Mammary gland involution and endocrine status in sows: effects of weaning age and lactation heat stress

The impact of the duration of lactation and / or thermal stress on the endocrine status of sows and the concentrations of indicators of mammary involution at weaning was investigated. Twenty-eight primiparous sows were Landrace x Yorkshire housed to 21 (CTL) or 29 ° C (HS) in lactation. Half of the sows on each treatment were randomly assigned to a weaning at 22 days (W22: CTL, n = 7; HS, n = 8) and the other half at 44 days (W44: CTL, n = 6; HS , n = 7) postpartum. Litters were standardized to 10 or 11 piglets at days 2 and 9 piglets on day 23 of lactation. Samples of blood and milk were obtained on days -1, 1, 2 and 3 in relation to weaning (day 0). The concentrations of prolactin, IGF-I and lactose were measured in milk and blood and those of Na, K and IGFBP-5 were measured in milk. The composition of milk has also been determined. There was less of lactose (P 0.1) compared with W44 to W22. Post-weaning, a failure of epithelial junctions (increased Na and decreased K) was apparent one day earlier (2 vs. 3) with W44 than W22, and was more marked in group HS. In agreement, there was a transient increase in concentrations of lactose that same day in HS W44. The higher ratio Na / K compared with W44 to W22 attached to increasing concentrations of lactose, especially in HS, indicating a failure of mammary epithelial junctions with advancing lactation. The duration of lactation has an impact on milk components that are connected to the status of mammary involution in the sow and some of these effects are more apparent during a heat stress