AN ESTIMATION OF THE MINIMAL-P REQUIREMENTS FOR GROWING-FINISHING PIGS, AS INFLUENCED BY THE CA LEVEL OF THE DIET

In a 3x3 factorial experiment (three dietary phosphorus (P) levels com bined with three dietary calcium (Ca) levels), the minimal P requireme nts of 180 growing-finishing pigs within the live weight range from +/ - 37 kg to +/- 100 kg were investigated. Analysis of the basal diet of wheat (37.7%), cassava (32.7%) and soybean oilmeal (24.7%), supplemen ted with 2000 IU vitamin D3, gave 0.36% total P (0.22% phytate P, 489 wheat phytase units kg-1) and 0.54% Ca. Phosphorus was supplemented as CaHPO4 to dietary levels of 0.40% or 0.44% and Ca, as CaCO3, to dieta ry levels of 0.74% or 0.94%. Daily gain and feed intake were significa ntly affected by the dietary P level, while feed efficiency was only i mproved during the first 5 week period. However, there were no main ef fects of the dietary Ca levels on any of the performance characteristi cs mentioned. Leg condition as well as carcass quality was not affecte d by Ca or P level. It can be concluded that 0.17% available (apparent ly digestible) P in the diet (0.44% total P) is close to the minimal r equirements for growing-finishing pigs. At that dietary P level an inc rease in dietary Ca has no adverse effect on any of the parameters stu died, while at the lowest dietary P level (0.11% available P, 0.36% to tal P) a decrease in daily gain and in feed efficiency, in serum inorg anic phosphate and in bone mineralization is clearly related to an inc reasing dietary Ca level. An increase in dietary Ca had no influence o n the availability of P. The normally recommended Ca/P ratio (1.3) or Ca/available P ratio (3.0) seems to be meaningless at the highest P le vel. The experimental figures support the hypothesis that the ratio of available Ca/available P is perhaps a better parameter to explain the apparent antagonism between Ca and P at low dietary P levels. The ava ilability of Ca from CaCO3 is much higher than from CaHPO4, resulting in a rapid rise of the ratio of available Ca/available P when CaCO3 is added to a low P diet.