Salt-regulated prepartum supplementation and parity effects on maternal performance, wool growth, and lamb development in Merino ewes grazing in semi-arid steppes

The impact of prepartum supplementation using a balanced diet incorporating salt as an intake regulator was assessed on maternal live weight, body condition, wool production, maternal and lamb behavior, and lamb growth up to 50 days of age in multiparous and primiparous Merino ewes under extensive grazing. On day −65 prepartum (Day 0 = Partum), 80 pregnant Merino ewes carrying a single fetus (40 multiparous; 40 primiparous) from fixed-timed artificial insemination, were randomly assigned to one of two dietary treatments, each with one repetition: grazing only (Control group) or grazing plus ad libitum supplementation with a balanced food containing salt as an intake regulator (Suppl group) for 60 days (Days −65 to −5 prepartum). Behavioral and performance variables were monitored in ewes and lambs from −65 days prepartum until 50 days postpartum. Blood metabolites (glucose, total proteins, and urea) were assessed in ewes during the same period. On day −35 prepartum, ewes were subjected to shearing. From day −50 prepartum until 30 days postpartum, ewe BW was significantly higher in the Suppl multiparous group compared to the other groups (P < 0.05). A marginal increase of 220 g in greasy fleece weight was observed in Suppl ewes after 30 days of supplementation (P < 0.1). However, no significant effects were observed in maternal or lamb behavior, lamb birthweight or lamb survival (P > 0.05). A marginal increase in lamb weight on days 30 and 50 postpartum was observed in the Suppl group compared to the Control group (P < 0.1). An increase in total proteins and urea was observed on day −5 prepartum in the Suppl group compared to the Control group (P < 0.05). Lambs from primiparous ewes took longer to suck compared with lambs from multiparous ewes (P < 0.05). Also, lamb birthweight, lamb weight on days 30 and 50 postpartum were significantly higher in lambs from multiparous ewes compared to lambs from primiparous ewes (P < 0.05). Neonatal mortality was higher in primiparous than in multiparous ewes, with survival rates of 65 % and 91 %, respectively (P < 0.05). In conclusion, Suppl primiparous ewes evidenced an improved maternal body status during the peripartum period. Prepartum supplementation showed a marginal increase in greasy fleece weight. However, no significant effects were observed on maternal behavior, lamb survival or lamb growth. Primiparous ewes exhibited a 26 % higher neonatal mortality than multiparous ewes, likely attributable to their inexperienced maternal behavior.