Strategies for optimizing nitrogen use by ruminants

Abstract

The efficiency of N utilization in ruminants is typically low (around 25%) and highly variable (10% to 40%) compared with the higher efficiency of other production animals. The low efficiency has implications for the production performance and environment. Many efforts have been devoted to improving the efficiency of N utilization in ruminants, and while major improvements in our understanding of N requirements and metabolism have been achieved, the overall efficiency remains low. In general, maximal efficiency of N utilization will only occur at the expense of some losses in production performance. However, optimal production and N utilization may be achieved through the understanding of the key mechanisms involved in the control of N metabolism. Key factors in the rumen include the efficiency of N capture in the rumen (grams of bacterial N per grams of rumen available N) and the modification of protein degradation. Traditionally, protein degradation has been modulated by modifying the feed (physical and chemical treatments). Modifying the rumen microflora involved in peptide degradation and amino acid deamination offers an alternative approach that needs to be addressed. Current evidence indicates that in typical feeding conditions there is limited net recycling of N into the rumen (blood urea-N uptake minus ammonia-N absorption), but understanding the factors controlling urea transport across the rumen wall may reverse the balance to take advantage of the recycling capabilities of ruminants. Finally, there is considerable metabolism of amino acids (AA) in the portal-drained viscera (PDV) and liver. However, most of this process occurs through the uptake of AA from the arterial blood and not during the 'absorptive' process. Therefore, AA are available to the peripheral circulation and to the mammary gland before being used by PDV and the liver. In these conditions, the mammary gland plays a key role in determining the efficiency of N utilization because the PDV and liver will use AA in excess of those required by the mammary gland. Protein synthesis in the mammary gland appears to be tightly regulated by local and systemic signals. The understanding of factors regulating AA supply and absorption in the mammary gland, and the synthesis of milk protein should allow the formulation of diets that increase total AA uptake by the mammary gland and thus reduce AA utilization by PDV and the liver. A better understanding of these key processes should allow the development of strategies to improve the efficiency of N utilization in ruminants. Keywords: ruminant, nitrogen efficiency ImplicationsRuminants have a low efficiency of N utilization compared with non-ruminants. This low efficiency has implications not only for production performance and economic efficiency but also for the emission of contaminants to the environment. The efficiency of N utilization can be improved through the understanding and modification of factors regulating the efficiency of N utilization in key processes, including N capture in the rumen, ...

Long-term effect of linseed plus nitrate fed to dairy cows on enteric methane emission and nitrate and nitrite residuals in milk

“…N balance was positive and similar between diets with the same N distribution between milk, faeces and urine. In addition, average N efficiency (N in milk/N intake) was similar between CON and LIN + NIT (30%) and close to the data given in the literature (25%, with a range between 15% and 40%, Calsamiglia et al, 2010). This result shows that dairy cows use nitrate in the same way as they use other N sources.…”

Effect of protein supplementation on ruminal parameters and microbial community fingerprint of Nellore steers fed tropical forages

“…It has been estimated that hyper-ammonia producing bacteria have a lower substrate affinity (K m ) than the mixed ruminal bacteria, but the V max of ammonia production is ∼12.5-fold greater than the mixed ruminal bacteria of forage fed animals (Rychlik and Russell, 2000). Therefore, a higher RDP content in the diet could impact both SAD and the concentration of ruminal ammonia, demonstrating the influence of the diet in the activity of rumen microorganisms and nitrogen metabolism in the rumen (Bach et al, 2005;Calsamiglia et al, 2010). Nonetheless, the RDP supplementation did not alter (P > 0.05) the concentration of microbial protein among treatments.…”

“…Although increasing dietary CP concentration in cattle fed silage-based rations has been related with small responses in BW gain and increased emissions of N and P (Huuskonen et al, 2014), feeding supplementary protein to cattle fed tropical forages can increase feed efficiency reduces excessive nitrogen losses to the environment (Agle et al, 2010;Calsamiglia et al, 2010) and increases overall animal performance . Detmann et al (2014) showed positive response to rumen degradable protein (RDP) supplementation on forage intake and nitrogen use efficiency with concomitant positive response in animal performance.…”

Diet effects on urine composition of cattle and N2O emissions

“…For example, univariate meta-analysis showed reduced N output in faeces and urine and improved N-use efficiency in dairy cattle, from 0.25 to 0.30, upon a decrease in N intake from 600 to 300 g/day, respectively (Kebreab et al, 2010). The average N-utilization efficiency in dairy cattle is some 0.25 (range: 0.15 to 0.40; Calsamiglia et al, 2010). Major improvements in N efficiency at the animal level have been shown in practice through increased production levels and reduced dietary N contents (Figure 1).…”