Sow body condition losses during lactation and relationwith litter gain

The increase in sow litter size has brought higherrisk of increased body condition losses during lactation. As modern sows also have a lowerbody fat mass, these body condition losses increasingly consist of protein compared to fat.This on farm study assesses the extent of these losses and the relation with litter gain (i.e.sow milk production) during a 26.8 ± 0.8 day lactation in 85 TN70 sows (parity 3.7 ± 0.2,litter size at birth 16.2 ± 0.4). Sows were transported to the farrowing pens and weighed8.1 ± 0.2 days before farrowing (283.5 ± 3.0 kg). Fifty-four sows were weighed afterfarrowing (260.6 ± 3.2 kg), and the body weight afterfarrowing of the other sows were estimated based on sow weight at entering the pens,days between entering and farrowing, and the litter weight at birth. Sow backfat (mm) andloin muscle thickness (mm) were measured at the last rib using a linear ultrasound probe(Aquilla, Easote, Genova, Italy) on the day before farrowing and weaning. Sows in thefirst two parities (N = 31) lost more body weight (45.4 vs 22.0 kg, 16.4 vs 8.2 %, P < 0.01),loin muscle (8.4 vs 4.8 mm, P < 0.01) but not more backfat (3.9 vs 3.6 mm) than sows inhigher parities (3 to 9, N = 54). Body weight loss and loin muscle losslinearly decreased from parity 1 to 9 (βbw = -3.4 kg/parity, P < 0.01; βlm = -0.8 mm/parity,P < 0.01, respectively). Litter gain was positively correlated with body weight loss,backfat loss and loin muscle loss in lactation. Every extra piglet at weaningwas associated with 7.3 kg more litter gain (P < 0.01), 0.7 mm more loin muscle loss (P <0.01) and 0.3 mm more backfat loss (P < 0.01) in lactation. The litter size at weaning wasnot related to total weight loss in lactation. In conclusion, lower parity sows lostmore body weight and loin muscle during lactation. The increasing litter size at weaningwas not only associated with greater litter gain, but also related to higher loin muscle andbackfat loss in both young and high parity sows in lactation.