Steve Wikse, a retired professor of large-animal clinical sciences, College of Veterinary Medicine at Texas A&M University, answers this month's beef cattle health question.
Q -- I've worked to keep my cows in decent shape during this drought. I'm worried worms have caused some cows to be thin. I didn't deworm my cows last fall. Should I deworm my cows in March before the grass comes on to keep wormy ones from infecting the pasture?
A -- Your question involves timing of deworming treatments for cow herds. Knowledge of the life cycle of stomach worms -- Ostertagia ostertagi -- is necessary.
The seasonality of transmission of stomach worms makes timing of deworming treatments critical for successful control programs. Stomach worms are only transmitted during cooler months when temperature and moisture conditions are favorable for survival and maturation of larvae.
Favorable conditions in the Brazos Valley usually occur in the spring and fall. Greater parasite numbers are acquired in the spring than fall. Transmission can also occur in mild-weather winter months. Transmission of Ostertagia is minimal during the "summer brownout."
During times of transmission, adult worms in the abomasum lay eggs that pass in manure. The eggs hatch into larvae (little wiggly immature worms) in the manure patties. Rains spread the larvae out onto grass. Numerous larvae within dewdrops then move up blades of grass. A cow eats the grass and also gets the dewdrops with hundreds of larvae -- the "deadly dewdrops."
After burrowing into glands in the wall of the abomasum, larvae burst out into the inside of the abomasum as adults and begin laying eggs. The entire life cycle from an adult laying an egg to an egg becoming an egg-laying adult is three to six weeks. Diarrhea, anemia and bottle jaw (swelling between the jaw bones) develops in cattle due to irritation of abomasal glands and thickening of the wall of the abomasums.
In late spring and early summer, as temperatures heat up and pasture conditions are unfavorable for survival of worm larvae, ingested larvae do not develop into egg-laying adults. They remain in abomasal glands in a state of hibernation or arrested development. They wait there over the summer then burst out of the glands and begin laying eggs when rains and cooler temperatures make completion of their life cycle possible. This fall transmission of stomach worms results in parasite burdens that lower appetite and interfere with digestion of winter feed. Severe diarrhea and even death can result.
There are two main approaches for deworming treatments. The first is an early spring/fall program used to eliminate worm larvae from pastures with two deworming treatments in the early spring (April/May). The first treatment is given six weeks after grazing. The second treatment is given four to six weeks later. Benzimidazole drugs, white liquids or pastes (albendazole, fenbendazole or oxfendazole), are usually used. These drugs kill nearly 100 percent of adult worms. They are only 70 percent to 80 percent effective against arrested larvae. They kill worms for up to one day following treatment. The goal of two spring treatments is to make the cows vacuum larvae from the pasture, then deworm the cows later when larvae are adults but not egg-laying adults. If done in early spring before pastures are heavily contaminated, there won't be many live larvae left. The herd is treated again in the fall -- October/
November.
In Central Texas and the Gulf Coast areas this method is only moderately successful because the grass mats in bermuda grass pastures allow significant numbers of larvae to survive the two treatments.
The second approach to control stomach worms is the late spring/fall program. This plan involves one treatment for stomach worms in late spring with a macrocyclic lactone (doramecin, eprinomectin, ivermectin or moxidectin) which are pour-ons or injectables. These drugs kill nearly 100 percent of adult worms up to two to four weeks following treatment and kill a higher percentage of arrested larvae -- nearly 100 percent. The goal is to free cows of adult worms and arrested larvae through the summer and into the fall. The herd is treated again in the fall.
Research has shown that this second approach works best for Central Texas and Gulf Coast areas.
Now back to your question. Your cows were not dewormed last fall and may be loaded with worms. I would treat them with a benzimidazole in mid-March to prevent them from infecting the pasture with large numbers of larvae. I would then put your herd on the late spring/fall program.
This column, although a good start, is not long enough to cover all details of control programs for stomach worms of cattle. My recommendation is for ranchers to consult their veterinarian on cattle health issues.
Proper timing of deworming treatments and administration of vaccines is critical to the success of herd health programs.
Mark March 4 on your calendar to attend a beef cattle producers meeting on herd health programs at the TAMU College of Veterinary Medicine. It will begin at 6:30p.m. at the Brazos Expo Complex in Bryan. Don't miss a chance to hear national and local experts discuss herd health programs.
