Resumo
This study aimed to determine the effect of using different sources of nitrogen to supply part of degradable intake protein needs in lactating goat performance and its effect on excretion of microbial purine derivatives and blood metabolites. Thirty-two lactating Saanen goats (body weight 38.85 ± 2.14 kg and 1979 ± 0.25 gday-1milk yield) were used in a one-way ANOVA completely randomized design. Goats were assigned to the following treatments for a 10-wk experimental period: 1) Control (canola meal as a nitrogen source); 2) Urea (0.5% urea); 3) Optigen (0.55% Optigen-Alltech.Inc., Lexington, KY) and 4) Polymer-Coated Urea (PCU-international patent number: A01K5/00, 0.7% PCU) based on dry mater intake. Non-protein nitrogen groups had a comparative effect (p > 0.05) between control and other treatments on milk composition, microbial protein synthesis and they affected on blood factors including urea, cholesterol, and ALT. Dry matter intake decreased (p > 0.05) in PCU, Optigen, Urea than Control goats. Synthesis of microbial protein in PCUgoats was 22.5 g day-1and it was greater (p > 0.05) than other treatments. Plasma cholesterol was increased in PCUand Optigen, whereas urea concentration was increased in Urea and Control goats. Milk production was higher in PCUthan Urea and Control. Feed conversion ratio was improved (p > 0.05) in PCU and Optigengoats versusother treatments.This study demonstrated that polymer-coated ureacan be utilized as a nitrogen source and improve goats milk performance.(AU)