26 April 1996

DRY COWS:BEST STRATEGIES

DRYCOWMANAGEMENT

Post-calving diseases can have a devastating knock-on effect on fertility performance. Judie Allen reports

HOW often do you have to call the vet out to deal with cows which have retained cleansings, whites, cystic ovaries or are simply not cycling?

A recent study carried out by Midlands vet Steve Borsberry and the University of Liverpools Prof Hilary Dobson examined the effects of post-calving diseases on fertility performance. It found that all these disorders were associated with longer calving intervals.

It examined data from 402 calvings (including the controls) and found that endometritis (an infection of the uterine lining) alone accounted for the greatest incidence (10%), then milk fever (7.5%) and cystic ovaries (6.7%). Further down the scale came endometritis as a result of retained cleansings (3.3%), endometritis due to milk fever (1.4%) and retained cleansing on its own (1.3%). Research also found that the calving index of cows which suffered such disorders was between 13 and 66 days longer than their herdmates average.

Mike Kerby, of the Delaware Vet Group, Castle Cary, Somerset, which has over 200 dairying clients, believes avoiding these problems and securing optimum fertility depends on careful management pre and post calving (see box).

"Dry cow management is still one of the most neglected areas," says Mr Kerby, "And maiden heifers, which are often forgotten, should be managed in the same way."

"We now have several herds which are separating dry cows into three groups on condition score. Others are even managing four: one for cows expecting twins," he adds. But he accepts that grouping is not possible in every situation.

Condition score at calving should be 2.5-3.0. "There is no harm in trying to slim down cows up to three weeks before calving," he says.

One diet suggested by Mr Kerby for a dairy farmer client with over-weight dry cows proved especially effective. "Cows were given a paddock for exercise and they had to walk 200 yards for their forage," he says. This comprised 10kg grass silage, 0.5kg of soya plus ad lib barley straw. Magnesium was added to the water at a rate of 57-85g (2oz-3oz) a cow.

Mr Kerby believes the over-riding aim in dry cow management is to feed the correct balance of protein and energy with good quality digestible fibre. The calcium: phosphorus ratio must be correct and for best results there should be sufficient supply of trace and major elements: selenium, iodine and copper are the most important.

Most can be supplied through feeding a specialist dry cow compound, he says. Ad lib barley straw and limited silage are also appropriate.

Careful dry cow feeding has fertility benefits. Mr Kerby explains: "It takes between 60 and 90 days from when a follicle first starts to develop to when it releases its egg. It is thought that energy, amino acid and, possibly, trace element status at this time may dictate whether a successful pregnancy occurs. So for cows served 40-90 days after calving, dry period nutrition would be critical."

As well as improved fertility, cows fed correctly when dry also suffer fewer post-calving disorders. They are, therefore, at less risk of suffering endometritis through damage done during calving.

The calcium:phosphorus ratio in the diet and magnesium supply is linked to milk fever. Although a metabolic disorder, milk fever effects how quickly the uterus shrinks after calving. Usually it takes six hours to return to normal, but it may take much longer when a cow has milk fever. The cervix may also close more slowly, exposing it to invasion by bacteria.

Ensuring an adequate supply of energy and protein before and after calving could ensure the uterus repairs and returns to its normal size more rapidly. And maximising high dry matter intakes before calving on feed to be offered after calving acclimatises the rumen bugs. This reduces the risk of ketosis after calving when energy requirements increase with lactation.

Ketosis has not been found to have a direct effect on fertility, says Mr Kerby, but the knock-on nutritional imbalance it creates could have.

Retained cleansing and endometritis, although they can occur separately, are often linked. "Research suggests risk of endometritis increases up to 25 times when the cleansing is retained," he says.

"Nobody really knows why cows fail to cleanse properly: it may be hormonal, or it could be that there is swelling which prevents tissue separation."

He cautions against attempting to remove foetal tissue too soon after calving for fear of damage. He prefers to leave a retained cleansing for up to seven days, when it is more likely to come away easily.

However, leaving cleansings in the cow for longer can encourage endometritis because the foetal tissue acts as a highway for bacteria to get into the uterus.

This highlights the need for a clean environment at calving.

Certain strains of bacteria are more aggressive than others, and tissue damage, caused by big or malpresented calves, coupled with a reduced immune defence mechanism at calving, could add up to an outbreak of endometritis.

And Mr Kerby has a hunch that some cows are better than fighting this disease than others. "It depends on the number of white blood cells, and their ability to kill the infection and the speed at which they kill it."

He attributes the fact that cows that have had twins are difficult to get back in calf to a lower condition score at calving. This is due to the limited amount of space the rumen has in the body cavity which reduces dry matter intakes. Correct dry cow nutrition is especially important for these cows, says Mr Kerby, since it is important to secure high dry matter intakes after calving.

Lameness creates problems in much the same fashion and cows should be nurtured by having easy access to food to maintain an adequate energy and protein balance. &#42


Pre-calving

&#8226 Choice of an easy-calving bull.

&#8226 Careful feeding management and condition scoring of cows in their dry period.

&#8226 Ensure environment in which cows calve is hygienic.

Post-calving

&#8226 Trouble-free calving and post-calving period.

&#8226 The uterus must shrink to its normal size when empty and repair any damage as quickly as possible.

&#8226 The ovaries should start functioning to induce normal cyclical activity.

Vet Mike Kerby believes correct dry cow management is central to preventing post-calving problems.

Feed dry cows well and the chances are the rewards will be a trouble-free calving, good fertility and improved performance in their next lactation.