Feeding cows

The stage of lactation, genetic predisposition, and salt all influence the cows’ dry matter intake, writes Malcolm Stewart-Burger.

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MANY FACTORS INFLUENCE a cows’ dry matter (DM) intake. What cows eat is converted into units of dry matter equivalents, leading to more efficient milk production. The cow gets increased nutrients from the forage, as less is exerted in the faeces and urine.

For example:

  • 2kg of hay @ 88% DM (12% moisture) = 1,76kg of DM.
  • 20kg of maize silage @ 35% DM (65% moisture) = 7kg DM.
  • 140kg of lush green pasture @ 9% DM (91% moisture) = 12,6kg DM.
    Getting cows to eat enough green, lush pasture is sometimes difficult. Dew, frost, rain and drizzle wet the green leaves. This exceeds the amount of water in the plant tissues, but cows have no option – they have to eat, water and all. Consider this analogy – on a hot day, you eat a quarter of a large watermelon for lunch, but by 3pm you feel hungry again. Why? Because you consumed a lot of water and a very low solid content. Cows are the same.

In the mid-1960s, I was conducting a weed-control trial in a vineyard in the Kimberley district. The farmer gave me permission to help myself to the huge Barlinka grapes. I got half way through the bunch and could manage no more – too much sugar and water!

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Factors influencing DM intake by cows:
Stage of lactation. In early lactation, appetite is depressed because of calving stress and a change of diet from a “dry cow” to a production ration. In later lactation, appetite is depressed because the foetus reduces the size of the rumen. Water. On average, a lactating cow needs 140â„“/day to 160â„“/day of cool water. Water from lush pasture counts for very little as the cow gets rid of most of it through benign diarrhoea. Protein concentration and the ratio of degradable to non-degradable protein. The higher the degradable portion, the slower the rate of passage of digesta. An ideal ratio would be about 40% bypass to 60% degradable protein. The 60% is essential to generate volatile acids. Energy concentration. That is, the sugar and starch content in the diet to continue contributing to microbe division.

Access time to the diet. Do cows have to walk a long way to the pastures or feed troughs? This might reduce the time available for eating. Physical characteristics of the diet. Extremely high moisture or very dry? A desirable mixed ration of about 40% moisture and friability is called for. Very fine diets aren’t desirable. Genetic pre-disposition. Like humans, some cows have larger appetites than others.

Ambient temperatures. The ideal temperature for cows to perform optimally is 4ºC to 16ºC. In South Africa, a very high temperature is detrimental to appetite and reproduction. Animal size. A large animal will eat more than a smaller, fatter animal of the same weight. Stress. Causes include high temperature (cows have no sweat glands), mud, high winds, excessive walking, in-herd competition, and biting flies.Herd group size. A large herd of 500 cows won’t perform as well as two groups of 250 cows each. This is especially so when first calvers are mixed with mature cows. Order of dominance. There’s a pecking order in every herd, which we’ll deal with in more detail when discussing cow psychology. Salt. A forgotten practice. Voluntary salt intake enhances appetite, so make sure salt licks are available.  

About Malcolm Stewart-Burger
Currently a part-time consultant to Nutex Feeds and De Heus, Malcolm Stewart-Burger has more than 40 years experience in ruminant husbandry. He was the founder of the Society of Master Dairymen and designer of the Maxi Milk System. A long-time senior technical advisor with Meadow Feeds, he was also the first to recognise dung as a diagnostic tool to measure the nutritional status of dairy cows, thereby earning himself the nickname “Dr Dung”.
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