Leptin in sow: influence on the resumption of cycle activity after weaning and on the piglet gain

In sows, a strong relationship exists between body condition and reproductive efficiency and milk yield. Leptin may act as a metabolic gate which permits the activation of reproductive axis: in the sow, serum concentration of leptin was positively correlated with adiposity at farrowing. An interesting aspect useful to clarify the biology of leptin, was the discovery that the placenta expresses the ob gene, the ob receptor gene and it is a site of leptin production, suggesting a possible role of the hormone in fetal growth; after birth, the placenta functions were taken over from milk, especially to the delivery of maternal hormones and growth factors to the neonate. The exact role of maternal leptin in the physiology of neonatal piglets remains to be determined. Our aim was to evaluate if maternal leptin levels at the beginning of lactation and at weaning could predict the resumption of cycle activity and/or the piglet gain. Thirty-eight Large White×Landrace pregnant sows (16 nulliparous and 22 pluriparous) were used. Blood samples were taken from sows and piglets at d 5 and d 21 after farrowing; in the same days, milk samples were taken after oxytocin injection by means of complete manual milking of all mammary glands of one side. On the basis of the blood leptin at d 5, sows were divided into 3 groups (Low: <2.3 ng/ml; Medium: 2.3 to 2.6 ng/ml; High: >2.6 ng/ml). Our results show a correlation at d 5 between backfat thickness and blood leptin (r=0.342; P<0.05). The resumption of the cyclic activity was faster in sows with a leptin level at d 5 greater than 2.3 ng/ml (P<0.01). Milk composition at d 5 and 21 was not affected by parity and leptin. Piglet ADG was significantly (P<0.05) influenced bysowleptin groups (0.180 kg day−1 for piglets from Low group and 0.224 for High group). Piglets weaned by High group sows have shown a greater blood leptin content at weaning (P<0.01) than other groups. In conclusion we have found a significant correlation between leptin and productive and reproductive performances of pigs. This paper underlines the pleiotropic actions exerted by leptin in the productive sow.