Improving bone health to optimise calcium metabolism in the dairy cow

NSA Concurrent Oral Session 5: Animal Nutrition & Human FoodImproving bone health to optimise calcium metabolism in the dairy cowBackground- Parturient paresis or milk fever in dairy cows results when the calcium (Ca) homeostatic mechanisms failto adequately replace the Ca lost from the blood at the onset of lactation. Ca lost from the blood has to be replaced byimproved absorption from the diet and also from the degradation of bone tissue. Most of the recent researches on bonewith regard to milk fever focus on the use of anionic supplements to alter the dietary cation- anion difference (DCAD) ofthe diet, which in turn alters the metabolic status in the animal promoting bone loss. Objective- The purpose of thefollowing experiment is to examine the possibility that manipulating the diet by addition of potassium (K) in latelactation alters the DCAD of the diet thereby preventing bone loss in the dairy cows which maybe useful in improvingbone mineral density in older cows, such that by calving their bone tissue is better able to mobilise calcium in responseto hypocalcaemia and subsequently reduce the risk of milk fever. Design- Twenty Four Holstein Friesian cows, 6 monthspregnant and in their third or more parity were allocated to two groups and fed a diet comprising a low K hay with apelleted concentrate containing either 1.25% K or 2.55% K as dry matter (DM). The K content of the diet of thetreatment group was increased by the addition of potassium carbonate (400g/cow/day) to the concentrate portion of thediet. The cows were fed their respective diets from the beginning of their sixth month of pregnancy until two weeks priorto parturition. Thereafter, all cows will be returned to the commercial herd and fed their normal commercial diet until sixweeks after calving. Bone biopsies, blood and urine samples were collected throughout the experiment.Outcomes - The animals were gaining weight satisfactorily from the start to the end of dry period and supplementationoPotassium Carbonate did not affect the overall weight gain. The urine pH was markedly higher in the cowssupplemented with K than that of the control group, following supplementation with K the urine pH averaged 0.25 ±0.10 units higher than that of the control group. The average urine pH at calving for the control and the treatment groupswere 8.21 ± 0.04 and 8.03 ± 0.20 respectively. There was no significant difference in the average daily milk yieldbetween the two groups in the first six weeks of calving. Conclusion - It is evident from the results on urine pH that theaddition of K to the diet has led to a change in the acid - base status of the animal, which may possibly benefit the bonemineral status of the cow. This should be confirmed by the soon to be performed analysis of the bone biopsies.