RETURN TO ESTRUS AFTER FIRST INSEMINATION IN SOW HERDS - (INCIDENCE AND ASSOCIATION WITH REPRODUCTIVITY AND SOME BLOODPARAMETERS)

As no systematic study has been done to get an accurate estimate of th e incidence of return to oestrus after first insemination in sows in t he Netherlands, tire objectives of this investigation were: 1) to obta in an estimate of the incidence of return to oestrus after inseminatio n at the herd level; 2) to investigate the association between inciden ce of return to oestrus after first insemination and reproduction char acteristics to get on impression of the economic importance. These obj ectives were investigated using the reproduction results of 240 swine breeding herds in The Southern Netherlands in 1987, using their CBK pl us computerized herd management records. The average incidence of retu rn to oestrus after first insemination on a herd level was 16.9 per 10 0 first inseminations. An increase of incidence with 10 returns per 10 0 first inseminations, corrected for confounders in a multiple linear regression model, was associated with a decrease of approximately 0.3 liveborn piglets/sow/year. Thereupon individual sows were followed in 1988 and 1989 prospectively in 37 sow herds from weaning to inseminati on, returning to oestrus or not after first insemination to farrowing. The investigation focused in particular on the relationship between r eturning to oestrus after first insemination and incident infection wi th porcine parvovirus (PPV) and Leptospira interrogans serovar bratisl ava (L. bratislava). During a number of consecutive farm visits sows w ere blood sampled al weaning and again a blood sample was taken 6 week s later. The final dataset that was analysed consisted of 161 animals that did not return to oestrus after first insemination and 158 animal s that returned to oestrus after first insemination. An incident infec tion was defined as a sero-conversion between tire hua successive bloo d samplings. There,was no indication of a relationship between the occ urrence of return to oestrus after first insemination and an incident infection, with L. bratislava or PPV. Littersize and between farrowing time of the last farrowing before the study period as not associated with occurrence of returning to oestrus after first insemination in th e study period. However, an increased weaning-to-insemination interval , a high progesterone level at weaning, a low albumin concentration at weaning and a decrease in albumin concentration between the consecuti ve samplings and an increase in gamma globulin concentration between t he two blood samplings increased the risk of occurrence of a regular r eturn to oestrus after insemination. An increased weaning-to-inseminat ion interval, an increase in leucocyte and gamma globulin concentratio n and a decrease in alfa(1,2) globulin concentration between the conse cutive samplings increased the risk of occurrence of an irregular retu rn to oestrus after insemination.