PSVII-24 Backgrounding carryover nutritional effects on nitrogen metabolism and water requirements onto grain or forage-fed finished cattle

Abstract The objective of this study was to examine how different backgrounding and finishing systems might affect nitrogen (N) metabolism, and consequently water requirements of cattle. Further, we investigated if the previous plane of nutrition might affect the results obtained in the subsequent phase. Cattle (n = 24) were randomly distributed into either a moderate (MP; crude protein (CP): 9.10%) or high (HP; CP: 12.62%) plane of nutrition during the background phase for 85 d. Animals were then blocked by their previous plane of nutrition and were moved onto a 105-d finishing phase. The forage-finished group received only high-quality alfalfa hay (CP: 21.3%), whereas the grain-finished group received a high grain diet (80% whole corn and 20% alfalfa hay; CP: 10.8%). Animals on MP diets excreted less N through urine (P < 0.01) and feces (P < 0.01), while retaining more N (P < 0.01), which resulted in an increased N efficiency (P < 0.01) when compared with HP animals. No differences were observed for water intake or microbial N being observed (P > 0.05). Grain-fed animals consumed less N and water (P < 0.01), but still had a greater amount of N being digested when compared with forage-fed animals (P < 0.01), as well as the least excretion of N through feces (P < 0.01) and urine (P < 0.01), and consequently a greater rate of N being retained (P < 0.01) and a greater efficiency on utilizing the ingested N (P < 0.05). Further interaction was also observed between treatment and previous plane of nutrition, where animals coming from a MP had the least dry matter intake, greatest amount of N being digested and least N excretion, fecal output, and excretion of N through the feces (P < 0.05). These results indicate that animals receiving MP will reduce their excretion of N without modifying the required amount of water while producing the same amount of microbial N due to more efficient N recycling. Extremely important is the fact that efficiency is carried over after these animals are transitioned to grain-fed finishing systems.