Nitrogen metabolism and blood metabolites in three goat breeds fed increasing amounts of protein

Twelve wethers (27–33 kg and 12–14 months of age) representing meat (Nubian), milk (Alpine) and mohair (Angora) producing goats were used to evaluate breed differences in protein utilization with diets containing 9 (L), 15(M) or 21% CP (H) and 2.4 Mcal ME/kg DM in a digestion trial. Fecal N, urine N and absorbed N as percent of N intake were not affected (P>0.05) by breed. Retained N as percent of absorbed N was not different (P>0.05) between breeds. Ruminal propionate (molar %) was lower (P<0.05) in Angora, but other ruminal VFA and ammonia-N were not affected (P>0.05) by diet or breed. Plasma urea-N increased (P<0.01) with dietary CP level (8.3, 22.0 and 33.3 mg/dl for L, M and H, respectively), and concentrations were lowest for Angoras and highest for Nubians (18.5 vs. 21.2 vs. 23.9 mg/dl) (P<0.01). Plasma total protein (mean 69.7 g/l), glucose (mean 83.1 mg/dl), non-esterfied fatty acids (mean 101.4 μEq/l) and cortisol (mean 10.8 ng/ml) were not affected (P>0.05) by breed or diet. Plasma glucagon concentrations increased (P<0.05) with increasing CP intake (72.4, 167.6 and 239.1 pg/ml for L, M and H, respectively). The study indicated that there was no apparent breed difference between Nubian, Alpine and Angora goats in nitrogen utilization when goats were fed pelleted diets containing 9 to 21% CP.