Transition cow energy metabolite assessment is frequently used by dairy practitioners to monitor dairy herds in order to prevent disease and optimize herd health and productivity. Since the most stressful time (metabolically speaking) for a cow is the transition period (late pregnancy to early lactation), most of the monitoring is done in cows during this critical time. Interpretation of data obtained for herd health monitoring differs from interpreting data for the purpose of disease diagnosis in individual animals. Abnormal test results (above or below) with respect to established reference intervals are used to obtain a diagnosis of disease in individual animals. For herd level testing, reference intervals are not relevant, rather the data is interpreted as either the proportion of tested animals with values above or below a specific cut-off value or as the average value which is above or below a specific cut-off value. These cut-offs are determined from research studies that measure statistical assocations between the analyte of interest and downstream effects. In dairy herd health, pertinent downstream effects include the incidence of metabolic (clinical ketosis, displaced abomasum) and infectious/inflammatory (e.g. metritis, mastitis) diseases in the postparptum period, subsequent reproductive performance and milk yield.
For herd health testing, it is imperative to sample a sufficient number of animals to obtain reasonable confidence limits that the sampled group is a true representative of the herd. Most investigators use 75% confidence limits; this equates to testing 12 animals in large herds (> 500 cows). Naturally, the more animals sampled, the higher the confidence intervals, however sampling very large numbers is frequently impractical and and not cost effective.
Transition cow energy metabolite assessment includes testing both prepartum and postpartum cattle, as indicated below.
- NEFA prepartum: Measurement of non-esterified fatty acids (NEFAs) alone in prepartum cows (2-14 days before calving).
- Transition cow energy profile postpartum: Measurement of non-esterified fatty acids and β-Hydroxybutyrate (BHB) as a panel in the immediate postpartum period (3-14 days in milk).
- “Metabolic profile” test postpartum: This panel includes NEFAs, BHB, albumin, urea nitrogen and AST and is done in postpartum dairy cows (3-14 days in milk).
Studies done at Cornell University (Ospina et al., 2013) for reproductive and milking performance in dairy herds show that postpartum NEFAs are more predictive of downstream diseases (displaced abomasum, metritis, mastitis) and decreased reproductive performance than prepartum NEFAs or postpartum BHB in dairy herds in the Northeastern USA.
Recommendations for sample collection for transition cow energy profile or “metabolic profile” testing
- Collection tube: A red top tube is recommended for sample collection. Serum should be separated from cells ASAP after collection and the serum placed in a separate tube. Corvac (serum separator) tubes are not recommended (values are significantly different in corvac versus red top tubes).
- Time of collection: Collect samples from cows that are 3-14 days in milk. Also sample cows as they are coming into the feeding stalls. Do not overstress cows – NEFAs increase with stress or excitement.
- Sample storage: Samples must be kept cool to minimize false changes in results (NEFAs are particularly unstable). Submit ASAP to the laboratory.
- Number of cows: A minimum of 12 animals per herd should be sampled for herd level testing. This can be a mixture of heifers and >2 parity cows.
- Pooled samples: Pooling of individual samples from cows to assess energy status of a herd is not recommended. Studies at Cornell University have shown that results from pooled samples are insensitive when using prepartum NEFA, postpartum NEFA or postpartum BHB for the detection of excessive negative energy balance in transition dairy cows.
Non-esterified fatty acids (NEFA)
Non-esterified fatty acids (NEFAs) are a biomarker of negative energy balance. NEFA concentrations are interpreted as the proportion of animals above a specific cut-off value. Based on studies done at Cornell University in total mixed ration (TMR)-fed dairy cows, we interpret results as follows:
- Individual cows: There is an increased incidence of postcalving diseases (displaced abomasum, metritis/retained placenta and clinical ketosis), decreased milk yield and decreased reproductive performance in the first 30 days in milk in Holstein dairy cows with NEFA values > 0.60-0.70 mEq/L when tested 3-14 days after calving.
- Herd-level: There is a significantly increased risk of post-calving metabolic and infectious diseases, decreased milk production or decreased reproductive performance if >15-20% of tested postcalving cows have NEFA values > 0.70 mEq/L.
β-Hydroxybutyrate (BHB) is used as a marker of subclinical ketosis and values are interpreted similarly to NEFAs.
- Individual cows: A post-calving BHB > 10 mg/dL is associated with a significant risk of post-calving metabolic or infectious diseases (displaced abomasum, clinical ketosis and metritis), decreased milk yield and decreased reproductive performance in individual TMR-fed Holstein cows.
- Herd-level: There is a significantly increased risk of these post-calving diseases, decreased milk production or decreased reproductive performance if >10% of tested post-calving cows have BHB values > 10 mg/dL.
Aspartate transaminase (AST)
Aspartate transaminase (AST) is a hepatocellular leakage enzyme used as a marker of underlying hepatic lipidosis. However, AST is not specific for liver injury and will be increased with skeletal muscle injury (creatine kinase or CK should be concurrently increased with muscle injury). In addition, AST does not appear to be a very sensitive test for lipidosis in dairy cows. Alternatives to AST for liver injury include glutamate dehydrogenase (GLDH), which is more stable than sorbital dehydrogenase (SDH).
- This is a reflection of the ammonia concentration in the rumen and the protein (and energy) content in the diet. Urea nitrogen can be measured in blood, serum, plasma or milk, with results being interpreted similarly. The current recommendation (based on previous studies in the literature) is that the average urea nitrogen concentration of the tested cows should be between 13-17 mg/dL. Both high and low values indicate the need for modifying the content of the ration.
Albumin values are also used to reflect the nutrient and energy content of the diet. Some investigators use a goal of > 3 g/dL for an average albumin value of the tested animals. Note that albumin concentrations are also affected by other conditions including inflammatory states (albumin will decrease because it is a negative acute phase protein), liver disease (albumin is produced in the liver), and renal and gastrointestinal disease (albumin can be lost in these disorders).