Ruminal ammonia load affects leucine utilization by growing steers1

Abstract

Six ruminally cannulated Holstein steers (initial BW = 189 +/- 11 kg) housed in metabolism crates were used in a 6 x 6 Latin square to study effects of ruminal ammonia load on Leu utilization. All steers received a diet based on soybean hulls (2.7 kg of DM/d), ruminal infusions of 200 g of acetate/d, 200 g of propionate/d, and 50 g of butyrate/d, as well as an abomasal infusion of 300 g of glucose/d to provide energy without increasing microbial protein supply and an abomasal infusion of a mixture (238 g/d) of all essential AA except Leu. Treatments were arranged as a 3 x 2 factorial and included Leu (0, 4, or 8 g/d) infused abomasally and urea (0 or 80 g/d) infused ruminally. Abomasal Leu infusion linearly decreased (P < 0.05) both urinary and fecal N excretions and linearly increased (P < 0.05) retained N, but the decreases in urinary N excretion in response to Leu tended (P = 0.07) to be greater, and the increases in retained N in response to Leu were numerically greater in the presence of the urea infusion. Although urea infusions increased (P < 0.05) plasma urea concentrations, urinary N excretions, and urinary urea excretions, retained N also was increased (P < 0.05). The efficiency of deposition of supplemental Leu ranged from 24 to 43% when steers received 0 or 80 g of urea/d, respectively. Under our experimental conditions, increasing ammonia load improved whole-body protein deposition in growing steers when Leu supply was limiting.

Effect of ruminal ammonia supply on lysine utilization by growing steers1

“…Some of the Gln can be catabolized in the kidney to generate urinary ammonia. Our observed increases in urinary ammonia excretion in response to urea supplementation were consistent with those of McCuistion et al (2004) when growing steers were limited by His and those of Awawdeh et al (2005) when growing steers were limited by Leu. In the current study, as well as in the work of McCuistion et al (2004) and Awawdeh et al (2005), the increases in urinary ammonia were not large.…”

“…Our observed increases in urinary ammonia excretion in response to urea supplementation were consistent with those of McCuistion et al (2004) when growing steers were limited by His and those of Awawdeh et al (2005) when growing steers were limited by Leu. In the current study, as well as in the work of McCuistion et al (2004) and Awawdeh et al (2005), the increases in urinary ammonia were not large. In the current study, urinary ammonia represented only 3% of the total urinary N, whereas urinary urea represented 84% of total urinary N at our highest level of urea infusion, suggesting that increases in total urinary N were mainly attributed to increases in urinary urea.…”

“…The increases in N retention in response to urea infusion were consistent with McCuistion et al (2004), who reported a numeric (P = 0.16) increase in N retention from 35.1 to 37.1 g/d when supplemental urea was increased from 0 to 80 g/d in growing steers limited by His. Awawdeh et al (2005) observed significant improvements in N retention from 24.7 to 29.2 g/d when ammonia loading was induced in Leu-deficient steers. In contrast, Awawdeh et al (2004) did not observe any changes in N retention of steers limited by Met when 40 and 80 g urea/d was ruminally infused.…”

“…Similar to plasma Gly, Ala concentrations were linearly decreased in response to ruminal ammonia loads, perhaps reflecting an increase in Ala utilization. Decreases in Ala were also reported when ammonia loading was induced in growing steers limited by Met , His (McCuistion et al, 2004), and Leu (Awawdeh et al, 2005). Via transamination reactions, Ala may be used as a source of Asp-N for ammonia detoxification (Harper et al, 1984).…”

“…When growing cattle were limited by Met, ammonia loading did not affect N retention , but Awawdeh et al (2005) reported significant improvements in N retention when steers limited by Leu were given increased ammonia loads. Thus, ammonia loading may have different effects when different AA are limiting.…”