CALCIUM, PHOSPHORUS AND MAGNESIUM RETENTION AND EXCRETION IN PREGNANTSOWS DURING 3 PARITIES

The validity of a theoretically minimal requirement of pregnant sows f or digestible phosphorus was tested during three parities. The effect of two diets, differing in total and calculated apparently digestible phosphorus, an retention and excretion of Ca, P and Mg was studied in mid-pregnancy (days 50-60; n = 22) and late pregnancy (days 105-112; n = 60). The control diet contained 7.2 g P, 9.4 g Ca and 2.6 g Mg kg(- 1) dry matter and the experimental diet 4.8 g P, 7.6 g Ca and 2.1 g Mg . Calculated levels of digestible phosphorus were 3.5 and 1.9 g kg(-1) DM, respectively. These values were based on phosphorus digestibiliti es that were measured in growing pigs. Daily feed allowance was 2.5 kg from day 0 to 85 of pregnancy and 3.0 kg from day 86 onwards. The est imated requirement for digestible phosphorus was 4.2 g day(-1) in mid- pregnancy and 6.0 g day(-1) in late pregnancy. For practical applicati on a safety margin is required to cover higher litter size, piglet bir th weights, maternal protein gain and to correct for a possible differ ence in phosphorus digestibility between sows and growing pigs. In thi s experiment, altering diet composition decreased the excretion of pho sphorus by 35%. (C) 1998 Elsevier Science B.V.