Nitrogen metabolism of diets differing in forage type and forage to concentrate ratio in sheep and goats

Abstract

2 páginas.-- Energy and protein metabolism and nutrition. 3rd EAAP International Symposium on Energy and Protein Metabolism and Nutrition (Parma, Italy, 6-10 September, 2010).--EAAP Publication No. 127The aim of this study was to compare the nitrogen (N) utilization in sheep and goats fed 4 medium-good quality diets at similar levels of intake. The diet ingredients were selected to represent those most frequently used under practical feeding conditions of both animal species in Spain. Four rumen-fistulated Granadina goats and 4 Merino sheep were used in 4 experimental periods. Four total mixed diets were formulated according to a 2 × 2 factorial arrangement of treatments. The diets had forage:concentrate (FC; dry matter (DM) basis) ratios of 70:30 (H) or 30:70 (L) with either lucerne hay (A) or grass hay (G) as forage and were designated as HA, LA, HG and LG. Nitrogen contents were 26.9, 28.3, 19.4 and 25.6 g/kg DM and neutral detergent fibre contents were 426, 374, 499 and 401 g/kg DM for the HA, LA, HG and LG diets, respectively. No difference was observed between animal species (AS) in N intake. The percentage of N intake excreted in urine was higher in goats than in sheep, but the percentage of N intake in faeces was lower in goats compared with sheep. Protein digestibility was greater in goats than in sheep, which was consistent with the greater ammonia nitrogen (NH3-N) concentrations observed in the rumen of goats. A significant AS × FC interaction was detected for N digestibility and ruminal NH3-N concentrations, but there were no AS × type or forage (FOR) interactions for any parameter. Goats showed lower N retention than sheep for all diets either expressed in absolute terms (g/day) or as g per kg of digestible organic matter intake (DOMI). These results indicated different N utilization in goats and sheep with similar N intakes. The interspecies differences in N digestibility and ruminal ammonia concentrations seemed to be modulated by the composition of the diet.Peer reviewe