The literature is inconsistent with regard to the effect of diet in the periparturient period on the health and production of dairy cows, and there is little or no data on the effect of genotype. Fifty-six dairy cows of two different genotypes (Overseas Holstein-Friesian (OSHF) and New Zealand Holstein-Friesian (NZHF)) were randomly allocated to two dietary regimens. Half of each genotype group received a pasture/pasture silage diet pre-calving and a pasture diet post-calving, while the other half received a total mixed ration pre- and post-calving. Cows receiving the total mixed ration pre-calving had a lower (P<0.05) plasma calcium concentration on the day of calving and the day following calving. Conversely, cows of both genotypes offered pasture had lower (P<0.01) plasma magnesium and phosphorus concentrations pre- and post-calving compared with cows fed a total mixed ration. OSHF cows had lower plasma calcium (P<0.05) and magnesium (P<0.001) concentrations post-calving. Plasma phosphorus concentrations were unaffected by genotype. Herds with a high proportion of OSHF genetics are at an increased risk of parturient hypocalcaemia and hypomagnesaemia. Recommended daily allowances for these minerals may need to be increased to allow for this predisposition.
Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 168-171, 2001
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