Maiden ewes were offered barley straw-based diets ad libitum containing very low (VLP), low (LP), medium (MP) and high (HP) levels of phosphorus (P) so that their intakes ranged from 14 to 118 mg P/kg LW.day. Dry matter intakes of ewes offered the VLP diet were 14 and 22% lower than those offered the HP diet in pregnancy and lactation, respectively. Plasma inorganic P (PIP) levels were significantly lower (<30 mg/L) in ewes offered the VLP diet in late pregnancy and throughout lactation. At the end of the experiment, the liveweight of ewes offered the VLP diet was 12% lower, rib bone P concentration 27% lower and the calcium: P ratio 37% higher than those offered the HP diet. Lamb liveweight gains of 30-70 day and tritiated water studies strongly suggest that the milk secretion was related to P intake and that most ewes were in negative balance in lactation. Using 32P as a marker, it was found that dietary P absorption was closely related to P intake. The coefficient of P absorption was low (0.52-0.56) in ewes offered the VLP diet, but high in all others (0.84-0.89). Endogenous faecal losses of P (19-45 mg/kg LW.day) were related either to P intake, or PIP and DMI. There was no difference between pregnancy and lactation in the gastrointestinal kinetics of P. Ewes offered the low P diets had similar high rates of reabsorption of P from the bones and soft tissues in both pregnancy and lactation so the lactating ewes were in more negative balance.
Phosphate‐dependent physiological changes during short‐term dietary phosphorus deficiency with or without a dietary phosphorus binder