Changes in acyl and total ghrelin concentrations and their association with dry matter intake, average daily gain, and feed efficiency of finishing beef steers and heifers.

Ghrelin is a peptide hormone produced in the gut that is implicated in signaling appetite and regulating dry matter intake (DMI). The objective of this experiment was to determine the change in acyl ghrelin, total ghrelin, and the ghrelin ratio (acyl ghrelin/total ghrelin) over an 84-d DMI and average daily BW gain (ADG) measurement period and to determine the association of those ghrelin measurements with DMI, ADG, ADG:DMI ratio (G:F), and residual feed intake in finishing beef steers and heifers. Blood samples were collected on day 0 and day 83 before feeding and between 0730 h and 1130 h. Samples were analyzed for acyl and total ghrelin using commercially available RIA. DMI in steers was greater during the last 35-d period of the experiment compared with the first 35 d (P < 0.01) and was greater than heifers regardless of period (P < 0.01). Steers had greater acyl ghrelin concentrations on day 0 than heifers, but concentrations decreased by day 83 to equal concentrations in heifers (P < 0.01). Total ghrelin concentrations were lower on day 0 in heifers but increased by day 83 and did not differ from steers on day 83 (P < 0.01). A mixed model analysis was used to determine the association of ghrelin concentrations and ratio with production traits, independent of breed and sire effects. There was an interaction of day 0 acyl ghrelin concentrations with time of sample collection for 84-d DMI (P < 0.01), ADG (P < 0.01), and G:F (P = 0.09), indicating a general positive association of acyl ghrelin with production traits, but the association weakened as time of sample collection increased. The mean ghrelin ratio tended (P = 0.08) to be positively associated with DMI in the last 35-d period. The ghrelin ratio on day 0 interacted with time of sample collection for ADG and G:F (P < 0.05), indicating an overall positive association of the ghrelin ratio with ADG and G:F. Results indicate that ghrelin is associated with DMI, ADG, and feed efficiency of finishing beef cattle, and data lend more evidence that ghrelin is involved in appetite regulation of ad libitum fed cattle.