Urea metabolism in beef steers fed tall fescue, orchardgrass, or gamagrass hays1,2

Abstract

Two experiments were conducted to assess effects of endophyte treatments (Exp. 1), forage species (Exp. 2), and supplementation (Exp. 2) on urea production, excretion, and recycling in beef steers. Infusion of (15,15)N-urea and enrichment of urea in urine samples were used to calculate urea-N entry and recycling to the gut. Acceptably stable enrichment of (15)N-urea in urine was obtained after 50 h of intrajugular infusion of (15,15)N-urea, indicating that valid data on urea metabolism can be obtained from steers fed forages twice daily. After adjustment by covariance for differences in N intake among treatments in Exp. 1, steers fed endophyte-infected tall fescue had less (P<0.10) urea-N entry, recycling to the gut, and return of recycled urea-N to the ornithine cycle than those fed endophyte-free or novel endophyte-infected tall fescue. However, urea-N urinary excretion or return to the gut was similar among endophyte treatments when expressed as a proportion of urea-N entry. Urea-N entry and return to the gut in Exp. 2 was similar in steers fed gamagrass or orchardgrass hay after adjustment by covariance for differences in N intake. Less (P<0.01) urinary excretion, expressed as grams per day or as a proportion of urea-N entry, with gamagrass than with orchardgrass was associated with faster in vitro NDF-N digestion with gamagrass. Supplementation of gamagrass or orchardgrass with 1.76 kg/d of readily fermentable fiber and starch decreased urea entry (P<0.06) and urinary excretion of urea (P<0.01). Interactions between hay source and supplement reflected a greater response to supplementation for steers fed orchardgrass than for those fed gamagrass. After adjustment for differences among treatments in N supply, results of both experiments support the concept of improved N use in response to increased carbohydrate fermentability in the rumen, due either to inherent differences in forage fiber or to supplementation with readily fermentable carbohydrate (starch or fiber). Closer coordination of ruminal fermentation of carbohydrate and N sources provided greater and more efficient capture of dietary N as tissue protein in forage-fed steers.

In vitro rumen simulated (RUSITEC) metabolism of freshly cut or wilted grasses with contrasting polyphenol oxidase activities

“…Greater N use efficiency in cattle on cocksfoot has previously been reported (Tyrrell et al. , 1992; Huntington et al. , 2009) compared with gamagrass ( Tripacum dactyloides ) and alfalfa ( Medicago sativa ) respectively.…”

A comparison of nitrogen utilization and urea metabolism between Tibetan and fine-wool sheep1

“…To date, physiological adaptation to inadequate N resources and feed supply have been investigated in dairy cattle (Marini and Van Amburgh, 2003), beef cattle (Archibeque et al, 2001;Huntington et al, 2009;Titgemeyer et al, 2012), yak (Guo et al, 2012), sheep (Sarraseca et al, 1998;Lobley et al, 2000;Marini et al, 2004), and goats (Brun-Bellut, 1997). The efficiency of N utilization and the ability of the animal to adapt to low N diets is affected by various factors, such as the dietary energy content, N digestion, urea kinetics, rumen microbial activity, urea reabsorption by the kidney, the physiological state of the animal, and animal species (Wang et al, 2011;Marini et al, 2004).…”

“…The experiment procedures were mainly according to those described by Lobley et al (2000) and Huntington et al (2009). The protocol consisted of 4 periods, each lasting 21 d, with 15 d for dietary adaptation (Marini and Van Amburgh, 2003) and 6 d for collection of feces and urine.…”

Rumen Microbiology: From Evolution to Revolution

“…Several inhibitors of ruminal urease activity substantially reduce urease activity; but, inhibitors usually provide a short-term effect because remaining urease capacity is still great enough to hydrolyze ruminal urea and possibly because of microbial adaptation to the inhibitors (Whitelaw et al 1991 ;Ludden et al 2000 ). Slow-release urea products provide constant supply of ammonia to rumen microorganism for their growth, which also improves nutrition utilization for low-quality forages and reduces plasma ammonia concentrations (Ribeiro et al 2011 ;Huntington et al 2009 ). Slow-release urea products provide constant supply of ammonia to rumen microorganism for their growth, which also improves nutrition utilization for low-quality forages and reduces plasma ammonia concentrations (Ribeiro et al 2011 ;Huntington et al 2009 ).…”