122 Dietary supplementation with an arginine product between Days 1

Low fertility limits reproductive efficiency in cattle. This study was conducted with multiparous Brangus cows receiving dietary supplementation of a rumen-protected arginine product (RPAA) or unprotected arginine product (RUAA). During the entire experimental period, cows grazed green pasture and had free access to drinking water and mineral blocks. At the onset of lactation, 107 cows were assigned randomly to one of three treatment groups: dried distillers grain (DDG) only (n=36), DDG top-dressed with RUAA (n=35); and DDG top-dressed with RPAA (n=36). After a two-month postpartum interval, cows underwent estrus synchronization and were then bred via artificial insemination (AI; the day of breeding = Day 0 of gestation). Each cow received AI only once. One day after breeding until Day 60 of gestation, cows were fed daily 0.64-kg DDG, 0.56-kg DDG + 0.28-kg RUAA (2% of estimated daily intake of 14-kg dry matter from pasture), or 0.56-kg DDG + 0.28-kg RPAA. On each day of the supplementation period, cows were moved to pens to receive supplement once and then returned to pasture. On Days 40 and 60 of gestation, ultrasound determinations of pregnancy were made. All pregnant cows carried a single conceptus. On Day 60 of gestation, blood samples were obtained from the jugular vein. All groups of cows grazed normally and appeared healthy. Dietary supplementation of RUAA and RPAA enhanced (P<0.05) the birth rate of live-born calves (the number of live-born calves/the total number of cows; X2 analysis) from 22% in cows receiving DDG alone to 34% (P<0.01) and 36% (P<0.01), respectively. The beneficial effect of arginine supplement was associated with increases in the concentrations of citrulline, arginine, ornithine and proline, but decreases in the concentrations of ammonia in plasma (P<0.05). Thus, our simple nutritional method increased the reproductive efficiency of lactating beef cows. Supported by Texas A&M AgriLife Research.