Authors : Dorinha M.S.S. Vitti , Ermias Kebreab , Jo?o B. Lopes , Adibe L.Abdalla and James France
Abstract: Phosphorus (P) metabolism in sheep was studied using 98 Suffolk sheep, which were given various levels of P supplementation in their diet and administered a single dose of isotopic 32P in their blood. About 62% of P intake was excreted in faeces. Endogenous loss in faeces ranged from 8.6 to 84.0 mg P/kg body weight (BW) daily and was linearly related to P intake. Minimum endogenous faecal P loss was estimated at 8.63 mg/kg BW/day. Dietary P absorption was positively and linearly related to P intake at all intake levels, but the efficiency of absorption decreased at higher intakes. This suggests that P absorption involves not only a passive mechanism but also an active process, possibly due to homeostatic control. Taking an average 63% absorption efficiency, requirement of dietary P for maintenance was calculated to be 28.3 mg/kg BW/day. For a 35-kg sheep, this is equivalent to 0.99 g P/day to replace endogenous P losses fed at maintenance. Non linear relationships of salivary P with absorbed, endogenous feacal P and dry matter intake were established, suggesting that regulation of P secretion in saliva could be by active and passive mechanisms. Urinary loss of P was low, even at high levels of P intake. The paper demonstrates the relevance of understanding P metabolism and the need to estimate P requirements for ruminants accurately, in order to optimise production but avoid excessive P outputs to the environment.
Dorinha M.S.S. Vitti , Ermias Kebreab , Jo?o B. Lopes , Adibe L.Abdalla and James France , 2005. Effects of Dietary Supplementation on Phosphorus Metabolism in Sheep . Journal of Animal and Veterinary Advances, 4: 349-355.