Nitrogen metabolism and recycling in yaks (Bos grunniens) offered a forage - concentrate diet differing in N concentration

Abstract

An experiment was conducted to characterise N use efficiency and quantify urea fluxes in yaks offered four levels of dietary N (1.43%, 1.97%, 2.45% and 2.90% of diet DM) in a 4 · 4 Latin square design. The incremental increase in N intake linearly increased N retention (P = 0.003) and the excretion of urinary N (P < 0.001), but no difference (P > 0.05) in faecal N excretion was observed in growing yaks fed any of the four diets. Microbial N production had quadratic (P < 0.001) responses to dietary N, characterised by the highest microbial N production occurring in the 1.97% N diet (P < 0.05). As the N content of the diet increased, the urinary excretion of urea increased from 13% to 27% of urea entry rate (quadratic, P < 0.001), whereas gastrointestinal entry urea returned to ornithine cycling decreased from 46% to 40% (linear, P < 0.001), and the gastrointestinal entry urea used for anabolism increased from 50% to 56% (linear, P < 0.001). Gastrointestinal entry urea incorporated into bacterial N decreased linearly (P < 0.001) with incremental increase in N intake, and the greatest concentration (23.5%) of bacterial N originating from plasma urea N was in yaks fed the 1.43% N diet. As much as 87% of the urea synthesised in the liver was returned to the gastrointestinal tract when the yaks were fed a diet with 1.43% N (1.1 times the maintenance N level). Moreover, constantly greater urea production than the intake of digestible N, and the gastrointestinal-urea clearance than the kidney-urea clearance were observed, respectively, in the growing yaks, regardless of the level of N intake. These results suggest that yaks might be more efficient at utilising N under harsh environment than are cattle.

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

“…Like in previous reports (Marini and Van Amburgh, 2003;Guo et al, 2012), we observed that the urea pool size became smaller as the level of dietary N decreased. In contrast, turnover time decreased with increasing dietary N, reflecting increases in GER and kidney urea clearance as dietary N increased.…”

“…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).…”

“…Urinary N, urinary urea N, and the proportion of urea N in total excreted urinary N increased as dietary N increased (Ergene and Pickering, 1978;Leng et al, 1985;Tebot et al, 1998;Marini et al, 2004;Guo et al, 2012), indicating that the increase in urinary N was largely associated with increases in the urinary urea N, especially when dietary N was sufficient .…”

“…The urea pool size and turnover time were calculated from the urea space and urea concentration in the urea pool according to Harmeyer and Martens (1980), assuming the urea space to be 48.7% of BW (Bartle et al, 1988) and the concentration of the urea pool to be equal to plasma urea N (Pun; Marini and Van Amburgh, 2003). Turnover time was estimated from urea N pool size and the rate of urea N production, assuming steady state conditions (Guo et al, 2012). …”

Effects of Starvation on Lipid Metabolism and Gluconeogenesis in Yak

“…The most recent research declared that yak have developed special regulating mechanisms in the kidney in terms of glomerular filtration rate and purine derivative excretion to help the animal to adapt the alpine environment (Wang et al, 2009). Another paper from the same research team showed that the yak might be more efficient at utilizing N in a harsh environment than are cattle (Guo et al, 2012). However, there is no information on yak’ fat storage mobilization and metabolism during starvation.…”