BUILD IMMUNITY AND HELP COWS
Have you vaccinated your dairy heifers against lungworm or
ensured they will be exposed to low levels of the disease to
build up natural immunity? If not, they risk developing husk
as adults. Our dairy vet John Dawson reports
ONCE a disease under control, lungworm infestation has seen a steady increase during the past decade as vaccination has taken second place to modern long-acting wormers.
It was traditionally a disease of cattle during the first grazing season, but has become common in adult cows with serious consequences to milk production and fertility.
Infection levels of lungworm have increased during the 1900s from a low level of under 100,000 infected animals to over 350,000 in 1996. During this period a corresponding decrease in vaccination has been recorded.
Lungworm is a very debilitating, with symptoms ranging from a mild husky cough to severe dry coughing bouts causing chronic lung damage or death. Increasingly it is seen in adult cows, with herd outbreaks in the autumn as modern long-acting anthelmintic treatments used on young grazing animals prevent build up of immunity.
The development of the slow-release anthelmintic boluses and long-acting ivermectin regimes have a double-edged negative effect – failure to develop adequate immunity in the animal and reduced levels of pasture infection. 1997 was a very high infection year as the weather worked to its advantage. A warm, wet season favours the pasture development stages of the lungworm, increasing the pasture contamination levels quickly in late summer.
In order to develop good immunity the animal needs adequate exposure to the lungworm. Lack of exposure, or very low exposure during the first grazing season can leave the animal open to developing clinical disease later in life.
Ideal preventative measures are vaccination, followed by a worming and grazing regime which allows exposure to the parasite during the grazing season following vaccination. Vaccination followed by use of an anthelmintic worming bolus, or a long-acting anthelmintic, can fail to give adequate exposure, especially if this regime has been used on a farm for some years.
During this time the pasture contamination level will have been reduced due to the hyper-effective cleaning of the pasture by bolus carrying animals. These animals clean the pasture as the anthelmintic is continually killing the larvae eaten by the animal before they can develop to adult worms and stimulate immunity.
Young animals in their first and second grazing seasons fail to develop adequate immunity, leaving the adult animal wide open to infection.
Adult lungworm infection has become an increasingly frequent diagnosis made in herds of dairy cows which start to cough. It has occasionally been diagnosed following a comment by a farmer that his cows dont seem to be milking as well as expected.
Preventive measures must be tailored to the individual farm. Herd immunity, pasture contamination levels, and recent worming policy affects the best regime. Some guidelines on how to establish good immunity under different regimes follow:
A) If a long-acting wormer has not been used in the first season: Vaccinate prior to turnout and rely on natural boosting for the rest of that season and subsequent seasons. This is the traditional method which works very well.
B) If a long-acting wormer has been used, four options are available which cover almost all situations:
Initially, all options require vaccination prior to first season turnout followed by:
1) If animals are not wormed with a long-acting wormer in the second season on normal pasture, then rely on natural boosting.
2) If a long-acting wormer is used in the second grazing season, a single booster dose of vaccine is given two to four weeks prior to second season turnout.
3) If animals are housed very soon after the first season wormer expires, then a single booster dose of vaccine two to four weeks prior to second season turnout.
4) If animals are housed very soon after the long-acting, first season wormer expires and put onto special reserved (clean) pasture for heifers in the second season, then blood test five animals at end of the season. If all have positive titres do nothing, all are immune. If a majority have positive titres then give a single booster dose of vaccine. If a minority have positive titres then they all need full re-vaccination.
In some cases leaving vaccination until the second grazing season may be the best option, especially if long-acting wormers are used in the first grazing season on pastures with low contamination levels.
A rule of thumb is that the more you spend on worming the more you must spend on vaccination.
As many factors influence the option best suited to a farm including grazing methods, wormer usage and the weather, then it is advisable to seek vet advice on the best policy.
Treatment of adult animals
As lungworm has been increasingly diagnosed in the adult lactating herd, treatment has posed a costly problem because of the milk withdrawal period. However, a nil milk withdrawal anthelmintic has overcome this problem.
The product, Eprinex, is a new generation avermectin called milbemycin and has activity against a wide range of internal and external parasites. Its long-acting effect makes it an ideal choice for treating the milking herd. With its advantages, will be a good choice of treatment, even in herds which dont show clinical signs of lungworm because subclinical levels may be present. The ideal time for treatment of such herds will be at housing when ectoparasites will also be eliminated, reducing the problem of lice and mange during the winter.
Lungworm has become an increasingly complex disease with serious consequences. Outbreaks in adult cattle will continue for some years until vaccinated replacements, which have developed good immunity from a good vaccination, worming and grazing policy, make up most of the herd. *
Postmortem shows adult lungworm
• Vaccinate then allow exposure to parasite during first grazing season.
• Vaccination plus worming bolus can fail to protect fully.
• More spent on worming then more spent on vaccination.
Vaccinated heifers should develop full immunity, grow well, get in calf and have good immunity when milking. Those unvaccinated are at risk.