Fever Tags for early detection of disease in calves

Author: Ben Thompson (IfA) - Date: January 29, 2019

Worgret farm is a dairy farm situated in Wareham (Dorset) with 280 Holstein-Friesian cows, calving all year round and rearing their own replacements. The milking herd graze during the summer months and are housed in the winter. The farm is owned and managed by John Baggs and partner Sophie.

John Baggs pictured with some his calves wearing fever tags.

Fever Tags

Fever tags are a temperature measuring ear tag; they are comprised of an ear tag sensor and a probe that goes into the ear canal. They measure the core temperature of the animal every 15 minutes. If the temperature is raised above 39.7⁰C for a period of 6 hours, then this will cause the ear tag to flash as an alert. This flash can then be seen by any staff on the farm, alerting them of a potential health or disease problem with that animal. This real-time temperature monitoring therefore gives confidence to farmers of the health status of their animals.


Worgret Manor Farm

John wanted to improve his calf rearing system, with focus on improving growth rates and reducing his mortality rate and antibiotic use. As a result of this and improving overall calf management at Worgret Farm, the long-term aim was to have healthier and more productive replacements, with an earlier age at first calving. Fever Tags were first used on Worgret Farm as part of a trial in 2014, to then be used permanently afterwards. The tags are put in at 2 weeks old and taken out at 11-12 weeks old. This being a critical period for immune system development and growth in calves. 

Design of Fever Tag, showing both the probe and flashing ear tag. 

For John and his staff at Worgret Farm, growth rates are of importance during rearing as they weigh calves at birth and 12 weeks. This is in order to achieve a steady plane of growth until service at 360-400kg.


Having the benefit of early detection of illness, means that calves can be treated at the sub-clinical stage. Earlier treatment has meant more care and attention and anti-inflammatories can be given, before considering antibiotic use. If antibiotics need to be used, during this stage treatment will be most effective and not as long. As a result of this, antibiotic use on their calves has reduced by over 50%. Having more control in disease management from using Fever Tags, has enabled John and his partner Sophie to reduce their mortality rate just from respiratory disease from 8% to below 1%.

Before the use of fever tags, replacement heifers were calving at 30 months and for John this was much too old. The reason for this John explained “is because of the altered or poor growth rates in our calf rearing system and therefore later service date”.

“From using the fever tags, we have been able to make any management adjustments, with nutrition, treatments or the environment a lot earlier”. As a result, the replacement heifers are now being calving at 26 months, which is a huge difference.

Table 1. Performance changes before and after using Fever Tags.

Another key benefit is that from making any management changes in e.g. nutrition, the effectiveness can be seen within 2-3 days on either a positive or negative scale. Therefore, solutions that can make the biggest positive impact are implemented quicker. As a result of this, growth rates have improved from 600g/day to 800g/day.

The true spread of disease in the calves can also be recognized a lot earlier. This has allowed the staff at Worgret Farm to keep on top of any health problems or new infections.


Overall, the key message is that there is no 100% certainty with using technology or good stockmanship on their own. With combining the use of both, Worgret Farm has reaped the benefits in their calf rearing system from using Fever Tags, which is having long term benefits for their milking herd.