Long-term infusions of ghrelin and obestatin in early lactation dairy cows

Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor and a potential orexigenic agent in monogastrics and ruminants. Obestatin has been reported to have the opposite (anorexigenic) effect. Fifty one multiparous cows were randomly allocated to 1 of 3 groups (n = 17): a control group and 2 groups with cows continuously infused with 0.74 mumol/d of ghrelin (GHR group) or obestatin (OBE group) subcutaneously. Infusions began 21 d in milk, and treatments continued for 8 wk. Generalized linear models were used to determine the treatment effect on average daily and cumulative milk production and composition, and plasma ghrelin, growth hormone, insulin-like growth factor (IGF)-1, leptin, nonesterified fatty acids, and glucose. Mixed models, with cow included as a repeated effect, were used to determine if treatment effects differed by week postcalving for milk production, body weight, and body condition score (BCS; scale 1 to 10). Parity, breed, week of the year at calving, treatment, week postcalving, and the 2 wk preexperimental average of each measure (covariate) were included as fixed effects. Treatment did not affect dry matter intake. Cows infused with GHR lost more BCS (-0.71 units) over the 8-wk study period than the control (-0.23 BCS units) cows, and on average were thinner than cows in either of the other 2 treatments (0.2 BCS units). Consistent with the extra BCS loss in GHR cows, plasma IGF-1, glucose, and leptin concentrations were reduced and plasma nonesterified fatty acid concentrations were greater in GHR cows. Despite a numerical tendency for GHR cows to produce more milk (1,779 kg) than control (1,681 kg) or OBE (1,714 kg) cows during the 8-wk period, milk production differences were not statistically different. However, the timing of the numerical separation of the lactation curves coincided with the significant changes in BCS, IGF-1, and leptin. Results indicate a positive effect of ghrelin infusion on lipolysis. Further research is required to determine if the numerical increase in milk production, which coincides with the increased negative energy balance, is real.