Replace those depleted minerals

Lack of quality pasture during the recent drought will have reduced the quantities of calcium and phosphate available to many cows over the past few months, according to Sue Macky, a Waikato based consultant in dairy cattle nutrition and management.

“Phosphorus and calcium are of major importance for health and productivity,” she said.

“Bone growth and density and reserves of these minerals are likely to be depleted in cows and young stock as they head into winter following last summer’s widespread drought conditions.”

Fast-growing late-autumn pasture may have reduced concentrations of these minerals or have created problems for absorption. Maize and cereal-based supplements are also low.

“Combined with this factor is the reduction in gut capacity of underfed cows following the lengthy dry spell,” Macky said.

“Reduced gut capacity takes time to reverse. When pasture feed supply increases, many animals will not be capable of immediately consuming the volumes of dry matter (DM) needed to regain condition and meet energy demands.”

The potential for nitrate poisoning is exacerbated when gut capacity is reduced. Moving from a high fibre diet, especially one fed with supplements such as palm kernel, to a low fibre/high protein pasture diet can adversely impact rumen function. Keeping a watchful eye on the cows’ dung, rumination and gut fill is an excellent way to monitor how rumen function is going.

Macky said a key sign of cows having lost excessive weight or being too thin is that they develop a “hairy” appearance, with their hair standing on end.

Shelter needed

“Underconditioned cows have trouble protecting themselves in cold and rainy weather so effective shelter should be considered in such conditions,” she said.

“A feed supply which includes hay or straw allows cows to keep warm, by generating more heat from rumen fermentation.”

Cows which have been dried off for longer than usual and given high-starch feeds can develop into fat couch potatoes. Both these cows and underfed, skinny cows have a high susceptibility to metabolic diseases including milk fever and ketosis at calving and in early lactation. Paying greater attention to cow behaviour at calving may be required to prevent potential problems.

“The nutritional support for in-calf heifers will also need extra attention following the drought,” Macky said.

“Too many heifers are both undergrown and underconditioned.

The key minerals for bone growth, calcium, phosphorus and copper, may also be lacking. Small pregnant heifers may struggle with adequate intakes of bulky forage.”

“With pasture feeding severely reduced over the summer period, large numbers of heifers have been struggling to grow themselves as well as growing their calves. From May onwards there is still the opportunity
to grow heifers by an extra 100kg liveweight before calving if feed choice, mineral intake and management are appropriate, and the heifer is in-calf to a sire of smaller breed.”

Macky said in some cases there will be more smaller calves this coming spring as calf size is determined by genetics and the nutrient supply from the placenta.

“Development of the placenta may have been compromised by poor nutrition at that earlier stage of pregnancy,” she said.

“Additional feeding in late pregnancy will not increase the size of the calf, but can ensure animals have enough energy to deliver calves quickly.

Feeding winter crops must be well managed, especially in the initial days with animals given short periods on kale, swedes or other fodder crops as well as access to balage, hay or straw.

“The better quality pasture you can produce, the higher your chances of maintaining a healthy and high producing herd. Even in the driest areas, the newer pastures have tended to perform best.”

Published courtesy of Dairy Exporter - June 2008