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Steve Wikse, a retired professor of large-animal clinical sciences, College of Veterinary Medicine at Texas A&M University, answers this month's beef cattle health question.Q -- I've worked to keep my cows in decent shape during this drought. I'm worried worms have caused some cows to be thin. I didn't deworm my cows last fall. Should I deworm my cows in March before the grass comes on to keep wormy ones from infecting the pasture?
A -- Your question involves timing of deworming treatments for cow herds. Knowledge of the life cycle of stomach worms -- Ostertagia ostertagi -- is necessary.
The seasonality of transmission of stomach worms makes timing of deworming treatments critical for successful control programs. Stomach worms are only transmitted during cooler months when temperature and moisture conditions are favorable for survival and maturation of larvae.
Favorable conditions in the Brazos Valley usually occur in the spring and fall. Greater parasite numbers are acquired in the spring than fall. Transmission can also occur in mild-weather winter months. Transmission of Ostertagia is minimal during the "summer brownout."
During times of transmission, adult worms in the abomasum lay eggs that pass in manure. The eggs hatch into larvae (little wiggly immature worms) in the manure patties. Rains spread the larvae out onto grass. Numerous larvae within dewdrops then move up blades of grass. A cow eats the grass and also gets the dewdrops with hundreds of larvae -- the "deadly dewdrops."
After burrowing into glands in the wall of the abomasum, larvae burst out into the inside of the abomasum as adults and begin laying eggs. The entire life cycle from an adult laying an egg to an egg becoming an egg-laying adult is three to six weeks. Diarrhea, anemia and bottle jaw (swelling between the jaw bones) develops in cattle due to irritation of abomasal glands and thickening of the wall of the abomasums.
In late spring and early summer, as temperatures heat up and pasture conditions are unfavorable for survival of worm larvae, ingested larvae do not develop into egg-laying adults. They remain in abomasal glands in a state of hibernation or arrested development. They wait there over the summer then burst out of the glands and begin laying eggs when rains and cooler temperatures make completion of their life cycle possible. This fall transmission of stomach worms results in parasite burdens that lower appetite and interfere with digestion of winter feed. Severe diarrhea and even death can result.
There are two main approaches for deworming treatments. The first is an early spring/fall program used to eliminate worm larvae from pastures with two deworming treatments in the early spring (April/May). The first treatment is given six weeks after grazing. The second treatment is given four to six weeks later. Benzimidazole drugs, white liquids or pastes (albendazole, fenbendazole or oxfendazole), are usually used. These drugs kill nearly 100 percent of adult worms. They are only 70 percent to 80 percent effective against arrested larvae. They kill worms for up to one day following treatment. The goal of two spring treatments is to make the cows vacuum larvae from the pasture, then deworm the cows later when larvae are adults but not egg-laying adults. If done in early spring before pastures are heavily contaminated, there won't be many live larvae left. The herd is treated again in the fall -- October/
November.
In Central Texas and the Gulf Coast areas this method is only moderately successful because the grass mats in bermuda grass pastures allow significant numbers of larvae to survive the two treatments.
The second approach to control stomach worms is the late spring/fall program. This plan involves one treatment for stomach worms in late spring with a macrocyclic lactone (doramecin, eprinomectin, ivermectin or moxidectin) which are pour-ons or injectables. These drugs kill nearly 100 percent of adult worms up to two to four weeks following treatment and kill a higher percentage of arrested larvae -- nearly 100 percent. The goal is to free cows of adult worms and arrested larvae through the summer and into the fall. The herd is treated again in the fall.
Research has shown that this second approach works best for Central Texas and Gulf Coast areas.
Now back to your question. Your cows were not dewormed last fall and may be loaded with worms. I would treat them with a benzimidazole in mid-March to prevent them from infecting the pasture with large numbers of larvae. I would then put your herd on the late spring/fall program.
This column, although a good start, is not long enough to cover all details of control programs for stomach worms of cattle. My recommendation is for ranchers to consult their veterinarian on cattle health issues.
Proper timing of deworming treatments and administration of vaccines is critical to the success of herd health programs.
Mark March 4 on your calendar to attend a beef cattle producers meeting on herd health programs at the TAMU College of Veterinary Medicine. It will begin at 6:30p.m. at the Brazos Expo Complex in Bryan. Don't miss a chance to hear national and local experts discuss herd health programs.