Quantitative Prediction of Magnesium Absorption in Dairy Cows

Abstract

The objective of the current study was to predict magnesium (Mg) absorption in dairy cows based on data from our own studies and those of other investigators. Balance data from 15 independent studies with 68 different rations and 323 dairy cows or cow-periods were used. In 12 studies, grass feeds were the main source of roughage and in about one-half of the studies, MgOsupplemented rations were used. Out of the 68 rations, 14 rations contained supplemental K in the form of bicarbonate, and in 2 rations additional K was incorporated mainly in form of KCl. The K content of the rations ranged from 6.9 to 75.6 g/kg of dry matter (DM; mean 29.4 g/kg of DM). In most studies (10/15), dry, nonpregnant cows were used. For lactating animals, milk yield ranged from 4 to 22 kg/d (mean yield, 15 kg/d). All studies provided quantitative information with respect to feed intake (DM intake, Mg, and K) and total Mg excretion in feces. The mean dietary Mg content was 4.5 g/kg of DM and ranged from 0.45 to 17.3 g/kg of DM. On average, Mg absorption (% of intake) was 26.2% and ranged from 9.9 to 73.7%. The variation in Mg absorption was at least partly explained by the variation in dietary K concentrations. Magnesium absorption (% of intake) was significantly decreased by 0.31 percentage units/g of K in the DM. To counteract the depressant effect of dietary K on Mg absorption, Mg intake must be increased by 4 g/d when the dietary K concentration increases by 10 g/kg of DM so that the amount of absorbed Mg is maintained.

Assessment of magnesium intake according to requirement in dairy cows

“…The meta‐analysis of Schonewille et al () (Equation 7) predicts an apparent Mg digestibility of 20% at 10 g K/kg DM of the diet. This utilization was also assumed in the recommendations of the GHE (), and a Mg content of 2.0 g per kg DM was proposed.…”

“…Schonewille et al () continued this meta‐analysis with a larger number of diets and cows:K in g/kg dry matter, all other variables in g/day, ± = standard error, 68 diets, 323 cows.…”

Nutrition and Health of Dairy Animals

“…The Mg concentrations in forage and subsequently in the blood of cattle are influenced strongly by high amounts of fertilizer K and, to some extent, fertilizer N. Absorption of Mg by plants is reduced by high levels of K in the soil (Mayland, 1988;Robinson et al, 1989). Mg absorption by ruminants is also reduced by a high intake of K (Schonewille et al, 2008), and by high content of Ca and P in the diet (Sansom et al, 1983). High concentrations of N in the forage may additionally decrease the availability of Mg (Mayland, 1988).…”

“…It may also occur because of a need for increased amounts of Mg during parturition and early lactation (Mayland, 1988). Clinical hypomagnesaemia in cows with plasma Mg concentrations bellow 0,4 mmol/L is manifested as grass tetany (Schonewille et al, 2008). Grass tetany has been investigated extensively, but its complex etiology is not well understood.…”

“…In its subclinical form, however, hypomagnesaemia may be risk factor for other diseases. Around calving it may be the important risk factor for MF (Sansom et al, 1983;Schonewille et al, 2008).…”