Effects of barley grain processing and dietary ruminally degradable protein on urea nitrogen recycling and nitrogen metabolism in growing lambs1

Abstract

The objective of this study was to determine how interactions between dietary ruminally degradable protein (RDP) level and ruminally fermentable carbohydrate (RFC) alter urea N transfer to the gastrointestinal tract (GIT) and the utilization of this recycled urea N in rapidly growing lambs fed high-N diets. Four Suffolk ram lambs (34.8 +/- 0.5 kg of BW) were used in a 4 x 4 Latin square design with 21-d periods and a 2 x 2 factorial arrangement of dietary treatments. The dietary factors studied were 1) dry-rolled vs. pelleted barley as the principal source of RFC and 2) dietary levels of RDP of 60 vs. 70% (% of CP). All diets contained 28.8 g of N/kg of DM. Experimental diets were composed of 80% concentrate mixture and 20% barley silage (DM basis) and were fed twice daily at 0900 and 1700 as total mixed rations. Nitrogen balance was measured from d 15 to 20, and urea N kinetics were measured from d 15 to 19 using intrajugular infusions of [(15)N(15)N]-urea. Nitrogen intake (P = 0.001) and fecal (P = 0.002) and urinary (P = 0.03) N excretion increased as dietary RDP level increased, but the method of barley processing had no effect. Feeding dry-rolled compared with pelleted barley (P = 0.04) as well as feeding 60% RDP compared with 70% RDP (P = 0.04) resulted in a greater N digestibility. Whole-body N retention was unaffected (P >/= 0.74) by dietary treatment. Dietary treatment had no effect on endogenous production of urea N and its recycling to the GIT; however, across dietary treatments, endogenous production of urea N (45.8 to 50.9 g/d) exceeded N intake (42.3 to 47.9 g/d). Across dietary treatments, 30.6 to 38.5 g/d of urea N were recycled to the GIT, representing 0.67 to 0.74 of endogenous urea N production; however, 0.64 to 0.76 of urea N recycled to the GIT was returned to the ornithine cycle. In summary, although dietary treatment did not alter urea N kinetics, substantial amounts of hepatic urea N output were recycled to the GIT under the dietary conditions used in this study, and additional research is required to determine how this recycled urea N can be efficiently captured by bacteria within the GIT.

Protein requirements for growth in male and female Saanen goats

“…In the present work, a relationship was found between metabolic body weight and endogenous urinary crude protein that was five times greater than that reported by NRC (2007). This value may appear inconsistent; however, other reports in the literature present similar (Ghassemi Nejad et al, 2014) or even greater values than ours for other small ruminants (Kiran and Mutsvangwa, 2007), raising the hypothesis that the excretion of nitrogen is dependent on metabolic processes through which balance is achieved in response to a dietary change (Waterlow, 1999). Indeed, Bohnert et al (2011) reported a variation of N excreted in urine of 400% depending on dietary manipulation.…”

“…This difference may be explained by differences in the diet characteristics because the NRC (2007) reported a DM digestibility coefficient of 0.88, which is greater than that found here. In addition, Lobley et al (2000) and Kiran and Mutsvangwa (2007) reported greater values of nitrogen in feces, approximately 4% of the DMI. This fact raises the hypothesis that the relationship between DMI and fecal crude protein or nitrogen may be different for animals under different conditions.…”

“…The literature has reported variations in nitrogen excretion in feces (Blaxter and Mitchell, 1948;Lobley et al, 2000;Kiran and Mutsvangwa, 2007;Huhtanen et al, 2009;Dias et al, 2011) and urine (Kiran and Mutsvangwa, 2007;Bohnert et al, 2011;Ghassemi Nejad et al, 2014) due to dietary changes and environmental conditions. The circumstances causing this phenomenon are poorly understood (O'Brien et al, 2010;Bernabucci et al, 2010;Mahjoubi et al, 2014).…”

Parameters of Protein Metabolism in Goats Fed Diets With Different Portion of Sugarcane Bagasse

“…The increase of concentrate proportion in a forage based diet did not affect on CP apparent digestibility in goats (CantalapiedraHijar et al, 2009) and in dairy bulls (Wanapat et al, 2013). There is some controversy regarding to the CP digestiblity when portion of dietary forage is increased, which is likely due to the type of ingredients used in some experiments (Lu et al, 2005;Kiran and Mutsvangwa, 2007). Moreover, in this study, the experimental diets were designed to isonitrogenous (Table 2).…”

“…Increasing concentrate proportion in grass hay based diet enhances urinary purine derivative significantly in goats (Cantalapiedra-Hijar et al, 2009). Processing of barley grain increases urinary purine derivatives slightly in rapidly growing lambs fed high nitrogen diets (Kiran and Mutsvangwa, 2007). Supplementation of barley grain enhances microbial protein synthesis in the rumen of steers fed low quality of forage (Marsetyo et al, 2006).…”