Effects of parity, litter size and lamb sex on maternal behavior of small Tail Han sheep and their neuroendocrine mechanisms

Abstract

• Parity, litter size, and lamb sex affect the maternal behavior of Small-tailed Han sheep. • Multiparous ewes, twin-lamb ewes, ewes with female lambs seemed to have better maternal behavior. • Our findings provide a theoretical basis for the further improving the survival rate and welfare of lambs. The high mortality of lambs has always restricted the development of Small-tailed Han sheep breeding, causing serious economic losses and welfare problems in the sheep breeding industry. Stable and good-quality maternal behavior is critical for the survival of offspring, and given the importance of maternal behavior on early lamb survival, improving maternal behavior in ewes seems to be an effective way to improve lamb survival rates. Thus, exploring the factors that influence maternal behavior is a good place to begin. Therefore, in this study, we investigated the effects of parity, litter size, and lamb sex on the maternal behavior of Small-tailed Han sheep. The neuroendocrine mechanism involved in regulating maternal behavior were also analyzed. Primiparous and multiparous ewes, ewes with different litter sizes, and ewes with different lamb sexes were selected, and their maternal behaviors, including lactating, grooming, following, looking, and udder refusal, were observed and analyzed using scanning and sampling methods during the first 7 days after parturition. The lambs’ body weights were recorded for the first 35 days after birth. The concentrations of estradiol, oxytocin, norepinephrine, dopamine, NO, and γ-aminobutyric acid (GABA) of ewes were measured with ELISA kits for 35 days after parturition. The results showed that the looking and udder refusal behavior of multiparous ewes was significantly lower than primiparous ewes (P = 0.004 and P = 0.036). The grooming behavior was significantly higher in both primiparous and multiparous ewes at Day 0 than at Day 1∼7 after parturition (P < 0.05). Ewes with two offspring expressed significantly more lactating behavior than ewes with single lambs in the first 3 days after parturition (P < 0.05). The looking behavior was significantly lower in twin-lambing ewes than in single-lambing ewes at Day 7 postpartum (P = 0.031). The grooming behavior was significantly higher in both single and twin lambing ewes at Day 0 post parturition than at Day 1∼7 post parturition (P < 0.05). Lactation behavior was significantly higher in ewes producing female lambs than in ewes producing male lambs at Day 2 after parturition (P = 0.018). When a female lamb was born, the looking behavior of ewes was significantly higher than ewes with male lambs on Day 3 after parturition (P = 0.01). The grooming behavior and the udder refusal behavior of male lambing ewes were significantly higher at the Day 0 after parturition than at the Day1∼7 after parturition, similar temporal trend was observed in female lambing ewes (P < 0.05). The body weight of lambs was higher in the multiparous ewes group. This was especially significant at Day 0 and Day3 after birth (P = 0.045 and P = 0.007). Single lambs seemed to have higher birth weights than twin lambs; however, the differences were not significant (P > 0.05). Male lambs were significantly heavier than female lambs at Day 0 and Day 7 after birth (P = 0.044 and P = 0.048); thereafter, the lambs of the two groups showed no significant difference in body weight. The level of oxytocin in multiparous ewes was significantly higher than that of primiparous ewes (P < 0.05). The levels of oxytocin, norepinephrine, dopamine, NO, and GABA in ewes with twin lambs were significantly higher than those of ewes with single lambs (P < 0.05). Ewes with female lambs had a significantly higher level of oxytocin than ewes with male lambs at Day 0 (P = 0.024). In conclusion, multiparous ewes exhibited better quality maternal behavior than primiparous ewes, and this was associated with the level of oxytocin in the serum. Ewes with twin lambs exhibited better quality maternal behaviors than the single lamb group, and this was related to the levels of oxytocin, norepinephrine, dopamine, NO, and GABA. Oxytocin was also found to be associated with the improved ewe maternal behavior with female lambs. Altogether, ewes with better maternal behavior have a higher level of oxytocin and noradrenaline. Moreover, the expression of maternal behavior in ewes is positively correlated with lamb weight. Our findings contribute the understanding of the neuroendocrine mechanisms of maternal behavior in Small-tailed Han sheep and provide a theoretical basis for the further exploration of artificial methods to improve ewe maternal behavior, and ultimately improve the survival rate and welfare of lambs.