Magnesium status of dairy herds in Matamata County, New Zealand. 2. Association of milkfat production and herd magnesium status

The magnesium (Mg) status of 119 dairy herds was determined in July (before calving) and September (early lactation) 1978. Information about relevant farm, herd, and management factors, including Mg supplementation and feeding, was also recorded. Milkfat production data for 1978-79 were obtained for 112 of the herds. Of the variation in milkfat production for 1978-79, 32% could be accounted for by regression on herd feeding level in September and July, rate of potassium (K) application, herd breed, and herd Mg status in September. The benefits of Mg supplementation estimated from the data would be smaller than milkfat responses that have been obtained in supplementation trials but, nevertheless, would be profitable.