Magnesium does not limit ewe milk production

Abstract

Extract

Madam:— I wish to draw to the attention of readers my serious reservations aQout the very strong statement made by the authors Bray, Burton and Cox in their paper “Magnesium supplementation of lactating ewes and lamb growth”. ⁽²⁾ Bray, A.R., Burton, R.N. and Cox, B.T. 1987. Magnesium supplementation of lactating ewes and lamb growth. N.Z. vet. J., 35: 55–57. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar] They claim categorically that “magnesium levels below 0.7 m mol/serum did not limit production” in sheep. This supposes that the supplement provided to half of 26 lactating ewes with serum levels below this threshold was in fact sufficient to reverse the hypomagnesaemia and provide adequate Mg for some critical function. There are very good grounds for belieiving that the supplement - once daily oral administration of 12.5 mg magnesium chloride - was totally inadequate to do this. The daily dietary requirement of the particular sheep can be calculated to be between 2.5–3.5 g Mg/ day ⁽¹⁾ Agricultural Research Council. 1980. The Nutrient Requirements of Ruminant Livestock, Slough: Commonwealth Agricultural Bureaux.  [Google Scholar] and 10.2 g Mg/d. ⁽³⁾ Grace, N.D. 1983. The Mineral Requirements of Grazing Ruminants, N.Z. Society of Animal Production. Occasional Publication 9 [Google Scholar] The supplement provided much less than 1% of this by comparison with either standard. My calculation would suggest that the minimum realistic supplement would have been 1.0–1.5 g Mg/d or 80–120 times the dose given. Comparisons with supplementation work with dairy cattle, in which 10 g Mg/d are given ⁽³⁾ Grace, N.D. 1983. The Mineral Requirements of Grazing Ruminants, N.Z. Society of Animal Production. Occasional Publication 9 [Google Scholar] to overcome hypomagnesaemia and its consequences, would have suggested that the equivalent dose in sheep would have been 1.5 g Mg/d.