Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2016
Publication Date: 8/24/2016
Publication URL: http://handle.nal.usda.gov/10113/63210
Citation: Foote, A.P., Hales, K.E., Freetly, H.C. 2016. 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. Domestic Animal Endocrinology. 57:100-107. doi:10.1016/j.domaniend.2016.05.004
Interpretive Summary: Feed intake of cattle given unlimited access to feed is a large contributor to the efficiency with which cattle use nutrients for growth. Little is currently known about factors that contribute to differences in feed intake of cattle. Ghrelin is a hormone that has been associated with feed intake in rodents and humans. This experiment was performed to determine if the concentrations of the two forms of ghrelin change over a period of time and if these concentrations and changes are associated with feed intake. Steers had greater initial acyl ghrelin concentrations than heifers, but decreased over time to be similar to concentrations in heifers. Total ghrelin concentrations were initially lower in heifers but increased to be similar to steers. Greater initial concentrations of acyl ghrelin were associated with greater feed intake, growth rates, and feed efficiency. This indicates that ghrelin is likely involved in the regulation of feed intake of cattle with unlimited access to feed, and could be a promising candidate for a marker for feed intake in beef cattle.
Technical Abstract: Ghrelin is a peptide hormone produced in the gut that is implicated in signaling appetite and regulating 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 ADG measurement period and determine the association of those ghrelin measurements with DMI, ADG, G:F, and residual feed intake (RFI) in finishing beef steers and heifers. Blood samples were collected on d 0 and d 83 and analyzed for acyl and total ghrelin using commercially available RIA. Steers had greater DMI during the last 35-d period of the experiment compared to 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 d 0 than heifers, but concentrations decreased by d 83 to equal concentrations in heifers (P < 0.01). Total ghrelin concentrations were lower on d 0 in heifers but increased by d 83 and did not differ from steers on d 83 (P < 0.01). A mixed model analysis was utilized to determine the association of ghrelin concentrations and ratio with production traits, independent of breed and sire effects. There was an interaction of d 0 acyl ghrelin concentrations with time of sample collection (P < 0.01) for the 84-d DMI, indicating a general positive association of acyl ghrelin with DMI, but the association weakened as time of sample collection increased. There was tendency (P < 0.10) for a positive association of the mean ghrelin ratio with DMI in the last 35-d period. There was an interaction of d 0 acyl ghrelin concentrations with time of sample collection for ADG (P < 0.01) and a tendency for G:F (P < 0.10), indicating a general positive association of acyl ghrelin with ADG and G:F, but the association weakened as time of sample collection within day increased. The d 0 ghrelin ratio interacted with time of sample collection similar to the other variables 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 efficiency of finishing beef cattle, and data lend more evidence that ghrelin is involved in appetite regulation of ad libitum fed cattle.