Determination of Optimal True Digestible Calcium to True Digestible Phosphorus Ratio in Growing Pigs

Three studies were conducted. In the first study, 12 Yorkshire barrows (initial BW of 23.2 ± 2.0 kg) were allotted to 2 dietary treatments with 6 replications per treatment using a completely randomized design to determine apparent Ca and P digestibility (AD), true digestibility (TD) and endogenous output (EO) in a corn/SBM-based diet. All pigs were placed in individual feeder pens that allowed for easy collection of individual feces. The AD of Ca and P were 28.4% and 23.9%, respectively. Their TD of 42% and 40% for Ca and P respectively were significantly (P < 0.05) higher than the corresponding AD. EO was 0.8g for Ca and 1.3g for P per kg of dry matter intake (DMI). In the second study, the optimal dietary ratio of true digestible Ca and P was determined in terms of its effect on growing pig performance, excretion of Ca and P in feces and urine in a corn/SBM-based diet using a randomized complete block design. Thirty six growing barrows (initial BW: 24.2 ± 1.9 kg) were allotted to 6 dietary treatments with 6 replications per block. Six corn/SBM-based diets with very similar nutrient contents were formulated but differed in their dietary ratio of Ca to P. The balances of Ca and P and their true digestibility/retention were calculated for each diet. Animal performance and true retention of both Ca and P was optimal (P < 0.05) with diet 2 with a true digestible Ca to P ratio of 0.82: 1 compared to other experimental diets. The third study was conducted with a similar protocol to that used in experiment 1 involving 12 barrows (initial BW: 23.9 ± 1.1 kg) to determine Mg, Cu, Fe, Mn, Se and Zn TD values for the growing pig. Se and Zn AD of 73.9% and 9.5% significantly (P < 0.05) underestimated their TD of 82.1% and 15%, respectively. Se and Zn EO were 0.00004mg and 0.01 mg/kg of DMI, respectively. The TD and EO for Mg, Cu, Fe and Mn could not be estimated because of their negative AD.