21 March 1997


High-yielding US dairy cows need careful feeding management. US trained nutritionist

Dr Christopher Reynolds now based at CEDAR, University of Reading,

outlines some of the findings from across the Atlantic

IN THE US, the economy of the dairy industry has been such that there has been an emphasis on increasing milk yields. In this country, there has also been a trend towards increased yields through the use of North American genetics, and when we talk about the fast track in dairy nutrition the analogy that immediately comes to mind is the high yielding dairy cow as being like a Thoroughbred race horse, bred for performance. In metabolic terms the comparison is in many ways appropriate. If we expect peak performance from our cows they must be managed and fed properly.

It is well known that cows lose body tissue in early lactation to provide energy – and protein – for milk production. This is an unavoidable consequence of the transition from the dry to the lactating state which can exacerbate with increasing yields. The aim then with higher yielding cows should be to maximise intake of a quality ration providing a balanced nutrient supply during early lactation. In many cows difficulties in the first few weeks after calving have a cumulative effect on performance which can be sustained and may even effect subsequent lactations. Theres been a great deal of research interest in the US on the management of high yielding cows during early lactation and there is now much greater emphasis on dry cow management and feeding during the approach to calving. We now know that feeding practices during the dry period determine performance in the next lactation.

Fatness disadvantages

One example of this, which the industry has long been aware of, is the negative effect of over conditioning. Fat cows tend to eat less and are more prone to developing fatty liver, which can impair performance, further reduce intake and is linked with the development of ketosis. Work at the University of Wisconsin has found that the development of fatty liver is proportional to the amount of time cows spend off their feed at calving; when cows go off feed, they begin to mobilise body fat which accumulates in the liver. To minimise fat mobilisation cows should be fed adequate amounts of roughage which will be digested slowly and maintain rumen function when cows stop eating at calving. Some cows may also need supplementary energy. The research has found that dosing cows with propylene glycol just before calving reduces liver fat concentration in the first few weeks of lactation. Obviously, easy calvers will be less prone to fatty livers.

As cows are loosing body fat and protein in early lactation, there is also a major increase in the nutrient requirements of the digestive tract and liver as their work load increases with increased production and intake. These tissues account for as much as half of body heat production and they are actually increasing in size as other body tissues are being depleted.

The growth of these tissues in early lactation adds to their already high requirement for amino acids, and so these tissues are in many ways competing with the udder for amino acids at a time when milk protein levels are at their lowest concentration throughout lactation. Recent work at Cornell University has found that the rate of protein synthesis in the liver increases nine days before calving, before feed intake is increased. The research has also shown that increasing dietary protein by feeding undegradable protein sources in the late dry period results in less metabolic disorders, less weight loss and higher intakes during early lactation. This mirrors work in the UK showing improvements in early lactation performance and milk protein percentage when cows are fed increased protein prior to calving.

After calving – feed to enable cows to maximise their dry matter intakes.

Feed a limited amount of a TMR in the late part of the dry period, says Dr Christopher Reynolds.


&#8226 Long forage or hay.

&#8226 Limit legume feeding.

&#8226 Offer minerals and vitamins.

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