Nutritional evaluation of lamb diets in a tropical setting formulated according to NRC (1985) and NRC (2007) specifications.

摘要

The objective of this research was to compare the National Research Council (NRC) 1985 (NRC85) and 2007 (NRC07) small ruminant nutrition recommendations for growing lambs in a tropical setting with tropical feeds. Twenty mixed breed Santa Ines males, 4 mo of age, with an average initial 19.5+or-3.5 kg weight were randomly distributed to four treatments to measure apparent digestibility, intake as well as ruminal and blood parameters. The four treatments consisted of diets formulated according to NRC85 or NRC07 recommendations, the latter at 20% (NRC07-20), 40% (NRC07-40) and 60% (NRC07-60) rumen non-degradable protein (NDP) concentration. The trial consisted of 10 d for adaptation to diet and 7 d for data collection. The NRC07 diets showed no differences (P>0.05) in disappearance of dry matter (DM), organic matter (OM) or their fractions as a result of NDP level. All diets formulated according to NRC07 resulted in greater (P<=0.05) consumption of CP and digestible protein (DP) compared to NRC85. Greater (P<=0.05) disappearance of DM and OM disappearance rates were measured for the NRC85 diet compared to NRC07 diets, with no differences (P>0.05) for CP. The NRC85 diet resulted in lower (P<=0.05) fiber intake while non-structural carbohydrate (NSC) intake was greater (P<=0.05) compared to NRC07 diets. Total digestible nutrients (TDN) were greater (P<=0.05) for NRC85 diets compared to NRC07 while there were no differences (P>0.05) among digestible (DE) and metabolizable energy (ME). Coefficients of digestibility of total carbohydrates (TC) were greater (P<=0.05) for the NRC85 than the NRC07 diets. Greater (P<=0.05) N intake was measured for NRC07-20 and NRC07-40 NDP. Urinary N in the NRC85 diet was lower (2.24+or-10% in ingested N; P<=0.05) than in the NRC07 diets. There was a greater (P<=0.05) balance of N in the NRC07-20 compared to NRC85-60 and NRC07-60 diets, while these three were similar (P>0.05) to values from NRC07-40 diet. More (P<=0.05) retained N was obtained in NRC85 compared to NRC07 diets. For diet NRC85, there was a greater (P<=0.05) concentration of N-NH₃ at 2 h post-feeding compared to feeding time while this was reversed by 5 h post-feeding. Rumen pH levels were greater (P<=0.05) in the NRC07-40 diet than the others. The greater digestibility of nutrients in diets with greater concentrate does not imply an increase in consumption of digestible nutrients. The NRC07 diets with proportional amounts of fiber and concentrate resulted in neutral detergent fiber (NDF) concentrations adequate for ruminal function. In contrast, the NRC85 diet resulted in greater (P<=0.05) N retention, possibly due to better protein:energy ratios. Diets NRC07-20 and NRC07-40 resulted in greater (P<=0.05) rumen liquid N-NH₃ than NRC85 of NRC07-60. Lambs on NRC07 diets also had an increase (P<=0.05) in blood urea that can be used as recycled N. None (P>0.05) of the diets resulted in a drop in ruminal pH.