
3.4. pH Alterations and Other Defects
Meat pH is one of the main measures used to monitor quality, however, in Chile it is not a routine measurement at lamb slaughterhouses. Physical and physiological stress of animals before slaughter in general affects animal welfare and also meat pH [66
]. Factors like high stocking densities during transport to slaughter [67
], duration and conditions of lairage [68
], adverse climatic conditions, social disruption, or a novel environment can cause pH decrease [69
]. Therefore a high final pH (usually measured at 24 h postmortem) in lamb carcasses, will be a reflection of the inadequate conditions and the stress that animals have undergone previous to slaughter and can be used as a postmortem welfare indicator.
Watanabe et al. [70
] categorize lamb carcass pH in three groups: normal or low (<5.8), intermediate (5.8–6.3), and high (>6.3) and state that meat with a pH between 6.2 and 7.0 will be dark, firm, and dry, useful only for manufacture. According to this, Pantanalli [43
] categorized 27,697 lamb carcasses at one slaughterhouse in the Chilean Patagonia, measuring pH in the leg (between the Semimembranosus and Semitendinosus muscles). This author found that 67% of the carcasses had a normal pH, 32.9% fell in the intermediate category, and only 0.1% had high pH. In another slaughterhouse, Tarumán et al. [63
] also measured pH in the leg of 1150 lamb carcasses and found that 45% fell in the intermediate range and none in the range of high pH. The latter authors found that transport time and presence and number of bruises were factors that had a significant association with pH (p
< 0.05). Due to this association, both bruising and meat pH could be used at slaughter plants as indicators of meat quality, and also of animal welfare.
shows the concentrations of muscle glycogen and the mean pH values found in several studies in Chile, where both variables were measured in the Longissimus thoracis muscle of lamb carcasses. The mean values of pH were similar in all studies and below 5.8, hence could be classified within the normal range according to Watanabe et al. [70
]. In the study of Vargas [40
], who transported lambs in four journeys that lasted between 32 and 42 h, 48% of the carcasses were categorized as intermediate pH according to Watanabe et al. [70
] and none in the high pH category. In the case of the study of Carter and Gallo [39
], 50% of the carcasses of lambs transported for 12 h and 40% of those transported for 46 h had intermediate pH and none had high pH. However, in general, there was no clear relationship between transport time, pH, and concentration of muscle glycogen. It is possible that the lack of relationship is due to the fact that there was a great variability between studies in the total fasting time. In the case of Carter and Gallo [39
] there was no difference in terms of pH nor muscle glycogen between the lambs subjected to 12 or 46 h transport; these lambs had been deprived of food for 8 h before transport (on farm) and then for 6 h after transport, during lairage; in farm the lambs had been driven from the fields, hence exercising, and then weaned. The low concentrations of muscle glycogen found in both groups are in fact similar to the 11.1 µmol/g found by Bond et al. [71
] in lambs exercised for 24 h. Jacob et al. [68
] found that the effect of stress during transport may be different than stress due to exercise, and travel time was correlated positively with glycogen concentration in the Semimembranosus muscle whereas farm curfew time was correlated negatively with glycogen concentration in the Semitendinosus muscle. So it could be that the exercise, due to the long walk during mustering and driving, and the stress of weaning had already depleted the glycogen reserves of sucker lambs before transport in the case of Carter and Gallo [39
]. In the study of Vargas [40
], the lambs used had been weaned more than a week before the experiment and were collected from fields close to the loading point, and then transported for 37 h and slaughtered immediately after arrival (short lairage) or after 20 h lairage (long lairage). In the study of Baeza [13
], the 10 loads of lambs were transported for 0.5 to 4 h only, with a total fasting time between 16 and 28 h, considering the time before loading and lairage at the slaughterhouse. The concentrations of muscle glycogen found by Vargas [40
] and Baeza [13
], shown in Table 3
, are closer to those published by Lowe et al. [72
] in lambs on pasture (25.4 and 42.5 µmol/g) and by Jacob et al. [68
]. The latter also concluded that lairage time did not have a clear effect on pH and glycogen concentrations, mainly because the consignments of lambs studied also had different origins, transport times, and different times off feed on the farms before loading. However, sucker lambs in general had lower glycogen concentrations in muscle and higher pH than carry-over lambs (weaned and older).
In order to try and elucidate the effect of fasting on muscle glycogen, we [73
] measured the concentration of muscle and liver glycogen experimentally in five muscles of eighteen weaned lambs of similar characteristics to those used in the Chilean Patagonia commercial studies. The lambs were kept in a pen and slaughtered after increasing time without feed (with access to water). The results are shown in Table 4
. Glycogen content was higher and depletion due to fasting was faster in liver than in muscle. Muscle glycogen concentrations decreased in general in all muscles with increasing fasting time between 0 and 56 h, and the Longissimus thoracis
(LT) muscle showed the highest values. The mean concentration of muscle glycogen in LT at 32 h of fasting was similar to the values reported by Vargas [40
] and Baeza [13
] in lambs with similar total fasting times, but still much higher than the values reported by Carter and Gallo [39
In general, the relationship between muscle glycogen concentration and pH in lambs seems less clear that in cattle, where many more studies have been performed and pH is regularly measured at slaughterhouses, which is not the case in Chile at least. Notwithstanding this, within the practical recommendations to address high pH problems are reduction of exercise and stress to the minimum possible on farm before transport, and reducing transport and lairage times, because this stops lambs from using their energy reserves before being slaughtered. In Chile, as in many South American countries, lamb is still mainly consumed fresh (refrigerated) and for special occasions only; therefore, there has not been much research in terms of the technological quality of lamb meat for further processing or the use of techniques like vacuum packaging to increase shelf life. The development of new techniques will require further knowledge about the biochemical processes involved in the transformation of muscle to meat in lambs and should also help improving lamb welfare and meat quality.