It’s not always easy to decide which vaccines are best when vaccinating calves. Producers use many different products, and it’s hard to know which one to choose, especially when vaccinating against infectious bovine rhinotracheitis (IBR).

Producers can choose from about 40 modified-live virus (MLV) vaccines and 17 killed products to protect calves against IBR, says Donal O’Toole, veterinarian and former director of the Wyoming State Veterinary Laboratory in Laramie, Wyo. His preference, at least for viral agents, is to use an MLV product — provided they are safe to use in that situation. For instance, you would not give nursing-age calves MLV vaccines if their dams have not been previously vaccinated (and don’t have adequate immunity), or the cows might pick up the virus from the calves and abort their current pregnancy.

“If you give a vaccine by a natural route, such as an intranasal vaccine for respiratory viruses, the modified-live product has advantages,” says O’Toole. “With killed products, the amount of antigen an animal receives is basically just what is in the syringe.”

In contrast, when using an attenuated MLV vaccine, the antigen can expand in the animal since it has the ability to replicate. It may also move to some of that agent’s target sites, like the lungs. An MLV vaccine essentially gives the animal a mild, subclinical infection, he explains. It stimulates a stronger immune response in the animal than a killed virus can.

“Another advantage, especially when using intranasal viral respiratory agents, is that it bypasses the effect of maternal antibodies.” — Donal O’Toole

“Another advantage, especially when using intranasal viral respiratory agents, is that it bypasses the effect of maternal antibodies,” O’Toole says. In young calves, many vaccines do not stimulate a strong immune response because those calves still have passive immunity from the dam (via antibodies in colostrum). The dam’s antibodies in the calf neutralize most, if not all, of the vaccine antigens, so the calf’s immune responses are minimal.

Most vaccines are ineffective in calves until antibodies from colostrum (passive transfer) wane, but the intranasal MLV vaccine can be given at a younger age with good results, says O’Toole. “It was surprising to see how long it took for vaccine companies to recognize this. Doctor John Ellis, who once worked in the Wyoming diagnostic lab, had difficulty persuading companies to establish whether the intranasal vaccination works in very young calves, so he did studies on his own and published them. He demonstrated that this route works well.”

If a producer sees a lot of respiratory disease in young calves, this would be the best option to try to prevent problems, says O’Toole, adding that he makes this recommendation not as a clinician, but as a pathologist who sees the wrecks (necropsies) instead of the good outcomes.

“When using modified-live vaccines, the only ones I have concerns about are the IBR products against bovine herpes virus 1 (when given to pregnant cattle) because of sporadic abortions, in which we find typical lesions of IBR and find the vaccine virus,” he says.

Killed vaccines are safer, but they need more booster shots to be fully protective.

Says O’Toole: “When producers use killed products, they give a primary shot followed by a booster two or three weeks later. This involves handling the cattle again.”

If producers know they won’t be able to give a booster, it’s probably best to use an MLV. They should talk to their veterinarian when making a plan for a vaccination program.

Editor’s note: Heather Smith Thomas is a freelance writer and cattlewoman from Salmon, Idaho. [Lead photo by Heather Smith Thomas.]