Effects of Slow-release Urea vs conventional urea and Molasses on Digestibility, Rumen Fermentation, Nitrogen Balance and Microbial Protein yield in Sheep

Résumé

The objectives of this study were to evaluate the effects of using a type of slow- release urea (SRU) and conventional feed grade urea (CFU) with or without molasses (MO) on the diets of growing sheep. An experiment was conducted by using 4 mature-male Lori sheep (24.7 ± 0.9 kg BW) cannulated in the rumen in a- 4×4 Latin-square design with a factorial arrangement of 2×2 to evaluate the effects of two main factors of urea sources (US) (feed-grade urea versus slow- release urea) and level of molasses (M) (0% versus 20%) on intake, nutrient digestibility, nitrogen retention, rumen fermentation, and microbial nitrogen in sheep. In addition, an in situ experiment was conducted to determine N disappearance of urea sources from polyester bags. The lambs were fed with 4 isonitrogenous and isocaloric diets consisting 70% concentrate and 30% sugar cane tops (DM basis) that were offered in two equal meals (08.00 and 20.00; 5 to 10 percent orts on an as-fed basis). The following treatments implicative of (UM0) feed-grade urea (16 g/kg DM) without molasses, (UM20) feed-grade urea (16 g/kg DM) with molasses (200 g/kg), (SM0) slow-release urea (18 g/kg DM) without molasses, and (SM20) slow-release urea (18 g/kg DM) with molasses (200 g/kg). Nutrient digestibility, nitrogen balance, total purine derivatives (PD( and estimated microbial protein synthesis were not different between the treatment groups although digestibility of OM tended to increase in 20% M supplemented groups (P= 0.057). Overall, the means of total VFA concentration and its proportions were not different (P> 0.05), but with the addition of molasses to the diets, the concentrations of propionate (P= 0.016) and butyrate (P= 0.024) decreased and increased, respectively. Ruminal pH, NH3–N, and plasma metabolites were not affected by the addition of US or M (P> 0.05). Significant effects of the sampling time on ruminal pH (P= 0.002), ruminal NH3–N (P<0.001), BUN, and plasma glucose (P<0.001) were observed. It could be concluded that the inclusion of M or US did not affect the feed intake, digestibility, blood metabolites, and generally, most of the ruminal fermentation parameters after evaluation; but, more research is required to evaluate their uses in diets.