L’ovulation après le tarissement des truies : mécanismes physiologiques et facteurs de variation

Abstract

This review analyses the physiological mechanisms which control the ovarian activity in sows after parturition, and the influence of factors that may delay the return to oestrus and ovulation after piglet weaning. During lactation, the sow is submitted to suckling-associated stimuli and must deal with the high nutritional requirements for milk production. These factors induce the inhibition of gonadotrophin secretions and consequently of follicular growth. Stimulation of the mammary glands decreases during lactation and activity of the hypothalamus-pituitary-ovarian axis progressively increases. After weaning, gonadotrophin secretions quickly increase and large follicles start their preovulatory growth, which results in oestrus and ovulation. The hormones which control nutrient metabolism and lactation (insulin, growth hormone, IGF-I, cortisol, prolactin, oxytocin) may influence follicular growth, either through direct action on the ovaries or via modulation of the gonadotrophin secretions. An increased nutrient deficit in the sow delays the onset of ovulation after weaning. Thus, feed intake during lactation has marked effects on the weaning-to-oestrus interval. Its duration is also dependent on factors related to the sow itself (genotype, parity, milk production), to the environment (temperature, photoperiod), or to management technics (lactation length, litter size, weaning method, social environment). Nutritional balance plays a key role and may explain, at least in part, the influence of many of the factors of variation, which may influence the level of milk production or the appetite of the lactating sows. Physiological mechanisms may implicate the three levels of the hypothalamus-pituitary-axis.