The problem with parasites in dairy cattle is the often invisible impact. If left uncontrolled, parasite infections in youngstock and adult cows can lead to a reduction in lifetime milk production and fertility.
The challenge for dairy producers is how to identify whether parasites are at fault when productivity wavers and when it is necessary to treat them.
Sioned Timothy, ruminant technical manager at Boehringer Ingelheim Animal Health, identifies some common methods which producers can use to monitor parasites and prevent their impact on production.
Growing heifers have significant nutrient requirements.
When you add a parasite challenge to this equation, it slows the time they take to reach their mature weight (1).
And, as the onset of puberty is more closely linked to weight than age, a delay in conception increases age at first calving.
Parasite control in grazed replacement heifers is crucial to protect lifetime productivity.
Young cattle need time to develop an immunity to the gutworm species Ostertagia ostertagi and Cooperia spp., and the cattle lungworm Dictyocaulus viviparus, while the liver fluke Fasciola hepatica poses a life-long threat since cattle never develop protective immunity.
There are several methods available to monitor individual heifers and groups of animals for a parasite challenge, identify the specific threat and take action if required.
Faecal egg counts can provide an indication of the dynamics of worm infection over the grazing season, but since cattle develop immunity to gutworm over time, these tests provide a less reliable means of assessing worm burdens in individual animals.
Where producers have access to weigh scales, regularly weighing both first- and second-season grazing heifers is an effective method to track performance.
Where an otherwise healthy individual animal is not meeting its growth target, despite sufficient nutrition, a gutworm challenge is the likely cause.
During the grazing season, heifers which are meeting their growth targets may not require treatment for gutworms while poorer performing members of the group will benefit from targeted treatment.
Leaving a proportion of the group untreated also has the additional benefit of reducing selection for anthelmintic resistance.
However, as all grazing cattle are exposed to parasites, treating youngstock at housing will remove burdens acquired during the grazing season, to help maximise growth and productivity over winter.
Once heifers join the milking herd, the impact of gutworm and other parasites is felt more in reduced productivity2.
By this time, grazed adult cows are likely to be immune to the clinical effects of gutworms, but the physiological impact of a gutworm burden may still be felt in reduced milk yield and increased calving to conception time (3,4).
These production-limiting impacts all chip away at profitability.
Bulk milk tests provide a simple method of regularly monitoring the level of antibodies to gutworms and liver fluke at the herd level.
This allows for anthelmintic intervention only when the level of challenge is high enough to be causing production loss.
The availability of zero milk withhold wormers containing eprinomectin means dairy cattle can be treated at the most appropriate time, without the need to dispose of milk.
For liver fluke, however, the situation is more complex.
Many flukicides are not licensed for use in cattle producing milk for human consumption.
Managing exposure to fluke habitats and taking steps to reduce pasture contamination, therefore becomes an important strategy.
Preventing access to wet or boggy pasture, fencing off natural watercourses and prioritising fluke control in youngstock all help reduce the challenge from this parasite.
For more information, and to discuss the various diagnostic methods, speak with your vet or animal health adviser.
1. Sanchez, J. et al. (2002) The effect of eprinomectin treatment at calving on reproduction parameters in adult dairy cows in Canada. Preventative Veterinary Medicine. 56:165-177.
2. Forbes et al.(2004) Impact of eprinomectin on grazing behaviour and performance in dairy cattle with sub-clinical gastrointestinal nematode infections under continuous stocking management. Veterinary Parasitology. 125,353-364.
3. McPherson et al. (1999) Proceedings of the American Association of Veterinary Parasitologists. 44th Annual Meeting, New Orleans, Louisiana, USA, Abstr. 28. 4. Sanchez-Vazquez, M.J., and Lewis, F.I.(2013) Investigating the impact of fasciolosis on cattle carcase performance. Veterinary Parasitology. 193 (1-3): 307-11.