MANAGING KETOSIS
Cows at grass come associated with various health problems, here Evolution Vet partner Sally Wilson focuses on the risks of ketosis
Challenges at grass
Maintaining milk production and fertility at grass can be challenging, however, with preparation these problems can be managed. From 2013 to 2014 average yields increased by 5.3% and are expected to rise by a further 6% this year, but milk from forage has not risen, with many cows now housed all year to achieve high yields. However, when cows are grazed
there are a number of issues which must be overcome in order to keep a decent volume of milk in the tank. To a cow, turnout represents a limitless amount of change - and cows don’t like change. They like everything to happen as they expect; they like routine. We know what effect a group change or a sudden change in diet can have on a dairy cow in terms of production and fertility: turnout must be off the scale. Having gone through the stress of turnout, however, high- yielding cows then simply cannot eat suffi cient grass to reach their yield potential. To produce 25kg a cow needs to eat 20kg dry matter (DM); to produce 55kg she needs to eat nearer to 30kg DM a day. DM in grass can be low at around 20%. So, if a cow eats 70kg of grass, this only equates to 14kg DM. When a cow cannot eat enough to sustain yields, her body tries to maintain her yield at all costs and this is where Ketosis can enter the picture.
When energy intake is less than energy required, the cow goes into negative energy balance (NEB). Fat reserves are broken down and ketone bodies are produced. This is usually a normal process. However, when it occurs to the extreme or for a prolonged period of time, it ultimately leads to health issues for the dairy cow. Eventually, this will have an effect on yield. A recent study suggested animals with blood ketone levels of >1.2 mmol/l during the fi rst week after calving produced about half a litre less per 0.1mmol/l blood ketone increase for the fi rst 30 days of lactation (Chapinal and others, 2012).This could equate to more than fi ve lost litres a day. Perhaps even more importantly, the effects on fertility can be profound. Ovulation can be halted, meaning the cow does not
36 THE JOURNAL JUNE 2015
return to oestrus after calving. Studies in ketotic cows have found various negative correlations between fertility and ketosis. These include a reduced chance of becoming pregnant within 70 days of the voluntary waiting period ending, poorer conception rates to fi rst service and increased calving interval. Just to complete the dismal ketosis picture, ketotic cows have been found to be more likely to suffer from conditions such as LDAs, metritis and retained cleansings. Perhaps not surprisingly, this leads to a higher chance of being culled earlier from the herd. A study in 2012 (McArt and others) found that animals with subclinical ketosis in the fi rst week post calving were three times more likely to be culled before 30 days into lactation than animals free of ketosis.
Ketosis monitoring
It is easy to ascertain whether ketosis is a problem in a herd. Blood samples taken from about 12 animals in a certain production group can be checked for BHB levels on a portable cow-side machine, giving immediate results. There are also cow-side milk testing kits available.
Ketosis Prevention
The science behind any ketosis problem can become complicated, but the basic principle is simple. Get enough energy into the cow, so she can produce milk without having to break down her fat reserves. In the case of grazing cows, this can mean altering the approach to grazing management as well as supplementary feed. However, there are basics to consider
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