The physical state and metabolic status of lambs of different birth rank soon after birth

This study investigated the physical state and metabolic status of lambs of different birth ranks soon after birth. The aim was to identify the factors that result in poorer survival rates in triplet than single or twin lambs. Six hundred and twenty one Romney ewes were mated over a 4-day period and 46 of them were observed continually from day 143 of pregnancy until they finished lambing. Blood samples, taken from all lambs within 5 min of birth, were placed on ice, centrifuged and the plasma harvested and subsequently analysed for glucose, fructose, lactate, thyroxine (T4) and gamma-glutamyl transferase (GGT). The rectal temperature of each lamb was recorded at birth and at 1, 2, 3 and 6 h of life. Lambs were weighed and measured at 3 h of age.At birth, triplet lambs were significantly lighter (P < 0.05) and had lower (P < 0.05) plasma fructose and thyroxine than twin and single lambs, higher (P < 0.05) lactate concentrations and a lower rectal temperature (P < 0.05) than twin lambs. These observations suggest that they are subject to placental insufficiency. The packed cell volume was significantly (P < 0.001) higher in twin than triplet lambs. The order at birth of twin or triplet lambs had no effect on birthweight or plasma metabolite concentrations. The smallest triplet was significantly lighter (P < 0.05) and had higher plasma lactate (P < 0.05) concentration than the largest triplet.These physiological limitations found in smaller triplet lambs at birth leave them prone to perinatal mortality. Management techniques, to increase triplet lamb birthweight and thereby improve their survival outcome need further investigation.