Vet Viewpoint: Advice for dairy farmers on heat stress, Johne’s and AI

Unsurprisingly, the heatwave has raised issues for vets across the UK. Rob Davies from Camarthenshire and David McCrea from Cumbria are both warning farmers to beware of heat stress and the effect on cow health and conception rates.

On the fertility front, Rose Jackson from Derbyshire shares some tips for improving artificial insemination (AI) best practice. And Kate Brodie from Wiltshire looks at some areas the farmers might be going wrong with Johne’s management.

© FLPA/REX/Shutterstock

Rob Davies

Allen & Partners, Whitland, Camarthenshire

At last we have had weather that we can call summer. People love it, but do cows? You may have noticed reduced milk yield, increased mastitis incidence and/or other diseases. You may have even seen cows bunching.

These are sure signs of heat stress – yes, even in west Wales.

See also: How to act on drought and tightening forage stocks

What you may not have seen is that conception rates will have crashed. This will manifest itself by significantly fewer cows calving in April.

The effect of heat stress is cumulative. So, even though cows may be stressed by heat for three to four hours a day, the effect is compounded by heat stress on consecutive days, making matters worse.

Help them by providing access to water, shelter and free-flowing air. Try sprinkling water over them in front of a fan at the back of the collecting yard before afternoon milking.

David McCrea

Capontree Vets, Brampton, Cumbria

The recent and ongoing hot weather is fantastic if you are on holiday, but not so good if working in waterproofs. It also increases disease for some animals.

Heat stress – The upper critical temperature for cattle is 25C. During hot weather the most visible symptoms of heat stress tend to be elevated breathing rates.

The first step in improving conditions for heat-stressed cows is to identify means of improving air flow and ventilation in buildings. You could replace doors with gates and fans can be installed where other improvements cannot be made.

The consequences of heat stress include reductions in feed intake, milk yield and fertility.

Cows can experience stress-related illnesses and depressed immunity. This can lead to a lowering of the cow’s defences against mastitis-causing pathogens.

This, coupled with conditions in cattle housing that may favour the spread of bacteria, can lead to an increase in clinical mastitis and raised somatic cell counts.

When this weather finally breaks and the rain returns, a sudden increase in nematode larvae on pasture may lead to outbreaks of parasitic gastroenteritis. 

Rose Jackson

Scarsdale Veterianry Group, Derby, Derbyshire

We are quick to blame cows for poor fertility rates, but we don’t often review AI techniques.  

Correct timing of insemination is important; the am/pm rule is still helpful, but it is old advice – first demonstrated in 1943.

Only 50% of Holstein cows will show standing to be mounted (STBM). Therefore, it is important to optimise heat detection, insemination technique and semen quality.  

Some 94% of ovulations are 16-40 hours after onset of heat; the recommendation for sexed semen is to AI 14-20 hours after observed heat.

My tips are:

• Check your flask – it shouldn’t lose >1cm liquid nitrogen per week
• Thawing technique should be 35-37°C for a minimum of 45 seconds
• Insert straw into a pre-warmed gun
• AI cow within 10 minutes; thaw one straw at a time
• Semen should be placed in the body of the uterus, not in the horns.

Kate Brodie

Drove Farm vets, Swindon, Wiltshire

Farmers supplying purchaser members of the National Johne’s Management Plan will need to have a written plan in place and co-signed a declaration of compliance with their BCVA-accredited vet by the end of October 2018.

While many of my herds have such a plan in place and adhere to it, they still have continued low-grade infection grumbling along.

At a recent meeting the following points came up that might be where we are going wrong:

• Infected calf dung is a source of infection for some weeks after birth. Do such calves or their dung come into contact with replacement heifer calves?
• “Red” Johne’s-positive cows with high SP (specificity) values at testing could well be “super shedders” of the organism and should be culled as a priority.
• Are all staff members and visitors disinfecting between the adult cow population and the calves?

Your plans should be reviewed regularly and these may be points worth looking at.