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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.
Modern pig breeds in Europe owe their origin to a mixture of Asian and European breeds and types. They evolved during the past two hundred years, and developed particular breed characteristics by the application of breed standards, which included specific reference to colour. DNA markers at two coat colour loci provide the potential for accurate breed assignation for wild boar, Berkshire and Tamworth breeds, and may also offer the potential to develop simple tools for the verification of the origin of pork products. The use of polymorphisms in genes determining coat colour is used to explore this potential in terms of breed identification for conservation of animal genetic resources, and product traceability for quality assurance.
The effect of a DNA polymorphism in the MC4R gene on fatness, growth and feed intake traits of pigs was first reported by Kim et al in 2000 (1). That study of 1720 animals showed significant effects in several selected breeding populations for days to 110kgs (p<.001), 10th rib backfat (p<.001), test daily gain (p<.001) and feed intake (p<.01). However, in the same paper the effect within a small sample (124) from a Meishan synthetic line was not significant and the (small) effect of backfat was in the opposite direction to that reported for other lines. Subsequently, Andersson and colleagues (2) reported a failure to detect an effect in a small QTL population derived from crossing Large White pigs with wild boar. Several explanations have been proposed (1,2) including an epistatic effect. Here we report the results of an experiment to test whether the results from the Meishan population was due to sampling. The results indicated an effect of MC4R within the Meishan line for fatness, growth and feed intake traits in the same direction as previously reported for other lines.
The heritable components of many traits in which livestock producers strive for improvement comprise a number of genetic loci. Many workers have now reported the identification of such quantitative trait loci (QTL) using model crosses between divergent breeds or lines in combination with whole genome scans using mapped DNA markers. Such methods rely on two or three generation pedigrees in order to be able to trace the inheritance of markers and the QTL. However, it is not yet clear if such QTL have application in commercial pig populations. The AFLP™ technology is a very efficient method for identifying markers segregating in any population. We have previously reported the successful use of the AFLP™technology and bulk segregant analysis (BSA) for the detection of markers associated with pig coat colour, a monogenic trait (Plastow et al 1998). We set out to determine whether these methods could be used for the detection of loci associated with quantitative traits directly in commercial populations.
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