Effects of exogenous melatonin in pregnant ewes on offspring performance, live weight and daily growth rate of lambs for fattening, as well as milk quality

Context Melatonin has been used in sheep as a means of increasing survival and growth of offspring. Evidence suggests that administering melatonin implants to pregnant sheep or lambs during their fattening period has positive effects. Aims To identify the optimal timing for melatonin treatments in ewes before lambing, and lambs during lactation. Methods Experiment 1 involved 49 pregnant ewes and their lambs (n = 61). Ewes were assigned to one of five groups that differed in whether and when they received a single melatonin implant before lambing (−45, −30, −15 days, or non-implanted control ewes); milk samples were collected at 30 days after lambing. Experiment 2 involved 44 lambs from 32 ewes, assigned to one of four groups that differed in when the lambs received two melatonin implants (15, 30 or 45 days of age) during lactation. Key results In Experiment 1, groups did not differ in live weight (LW) at birth, or at 15, 30, and 45 days after birth. Male lambs in the −30 group had (P < 0.05) higher LW30 and LW45 than did group 0 male lambs. The interaction effect of treatment × sex was significant for average daily growth 0–30 and 0–45; specifically, −30 male lambs grew faster than male lambs in the other three groups (P < 0.05). Milk samples from implanted ewes had (P < 0.05) higher fat content than milk from control ewes. In Experiment 2, at slaughter (90 days of age), lambs in group 45 had higher (P < 0.05) LW and average daily growth from weaning to 90 days of age than lambs in the other four groups. Lambs in the three groups that had received melatonin implants put on more weight (P < 0.05) than did the control lambs, especially lambs in group 45, which translated into significantly (P < 0.05) higher feed conversion rates in the treatment groups. Conclusions Implanting ewes 30 days before lambing was associated with increased growth rates during lactation; particularly in males. Implanting lambs at 45 days of age produced the highest growth and feed conversion rates in the fattening period. Implications Melatonin treatments of ewes in pregnancy and lambs during lactation are promising methods for increasing the productivity of lamb meat production systems.