Evaluating slow-release urea as a replacement for soybean meal in Awassi lamb diets: effects on growth performance,...

This experiment examined the effect of replacing soybean meal with slow-release urea (SRU) on growth, nutrient digestion, and rumen fermentation in twenty-eight Awassi lambs over 75 days. The lambs were 4 to 5 months old and initially weighed close to about 25 kg. They were randomly distributed into four groups receiving varying levels of SRU: 0.00%, 0.50%, 1.00%, and 1.63% on a dry matter basis (n = 7 per treatment). The lambs were kept and fed separately in pens to closely monitor their intake of feed. The diets contained a hay-to-concentrate ratio of 28:62 and contained 1.9 Mcal of gross energy and 100 g of crude protein per kg of DM, and were fed three times a day to demand. Growth and intake data were recorded weekly. A digestibility test was conducted on three animals within each treatment between days 65 and 72, and all their feces were collected. Rumen fluid was sampled at 0, 3, and 6 h post-feeding to analyze pH, ammonia (NH₃), and volatile fatty acids (VFAs) by using gas chromatography. Data were analyzed using one-way ANOVA to analyze growth and digestibility and repeated-measures ANOVA to analyze rumen fermentation using Tukey's post-hoc test to make comparisons. A significance level of P ≤ 0.05 was set. There were no significant (P > 0.05) differences between treatments for dry matter intake, weight gain, and nutrient digestion. Rumen pH and NH₃ concentrations were not influenced by diet (P > 0.05), but a significant effect was observed with respect to diet (pH and NH₃: pH: p < 0.001; NH₃: p < 0.001), with pH decreasing and NH₃ increasing following intake. Total VFAs were significantly different between diets (P < 0.01), and highest and lowest were found, respectively, in the control and highest SRU dietary groups; acetate and propionate were different (P < 0.05) between diets. The acetate: propionate ratio was significantly (P < 0.05) influenced by diet. The results indicate that SRU can replace soybean meal without compromising growth, and can regulate rumen fermentation to benefit its inclusion as a sustainable source of protein in diets of lambs.