Plasma ghrelin concentrations of beef cattle consuming a similar amount of dietary energy supplied by different ingredients1

Abstract

Previous research demonstrated increased plasma ghrelin concentrations in beef cattle when intake of a high-grain diet was restricted. Two experiments were conducted to determine whether differences in DMI influenced plasma ghrelin concentrations when energy intake was similar but cattle were in either an anabolic or a catabolic state. In Exp. 1, five steers (BW = 592.6 +/- 9.3 kg) were offered dietary treatments of 1) 50:50 hay:concentrate (HY) to meet the NE(m) requirement and were supplied an additional 3.4 Mcal of NE(g) daily, 2) or a diet composed of 10:90 hay:concentrate but were limit-fed to achieve an energy intake similar to that of the HY steers (LFC). The LFC treatment met the NE(m) requirement of each steer and supplied 3.6 Mcal of NE(g) daily. The experiment was conducted as a crossover design composed of 2 21-d periods. In the first period, 2 steers were assigned to the HY treatment and 3 steers were assigned to the LFC treatment. On d 21 after initiation of the dietary treatment, serial blood samples were collected via indwelling jugular catheter, using periods of frequent sampling in which samples were collected at 15-min intervals. The periods of frequent sampling were spread throughout the beginning, middle, and end of the 12-h feeding interval. After the first period, steers were weighed, dietary treatments were switched between steer groups, and intake amounts were recalculated on the basis of the first-period ending BW. The second-period adaptation and sampling were repeated as described for the first period. Plasma samples were assayed for ghrelin, insulin, GH, and NEFA concentrations. Experiment 2 was conducted using the same methodology as Exp. 1, except that steers were in a catabolic state. Five steers (BW = 718.3 +/- 12.8 kg) were offered the HY or LFC diet at an amount that would supply 80% of the NE(m) required to maintain BW. For Exp. 1, energy intake was sufficient to result in similar (P = 0.14) BW gains between treatment groups. Experiment 2 energy intake resulted in a loss of BW that was similar (P = 0.66) between treatment groups. In both experiments, the decreased energy density of the HY diet resulted in greater (P < or = 0.001) DMI for HY steers compared with LFC steers. Regardless of catabolic or anabolic state, plasma ghrelin, GH, and insulin were similar (P > or = 0.44) when energy intakes were similar despite differences in DMI between HY and LFC steers. Plasma NEFA concentrations were similar (P > or = 0.45) between treatment groups in an anabolic state but tended to differ (P = 0.09) as a result of treatment for cattle in the catabolic state. These data are consistent with the hypothesis that quantity of DMI does not influence plasma ghrelin concentrations of steers when energy intake is similar.