Developments of carcass cuts, organs, body tissues and chemical body composition during growth of pigs

Abstract A serial slaughter trial was carried out to examine the developmental change of physical and chemical body compositionin pigs highly selected for lean content. A total of 48 pigs (17 females and 31 castrated males) were serially slaughteredand chemically analysed. Eight pigs were slaughtered at 20, 30, 60, 90, 120 and 140kg live weight, (LW) respectively.The carcass was chilled and the left carcass side was dissected into the primal carcass cuts ham, loin, shoulder, bellyand neck. Each primal carcass cut was further dissected into lean tissue, bones and rind. Additionally, the physical andchemical body composition was obtained for the total empty body as well as for the three fractions soft tissue, bones andviscera. Viscera included the organs, blood, empty intestinal tract and leaf fat. The relationship between physical orchemical body composition and empty body weight (EBWT) at slaughter was assessed using allometric equations (log 10 y ¼ log 10 a þ b log 10 EBWT). Dressing percentage increased from 69·4 to 85·2% at 20 to 120kg and then decreased to83·1% at 140kg 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 carcasscuts 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 to140kg. Soft tissue fraction showed an allometric coefficient above 1 (b ¼ 1·14) reflecting higher growth rate in relation tothe total empty body. The coefficients for the fractions bones and viscera were substantially below 1 with b ¼ 0·77 and0·79, respectively, indicating substantial lower growth relative to growth of the total empty body. Lean tissue allometricgrowth rate of different primal cuts ranged from b ¼ 1·02 (neck) to 1·28 (belly), whereas rates of components associatedwith fat tissue growth rate ranged from b ¼ 0·62 (rind of belly) to 1·79 (backfat). For organs, allometric growth rate rangedfrom b ¼ 0·61 (liver) to 0·90 (spleen). For the entire empty body, allometric accretion rate was 1·01, 1·75, 1·02 and 0·85for protein, lipid, ash and water, respectively. Extreme increase in lipid deposition was obtained during growth from 120 to140kg growth. This was strongly associated with an increase in backfat and leaf fat in this period. Interestingly, breedsselected for high leanness such as Pie´train sired progeny showed an extreme increase in lipid accretion at a range of LWfrom 120 to 140kg, which indicates that selection has only postponed the lipid deposition to an higher weight comparedwith the normally used final weight of 100kg on the performance test. The estimates obtained for allometric growth ratesof primal carcass cuts, body tissue and chemical body composition can be used to predict changes in weight of carcasscuts, determine selection goals concerning lean tissue growth, food intake capacity, etc. and generally as inputparameters for pig growth models that can be used to improve the efficiency of the entire pig production system for pigshighly selected for lean content.Keywords: allometry, body composition, carcass composition, growth, organs, pigs.