Phosphorus requirements of ewes in pregnancy and lactation

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Abstract
SUMMARY: The adequacy of the Agricultural Research Council (1980) recommendations for phosphorus for pregnancy and lactation has been investigated in ewes given a plentiful supply of dietary calcium.The efficiency of absorption of P remained high and fairly constant throughout the whole experimental period and the rate of P absorption varied in direct relation to the P intake.The endogenous faecal loss of P also varied with P intake and at all stages of pregnancy and lactation was higher than the value assumed by the Agricultural Research Council (1980) in their calculations of P requirements.Bone mineral stores of Ca and P were lost in the normal way during late pregnancy and early lactation but were not replaced, as normal, in mid- to late lactation. At the end of the lactation, ewes were still in deficit of 125 g P and 100 g Ca.It is argued that the Agricultural Research Council (1980) recommendations for P, particularly in mid- to late lactation, are too low and it is recommended that future calculations of requirements for pregnancy and lactation allow for the inevitable loss and subsequent replacement of skeletal mineral stores and also for the increased endogenous faecal losses of P that appear inevitable at the high P intakes needed to meet the increased demands.