Disease Prevention

BVD Control and Prevention

Some countries in the world have achieved the eradication of BVDV. This has not been attempted in New Zealand. Whether considering a country or a herd the strategies are the same: either vaccinate and manage to limit the spread and impact of the disease or test and cull, removing the virus with strict biosecurity to keep it out.

Control and Prevention programs are based around a thorough understanding of infection dynamics and a systematic approach. We highly recommend that you undertake a Risk Analysis before jumping into something that may be very expensive and time consuming but may not achieve the outcome you want. Following a risk analysis by a trained vet, the program is built around

1. Defining the status of your herd
2. Assessing the BVD biosecurity of your herd.
3. Actioning the most appropriate control plan
4. Monitoring the status of your herd.

The program must be practical and sustainable; financially and physically. Thus it is very important you set it up well.

Defining status

A bulk milk sample is taken from your vat. This classes your herd as currently infected, recently infected or not infected for some time. If not infected, this means you are vulnerable if the virus hits during mating.

If the infection is current, a further vat milk test can indicate whether there are current PI animals in the herd. Remember the vat test only covers animals contributing to it that day. Any cows out of the vat or animals not in milk are not covered.

If wanting to clean up existing PI animals you can look for poor performers based on herd test, then blood test groups of individuals and consider culling. You can also blood or ear knotch test calves and cull PIs before they go any further.

Assessing Biosecurity

“In, out and over” are the 3 biosecurity risks.

Cattle coming onto the property, including their foetuses can pose risk. This includes your own heifers returning from grazing, as well as leased animals (cows and bulls). The virus can survive a week in soil etc, so be careful with people, equipment and vehicles.

Cows going off the property in late pregnancy, are OK, but watch out for bought in cows...

Lastly, consider contact with neighbouring properties. The virus can spread across fencelines, or with rogue animals breaking through boundary fences.

Action

The No. 1 goal is to minimise the exposure of early pregnant cows and heifers to the virus. This will eliminate the ongoing supply of PI animals. Cleaning up the current PI “crop” is also helpful. There are basically 3 types of action:

• Test all incoming animals. Cull PIs and consider vaccinating the animals (especially service bulls)
• Vaccinate cows and heifers with a vaccine that protects the foetus.
• Change management/biosecurity practices to prevent virus introduction and pregnant cow exposure, eg electric fence outriggers on boundary fences to prevent nose to nose contact with neighbouring stock.

There are a lot of practical and cost considerations in an action plan, hence we usually need to formally sit down and work it through with you. The vaccine is not cheap, and if buying it we need to ensure you are using it most effectively.

Monitor

Monitoring is important to both measure progress and detects any breakdown rapidly.

This can be done by either annual bulk milk testing or testing the status of heifer replacements.

If you have read this article this far you will now know that BVD is complex!

The take home message is – before embarking on a prevention or control program, speak to us first!!!

Leptospirosis Control

Leptospirosis is not only a disease of cattle, but it is a disease of many species and one that many farmers have experienced first-hand. The bacteria have a wide variety of species, each one at home in mostly one species of animal – the maintenance host.

These bacteria enter the body via penetrating body membranes and broken skin. They have a corkscrew shape, which assists this penetrating function. Once entering the body, the bacteria multiply in the blood and are spread around many organs. Eventually they settle in the kidneys, where they reside for weeks to months, multiplying and being shed to the outside world. From the urine of one animal, they infect another. Because humans can be infected from animal urine leptospirosis is considered a zoonosis. Both humans and cattle can get lepto from rats and wildlife. Pigs are commonly infected. Infections are also showing up in sheep flocks.

One of the most common routes of infection in dairy sheds is believed to be urine splashes from cows into the eyes of farmers or on their hands which have cuts and abrasions. For meat workers, it is the urine splash as the bladder is cut or sometimes comes from other tissues such as the kidney.

The effects on the body of the infected host vary widely, depending entirely upon which strain of lepto is involved. If it is the normal host adapted strain of lepto affecting the maintenance host there is virtually no effect, but the shedding period is long, eg in cattle, the hardjobovis variety is shed for 9 months.

When a non host adapted strain is the source of infection (ie an accidental host), all hell can break loose, potentially fatally. Well recognised syndromes in dairy cattle are redwater in calves (ie blood in urine from damaged kidneys), milk drop (sudden, severe drops in production) and abortion storms, where a high percentage of calves are aborted in the second trimester of pregnancy.

In humans there is no natural strain – all infections are accidental. Historically the most common type of infection has been from the cattle variety, but other varieties are involved as well. Human leptospirosis causes fevers, major headaches and ‘flu like symptoms. It is one of the most common occupational infections in agricultural workers and can last for months to years. In severe cases there can be significant kidney and liver damage, very occasionally leading to death.

Leptospirosis control is based around vaccination. Typically vaccines cater for the normal cattle strain to prevent human disease and the pig lepto variety (Pomona) to prevent major cattle disease. Other strains are sometimes included as well. Vaccination programs currently involve primary courses for calves, followed by annual booster vaccinations.

It is important to get the timing of vaccination right, as human health depends on it. If given too early the mother’s colostrum antibody to Lepto can interfere with the vaccination response. Also if the boosters are not annual it can create a few hiccups with immunity and protection. Vaccine must be stored and administered correctly; under the skin and at the right dose. It is also surprisingly easy to not vaccinate all animals on your farm or forget mobs of stock off grazing elsewhere. Make sure you talk to us about getting the job done properly or better still get us out on the farm to do it at planned appointments. We can also give you a certificate showing your herd vaccination status.

There are other “not to be neglected” aspects to Lepto control.  These can be covered in formal consultation with ourselves, but in summary, they include:

• Insisting that any new cattle arriving on the farm have been vaccinated at least a month prior to arrival. Don’t forget the leased bulls!
• Hygiene in the milking shed. No smoking, wearing thongs/jandals, bandage cuts on arms and wear milking gloves.
• Hygiene when doing obstetrics.
• Control rodent populations, particularly around cattle feed supplies.
• Separate cattle from pigs and sheep.
• Fence off waterways, particularly if they could contain effluent from other farms.