Prevent lice, flies and mange from limiting your dairy herd’s milk production
What are cows doing if parasites are hanging around? Certainly not what they’re supposed to be doing.
Populations of external parasites such as mange and lice typically peak in the winter months, so it’s important to have strategic deworming protocols in place prior to when they can do the most harm.
External parasites threaten cow comfort
Typically found in colonies on the tail, shoulders and back, biting lice feed on cattle by scraping the skin or hair. Sucking lice, such as the short-nosed, long-nosed and small blue lice, extract the blood of their host. Both biting and sucking lice are known to reduce weight gain and decrease general thriftiness.
Clinical signs of lice include intense itching and hair loss. The greater the percentage of animals with clinically apparent lesions within a herd, the greater the herd’s milk production losses. And while they present a year-round threat, lice burdens are greatest during the winter months.
Mange mites attack and damage the skin and hair. Chorioptic mange (C. bovis) can cause hair loss, scabbiness and dermatitis around the feet, legs and tailhead. Mange-infested skin typically swells and can become inflamed.
Sarcoptic mange (S. scabiei), a quarantinable mite, causes even more severe skin lesions than C. bovis. Infection by just a small number of these mites can be detrimental to an animal’s comfort, health and production.
Clinical signs of mange are the development of crusty, asbestos-like lesions near the tailhead, caudal udder and inner thighs. These lesions cause intense itching and restlessness, leading to decreased cow comfort and milk loss.
Horn flies are a costly external parasite for producers. The sheer number of flies typically found in a herd during the biting fly season renders them a constant threat to cow comfort. Cattle are frequently playing defense against the flies, which can lead to reduced milk production.
Designing a cost-effective external parasite program
Dr. van der List recommends producers include the following steps when developing a whole-herd external-parasite control program that includes a pour-on dewormer:
- Complete a whole-herd pour annually.Because lice and mange spread through direct contact, being proactive and treating the entire herd — not just those showing obvious clinical signs — is the best way to prevent an outbreak. External parasites typically peak in January and February, so late fall is the ideal time to treat the herd.
- Apply properly.A proper application includes pouring along the back of the animal, from the poll to the tailhead.
- Pour new additions.As new animals join the adult herd, they should be poured upon arrival and kept isolated from the herd for 14 days. This would include replacement heifers, as these animals may have been exposed to mange and lice, putting the entire herd at risk of having external parasites reintroduced. Selection of the appropriate pour-on product will also ensure that any internal parasites the heifer may have acquired while on grass will be eliminated.
- Re-pour as needed.Animals that are the most severely infected with lice and mange at the time of the whole-herd pour should be re-poured three weeks later for optimal control. To control biting flies, additional treatments during the biting fly season can prove to be cost-effective. For horn fly treatments, you often do not have to apply product to the entire milking herd. Instead, you can focus on the transition animals, as they are most vulnerable to discomfort.
“Any interference with feed intake or resting time due to parasites will be reflected in lost milk production,” concluded Dr. van der List. If you see a significant milk production response after treatment, parasites have most likely been impacting your herd for some time. Be sure to consult your local veterinarian to determine ideal treatment timing for your operation.
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