Monitoring of Subclinical Ketosis in Dairy Herds MSD Animal Health

Monitoring of Subclinical Ketosis in Dairy Herds MSD Animal Health

By: Dr. W. Gratwick

Introduction

Metabolic disease presents a significant challenge to the modern dairy industry worldwide due to the continued genetic selection for greater milk production.  As a result, the natural mechanisms by which all mammals adapt to the transition from pregnancy to lactation may fail to cope with the extent of the increase in demand for nutrients for milk production.  A wide range of infectious and inflammatory diseases occur with much greater frequency during the transition period in addition to traditional metabolic diseases such as ketosis and milk fever, forming a periparturient disease complex.

Current research is highlighting the associations between the metabolic stress to which dairy cows are exposed and the function of the immune system, thus providing an explanation for the strong epidemiological associations between these conditions.   As such, subclinical ketosis should be considered as a ‘gateway’ disease which increases the risk of a range of production diseases including retained foetal membranes, displaced abomasum, mastitis and uterine infection as well as clinical ketosis.  Regular monitoring of the incidence of subclinical ketosis provides the basis of a metabolic disease control program.

Ketosis and hepatic lipidosis

Ketosis generally occurs in dairy cows during early lactation following an increase in the levels of nonesterified fatty acids (NEFAs), which are released from adipose tissue.  As well as being used by the udder to produce milk fat, NEFAs undergo metabolism in the liver.  This metabolism may follow three different routes; complete oxidation to release energy, partial oxidation into ketone bodies and re-esterification to form triglycerides.  The level of complete oxidation is limited by the availability of propionate from the digestion of carbohydrates in the rumen.

As such, especially when feed intakes are decreased or the levels of NEFAs are high, a proportion of the NEFAs will undergo partial oxidation to ketone bodies.  The predominant ketone bodies are acetone, acetoacetic acid (AcAc) and beta-hydroxybutyric acid (BHB). This pathway predominates during type 1 ketosis, which generally occurs as the cow approaches peak lactation if the diet is deficient in energy and is characterised by low blood glucose.  Control of type 1 ketosis can be achieved by ensuring that the diet delivers adequate energy to meet the requirements of lactation.

The re-esterification of NEFAs to form triglycerides is favoured when blood glucose concentrations are not significantly decreased as is often the case during very early lactation, despite negative energy balance, due to a combination of low insulin levels and insulin resistance.  Triglycerides are exported from the liver in the form of very low density lipoprotein (VLDL) and used by the udder to produce milk fat.  This process is inefficient in ruminants and if the level of production of triglycerides exceeds the rate at which they can be exported they are accumulated in the hepatocytes giving rise to hepatic lipidosis.

This pathway typically occurs during type 2 ketosis which is normally seen during the transition period (3 weeks before and after calving).  This accumulation of triglyceride impairs hepatic gluconeogenesis which further exacerbates negative energy balance and is associated with increased production of ketone bodies.  Both NEFAs and ketones have been linked to an increased risk of both metabolic and infectious/ inflammatory diseases during the transition period, including clinical ketosis, displaced abomasum and metritis. In addition, subclinical ketosis has been associated with reduced milk yield in various studies, ranging from 1.0 to 3.30kg/day across the entire lactation.

Monitoring of Ketosis in a Dairy Herd

Testing for Ketones

Various methods are available for measuring the level of ketones.  The Ketostix strip (Bayer Animal Health) measures AcAc in urine and has a sensitivity and specificity of 90% and 86% respectively when compared to serum BHB with a cut-off of 1.4mmol/l.  This test has a low cost but is inconvenient due to the requirement for a urine sample. The Freestyle Optium (Abbot Diabetes Care) is a low cost portable hand-held device capable of measuring BHB in a drop of blood. The strips can be purchased for under R10 each and the sensitivity and specificity are 96% and 97% respectively compared to a laboratory method using the standard cut-off of 1.4mmol/l for the diagnosis of subclinical ketosis.  The meter can be used to aid in the diagnosis of clinical ketosis in individual cows, for which a cut-off of 2.0mmol/l is used, as well as for the monitoring of subclinical ketosis on a herd level.

Which animals to sample

Type 1 ketosis occurs due to insufficient energy intake to match milk production and is best identified by sampling cows 25-40 days in milk.  Type 2 ketosis is caused by excessive lipid mobilisation and insulin resistance and usually occurs at 0-15 days in milk.  Sampling of at least 12 animals at each of these stages of lactation will allow the accurate classification of the herd according to the risk of each type of ketosis.  In small herds, sampling may need to be carried out on repeated occasions to obtain the necessary number of results.  Regular sampling of cows presented for routine fertility examination is a convenient way to collect sufficient data without any additional handling of the cattle.

