In early lactation, all cows are in a state of negative energy balance; however, the magnitude of this can vary. During severe negative energy balance, the cow mobilises excessive amounts of body fat but cannot convert this to energy through the usual pathways. Instead, ketone bodies such as β-hydroxybutyrate (BHB, also called BHBA or BOH) are produced. In small amounts, the cow can use BHB as an alternative energy source.
However, when ketone production is high, the cow cannot use all the ketone bodies for energy and BHB concentrations 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 or floods) that prevent the cows from eating sufficient amounts of dry matter.
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) are particularly at risk. For example, cows that calve at BCS 6.0 are twice as likely to suffer from ketosis than cows that calve at BCS 5.5.
- Cows that have been overfed pre-calving are also at risk of type 2 ketosis, hence the feeding guidelines for transition cows.
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.
What are the signs of clinical 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 is ketosis diagnosed?
Because clinical signs may not always be present, ketosis is often diagnosed based on the level of circulating BHB in the blood to classify cows as either clinical or sub-clinical:
- Clinical ketosis: blood BHB concentrations greater than 2 mmol/L
- Sub-clinical ketosis: blood BHB concentrations between 1.2 and 2.0 mmol/L.
However, because butyrate is a volatile fatty acid that is produced in the rumen, concentrations of BHB in the blood are also affected by diet. Blood BHB concentrations are naturally higher in cows eating a predominantly pasture-based diet, compared with those eating a diet high in grains.
Further, DairyNZ research indicates that a threshold of 1.2 mmol/L BHB in blood is not always associated with poor animal performance in a pasture-based system. Based on this research, and because diet can influence blood BHB concentration, we recommend that:
- In our pasture-based systems, sub-clinical ketosis should not be diagnosed on BHB concentrations alone.
Although BHB concentrations greater than 1.2mmol/L are associated with reduced reproductive performance and health outcomes in housed systems, these relationships are inconsistent between herds under grazing conditions.
Therefore, BHB concentrations greater than 1.2 mmol/L are not necessarily indicative of sub-clinical ketosis.
- Additional indicators of energy balance should be considered.
Non-esterified fatty acids (NEFA) concentrations and, if possible, glucose, should be measured in the blood as well as BHB. If NEFA concentrations are greater than 1.0 mmol/L and glucose concentrations are lower than 3.0 mmol/L, then the risk of clinical and sub-clinical ketosis is increased.
For example, during spring in pasture-based systems, if there are high BHB concentrations but NEFA concentrations are within the optimal range, then this is unlikely to represent ketosis. If high BHB concentrations are associated with high NEFAs, then this may reflect a severe negative energy balance and is likely to represent ketosis.
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.
Management strategies 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 2-3 weeks pre-calving.
- Ensure cows have adequate feed allocated post-calving by using the spring rotation planner. 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, try to introduce the feed deficit gradually and consider using once-a-day milking to improve cow energy balance.
- Ensure any silage fed is of high quality and stored correctly.
- Cows that have had difficulty calving or metabolic issues, such as milk fever, can benefit from a starter drench that provides immediate energy, particularly if they have a poor appetite.
- For more information on management in the period 2-3 weeks pre-calving through to the end of the colostrum period see transition cow.
Does Rumensin™ reduce the risk of ketosis?
Rumensin™ contains monensin sodium, which alters the rumen microbial population to increase production of propionate relative to butyrate. Rumensin™ lowers blood BHB concentrations and may reduce the risk of ketosis in grazing dairy cows; however, it does not improve BCS or reproductive performance.
Treatment of clinical ketosis
If a cow shows clinical signs of ketosis, seek advice from your vet. Successful treatment of clinical ketosis will involve providing cows with oral drenches or 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 can you do?
If the affected animal is still able to stand, increase energy content of the diet supported by oral drenching (twice daily) of glucose precursors such as monopropylene glycol (e.g. KetolTM).
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.
- 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. For more information on lifting see down cows.
Is there value in treating subclinical ketosis?
Recent US studies indicate that using monopropylene glycol drench to treat housed cows with elevated blood BHB (≥ 1.2 mmol/L) improves their metabolic status, survival, and reproduction.
However, DairyNZ research indicates that although this strategy reduces blood BHB, the effects vary between herds under pasture-based systems, and in some cases reproductive performance may actually be reduced.
Therefore, using a threshold of 1.2 mmol/L BHB in blood to treat cows with monopropylene glycol drench (without other symptoms of metabolic illness) is not recommended to improve cow performance in pasture-based systems.