Prolonged, moderate nutrient restriction in beef cattle results in persistently elevated circulating ghrelin concentrations

Four ruminally cannulated steers (BW 581 +/- 12.8 kg) were used in a crossover design to determine the effects of prolonged, moderate nutrient restriction on plasma ghrelin concentrations and to establish the relationship of plasma ghrelin concentrations with hormones and metabolites indicative of nutritional status and end products of rumen fermentation. A high-grain diet was offered at 240% of the intake needed for BW maintenance (2.4 x M) or 80% of the intake needed for BW maintenance (0.8 x M). To standardize, all steers were acclimated to 2.4 x M before initiation of the treatment periods. During period 1, 2 steers continued at 2.4 x M, whereas intake for the remaining 2 steers was restricted to 0.8 x M. On d 7, 14, and 21 after initiation of the restriction, serial blood samples were collected at 15-min intervals via indwelling jugular catheter and were assayed for ghrelin, GH, NEFA, insulin, and glucose concentrations. Rumen fluid was collected at hourly intervals for evaluation of pH and VFA concentrations. After period 1, steers were weighed, the treatments were switched between steer groups, and the intake amounts were recalculated. Intake of 2.4 x M was established for previously restricted cattle, and period 2 was then conducted as described for period 1. Data were analyzed statistically as repeated measures in time, and stepwise regression was used to define the relationship of plasma ghrelin with hormones, metabolites, and end products of rumen fermentation. Throughout the 21-d treatment period, plasma ghrelin concentrations were elevated (P <= 0.001) for steers offered the 0.8 x M diet. Plasma GH and NEFA concentrations were increased (P <= 0.001) and insulin concentrations were decreased (P <= 0.001) for steers offered 0.8 x M, indicating a catabolic state throughout the treatment period. Stepwise regression indicated that the fluctuation in plasma ghrelin was correlated weakly with hormones and metabolites indicative of nutritional status as well as end products of carbohydrate fermentation in the rumen. These data are consistent with the hypothesis that plasma ghrelin concentrations are elevated for cattle experiencing prolonged, moderate nutrient restriction that results in a catabolic state. Fluctuations in plasma ghrelin concentrations, however, have a weak relationship with hormones, metabolites, and end products of rumen fermentation.