Effect of live weight development and reproduction in first parity on reproductive performance of second parity sows

An impaired reproductive performance in second parity compared to first parity sows, decreases reproductive efficiency and, perhaps, longevity of sows. This study aims to quantify the effect of live weight development and reproduction in first parity on reproductive performance of second parity sows, i.e. pregnancy rate as well as litter size. Measures of sow development (live weight at first insemination, farrowing and weaning) and reproduction (total number of piglets born, weaning to insemination interval, lactation period, number piglets weaned) were recorded on two experimental farms. Logistic regression analysis was done for the binary outcome 'non-pregnancy from first insemination after first weaning' (yes/no). General linear regression analysis was used for litter size from 1st insemination in second parity. Repeat breeders were omitted from the analysis on litter size in second parity, since a prolonged period between weaning and conception can positively influence litter size. Farms differed significantly in measures of sow live weight development and therefore data were analyzed per farm. Compared with gilts from farm A, gilts from farm B were older and heavier at: first insemination (275±0.9 days and 145±0.8kg for farm B vs. 230±0.6 days and 124±0.5kg for farm A), first farrowing (resp. 189±1.1 vs. 181±0.9kg) and first weaning (resp. 165±1.1 vs. 156±0.9kg). Weight loss during pregnancy was similar for both farms (resp. 24.9±0.7 and 23.7±1.0kg). Gilts from farm A, however, gained more weight in the period between first insemination and first weaning compared with gilts from farm B (resp. 36.1±0.8 and 20.9±1.3kg). Non-pregnancy in second parity was 11% for farm A and 15% for farm B. Litter sizes in first and second parity were, respectively, 10.7±0.1 and 11.6±0.2 for farm A and 11.8±0.1 and 11.6±0.1 for farm B. Variables associated with non-pregnancy and litter size in second parity differed between farms. On farm A, mainly sow live weight development was associated with non-pregnancy and litter size in second parity, whilst on farm B variables like total number born in 1st parity and sow line, were associated with non-pregnancy and litter size in second parity. On both farms, higher weight gain from first insemination to first weaning was associated with a decrease in non-pregnancy (odds ratio 0.7 per 10kg for farm A and 0.8 per 10kg for farm B) and on farm A with higher litter size in second parity (β=0.42 per 10kg weight gain). Results show that sow live weight development affects reproductive performance in second parity, especially on farm A where gilts are relatively light or young at first insemination. Management of these animals should aim to optimize development at first insemination and to increase growth between first insemination and first weaning in order to optimize production in second parity.