Dietary calcium and phosphorus repletion of lambs

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Abstract
Three-month-old Corridale lambs, confined in metabolism crates, were repleted with calcium or phosphorus or both Ca and P for 6 weeks (repletion diets HL, LH, HH, respectively, Ca 5.0 and P 3.7 g/kg) after being offered a low Ca and P (Ca 1.25 and P 0.66 g/kg) roughage-based diet (LL) for 12 weeks. At the end of the experiment, the Ca and P kinetics of the lambs was studied using a combination of balance studies and isotope techniques. The depletion diet substantially reduced the plasma P concentrations, DM intake and digestibility, liveweight gain, and Ca and P content of the bones. During repletion, lambs fed on the HL, LH and HH diets consumed minus16, 28 and 46% more DM than the lambs on the LL diet. The liveweight gains were 15.5, minus17.8, 41.1 and 134.5 g/day for lambs given diets LL, HL, LH and HH, respectively, during the repletion period. During the 6-week repletion period, there was complete remineralization of the rib bones of lambs fed on diet HH, but only partial remineralization of the metatarsal bones. The results indicated the need to feed supplementary Ca as well as P during dietary mineral repletion. The DM digestibilities of the lambs fed on the LL depletion diet did not improve during repletion. There were strong correlations between DM intake and plasma inorganic P, muscle P or exchangeable P pool, but not DM digestibility, suggesting that the reductions in feed intake with P deficiency are due to some effect on intermediary metabolism of the animal rather than on the gastrointestinal tract. When the lambs were repleted with diet HL, they had the highest Ca absorption coefficient, level of exchangeable body Ca, bone accretion of Ca and bone resorption of Ca. The LH repletion diet lambs had the highest rate and coefficient of absorption of P, but HH lambs had the highest levels of exchangeable body P, and rates of accretion and resorption of soft tissue and osseous P.

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