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Pre-slaughter stress has a negative impact on animal welfare and on meat quality. Aggressive behaviour when pigs are mixed together for transportation to, or on arrival at, the abattoir is an important factor in pre-slaughter stress. Aggressiveness of pigs varies between individuals in the population, and this study investigated its effects on stress and meat quality at slaughter. We mixed pigs at a young age to identify individuals of high (H) or low (L) aggressive temperament using the previously validated approach of lesion scoring. To contrast extremes of social stress single-sex groups of eight pigs were mixed according to their aggressiveness in HH, HL or LL combinations or left unmixed (U) prior to transport and slaughter (n = 271). Each treatment was replicated in at least two groups in each of four slaughter batches. Mixing per se had little effect, but mixed groups composed of aggressive pigs (HH) had more carcass skin lesions and higher levels of plasma cortisol at slaughter and had loin muscle samples with higher pH at 24 h, and lower redness (a*) and yellowness (b*) compared to the other treatments. Females had higher levels of plasma cortisol at slaughter, a more rapid decline in pH post-slaughter and greater lean content of meat. Lactate and creatine kinase (CK) levels and meat pH were affected by the interaction of sex and treatment. Genetic factors, dam and sire line composition, and halothane locus (ryanodine receptor 1, RYR1) genotype, also affected a number of production and meat quality parameters as expected. Additionally, ‘commercially normal’ levels of social stress were studied in four further slaughter batches with no manipulation of group composition (n = 313). In these pigs, the proportion of unfamiliar pigs and group size of lairage groups explained limited variation in lesion scores at slaughter, but earlier aggressiveness did not. High numbers of skin lesions on the carcass were associated with high levels of cortisol and lactate and low glucose at slaughter, but not with meat quality measures. When stress and meat quality measures were compared for all pigs, high lactate was associated with low early pH and high drip loss, while high cortisol and CK were associated with high pH at 24 h and changes in meat colour. In conclusion, mixing pigs of above average aggressiveness resulted in greater aggression and stress, and changes in meat quality parameters, consistent with the effects of pre-slaughter stress on muscle chemistry.
A serial slaughter trial was carried out to examine the developmental change of physical and chemical body composition in pigs highly selected for lean content. A total of 48 pigs (17 females and 31 castrated males) were serially slaughtered and chemically analysed. Eight pigs were slaughtered at 20, 30, 60, 90, 120 and 140 kg live weight, (LW) respectively. The carcass was chilled and the left carcass side was dissected into the primal carcass cuts ham, loin, shoulder, belly and neck. Each primal carcass cut was further dissected into lean tissue, bones and rind. Additionally, the physical and chemical body composition was obtained for the total empty body as well as for the three fractions soft tissue, bones and viscera. Viscera included the organs, blood, empty intestinal tract and leaf fat. The relationship between physical or chemical body composition and empty body weight (EBWT) at slaughter was assessed using allometric equations (log10y=log10a+b log10 EBWT). Dressing percentage increased from 69·4 to 85·2% at 20 to 120 kg and then decreased to 83·1% at 140 kg LW, whereas percentage of soft tissue, bones and viscera changed from 23·5 to 33·0%, 10·1 to 6·3% and 14·7 to 10·3%, respectively, during the entire growth period. Substantial changes in proportional weights of carcass cuts on the left carcass side were obtained for loin (10·5 to 17·5%) and belly (11·3 to 13·8%) during growth from 20 to 140 kg. Soft tissue fraction showed an allometric coefficient above 1 ( b=1·14) reflecting higher growth rate in relation to the total empty body. The coefficients for the fractions bones and viscera were substantially below 1 with b=0·77 and 0·79, respectively, indicating substantial lower growth relative to growth of the total empty body. Lean tissue allometric growth rate of different primal cuts ranged from b=1·02 (neck) to 1·28 (belly), whereas rates of components associated with fat tissue growth rate ranged from b=0·62 (rind of belly) to 1·79 (backfat). For organs, allometric growth rate ranged from b=0·61 (liver) to 0·90 (spleen). For the entire empty body, allometric accretion rate was 1·01, 1·75, 1·02 and 0·85 for protein, lipid, ash and water, respectively. Extreme increase in lipid deposition was obtained during growth from 120 to 140 kg growth. This was strongly associated with an increase in backfat and leaf fat in this period. Interestingly, breeds selected for high leanness such as Piétrain sired progeny showed an extreme increase in lipid accretion at a range of LW from 120 to 140 kg, which indicates that selection has only postponed the lipid deposition to an higher weight compared with the normally used final weight of 100 kg on the performance test. The estimates obtained for allometric growth rates of primal carcass cuts, body tissue and chemical body composition can be used to predict changes in weight of carcass cuts, determine selection goals concerning lean tissue growth, food intake capacity, etc. and generally as input parameters for pig growth models that can be used to improve the efficiency of the entire pig production system for pigs highly selected for lean content.
The objective of this study was to develop accurate mathematical-statistical functions to estimate body composition of live pigs between 20 and 140 kg weight from total body water (TBWA) determined by the deuterium dilution technique. Chemical body compositions during the growth period are essential input parameters for biological pig growth models, which are used to estimated the nutrient requirements, improve the entire production system, determine optimal slaughter weight, optimize selection for food intake, etc. In the present study, 48 pigs (17 female and 31 castrated males) were used in an experimental station to obtain protein, lipid, ash and water content at 20, 30, 60, 90, 120 and 140 kg live weight. At each target weight, body water of the animals was determined by the deuterium dilution technique. Eight pigs of each live-weight group were slaughtered and chemically analysed. Water content of the empty body decreased from 74 to 53%, whereas lipid content rose from 7 to 30%. Between 20 and 30 kg body weight, protein content increased from 16 to 17% and thereafter decreased to 16%. Ash content was constant at 3%. To estimate body composition of the remaining animals from TBWA (%) determined by deuterium dilution technique, two sets of exponential prediction functions were used to describe the relationship between chemically analysed body components and TBWA (%). The first set of prediction functions fitted one intercept for the entire growth period and the second set of prediction functions fitted a different intercept for each weight class. Correlation coefficients between estimated and chemically determined empty body water, lipid, protein and ash for the first set of functions were 0·93, 0·86, 0·83 and 0·65, respectively. The second set of prediction functions showed higher accuracy (2 to 10%), but had the disadvantage of non-continuous estimates over the entire growth period. In contrast, by using the first set of prediction functions, a continuous accurate estimation of body composition of live pigs was obtained over a large range of growth (20 to 140 kg) based on deuterium dilution space.
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