Prediction of endogenous urinary nitrogen of goats

J. Luo¹, A. L. Goetsch¹, J. E. Moore², Z. B. Johnson³, T. Sahlu¹, C. L. Ferrell⁴, M. L. Galyean⁵, and F. N. Owens⁶

¹E (Kika) de la Garza Institute for Goat Research, Langston University, Langston, OK
²Department of Animal Science, University of Florida, Gainesville, FL
³Department of Animal Science, University of Arkansas, Fayetteville, AR
⁴US Meat Animal Research Center, Clay Center, NE
⁵Department of Animal Science and Food Technology, Texas Tech University, Lubbock, TX
⁶Pioneer Hi-Bred International, Crop Genetics Research and Development, Johnston, IA

Three databases were constructed to estimate endogenous urinary nitrogen (EUN) in nonlactating and lactating goats. The first database consisted of 22 observations of direct measurement of EUN with low-N diets. A log-log weighted linear regression of EUN (g) on BW (kg) indicated that 0.75 was the most appropriate power of BW on which to express EUN. The second database, with 186 treatment mean observations for nonlactating goats, was split into a development set (n = 121) and a set for evaluation (n = 65). With the development set, urinary N (UN; g/kg BW^0.75) was regressed on total N intake (TNI; g/kg BW^0.75) and apparent digestible N intake (DNI; g/kg BW^0.75). After removing outliers from the development set, equations validated with the evaluation set were: UN = 0.092 + (0.288 x TNI) [n = 79; R² = 0.59] and UN = 0.165 + (0.340 x DNI) [n = 79; R² = 0.59]. At 0 DNI, truly digestible N intake should equal metabolic fecal N; thus, the DNI estimate of EUN may be most appropriate for nonlactating goats with above maintenance feed intake. Prediction equations for lactating goats with above maintenance feed intake were: UN = 0.182 + (0.235 x TNI) [n = 33; R² = 0.65] and UN = 0.160 + (0.354 x DNI) [n = 52; R² = 0.72]. In summary, based on databases constructed from publications on goat feeding and nutrition, EUN of nonlactating goats with feed intake above maintenance was 0.165 g/kg BW^0.75; EUN of lactating goats appeared similar to that for nonlactating goats.