Effects of Guanidinoacetic Acid, Creatine, and Choline on Protein Deposition and Creatine Status in Growing Cattle
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Abstract
Creatine is a molecule that stores energy in muscle tissue and is produced in the liver when guanidinoacetic acid is methylated. Guanidinoacetic acid supplementation can improve creatine supply in growing cattle and possibly improve performance when the methyl group (i.e., methionine) supply is adequate. Creatine synthesis increases methyl group consumption, so providing methyl group sources other than methionine, such as choline, may also allow for benefits to guanidinoacetic acid supplementation. Our objective was to evaluate the effects of guanidinoacetic acid and creatine supplementation in the presence or absence of supplemental choline on protein deposition (lean tissue growth) in growing steers. Six ruminally cannulated Holstein steers were housed in metabolism crates to allow for total collection of urine and feces to measure nitrogen retention. The experiment consisted of six 10-day periods, with each animal receiving one of the six treatments in each period. The six treatments included a saline control; 15 g/day guanidinoacetic acid (which consumes methyl groups); or 16.8 g/day creatine (which spares methyl groups), each in the presence or absence of 5 g/day supplemental choline. Relative to control, protein deposition increased when guanidinoacetic acid was provided, but creatine did not affect protein deposition. Supplemental guanidi-noacetic acid and creatine both increased plasma creatine concentrations compared to control, with guanidinoacetic acid leading to a larger increase than creatine. This demonstrates that guanidinoacetic acid was effectively methylated in the body to form creatine. Choline supplementation did not affect protein deposition but increased