Effect of slaughter weight and sex on carcass composition and N-and P- efficiency of pigs

This study aimed at assessing the effect of sex and slaughter weight and their interaction on carcass composition and N- and P- efficiency of pigs between 25 and 130 kg. In 2 rounds, 24 pens of 4 pigs per sex (entire males (EM), barrows (BA), immunocastrates (IC) and gilts (GI)) were raised. They were fed ad libitum on a multiphase feeding regime (NE: 9.7; 9.5; 9.5; 9.3 MJ/kg and SID LYS: 9.0; 8.2; 7.7; 7.0 g/kg for phase 1, 2, 3, and phase 3 of the BA respectively). Pens were randomly divided into 3 groups of different slaughter weights: 105, 117 and 130 kg. Four piglets of each sex (21±0.6 kg) and one pig per pen at slaughter weight were euthanized and used to analyze the carcass composition at start and at slaughter. Nutrient accretion (dry matter, crude protein, crude fat, crude ash, and P) in the carcass was calculated as [mean bodyweight of the pen at slaughter, multiplied by nutrient contents of the carcass] minus [mean bodyweight of the pen at start multiplied by nutrient content of the piglets]. Nutrient intake was calculated as the sum of feed ingested per feeding phase multiplied by the nutrient content of the particular feed for the three phases. The efficiency of nutrient use was calculated as the nutrient accretion divided by the nutrient intake. Slaughter weight did not affect the protein content per kg carcass. BA had a lower crude protein content (16.9%) compared to EM (17.7%) and GI (17.8%) with IC (17.5%) as intermediates. Slaughter weight and sex had an interacting effect on N- efficiency: only in BA, N- efficiency decreased with higher slaughter weights (49%, 45%, 42% for 130, 117 and 105, respectively). In EM, GI and IC, no effect of slaughter weight was observed. Overall, BA (46%) had the lowest N- efficiency compared to EM (54%) and IC (52%), with GI (49%) as intermediates. Carcass phosphorus content (0.47% on average) or P- efficiency (45% on average) was not affected by sex or slaughter weight. In conclusion, we can state that EM were fed the most efficient in this trial and although BA received an adapted diet in phase 3, the ideal protein content can still be lowered to increase N-efficiency.