Wednesday, July 6, 2022

Care for cattle after drought

What disease risks in cattle are heightened by a drought? Really, it is just the consequences of underfeeding that is the biggest challenge. But a disease that is set up by a big summer dry is liver fluke. The intermediary host of this disease is a snail that distributes the precursor stage of the fluke that we see. It is a very specific snail that does this and it lives typically in swampy areas. When feed gets short and the dry opens up access to wet areas that are not usually heavily grazed, animals can get a much higher level of challenge than normal. On farms that have a history of liver fluke there should be extra vigilance in monitoring and treating for fluke. A limitation we have in managing liver fluke is that the diagnostic tests do not quantify the level of infestation. Even the standard works monitoring is notoriously inaccurate in reporting the level of fluke present.

That diagnostic pathway has to be more directed than just waiting for a works report.

A few fluke in the liver are unlikely to cause any problems but for pregnant cattle in particular a decent burden can cause havoc.

Maintaining pregnancy requires a lot of liver function and when some fluke reduce that level of function the consequences as pregnancy progresses are excessive loss of condition and very often recumbency. Once this happens there is no return. This is a winter to be wary.

It is the breaking of a drought that often brings the biggest issues.

In sheep systems it is typically Haemonchus challenges in the North Island. We do not see the same level of elevated challenge in cattle systems, particularly if the drought has been long.

In shorter droughts the worm species Trichostrongylus seems to be able to survive better than the others and sudden outbreaks of scouring and weight loss a couple of weeks after the rain can happen.

But the dry does not ever take out the whole worm population because severe Ostertagia burdens in cattle in the winter following a drought are common. There is no question that this is very much driven by underfeeding but, nevertheless, the worm larvae are there to be picked up.

By far the biggest threat to cattle as the consequence of a long drought is winter starvation.

Growing cattle can be held on maintenance or even below for only so long. But for too long and it puts a lifetime ceiling on frame size and performance.

For pregnant cattle, though, it is a matter of life and death. Being thin, hungry and pregnant is a very risky state to be in. The earlier that steps are taken to rescue light condition cows and secure some feed for later in pregnancy, the better the prospects for a good outcome.

A month before calving starts there has to be enough feed to ensure that cows do not lose condition from then. This is important to maximise production but also to increase the survival chances.

Experiences from past droughts have shown us how susceptible mature cows can be to Ostertagia when they are very underfed. The pre winter pasture covers are low on the majority of farms so there is a strong prospect that cows will be under pressure.

When Ostertagia becomes established in these cows it is almost irreversible. Their appetite is lowered, they lose protein and effective digestion declines. Treatment once this has happened often does not save them. That month before calving starts is an ideal time to intervene.

All of these challenges to beef cows in late pregnancy also set them up for being low in magnesium. This is almost a predictable threat, even this far out. The syndrome that we see so frequently is light condition cows that are not getting enough to eat close to calving and have some worms in their bellies in which the final blow is a hypomagnesaemia.

Trace element deficiencies tend to get blamed for poor outcomes following droughts. Copper status is the only one that is likely to be specifically influenced by a long dry and that effect is to lift the copper stores.

But ongoing underfeeding could totally counter that extra accumulating effect. This highlights the need to do extra monitoring when normal patterns are altered. Those slaughtered cattle are useful for that as well. Those reports are very valid.

Managing droughts and, in particular, after droughts requires more monitoring and smart decision making than usual. Most North Island feed budgets already show a spring deficit. Careful allocation now of limited feed is highly rewarded. Maintaining feeding priority lists and keeping key dates for actions to the fore long after the rain has come are vital for making the most from the devastation of a long drought. 

– Trevor Cook is a veterinarian at Totally Vets, Feilding

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