The second parity sow : causes and consequences of variation in reproductive performance

Many sows show reduced litter sizes in their second parity compared with their first parity. The aim of the current thesis was to describe causes and consequences of variation on second parity reproductive performance and to evaluate if feeding strategies during early gestation affect reproductive performance and sow body weight recovery after first lactation. In a first study, effects of sow weight development from first insemination up to first weaning on second parity reproductive performance were studied. Weight gain from first insemination up to first weaning showed a positive effect on non-pregnancy as well as on litter size, especially on a farm where gilts were relatively young and light at time of first insemination. In a second study, effects of weight loss during lactation were evaluated on embryonic survival and metabolic parameters during lactation and gestation in primiparous sows that were fed close to ad libitum. Sows with a high (>13.8%) weight loss showed a lower embryonic survival and fewer vital embryos at day 35 of gestation compared with sows with a lower weight loss, whilst no differences in metabolic parameters (IGF-1, NEFA, urea) were seen. The fact that the number of implantation sites was lower in high weight loss sows compared with low weight loss sows indicates that the negative effects of weight loss were already present during late lactation or early gestation. In a third study, a data-analysis using 46,500 sows was performed to assess relations between second parity performance and reproductive performance in later parities. Results showed that farrowing rate and litter size in parity 3 and up, as well as parity at culling, were related to second parity reproductive performance. These relations with second parity litter size were affected by first parity litter size. In practice, feed allowance during early gestation is often limited and might not be sufficient to support growth and recovery from lactation. The question was therefore raised if increased feed or protein intake during early pregnancy could improve litter size. In two experiments, the effects of an altered feeding strategy during the first month of gestation on farrowing rate and litter size (exp. 1) and embryonic survival and embryonic and placental development and metabolic parameters (exp. 2) were assessed. In Experiment 1, a 30% higher feeding level increased litter size with two piglets, without negatively affecting piglet birth weight. In Experiment 2, designed to find a physiological explanation for these results, an increased feeding level did not affect embryonic survival, embryonic development or placental development. Furthermore, no relations with metabolic parameters were found. From this thesis it can be concluded that second parity reproductive performance is related to reproductive performance in later parities. In order to improve second parity reproductive performance, weight loss during first lactation should be limited and gilts should be heavier at first weaning than at first insemination. Further, increased feeding levels during early gestation improve sow body weight recovery, without negatively affecting reproductive performance.