Effect of high magnesium intake on apparent magnesium absorption in lactating cows

Abstract

We investigated whether the percentage of apparent magnesium (Mg) absorption in dry cows with a low level of dry matter intake is comparable to that in lactating cows with high feed intake, but fed the same diet in terms of composition. Lactating cows were fed rations with an ingredient and nutrient composition which was identical to the rations that were used in a previous study in dry cows. The trial had a 16×16-day cross-over design and was preceded by a 10-day run-in period. The six non-pregnant, lactating, multiparous cows (Friesian–Holstein × Holstein–Friesian cross) were fed rations with low and high Mg content, the levels being 3.7 and 6.3 g Mg/kg dry matter at a constant dietary potassium (K) concentration of 30.7 g K/kg dry matter. Increasing the level of Mg intake from 68.1 to 116.3 g Mg per day resulted in absolute Mg absorptions of 9.0 and 18.5 g Mg per day ( P=0.005). Mg absorption, expressed as a fraction of intake, for the low and high-Mg rations was 0.131 and 0.159 ( P=0.183) these values being similar to those observed earlier in dry cows. Milk production was not significantly influenced by the level of Mg intake ( P=0.075). The combined results of this experiment and that of an earlier one with dry cows indicate that absolute apparent Mg absorption (g per day) depends on dietary Mg intake rather than on dry matter intake and physiological status. Thus, lactating and dry cows are equally efficient in Mg absorption, justifying the use of dry cows as a model for lactating cows.