Author: Dr. Maarten Crivits (ILVO) - 23 December 2016

Subacute ruminal acidosis (SARA) is a metabolic disorder that can become a serious economic problem in dairy herds. Dairy herds experiencing SARA will have a decreased efficiency of milk production as well as impaired cow health leading to involuntary culling. In practice, SARA is often overlooked and underestimated: neither the treatment costs nor the disease costs have been thoroughly investigated. Moreover, from the perspective of the farmer, SARA is very difficult to detect due to its lack of clear symptoms.

Precisely because the disease is so difficult to detect, precision livestock farming technology (PLF) can become an important tool to monitor SARA in dairy cows. But is monitoring also the most economical choice?

Recent research at ILVO and Ghent University assesses the economic value of the farmer’s choice on how to deal with SARA. Based on existing data of prevalence, treatment costs and disease costs, several scenarios are explored in terms of expected monetary value between either monitoring or not monitoring SARA. For dairy farmers, two important conclusions can be drawn from the research:

• When a dairy farm has a low prevalence of SARA (less than ¼ of the herd infected) the economically soundest option is to stay away from monitoring. In this case, a farmer can best make treatment decisions on herd level, i.e. choosing between preventively treating all cows or treating none of them all.
• When a dairy has medium to high prevalence of SARA (between 25% and 80 % infected) then monitoring is the best option, provided that a specific monitoring system (i.e. fatty acid analysis of milk) is used.

Fatty acid analysis to detect SARA

When a farmer decides to monitor SARA on the individual cow-level, what are his or her options?  The research shows that making use of the fatty acid profile is the most efficient way to guarantee an accurate diagnosis of SARA. This test delivers the most reliable results. At this moment there are, however, no PLF technologies that provide continuous monitoring by means of fatty acid analysis. A farmer will, thus, have to outsource the analysis to a qualified lab. In this case it might be beneficial to monitor cows in critical risk periods. The probability that the disease occurs is greater when cows are 15-30 days in milk or in periods of heat stress. High-concentrate diets are also a critical factor in the disease’s occurrence.  Monitoring at these critical moments is key.

The different dietary measures which are taken to prevent or treat SARA can be very diverse. First of all, rumen buffers can be supplemented to the diet. There are several commercial buffers available in the market. The most common are sodium or potassium bicarbonate, with doses varying between 110 - 225 g/cow/day which was reported to positively affect the milk production, the fat percentage and the dry matter intake (DMI). To give an idea of the costs, for sodium bicarbonate costs will be varying between €0.40/kg and €0.45/kg. These costs total to an average annual cost of €16 to 36/cow/year.

However, the supplementation of buffers alone is not considered a solution in the long term when not accompanied with optimization of the feeding management. One strategy that will significantly lower the changes of SARA breaking through lies in reducing the amount of concentrate, avoiding the supply of highly fermentable carbohydrates in the concentrate to increase the effective fiber in the ration.

New roads for PLF technologies?

At this moment there are no PLF technologies performing fatty acid analysis of milk to diagnose SARA. Might it be a promising road to invest in developing sensors to address this important disease?  In terms of predictive values the research shows that for all available analyses (fatty acid profile, fat/protein ratio, no monitoring), given the most probable values of prevalence, the value of specificity is more important than the value of sensitivity. Sensitivity of a test refers to the test’s capability to correctly diagnose sick cows while the specificity refers to the ability to detect healthy cows. Put simply, if a test is highly specific, it will perform well in detecting healthy cows leading to fewer false alarms. Despite that the focus for many technology developers is to have a high sensitivity, this research showed that the economic value of using a test to detect SARA, increased more with a higher specificity than with sensitivity.  As such, these are important insights for technology providers targeting SARA.