A kinetic model of phosphorus metabolism in growing goats.
The effect of increasing phosphorus (P) intake on P utilization was investigated in balance experiments using 12 Saanen goats, 4 to 5 mo of age and weighing 20 to 30 kg. The goats were given similar diets with various concentrations of P, and 32P was injected to trace the movement of P in the body. A P metabolism model with four pools was developed to compute P exchanges in the system. The results showed that P absorption, bone resorption, and excretion of urinary P and endogenous and fecal P all play a part in the homeostatic control of P. Endogenous fecal output was positively correlated to P intake (P < .01). Bone resorption of P was not influenced by intake of P, and P recycling from tissues to the blood pool was lesser for low P intake. Endogenous P loss occurred even in animals fed an inadequate P diet, resulting in a negative P balance. The extrapolated minimum endogenous loss in feces was .067 g of P/d. The minimum P intake for maintenance in Saanen goats was calculated to be .61 g of P/d or .055 g of P/(kg(.75) x d) at 25 kg BW. Model outputs indicate greater P flow from the blood pool to the gut and vice versa as P intake increased. Intake of P did not significantly affect P flow from bone and soft tissue to blood. The kinetic model and regressions could be used to estimate P requirement and the fate of P in goats and could also be extrapolated to both sheep and cattle.
Vitti
D M
DM
Animal Nutrition Laboratory, Centro de Energia Nuclear na Agricultura, Piracicaba, SP, Brazil.
Kebreab
E
E
Lopes
J B
JB
Abdalla
A L
AL
De Carvalho
F F
FF
De Resende
K T
KT
Crompton
L A
LA
France
J
J
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle; D004435:Eating; D005243:Feces / Q000737:chemistry; D005260:Female; D006041:Goats / Q000254:growth & development* / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D010758:Phosphorus / Q000493:pharmacokinetics*
D010758:Phosphorus