Given the hypothesis that Ca status may be implicated in bearings, the purpose of the research in experiment 1 was to observe Ca status in old twinewes in normal commercial conditions to determine whether an association exists, and in the second experiment to manipulate Ca status to determine its effects on the incidence of bearings. In experiment 1, Romney ewes, scanned as twin (n=12) or single (n=12) pregnant, on each of 7 farms were identified and sampled at approximately 60, 30 and 7 d before the onset of flock lambing. Whole flock bearing incidence was recorded. Eleven to 41% of pregnant ewes from different farms had marginal serum Ca and Mg concentrations at 60 and 30 d before onset of lambing. No relationship was found between serum minerals and metabolite concentration and bearing incidence among farms. The objective of experiment 2 was to reduce bearings on farms with high historical incidences of bearings by increasing Ca loss in urine in mid-pregnancy (60 to30 d pre-lambing) followed by increasing Ca supply in late-pregnancy (30 to 0 d pre-lambing). Five farmers fed 100 twin pregnant ewes 35 g of anionic salts in 300-500 g of supplemental pellets (DCAB -814 meq/kgDM) from 60 to 30 d before lambing. From 30 d these ewes were then injected with 4 ml of a long-acting vitamin D formulation (5 farms) while one farm also had an additional group supplemented with Ca (8g lime (ground calcium carbonate) /ewe) in an attempt to increase Ca availability. In addition, groups of ewes not treated withanionic salts were injected with vitamin D (2 farms) or supplemented with Ca (1 farm) from 30 d. Following consumption of anionic pellets in mid-pregnancy, the pH of the ewes’ urine was lower and urinary Ca:creatinine ratios were higher after 2 (6.73 vs. 7.32, P<0.002; 0.47 vs. 0.16, P<0.003) and 4 weeks (6.26 vs.7.23, P<0.001; 0.58 vs. 0.14, P<0.003) of treatment. However, neither the feeding of anionic salts in mid-pregnancy nor the Ca or vitamin D supplements in late-pregnancy consistently changed Ca serum concentrations or bearing incidence.
Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 61-67, 2007
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