The effects of crude protein concentration and slow release urea on nitrogen metabolism in Holstein steers

Abstract

This experiment was conducted to determine the effects of slow release urea (SRU) and its interaction with crude protein (CP) level in the diet on N metabolism in Holstein steers. Eight rumen-cannulated Holstein steers (body weight 265 ± 18 kg) were used in a replicated 4 × 4 Latin square design with a 2 × 2 factorial treatment structure. Treatment factors were the CP level in the diet, 10.9% versus 12.1% CP, and the non-protein nitrogen source used, urea versus SRU. Total collection of urine and faeces for 7 days allowed the estimation of N retention and diet digestibility. In addition, blood and rumen sampling allowed estimation of rumen fermentation and blood N profiles. Decreasing CP intake from 12.1% to 10.9% reduced urinary N output, but also reduced diet digestibility and N retention. When compared to urea, SRU did not alter N retention, but reduced ruminal ammonia and plasma urea concentrations. Although SRU did not improve N retention at either CP level, rumen ammonia and plasma urea concentrations were reduced, which may indicate that SRU may carry a lower risk for toxicity when compared to urea when fed at higher dietary concentrations.

Influence of polymer-coated slow-release urea on total tract apparent digestibility, ruminal fermentation and performance of Nellore steers

“…Animals fed the diets containing slow-release urea (SRA2 and SRB2) showed lower ammonia concentration in ruminal fluid compared to those fed feed grade urea, suggesting a decrease of urea hydrolysis in rumen or a greater nitrogen utilization by rumen microorganisms. The latter result was reported in in vitro [30], in situ [5], and in vivo studies [31]. Diets containing slow-release urea sources showed higher propionate compared to feed grade urea.…”

Metabolic profiles of cow's blood; a review

“…However, ammonium acetate, ammonium succinate, acetamide and diammonium phosphate are better substrates for microbial protein synthesis than urea . Holder et al . reported that slow release urea did not alter N retention but reduced ruminal ammonia and plasma urea concentrations.…”

Effects of polymer coated slow-release urea on ruminal fermentation and nutrient total tract digestion of beef steers

“…However, we did not observe statistically significant differences among the urea sources (SRU and U) for nutrient intake and digestibility (P>0.05). Previous studies (Puga et al, 2001;Galina et al, 2003;Galo et al, 2003;Xin et al, 2010) showed that SRU supplementation may improve the intakes of DM and nutrients when compared with U due to a higher activity of fibrolytic bacteria, resulting from an improved energy and N utilization by these microorganisms (Pinos-Rodríguez et al, 2010;Xin et al, 2010), with a consequent increase in the fiber fermentation (Taylor-Edwards et al, 2009;Xin et al, 2010;Holder et al, 2013). Lean et al (2005) analyzed data from continuous culture fermenter studies and reported enhanced microbial CP synthesis and increased total tract digestion of CP and DM when a slow-release urea was used.…”

“…According to Russell et al (2009), cellulolytic ruminal bacteria are unable to grow on other N sources in the absence of NH 3 and the stimulation of cellulolytic species by precursors of various N sources suggests a quantitative dependence on NH 3 -N-release rate for optimum growth (Cherdthongand Wanapat, 2010). Thus, the use of SRU should result in a better synchrony between the urea hydrolysis and ammonia utilization by ruminal bacteria (Holder el al., 2013), which would be demonstrated by higher N mic and microbial CP values for diets with SRU. Mehrez et al (1977) stated that the ammonia concentration in the rumen needs to be 23.5 mg dL −1 for maximal fermentation rate.…”