Variability of ovulation in gilts ; associated factors and consequences on reproductive performances

Adequate timing of insemination close to ovulation is a key determinant of reproduction performances ( Kemp and Soede, 1996). At farm level, liberal insemination strategies (>2 semen doses) are oft en recommended to compensate for variable and unknown ovulation time. Efficient prediction or control of ovulation could improve labor costs ( Soede et al. 2002). The objective of this work was to investigate factors associated with variability of ovulation in different herds and possible impacts on reproduction. The study was performed in 4 conventional farms: 300 to 1000 sows, weaning at 3 weeks, insemination (2–4 / sow), herd fertility >85%. Measurements were performed on several batches on a total of 314 gilts and weaned sows. They included daily recordings of estrus and ovarian status using transcutaneous ultrasound technique (3.5–5 Mhz probe, Exago®, ECM). We collected information about number and timing of inseminations (AI), backfat (BF) at AI, weaning-to-estrus or last altrenogest-to-estrus intervals (gilts), parities, previous litter size or lactation duration, health status, treatments, and subsequent performances. Results were analysed using GLM or LOGISTIQ procedures (SAS 9.2) for quantitative or qualitative data, respectively. Within 8 days after weaning, 97.5% females exhibited estrus and ovulated, 2.5 % remained anestrus and one ovulated silently. Ovulation occurred at 76 ± 8 % of estrus duration, 44.1 ± 18.7 h aft er the onset of estrus, with large individual variations (-3 h to +105 h). Gilts had shorter estrus and ovulated earlier (p