Specialist Advocates Careful
Attention To Cattle Immmunity

By David Bowser

PLANO — Developing a herd immunity program depends upon where a producer lives, what the cattle are exposed to, the production system and what the rancher does with the cattle after weaning.

"A whole host of things come into play here," says Dr. Ron Gill, Extension livestock specialist in Dallas. "There is not a silver bullet from an animal health standpoint. It comes down to management and proper implementation of a program."

Part of a good immunization program includes proper nutrient intake, Gill says, to make sure the animal's immune system functions properly.

"Cattle that are in good physical condition can stand more stress and exposure than an animal that's been subjected to environmental or management stress," he notes.

While a good herd immunity program costs money, throwing money at health problems isn't the answer. However, there are times when a producer can net more dollars even if he spends more money.

"We have to look at it from a net income standpoint," Gill says.

The ramification of not spending money is loss of production, he says.

There are people, however, who waste a lot of money. He said he did an analysis of one East Texas rancher who was spending $30 a year per cow on health costs. Half of that was deworming.

"On average, most of the time, we look at something around $15 a cow per year as reasonable health costs," he says.

However, Gill cautions, a lot of things have to be considered.

"It's not just as easy a saying it has to be $10 a cow or nothing," he says. "A lot of factors come into play."

Each producer must develop his own management plan concerning vaccinations, but there must be a plan, Gill insists. Lack of a vaccination program will result in lost production.

"It doesn't take many pregnancies to pay for a vaccination program," Gill says. "It's good money spent."

Developing herd immunity is becoming more important as the incidence and spread of disease continues to increase.

Increased movement of cattle throughout the industry increases the odds of exposure to pathogens that were not common in the cow-calf industry several years ago.

"There is no one program that fits everyone," Gill says. "I can't tell you in March or April to go vaccinate your cows, because I don't know when they calve."

There's no way to have appropriate timing on a vaccination program if the producer doesn't have a controlled breeding season.

Herd immunity begins with proper immunization and management of replacement females entering the herd.

"It doesn't matter whether cows are purchased or raised and retained into the breeding herd, the time to immunize replacement females is prior to placement into the breeding herd," Gill says.

Replacement heifers that are retained in the herd should be immunized against as many potential pathogens as possible between weaning and breeding.

"This is normally a six-month window in which valuable management practices can be implemented," he says.

Unfortunately, he adds, most of the time, little is done to immunize these heifers.

"Lifelong immunity can be established during this weaning phase with virtually no risk to the rest of the cow herd," Gill contends.

Purchased cows should be quarantined from the rest of the herd for at least three weeks.

"This allows time to establish immunity in these cows before they expose the rest of the herd to pathogens," Gill points out, "or before the rest of the herd exposes them to potentially harmful organisms."

Regardless of the diseases targeted in the immunization program, all cattle should have two vaccinations for each disease. An initial vaccination and a booster vaccination need to be given to each animal to establish immunity. Vaccines also have to be handled and administered properly.

Gill recommends an Extension publication available at most county agents' offices called "Chute-Side Cattle Working."

"It is difficult to make blanket statements about what a herd needs to be immunized against," Gill says. "However, there are several diseases that are prevalent enough and costly enough to the industry that all producers should include them in a vaccination and immunization program."

The most common disease causing a problem in Texas cow herds is leptospirosis.

"There are several strains of lepto," Gill says. "Most vaccines provide protection for the five most common strains."

Lepto can be spread between cattle and wildlife, and it can be spread through drinking water and through animal contact.

"Never assume your cattle will not be exposed," Gill warns.

Lepto vaccines, even under the best of conditions, do not provide for more than six months of adequate immunity to vaccinated animals, however. They need to be bolstered 30 to 60 days prior to the beginning of the transmission season. Initial immunization should be given during the development phase for heifers and the quarantine period for replacement cows and bulls.

The pathogens involved in the bovine respiratory disease (BRD) complex can cause problems in the reproductive performance of the breeding herd. By immunizing the cow herd, a producer can protect against reproductive losses and reduce death and sickness losses in the calf crop resulting from viral infections.

The viral component of BRD is comprised of infectious bovine rhinotracheitis (IBR), parainfluenza 3 (PI3), bovine viral diarrhea (BVD) and bovine respiratory syncytial virus (BRSV).

BVD can manifest itself in a whole host of ways, Gill says. BRSV, however, is not currently prevalent in North or East Texas. It is more prevalent in cow herds in the Northwest and Midwest.

Several strains of bacteria are also components in BRD.

