Worms in Dairy Cattle
The important worms in our region are the small brown stomach worm (Ostertagia ostertagi), stomach hair worm (Trichostrongulus axei), lungworm (Dictyocaulus viviparus) and occasionally the small intestinal worm (Cooperia spp.). Interactions between age, body condition, nutritional status, pasture and weather conditions determine which animals and how badly, they are affected by worms.
Stomach worms
The eggs of the stomach worms are passed onto pasture where they hatch, develop and are ingested by cattle. The larvae can survive over winter on the pastures, but are susceptible to desiccation in the hot and dry weather over summer.
A peculiarity with the lifecycle of Ostertagia is that over summer some of the larvae can bury themselves into the stomach wall until the weather conditions become more favourable, usually in autumn, when they emerge in large numbers and cause disease.
While reasonable natural immunity develops with age, we still see some clinical problems in adult cattle and the majority of trials have shown a positive production response to treatment of milkers around calving or drying off.
The majority of clinical problems are seen in young stock.
The clinical signs seen with infestation are a scour, weight loss and in severe infections, bottle jaw and death. Sub clinically, parasitism shows up as poor growth rates.
Lungworm
The eggs of the lungworm also can survive the winter conditions on pasture and will cause disease in young stock in spring. Coughing, and poor growth rates are the usual signs of lungworm infestation.
Good immunity develops to this particular worm, and lungworm is almost exclusively a problem in young stock.
Worm egg counts
Faecal egg counting is an effective and underutilised tool in worm control of young dairy cattle. Monitoring faecal egg counts enables us to measure the effectiveness of drenching and other worm control measures and enables us to determine if another drench is needed.
In many situations, calves are routinely drenched every 4 to 8 weeks. While this ensures that worms are not causing any production losses it is costly and increases the risk of developing worm resistance to the drenches.
Monitoring is a simple and inexpensive procedure and involves collection of a small sample from the faeces of 10 calves. It becomes less reliable in calves over 12 months of age.
Drench Types
Mectins (macrocyclic lactones) e.g. Vetmec, Ivomec, Cydectin: Very effective against inhibited larvae and have residual effect and are available as an injectable and pour on. Best drenches for strategic summer drench and usually best if lungworm present.
Benzimadazole (white drenches) e.g. Panacur. Variable effect against inhibited larvae. Mostly oral drench. Suitable for treatment of calves.
Levamisole (clear drenches) e.g. Nilverm. Not effective against inhibited larvae. Suitable for calves.
Not all drenches are suitable for use in milking cows and some are not recommended for use in young calves.
Always read the label to ensure that the product is safe and suitable for the animals you are treating.
Worm Control
The provision of safe pastures allows calves to grow with minimal production loss and allows some exposure to develop natural immunity. This is often very difficult in dairy operations where other factors such as Johnes disease control, limit the area available to young stock.
Drenching with a registered anthelmintic will nearly always be required.
The frequency and type of drench required will need to be finetuned for each farm situation however a basic program for June calving cattle is as follows:
Sept/Oct : Drench calves.
Sept to Jan: May need extra drenches for calves in contaminated situations.
Jan/Feb: Strategic summer drench, all young stock and bulls.
Apr/May: Drench yearlings and bulls, 2-3 weeks after autumn break.
June/July: May need drenches in yearlings in contaminated situation.
At drying off or calving: Consider drenching milkers.
In heavily contaminated situations extra drenches will be required especially for calves under 12 months of age.
Drenching Adult Dairy Cows.
A review of the literature shows that around 75% of trials conducted on drenching adult dairy cows show a positive response. Most trials involved drenching cows at drying off or at calving. The response is usually seen as an increase in production especially in the first half of the lactation and occasionally a slight improvement in reproductive performance.
The milk response is in the order of 0.5-1 litres per day.
Summary
- Worms are still a significant cause of production loss in young stock
- Production responses to drenching have also been shown in milkers
- Effective control programs involve pasture management and efficient drench use.
- Worm control in young stock can be monitored using faecal egg counts.
Call in to TVG for advice on the range of Vetmec products. You will be surprised at our competitive pricing.
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