Effects of dietary phosphorus deficiency in pregnant and lactating ewes

Abstract

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.