Association of plasma ghrelin concentrations with feed intake in beef cattle

Abstract Text: Active ghrelin is an acylated peptide produced in the gastrointestinal tract of animals that is thought to stimulate appetite. Cattle used in this experiment were sired by bulls representing five breeds in the U.S. including: Hereford, Angus, Limousin, Charolais, and Gelbvieh. Steers (n=128) and heifers (n=133) were fed a finishing diet and individual intake was recorded for 84 d.  Blood samples were collected via jugular puncture at 113 d on feed. Active ghrelin was protected by acidifying the blood plasma and adding a protease inhibitor. Active ghrelin was quantified using a commercial RIA specific for the acylated form of ghrelin. The mixed model procedure of SAS was utilized to determine factors influencing active ghrelin levels. Fixed effects included sex, sire breed, dam breed, total dry matter intake (TDMI), and BW at time of blood collection. Sire nested within sire breed was included as a random effect. A mixed model was also used to determine if concentrations of active ghrelin could be used to predict TDMI. Fixed effects included concentrations of active ghrelin, sire breed, dam breed, sex, BW, and sire nested within sire breed was included as a random effect. Concentrations of active ghrelin were positively associated with TDMI (P = 0.012) when sex and breed effects were accounted for in the model. Regardless of breed, heifers had lower TDMI than steers (P = 0.012) but tended to have greater concentrations of active ghrelin (P = 0.099). Gelbvieh-sired cattle had the greatest concentrations of active ghrelin and Angus, Limousin, and Charolais had the lowest concentrations while concentrations of ghrelin in Hereford-sired cattle were intermediate (P = 0.003). Angus-sired cattle had the highest TDMI while Limousin-, Charolais-, and Gelbvieh-sired cattle had the lowest TDMI with Hereford cattle intermediate (P < 0.001). Modeling the data showed that active ghrelin concentrations had a positive association with TDMI; however, both the sex and sire breed effects indicate that cattle with lower intakes (e.g. heifers and Gelbvieh-sired cattle) tend to have greater concentrations of active ghrelin than cattle with higher intakes. Data indicate there is a genetic effect on active ghrelin levels that may affect the association with intake. USDA is an equal opportunity provider and employer. Funded in part by NIFA Grant 2011-68004-30214 through the National Program for Genetic Improvement of Feed Efficiency in Beef Cattle. 

Keywords: breed differences, feedlot cattle, gut peptides