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

¹ Department of Animal and Range Sciences, South Dakota State University, Brookings, 57007
² Department of Animal Sciences, Berry College, Mt. Berry, GA 30149
³ Department of Animal Science, Iowa State University, Ames, 50011

^* To whom correspondence should be addressed. E-mail: aimee.wertz{at}sdstate.edu.

	Abstract

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 intake needed for BW maintenance (2.4xM) or 80% of intake needed for BW maintenance (0.8xM). To standardize, all steers were acclimated to 2.4xM before initiation of the treatment periods. During period I, 2 steers continued at 2.4xM, whereas intake for the remaining 2 steers was restricted to 0.8xM. On d 7, 14, and 21 following initiation of the restriction, serial blood samples were collected at 15-min intervals via indwelling jugular catheter and assayed for ghrelin, GH, NEFA, insulin (INS) and glucose (GLU) concentrations. Rumen fluid was collected at hourly intervals for evaluation of pH and VFA concentrations. Following period I, steers were weighed, treatments were switched between steer groups, and intake amounts were recalculated. Intake of 2.4xM intake was established for previously restricted cattle, and period II then was conducted as described for period I. 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 0.8xM steers. Plasma GH and NEFA concentrations were increased (P 0.001) and INS concentrations were decreased (P 0.001) for 0.8xM steers indicating a catabolic state throughout the treatment period. Stepwise regression indicated that the fluctuation in plasma ghrelin was correlated weakly to hormones and metabolites indicative of nutritional status as well as end-products 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 result in a catabolic state. Fluctuations in plasma ghrelin concentrations, however, have a weak relationship with hormones, metabolites, and end-products of rumen fermentation.

Key Words: cattle, ghrelin, nutrient restriction