Variation in weaning-to-oestrus interval in sows: Causes and consequences

The activity of the hypothalamic-pituitary-ovarian axis is highly inhibited in early lactation due to suckling-induced inhibition of GnRH secretion. I t progressively and partially resumes over the first weeks of lactation. Nu tritional deficit may extend this inhibition especially in first- or second -litter sows. Al weaning, gonadotrophin secretions quickly increase and sti mulate follicular preovulatory growth that leads to oestrus and ovulation. All factors that modulate suckling intensity or the nutritional balance of the sow during lactation are likely to influence the WOI. The variation in WOI has clear consequences for subsequent reproductive performance (both fa rrowing rate and litter size), which can be explained through carry over ef fects of lactation on subsequent ovulation rate, fertilisation rate and emb ryo survival.