Good management, antibiotic resistance awareness, and biosecurity are increasingly important in dairy farming. Improvement of farm management can be achieved by the use of on-farm diagnostic tests. These tests make early detection of diseases possible and reduce inappropriate use of antibiotics. Examples of on-farm tests are the ATP meter for monitoring of drinking water quality, the California mastitis test for detection of subclinical mastitis and the ruminal pH test for investigation of feed management. These tests will be discussed in this newsletter.

This newsletter is based on an article written for the 36th Tanzanian Veterinary Association meeting in December 2018. Written by our Technical Manager Josje Hakker and an animal nutrition specialist. If you want to receive the whole article, please use this link to request it.

Introduction
Veterinary diagnostics on farm is an important aspect of veterinary science. Analysis of symptoms and determining the correct diagnosis are the first steps in the development of a successful treatment plan, the prevention of disease spreading, and improvement of general health status.

Monitoring health status on farms is becoming more and more important, because early diagnosis of health problems enables a farmer to act in the early stages of a health issue. This will help to reduce the use of drugs and reduce the development of resistance against antibiotics. Antimicrobial resistance, induced by excessive use of antibiotics, is considered a serious threat to public health.

On-farm diagnostics
Enabling dairy cattle farmers to keep a close eye on the health status of their herd is crucial for preventive and curative on-farm health care. Products for diagnosing health issues and disease in livestock are widely available worldwide. These products for on-farm, cow-side diagnosis are usually offered in the form of test kits. 
On a dairy farm, next to urine, manure and blood, milk is an easily available substance to sample and analyse for health monitoring. Milk composition is already used to monitor metabolic status and energy balance of dairy cows.

Diagnostic tools for the detection of sub-clinical ketosis in dairy cattle
Hyperketonaemia occurs when a cow needs more energy than is produced from eating the feed. This will cause the cow to burn its own fat and produce keton bodies. An excessive amount of keton bodies in the cow will make the animal feel ill and eat less. Read more about the process of ketosis in this newsletter.

Dexamethason inj. ensures that nutrients will be used in stead of the fat of the cow. This will decrease the production of keton bodies.

Diagnosing hyperketonaemia based on milk, urine or blood testing are all valid options. However, urine and milk samples yield more diagnostic inaccuracy than blood samples. Handheld meters to measure beta-hydroxybutyrate levels in blood serum or plasma are reliable devices to detect sub-clinical ketosis in dairy cows.

Diagnostic tools for the detection of sub-acute rumen acidosis in dairy cattle
Sub-acute rumen acidosis (SARA) is a frequently occurring health issue in dairy cattle in early and mid-lactation: up to one quarter of the animals in a dairy herd may suffer from SARA, which is caused by eating too much concentrate and not enough fibres, causing an acidosis in the rumen. Improper transition management and/or a too sudden change of ration composition around calving may trigger the disease.

• Feed intake
• Rumination
• Fiber fermentation
• Milk fat content 

More serious symptoms include:

• Diarrhea
• Laminitis
• Parakeratosis of the rumen wall
• Liver abscesses
• Increased production of bacterial endotoxin 
• Inflammation characterized by increases in acute phase proteins 

It is clear that early diagnosis of SARA is of utmost importance to maintain a high health status on a dairy farm. Usually, depressed milk fat content is a practical tool for the detection of SARA in mid-lactation. Another option is measuring the pH of rumen fluid. Not many techniques are available for measuring rumen pH under field conditions. There are two options: rumenocentesis and oral stomach tube. Research concluded that rumenocentesis (sampling fluids directly from the rumen, see image 1) was more sensitive and more accurate than pH measurements based on the oro-ruminal probe.

Diagnostic tools for the detection of (sub)clinical mastitis in dairy cattle
Somatic cell count (SCC) in milk is widely used to asses udder inflammation in dairy cows. The California mastitis test (image 2) provides a simple indicator of subclinical mastitis, by detecting bacterial DNA in milk samples. To select adequate control measures, however, it is crucial to identify the causative pathogen.