Intervention

The diagnosis of either type 1 or type 2 ketosis will identify an opportunity to improve herd performance through a reduction in the prevalence.  Control of type 1 ketosis will involve increasing the energy intake of cows as they approach their peak milk yield.  This may involve an increase in the energy density of the ration or taking steps to maximise dry matter intake through environmental and managemental interventions.

Interventions for the prevention of type 2 ketosis should be focused on reducing the release of NEFAs by the adipose tissue around the time of parturition.  This release of NEFAs is a normal physiological response during the periparturient period.  The extent to which it occurs correlates to the rate of loss of body condition score (BCS) following parturition.

This loss of BCS is dependent on the BCS at parturition to a much greater extent than energy balance after calving has taken place.  As such, preventing cows from becoming over conditioned during late lactation or the dry period of paramount importance.  The risk of metabolic disease has been shown to increase above a BCS of 2.75 at parturition (using the 5 point Penn State body condition scoring system).

However, due to negative effects of lower BCS on milk production and fertility the ideal target for a Holstein type cow is around 2.75-3.25 at drying off with no changes occurring during the dry period, with cows at a BCS of 3.5 or greater being at significantly greater risk of developing type 2 ketosis. While there is some controversy surrounding the optimal feeding strategy during the ‘close-up’ period (21-28 days prior to calving) this ration should not provide more than 110% of the requirements for maintenance of body condition.  Traditional ‘steam-up’ type rations have been associated with greater lipid mobilisation after calving with higher levels of both NEFA and BHB.

During the ‘far-off’ period only the cow should only be fed enough energy for maintenance of BCS.  A loss of BCS during the dry period can lead to excessive release of NEFA’s before parturition and is not advisable.  As such, it is impossible to safely correct the BCS of cows which are over conditioned at drying off.  If this is the case it is likely that poor fertility is leading to extended lactations and this must be addressed as part of the long term strategy to control type 2 ketosis.

In the short term, the impact of type 2 ketosis on herd performance can be reduced through strategic dosing with propylene glycol (300ml daily for 5 days for a Holstein cow, 200ml for a Jersey cow).  The following guidelines should be used in order to ensure the cost-effectiveness of propylene glycol treatment based on the classification of the herd for type 2 ketosis (see Table 1):

Table 1: Prevalence of subclinical ketosis based on a sample size of 12 cows.

Number of cows >1.4mmol/l

Prevalence of subclinical ketosis

Classification of herd

0-1

<15%

Low

2-5

15-40%

Medium

>5

>40%

High

At the herd level a prevalence of subclinical ketosis >15% has been associated with a decrease in fertility and milk production and an increase in metabolic disease.

Table 2

Classification

Action

Action

Continue to monitor herd level prevalence every 2 weeks.

Medium (15-40%)

Test all cows 3-9 days in milk at twice weekly intervals (e.g. every Tuesday and Friday).

Treat all positive cows for 5 days.

High (>40%)

Treat all cows for 5 days starting at 3 days in milk.  Re-check prevalence in 2 weeks.

Conclusion

Regular testing of BHB using a portable handheld meter is a practical and cost effective method of monitoring subclinical ketosis in dairy herds.  The devise can be used by the herd veterinarian to test at risk cows during routine fertility visits. In high risk herds, more regular testing of by the farmer can be used to target treatment with propylene glycol.  The exact protocol should be adapted to the specific herd, depending on the risk, in order to fit in with current management procedures.

The prevention of type 1 ketosis should be focused on the nutrition and feed intake of cows in early lactation.  Control of type 2 ketosis depends on ensuring that the BCS of dry cows is maintained between 2.75 and 3.25 for the duration of the dry period.

Further reading

  • Ospina et al., 2013. Using Nonesterified Fatty Acids and b-Hydroxybutyrate Concentrations During the Transition Period for Herd-Level Monitoring of Increased Risk of Disease and Decreased Reproductive and Milking Performance. Veterinary Clinics of North America Food Animal Practice.
  • Hayton et al., 2012. Nutritional Management of Herd Health.  In ‘Dairy Herd Health’ (CAB international)
  • Penn State body condition scoring system. http://extension.psu.edu/animals/dairy/nutrition/nutrition-and-feeding/body-condition-scoring

 

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