The plane of nutrition and dietary protein level during backgrounding and finishing phases affect nitrogen and water metabolism in beef cattle

This study aimed to examine how varying planes of nutrition during the two phases: backgrounding (BP) and finishing (FP) impact nitrogen (N) metabolism and, consequently, the water requirements of beef cattle. Twenty-four crossbred Angus steers (298.01 ± 10.17 kg) were randomly distributed in a completely randomized design following a 2 × 2 factorial arrangement of treatments (two phases and two nutritional planes). The phases being BP (85 d) and FP (105 d); and plane of nutrition being moderate (MP; crude protein-CP: 9.10 %) or high (HP; CP: 12.62 %) for BP and forage (high-quality alfalfa hay; CP: 21.3 %) or grain-finished (80 % whole corn and 20 % alfalfa hay; CP: 10.8 %)) for FP. There was a significant interaction between BP and FP (P < 0.1) for dry matter intake (DMI), N-ingested (g/d), fecal (g/d), N-urinary (% of N-excreted), and total N-excreted (g/d). There was no interaction observed for microbial N and microbial protein synthesis (P > 0.1). Animals fed HP diets excreted less N-urinary and N-fecal and therefore retained more N (P < 0.01), increasing N-efficiency (P < 0.01) compared to MP animals. No differences were observed for water intake or microbial-N (P > 0.05). Grain-fed cattle consumed less N and water compared to forage-fed cattle, as well as the lowest excretion of N-fecal and urinary-N, and higher rate of N-retained and higher efficiency on utilizing the N-intake (P < 0.05). Animals fed HP lowest DMI N excretion, fecal output, and N-fecal (P < 0.05). Cattle receiving HP during backgrounding will reduce their N-excretion without modifying the required amount of water while producing the same amount of microbial-N due to more efficient N-recycling. This N and water use efficiency pattern carried over when these animals transitioned to grain-fed finishing systems.