Dietary sodium and the production, health and behaviour of lactating dairy cows

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The effect of supplementary sodium on the health and the behaviour of housed dairy cows

Increasing sodium in herbage for grazing dairy cows can reduce the milk somatic cell count (Phillips et al., 1996), but the effects of providing salt supplements for cows fed conserved feeds indoors are less clear. Supplementary salt can also reduce oral stereotypic behaviour in individually-housed calves (Phillips and Youssef, 1994). Tethered dairy cows are also behaviourally restricted, demonstrate stereotyped behaviours and might similarly benefit from supplementary salt.In experiment 1, 36 tethered Estonian Red cows were allocated for nine weeks to a randomised block experiment in which they received a daily restricted allowance of 7.5 kg DM grass silage, 6.6 kg DM grass hay and 2.2 kg DM barley/cow, with the addition of 0, 200 or 400 g NaCl. The salt supplements increased the Na content of the diet from 1 (control treatment) to 6 and 11 g/kg DM respectively. Milk yield was recorded every ten days and somatic cell count (SCC) by fluorescence microscopy. A blood sample was taken from the milk vein of each cow at the end of the experiment for mineral analysis.</jats:p

The effect of supplementary sodium on the health and the behaviour of housed dairy cows

Increasing sodium in herbage for grazing dairy cows can reduce the milk somatic cell count (Phillips et al., 1996), but the effects of providing salt supplements for cows fed conserved feeds indoors are less clear. Supplementary salt can also reduce oral stereotypic behaviour in individually-housed calves (Phillips and Youssef, 1994). Tethered dairy cows are also behaviourally restricted, demonstrate stereotyped behaviours and might similarly benefit from supplementary salt.In experiment 1, 36 tethered Estonian Red cows were allocated for nine weeks to a randomised block experiment in which they received a daily restricted allowance of 7.5 kg DM grass silage, 6.6 kg DM grass hay and 2.2 kg DM barley/cow, with the addition of 0, 200 or 400 g NaCl. The salt supplements increased the Na content of the diet from 1 (control treatment) to 6 and 11 g/kg DM respectively. Milk yield was recorded every ten days and somatic cell count (SCC) by fluorescence microscopy. A blood sample was taken from the milk vein of each cow at the end of the experiment for mineral analysis.</jats:p

The effects of supplementary sodium on the magnesium status and behaviour of dairy cows fed silage and concentrates

Recent research has demonstrated that supplementary sodium enhances the magnesium status of cattle fed fresh herbage by limiting the antagonism of potassium to magnesium absorption in the rumen (Chiy and Phillips, 1993). This may explain the observed reduction in the somatic cell concentration in the milk of grazing dairy cows when they are offered a sodium supplement (Phillips et al. 1996). Magnesium has been recognised as the main macroelement affecting immunocompetence in laboratory animals (Miller, 1985), and it is likely that it is important for grazing ruminants, which are prone to hypermagnesaemia. It is unclear whether sodium supplements would be beneficial to cattle fed conserved feeds, where hypomagnesaemia is less common.</jats:p

A simulation of the effects of changes in the Na and K content of milk during mastitis on the growth of <i>Staphylococcus aureus</i>, <i>Streptococcus uberis</i> and <i>Escherichia coli</i>

In a mastitic event damage to the epithelial tissue of the mammary gland, and in particular an increase in paracellular permeability allows sodium to enter the milk from the blood (Schaar and Funke, 1986). Normally there is a stepwise gradient of declining sodium concentration from the interstitial fluid to the epithelial cells to the milk (Berga and Neville, 1985). Milk potassium content is reduced in milk of cows with mastitis, but the proportional change is less than that of sodium (Wegner and Stull, 1978). An experiment was conducted to investigate the response of three mastitis pathogens to the changes in sodium and potassium concentrations in their growth media that are typical of the changes occurring during a mastitic event.</jats:p

A simulation of the effects of changes in the Na and K content of milk during mastitis on the growth of<i>Staphylococcus aureus</i>,<i>Streptococcus uberis</i>and<i>Escherichia coli</i>

In a mastitic event damage to the epithelial tissue of the mammary gland, and in particular an increase in paracellular permeability allows sodium to enter the milk from the blood (Schaar and Funke, 1986). Normally there is a stepwise gradient of declining sodium concentration from the interstitial fluid to the epithelial cells to the milk (Berga and Neville, 1985). Milk potassium content is reduced in milk of cows with mastitis, but the proportional change is less than that of sodium (Wegner and Stull, 1978). An experiment was conducted to investigate the response of three mastitis pathogens to the changes in sodium and potassium concentrations in their growth media that are typical of the changes occurring during a mastitic event.</jats:p

Interactions between housed dairy cows during feeding, lying and standing

Three experiments examined the extent of behavioral interactions between housed dairy cows. In Experiment 1, 6 different cows were selected every other day from a dairy herd and allocated to 3 pairs for recording of feeding, standing, lying, and leg-raising behaviors. There was no difference in the between-pair and within-pair coefficients of variation for the behaviors, suggesting that the performance of these behaviors was independent of influences of other cows. Experiment 2 used 9 pairs of cows in a 3-period changeover design. The same behaviors were recorded as in Experiment 1, and data were used only from the last 2 periods, which ensured that cows had been together previously for at least one 48-hour period. There were again no differences in the between- and within-pair coefficients of variation when using behaviors as replicates, either for the first 2 hours, during which time no treatments had been applied, or the entire 4 hours, when some cows had been prevented from lying down and feeding. Experiment 3 investigated the consistency of between-cow associations for repeated observations of feeding, lying, and entering the milking parlor. Although there was evidence of a similar order of entry into the milking parlor between days, the number of feeding associations was similar to that predicted by a model of random behavior, and the pattern of lying associations also suggested a random pattern of associations. Across behaviors, cows were observed with specific partners more often than expected by chance. Thus although there was no evidence of interdependence of feeding, lying, or standing behavior, consistent associations were observed, particularly in parlor entry