Abstract
The purpose of this study was to investigate the effects of oscillating crude protein (CP) concentration diet on the nitrogen utilization efficiency (NUE) of calves and determine its mechanism. Twelve Holstein calves were assigned randomly into static protein diet (SP, 149 g/kg CP) and oscillating protein diet (OP, 125 and 173 g/kg CP diets oscillated at 2-d intervals) groups. After 60 days of feeding, the weights of total stomach, rumen and omasum tended to increase in calves fed OP. The apparent crude fat digestibility, NUE and energy metabolism also increased. In terms of urea-N kinetics evaluated by urea-15N15N isotope labeling method, the urea-N production and that entry to gastrointestinal tended to increase, and urea-N reused for anabolism increased significantly in calves fed OP during the low protein phase. These data indicate that urea-N recycling contributed to improving NUE when dietary protein concentration was low. In addition, the differentially expressed genes in rumen epithelium and the rumen bacteria involved in protein and energy metabolism promoted the utilization of dietary protein in calves fed OP.
Highlights
Ruminants convert about 20% to 30% of dietary nitrogen (N) into animal protein, and the rest is excreted in urine and feces [1], which has adverse economic and environmental implications
In terms of energy metabolism, GE intake, digestive energy, net energy for maintenance, and combined net energy were higher in calves fed OP than those fed SP (P < 0.05), while the other indexes considered were not significant affected by diet (P > 0.05)
We found an increase in the gastrointestinal entry rate of urea during the low protein phase, which was consistent with the higher apparent crude fat digestibility and energy metabolism in calves fed OP
Summary
Ruminants convert about 20% to 30% of dietary nitrogen (N) into animal protein, and the rest is excreted in urine and feces [1], which has adverse economic and environmental implications. It has become important to develop nutritional management practices to improve the nitrogen utilization efficiency (NUE) of ruminants. Several animals, microorganisms, and plants experience seasonal periods of nutrient enrichment followed by undernourishment. This nutritional oscillation seems to cause compensatory growth. When dietary CP has been oscillated, the growth
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
