Vet’s Voice: Beware of winter lice populations | TSLN.com

Vet’s Voice: Beware of winter lice populations

Dave Barz, DVM

For the November 19, 2011 edition of Tri-State Livestock News.

I can’t believe how rapidly the fall weather is turning into winter. Most of the calves are worked and many are already sold. The market has been great and buyer demand remains high. Now is the time to prepare cows for winter.

Over the past several years we have seen resistance building to pour-on products which remove lice and internal parasites. To cheapen lice treatment cost, producers were pouring with about 20 percent of the suggested dose. At the time it seemed to work, but as a result lice have been produced which are resistant to the product.

Lice are a problem in our area as well as other cold areas. They survive on the animal year-round, with populations increasing during winter months. Lice cause irritation to cattle, causing cattle to rub, lick and chew to relieve their discomfort rather than eating.

There are two types of lice that affect cattle – chewing lice and sucking lice. Chewing lice are probably the most common and can increase to large populations during winter. These lice chew on the surface of the skin and don’t draw blood. This makes it hard to remove these lice with injectable or pour-on products which are absorbed into the blood. Sucking lice, on the other hand, have mouth parts which allow them to pierce the skin and actually suck blood. These lice can cause anemia if populations rise on the animal. This sucking louse is usually susceptible to pour-ons and injectables.

Timing is very important in controlling lice. Most producers apply control too early in the season. This allows populations to increase again before winter. The life cycle of the parasites require only 20-30 days. Eggs are attached to hairs and the nymphs emerge in 5-14 days. These nymphs mature and are able to become egg-laying adults in 14 days.

Lice populations increase dramatically in winter because the cow’s hair coat gives them great protection. The lice don’t live for prolonged periods off of the host animal.

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Treatments with systemic products in September and October control sucking lice, internal parasites and horn flies, but have little control of chewing lice. Treatment in November and December will minimize the ability of populations to increase before spring. Most veterinarians now recommend pouring cows twice. If cattle were poured early, follow up with the same product when vaccinating the herd for scours. If there were resistance problems last year, try a pyrethrin product. These are not absorbed into the blood and work well on chewing lice. Dust bags and back rubbers will also help individual animals to treat themselves.

Typically lice populations are highest on weaker animals in the herd. If cattle maintain a high plane of nutrition there will be lower populations of lice. Some producers feed high levels of protein to increase the oil levels in cow’s skin and hair. By doing this, producers believed they helped decrease louse populations in a natural way.

Lice cause economic loses to producers. Timing and careful selection of products can minimize herd problems. Visit with a veterinarian and establish a program specific to your herd.

I can’t believe how rapidly the fall weather is turning into winter. Most of the calves are worked and many are already sold. The market has been great and buyer demand remains high. Now is the time to prepare cows for winter.

Over the past several years we have seen resistance building to pour-on products which remove lice and internal parasites. To cheapen lice treatment cost, producers were pouring with about 20 percent of the suggested dose. At the time it seemed to work, but as a result lice have been produced which are resistant to the product.

Lice are a problem in our area as well as other cold areas. They survive on the animal year-round, with populations increasing during winter months. Lice cause irritation to cattle, causing cattle to rub, lick and chew to relieve their discomfort rather than eating.

There are two types of lice that affect cattle – chewing lice and sucking lice. Chewing lice are probably the most common and can increase to large populations during winter. These lice chew on the surface of the skin and don’t draw blood. This makes it hard to remove these lice with injectable or pour-on products which are absorbed into the blood. Sucking lice, on the other hand, have mouth parts which allow them to pierce the skin and actually suck blood. These lice can cause anemia if populations rise on the animal. This sucking louse is usually susceptible to pour-ons and injectables.

Timing is very important in controlling lice. Most producers apply control too early in the season. This allows populations to increase again before winter. The life cycle of the parasites require only 20-30 days. Eggs are attached to hairs and the nymphs emerge in 5-14 days. These nymphs mature and are able to become egg-laying adults in 14 days.

Lice populations increase dramatically in winter because the cow’s hair coat gives them great protection. The lice don’t live for prolonged periods off of the host animal.

Treatments with systemic products in September and October control sucking lice, internal parasites and horn flies, but have little control of chewing lice. Treatment in November and December will minimize the ability of populations to increase before spring. Most veterinarians now recommend pouring cows twice. If cattle were poured early, follow up with the same product when vaccinating the herd for scours. If there were resistance problems last year, try a pyrethrin product. These are not absorbed into the blood and work well on chewing lice. Dust bags and back rubbers will also help individual animals to treat themselves.

Typically lice populations are highest on weaker animals in the herd. If cattle maintain a high plane of nutrition there will be lower populations of lice. Some producers feed high levels of protein to increase the oil levels in cow’s skin and hair. By doing this, producers believed they helped decrease louse populations in a natural way.

Lice cause economic loses to producers. Timing and careful selection of products can minimize herd problems. Visit with a veterinarian and establish a program specific to your herd.

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