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Ketosis

Friday, 26 November 2021

Ketosis

If you could have a superpower, what would it be? Perhaps you would be able to predict which animals would fall unwell, before it happened? Or perhaps you would be able to see into the future and prevent animals getting ill in the first place? And what if I told you that in some circumstances, we can already achieve this?

If you could have a superpower, what would it be? Perhaps you would be able to predict which animals would fall unwell, before it happened? Or perhaps you would be able to see into the future and prevent animals getting ill in the first place? And what if I told you that in some circumstances, we can already achieve this?

Negative energy balance and ketosis

In all animals energy balance describes the difference between energy intake via food and energy expenditure; to keep warm, to walk about, to urinate and defecate as well as (sometimes) to produce milk. An individual is in a positive energy balance when the energy they eat is greater than the energy they expend; something we aim for to ensure our stock are growing. Conversely, when the amount of energy an animal eats is less than the energy they expend, we describe it as a negative energy balance. In such circumstances, the animal must metabolise their own body reserves of fat and muscle in order to compensate.

A common example of this scenario is soon after calving in dairy cows. At this point in time, dry matter intake is low, but milk yield is increasing rapidly. Peak negative energy balance usually occurs within the first 10 days of lactation, and cows return to positive energy balance between 30 and 100 DIM.

If a large amount of fat is metabolised during early lactation ketone bodies - acetone, acetoacetate, and BHB are produced, or fat is stored in the liver as tryglyceride. Subclinical ketosis is when these levels of ketone bodies are high enough to have consequences, although may not be associated with clinical signs at the time of measurement.

Consequences of ketosis

The main costs associated with subclinical and clinical ketosis are due to losses of reproductive performance and losses of milk productivity. The cost of each case of subclinical ketosis is estimated to be between £110-220. Furthermore, cows with elevated ketone body levels are also more likely to encounter left displaced abomasum, metritis, retained foetal membranes, mastitis, increased somatic cell count and are more likely to be culled early (Lei and Simoes, 2021).

We generally see clinical ketosis quite rarely nowadays. Most commonly it is associated with reductions in milk production and appetite, as well as condition loss; the relative frequency of associated clinical signs are shown in the image below.

Prevention is better than cure

The causes of ketosis are multifactorial but are commonly associated with inadequate nutrition, which does not meet the needs of the cow; or depressions in dry matter intake – most commonly associated with cows that are over-conditioned prior to calving. Prevention centres around maintaining high dry matter intakes prior to, during and after calving as well as preventing cows from becoming over-conditioned at calving (BCS ≥3.5).

We can also monitor how well cows are getting on with the ration using metabolic scoring. Whilst this is commonly perceived to be an expensive and time-consuming task, in reality it can be performed informally very easily. Regular blood sampling of cows 2-14 days pre-calving, and 2-3 weeks after calving for measurement of BHBs (a ketone body) gives a useful indication of whether levels of subclinical ketosis are increasing, allowing further investigation and preventative strategies to be implemented before more severe consequences ensue. In such a way, BHBs really do allow you to predict the future…

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