Simple Summary
High rates of embryonic deaths are a major factor limiting reproductive efficiency in cattle, particularly in tropical and subtropical regions of the world. However, effective nutritional methods to prevent or alleviate this problem are not available. Results of studies with swine, sheep, rats, and humans revealed an important role of arginine (a conditionally essential amino acid for gestating mammals and their fetuses) in embryonic and fetal survival, growth, and development via the production of bioactive molecules, including nitric oxide, polyamines, and creatine. Because arginine is extensively degraded by ruminal microbes, it must be supplied to ruminants either as a rumen-protected supplement or via intravenous or intragastric administration to impact reproductive performance. An alternative to arginine is the use of citrulline based on our recent discovery that extracellular Cit does not undergo catabolism by ruminal microbes in cattle and sheep. Results from the present study indicate that dietary supplementation with 0.5% citrulline (in either a rumen-protected or unprotected form) to lactating beef cattle between Days 1 and 60 of gestation increased concentrations of citrulline, arginine, and insulin in maternal blood, decreased those of ammonia (a metabolite that is highly toxic to embryos and fetuses at elevated concentrations), and improved embryonic survival. This simple method of dietary supplementation for pregnant cows eliminates the need for encapsulation of citrulline or arginine via expensive engineering techniques and the impractical intravenous or intragastric infusions of citrulline or arginine in production settings.
Abstract
Low fertility limits reproductive efficiency in cattle. This study was conducted with multiparous Brangus cows receiving dietary supplementation with or without L-citrulline [Cit; an immediate precursor of L-arginine (Arg)]. During the entire experimental period, cows grazed green pasture and had free access to drinking water and mineral blocks. One hundred and seven (107) cows were assigned randomly to one of three treatment groups: dried distillers grains with solubles (DDGS) without Cit supplement (n = 36); DDGS top-dressed with rumen-protected Cit product (RPAA; n = 36); or unprotected Cit product (RUAA; n = 35). After 2 months of lactation, all cows were synchronized to estrus and were bred once via artificial insemination. From Day 1 to Day 60 of gestation, cows were individually fed once daily 0.84 kg of a supplement (DDGS; control), 0.56 kg of DDGS plus 0.28 kg of RUAA (containing 0.07 kg of unencapsulated Cit), or 0.56 kg of DDGS plus 0.28 kg of RPAA (containing 0.07 kg of rumen-protected Cit). The supplemental dose of Cit was equivalent to 0.5% of the estimated daily intake of 14 kg dry matter from pasture. On Days 40 and 60 of gestation, ultrasound was used to determine pregnancy rates. Each pregnant cow had a single conceptus. On Day 60 of gestation, blood samples were obtained from the jugular vein. All cows grazed normally and appeared healthy. Birth rates for live-born calves were 22% and 35% in cows receiving DDGS alone and Cit supplementation, respectively (p < 0.05). The beneficial effect of Cit was associated with increases in concentrations of Cit (+19%), Arg (+20%), ornithine (+19%), proline (+17%), and insulin (+82%) but decreases in concentrations of ammonia (–14%) in maternal plasma (p < 0.05). Thus, dietary supplementation with Cit is a simple, novel, and cost-effective nutritional method to increase the reproductive efficiency of lactating beef cows.