In early lactation, all cows are in a state of negative energy balance; however, the magnitude of this can vary. While in a negative energy balance the cow will mobilise body fat but cannot convert this to energy through the usual pathways. Instead, ketone bodies are produced which in small amounts can be used by the cow for energy.
However, when ketone production is high, the cow cannot use all the ketone bodies for energy and ketone levels increase in the blood. When this occurs, the cow may suffer from ketosis.
Types of Ketosis
Type 1 - Sudden drop in energy intake
Ketosis is a result of a sudden drop in energy intake. This can be due to underfeeding or adverse weather events (e.g. snow storms) that prevent the cows from eating sufficient amounts of dry matter.
This type of ketosis can be prevented by ensuring cows are adequately fed or by ensuring any feed restriction is imposed gradually (e.g. over a week). Proper use of the spring rotation planner along with appropriate use of supplementary feeds should prevent the occurrence of Type 1 ketosis.
Type 2 - Post Calving
Ketosis generally occurs post-calving, when the cow is mobilising excess body fat to meet the demands of milk production. Cows that are too fat at calving (BCS > 5) or cows that have been overfed pre-calving are particularly at risk.
The risk of Type 2 ketosis doubles when calving BCS increases from 5.5 to 6.0; therefore, carryover cows tend to be particularly at risk
Type 2 ketosis is also affected by the level of feeding pre-calving hence the feeding rules for transition cow.
Type 3 - Silage Ketosis
Silage ketosis is due to cows ingesting poor quality silage. The silage undergoes a secondary fermentation and when ingested will increase the risk of ketosis. See grass silage for more information on silage quality and testing.
Reducing the Risk of Ketosis
Ketosis can be prevented by managing feed allocation and BCS (both pre and post-calving) and by paying attention to cow behaviour and adverse weather conditions. Ensure feed supply meets feed demand.
Checklist of management strategies that can be used to reduce the risk of ketosis:
- Ensure cows calve at recommended BCS targets: BCS 5.0 for mixed aged cows and 5.5 for heifers and second calving cows.
- If at or above target BCS, feed springers 90% of their energy requirements during the last two to three weeks pre-calving.
- Ensure cows have adequate feed allocated post-calving. Target post-grazing residuals of 1500 – 1600 kg DM/ha taking into account weather conditions and pasture utilisation.
- Avoid sudden feed shortages if possible. Allocate pasture accurately and use supplementary feeds if there is a pasture deficit. If feed restrictions are unavoidable, introduce the feed deficit gradually and use once-a-day milking to improve energy balance.
- Ensure any silage fed is of high quality and stored correctly.
- For more information on management in the period 2-3 weeks pre-calving through to the end of the colostrum period see transition cow.
What are the signs of ketosis?
Ketosis can be displayed in two ways:
- Lethargy (head down, lack of energy)
- Decreased dry matter intake
- Decreased milk production
- Often a sweet smell on the breath (acetone)
- Excitable, uncoordinated and can become aggressive
- Strange behaviour such as eating soil, licking fence posts and gates, walking in circles, or standing with heads raised up and pushed into a corner etc.
How ketosis is diagnosed?
A blood test can be used to diagnose ketosis, but in order to diagnose this condition correctly; measurements should include the ketone body “BOH” along with glucose and non-esterified fatty acids (NEFA).
Ketosis is often diagnosed based on the level of circulating BHBA in the blood and is deemed to be clinical or sub-clinical: Clinical ketosis: cows with blood BHBA levels greater than 2 mmol/l and Sub-clinical ketosis: cows with blood BHBA levels between 1.2 and 2.0 mmol/L.
However, because butyrate is a volatile fatty acid that is produced in the rumen, the level of BHBA in the blood is also affected by diet, or more specifically the carbohydrate source in the diet. Further, preliminary research results indicate that a threshold of 1.2 mmol/L BHBA in the blood does not indicate a metabolic disorder.
Based on this research, and because diet can influence blood BHBA content we recommend that:
- In our pasture-based systems sub-clinical ketosis should not be diagnosed on BHBA levels alone.
BHBA levels of 1.2 mmol/L are not indicative of sub-clinical ketosis and sub-clinical ketosis should not be diagnosed on BHBA levels alone, particularly when the diet is predominantly pasture.
- Additional indicators of energy balance should be considered. Additional indicators of energy balance, in particular nonesterified fatty acids (NEFA), and, if possible glucose, should be measured in the blood. If NEFA levels are greater than 1.4 mmol/L and glucose levels are lower than 3.0 mmol/L, then the risk of clinical- and sub-clinical ketosis is increased.
For example, in spring on pasture-based systems, if there are high BOH concentrations but NEFA concentrations are within the optimal range, then this is unlikely to represent ketosis. If high BOH concentrations are associated with high NEFAs, then this may reflect an inability of the cow to eat sufficient pasture and is likely to represent ketosis.
Treatment of ketosis
If a cow shows clinical signs of ketosis, seek advice from your vet. Successful treatment of clinical ketosis will involve veterinary intervention to provide cows with drugs that stimulate an increase in blood glucose.
Treatments that have been used in severely affected cows include intravenous metabolic solutions (e.g. 4-in-1; Ca, Mg, P, glucose), intravenous dextrose and multivitamin injections.
What you can do
If the affected animal is still able to stand increase energy content of the diet.
If the animal is not able to stand:
- Provide it with shelter, soft bedding and continued nursing, including regular rolling from side to side to avoid sores.
- Provide water and high-quality supplements, supported by oral administration (twice daily) of glucose precursors such as propylene glycol.
- Use hip-lifters or similar lifting devices to assist the affected cow to her feet for some time. Hip clamps can only be used to help a cow stand, but not to keep her standing. A sling may be used for up to one hour only if the cow cannot support her own weight. For more information on lifting see down cows.
Starter drenches can be used to treat ketotic cows
Mono propylene glycol (MPG) can be given as an oral drench that can be used to improve performance in cows at risk of ketosis with elevated BHBA and NEFA concentrations. However, the lack of a consistent performance response in cows not at risk of ketosis indicates that MPG should not be administered routinely to the herd. Results from recent research indicate there is no benefit to cow performance (milksolids production, BCS or reproduction) of treating cows that had BHBA levels greater than 1.2 mmol/L with MPG. With a downer cow that has had a calving difficulty or metabolic issue such as ketosis, a starter drench may provide immediate energy, particularly if she has a poor appetite.
Is rumensin ever worth adding to feed?
Rumensin can be an effective bloat control agent. Even though it cannot prevent acute/severe bloat, it can be used as a mild bloat control or prevention agent. In terms of milk production, results are variable. The average milksolids response to 300 mg of rumensin is about 30g of extra milksolids. However, responses range from -80g to +80g of milksolids. To date, it is not known how and why rumensin causes negative or positive production responses and more experiments are necessary to gain a better understanding of the effects of rumensin in pasture-fed dairy cows and the interactions with fibre and starch. In terms of reproduction or BCS, rumensin has no benefits in the New Zealand pasture-based system.