Dietary nitrogen sources with differents ruminal degradability rates in sheep nutrition

Author(s)

Clayton Quirino Mendes

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2010-02-01

Examining board members

Ivanete Susin; Claudete Regina Alcalde; Iran Borges; Wilson Roberto Soares Mattos; Enrico Lippi Ortolani

• Advisor: Ivanete Susin

Abstract

Three trials were conducted to evaluate the effects of increasing dietary RDP through the use of nitrogen sources with differents rumen degration rates. Trial 1: Twenty-eight Santa Ines ram lambs were used to evaluate the effects of replacing soybean meal by urea in high grain diets on performance, carcass characteristics, meat quality and blood parameters. In addition, were assessed the ability of SRNS to predict dry matter intake and average daily gain of lambs. Soybean meal in control diet was replaced by urea at 0.7; 1.4 e 2.1% on a DM basis. There were no differences among experimental diets for dry matter intake, carcass characteristics and meat parameters. However, average daily gain and final weight decreased linearly as the urea replaced soybean meal. Likewise, feed conversion and plasma urea nitrogen concentration increased linearly with the addition of urea in experimental diets. The SRNS model tended to underestimate dry matter intake and overestimate the average daily gain. Trial 2: Sixteen ruminally cannulated Santa Ines ram lambs were placed in metabolism crates and fed the same TMR used in Trial 1. There was no effect on DM intake, apparent digestibility of dry matter, organic matter, crude protein and neutral detergent fiber, as well as, ruminal pH. Acetate concentration and total short-chain fatty acids concentration showed a quadratic response, while ruminal ammonia concentration increased linearly with urea inclusion to the diet. The nitrogen metabolism, urinary excretion of purine derivatives, microbial nitrogen production and microbial protein synthesis was not influenced with the replacement of soybean meal by urea. Although decreased average daily gain in 14.3%, urea can be used as an exclusive N source in high grain diets fed to feedlot lambs. Trial 3: Forty-eight Santa Ines lactating ewes were used to determine the effects of diets containing N sources with different ruminal degradability. Soybean meal, corn gluten meal plus urea, corn gluten feed plus urea or urea were used as N source, resulting in diets with 9.88, 10.4, 12.0 and 13.4 % of RDP, respectively. Dry matter intake was higher, milk production and fat-corrected milk tended to be higher (P<0.10) and milk fat content was lower for soybean meal diet. Daily milk protein production was higher, and milk urea nitrogen content was lower for diets containing soybean meal or corn gluten meal plus urea as N source. The lower N efficiency was associated with high protein ruminal degradation rate, once the diets containing 12.0 or 13.4% RDP resulted in reduced milk protein production, higher milk urea concentration and loss of weight and body condition score. Furthermore, a higher RDP with the total replacement of the true protein by urea affected dry matter intake and milk production of lactating ewes. (AU)