Endogenous fraction of purine derivatives excreted in the urine of small ruminants

Abstract

Goats seem to be more efficient in fiber utilization and nitrogen utilization than sheep, but there are no good explanations or reasons in the literature. Digestibility data for these nutrients comparing the two species are few. The main aim of this study was to evaluate the nutrient digestibility, nitrogen utilization efficiency. Therefore, the digestibility of nutrients, excretion of urinary purine derivatives (PD) and nitrogen (N), estimation of microbial N synthesis and N utilization efficiency were determined in twelve Boer goats (17.3 kg±1.8 BW) and twelve Dorper sheep (20.7 kg±2.8 BW), all males, not castrated and aged four months. The animals were fed 4 diets with different levels of N concentration [6.4, 12.8, 19.2 and 25.6 g N/kg of dry matter (DM)] in 6 simultaneous designs of Latin squares 4 × 4. Only the intake of CP and EE had diet x species interaction. Nutrient intake was significant between diets and species (P<0.001). Sheep had higher nutrient intake (P < 0.01) than goats. The apparent digestibility of nutrients was similar (P > 0.05) in both species. Except for digestibility from CP (P=0.02) and aNDFn (P=0.01), which was higher for goats. The sheep indicated higher urinary N excretion (P<0.001), however, N retention (g/day; P =0.89) was similar for both species. The ration between N retained, ingested (P<0.001) and apparently digested (P<0.001) was higher in goats. Microbial efficiency (P < 0.001) increased linearly with the addition of N content in the diet. When fed a low-N diet (40g/kg DM), N consumption, urinary N excretion and N absorption were similar between species. Plasma urea concentration (P<0.001) and urinary urea excretion in g/day (P<0.001) indicated an increasing linear effect with increasing dietary N and differed (P<0.001) between species, 17 with goats with higher concentration in plasma and lower excretion (g/day) in urine. Small ruminants challenged to low (40 g/kg DM) dietary N supplementation required greater metabolic adaptation to more pronouncedly conserve N as a survival mechanism. Diets with higher CP content (160 g/kg) and 700 g/kg of forage increase the growth of ruminal microorganisms and improve microbial efficiency, resulting in increased intake of dry matter and nutrients, as well as promoting the digestion of fibers and proteins in goats and sheep.