"These bacteria are normally associated as secondary infections that occur after viral lesions are formed and immunity is impaired by one or more of the viral components," Gill says. "When death occurs due to respiratory disease, it is usually due to complications from bacterial infections."

Bacteria most commonly associated with BRD are pasteurella hemolytica, pasteurella multocida and haemophilus somnus. Of these bacterial pathogens, pasteurella hemolytica is the most prevalent.

"In calves, there can be losses simply due to bacterial infections," Gill says. "Calf pneumonia causes a fairly quick death in infected calves. Often calves will die within 48 hours of initial symptoms if not treated with antibiotics."

Research indicates modified live vaccines are effective in establishing herd immunity. Although currently limited to use in non-pregnant cows, calves nursing non-pregnant cows, and weaned calves, these products establish a higher level of immunity than killed viral vaccines.

"These killed products can be used effectively when the modified live vaccines cannot be used," Gill says.

The most logical time to use killed vaccines is in the immunization of pregnant purchased cows during the quarantine period. Other animals can be immunized more effectively with use of MLV vaccines, he says. Retained heifers should be immunized with MLV products during the weaning and development phase.

Some veterinarians are recommending vaccination of one to two month-old calves with MLV vaccines prior to the breeding season for the cow herd. This may not be practical for most operations, but if BRD or its associated pathogens are a problem it may be the best approach to controlling losses, Gill says.

Of particular concern in the breeding herd is haemophilus somnus.

"This bacteria can also cause late term abortions," Gill notes.

Control is possible with a vaccination program and sanitary management of the cow herd.

"Since these organisms are a problem primarily in weaned calves, it makes sense to include these in the vaccination program during the weaning and development phase," Gill says.

The most common sexually transmitted diseases are campylobacteriosis, (more commonly referred to as vibriosis or vibrio) and trichomoniasis (trich).

Vibrio is a bacterial infection that causes pregnancy losses in early gestation. It can be controlled with a properly timed vaccination program. The breeding herd should be vaccinated about 60 days prior to the onset of the breeding season.

"This is not a time that we normally gather cows and work them through the chute," Gill admits. "However, if vibrio is a problem, this will be necessary to prevent the spread of the disease. Realistically, vibrio vaccines can be given when the calves are weaned and the cows are palpated, dewormed and other annual vaccination boosters are given."

Trichomoniasis is an infection caused by a protozoa.

"This is becoming more of a problem," Gill says.

It also causes early embryonic losses, but unlike vibrio there is normally a severe infection associated with trichomoniasis.

Moreover, Gill points out, "This disease is difficult to isolate in cultures taken from cows or bulls."

The most effective way to avoid infecting the herd is to purchase bulls of known origin and quarantine all incoming cows.

"If you want to purchase bulls of unknown origin, three cultures are normally needed before the bull can be called clean," Gill says. "If the cow herd is infected, it is common to see conception rates in the 30 to 40 percent range during the first year."

Conception will normally increase in the following years. It will usually take five years or longer for pregnancy rates to approach normal after a herd infection with trichomoniasis.

"The most effective way to deal with trich is through management, not vaccination," Gill advises. "Do not purchase bulls of unknown origin."

Brucellosis is another disease that has plagued the industry, though the brucellosis eradication program is close to showing long-awaited results.

"Texas is very close to eradicating the disease," Gill says. "However, we are not there yet."

It is still wise to vaccinate heifers against brucellosis before they reach 10 months of age, preferably between three and six months old.

"From a practical standpoint it makes sense to vaccinate all potential replacement heifers against brucellosis at weaning," Gill says. "The older a heifer is, the greater the chance of her becoming a false positive on the card test."

Heifers over a year old are not vaccinated against brucellosis.

A licensed veterinarian must administer the vaccine, which does not have to be boostered.

With the exception of brucellosis, the cow herd should be given a booster annually two to three months prior to calving to stimulate the production of higher quality colostrum for newborn calves. The exception, Gill says, is sexually transmitted diseases, for which the vaccines should be given 60 days prior to the breeding season.

"At lot of times, we can eliminate most of the health risks if we can control the environment that we run our cattle in," Gill says. "I think that needs to be the number one focus in the health program, preventing exposure and contamination of areas where you're going to be running cattle."

The stocker and feedlot phase is where most of the documentation on the importance of health has been done.

"Most of that is focused on respiratory disease," Gill says.

But respiratory disease is not usually a problem for cow-calf operators. Ranchers, however, can prevent future problems by vaccinating their weaning calves.

At the stocker and feedlot phase, Gill says, stress plays an important part.

"It's not just vaccinations," he notes.