Russ Daly: Understanding what vaccines work – or don’t work – in the young beef calf

For many beef producers, preparing for the onset of calving includes assessing what vaccines should be given to newborn calves to ward off infectious diseases. A better approach may instead be to assess the what threat are important at that age, and formulate a plan to protect against those threats.

Those threats – to calves less than 2 months old – come from germs either in their environments (calf scours, Clostridial diseases, and septicemia) or from other animals (such as viral and bacterial respiratory germs, and Mycoplasma). Vaccines can help protect against some, but not all, of these conditions. But even a vaccine is available for one of these problems, will it work in a calf less than 2 months old?

Passive immunity (antibodies and immune cells delivered to the calf through colostrum) are the most important aspect of disease protection in the young calf. The active immune system is functional in a young calf, but not robust enough on its own to protect the calf from early infections. Therefore, disease issues occurring during the first weeks of life are best addressed by making sure colostrum of good quality and quantity gets into the calf given shortly after birth.

A concern arises about the possibility those colostral antibodies may interfere with the calf’s ability to respond to vaccines. This effect could last for 2-7 months, depending upon the germ and the level of antibodies the calf took in through colostrum. When antibody levels pre- and post-vaccination are used to determine vaccine effectiveness, many vaccines show unimpressive results when given to young calves.

For certain modified-live viral vaccines, protection against clinical disease has been demonstrated in calves when vaccinated at 4-6 weeks of age. This suggests that these vaccines effectively stimulated cell-mediated immunity even when maternal antibodies were present. It’s worthwhile to remember these studies examined calves vaccinated at several weeks – not several days – of age.

For calves in the first weeks of life, evidence shows that intranasal vaccines (with IBR, BRSV, and PI3 viruses) adequately protected calves from disease challenges months after vaccination. Similar evidence exists for the effectiveness of a modified-live bovine coronavirus intranasal vaccine given to calves during the first week of life.

For vaccines against enterotoxemia or Clostridial diseases, published evidence for effectiveness in young calves is more lacking. It’s believed, though, that young calves’ immune systems may respond relatively well to the simpler antigens found in these vaccines. Challenge studies are difficult to perform for these diseases, so anecdotal evidence is used to suggest that these vaccines provide some protection against these conditions when given shortly after birth.

Because exposure to many important neonatal calf pathogens occurs soon after birth, and clinical illness follows just days afterward, even the quickest-acting vaccines are unable to act soon enough to prevent illness. For these conditions (particularly gut diseases such as rotavirus, coronavirus or Clostridial enteritis), enhancing the colostrum produced by the dam represents the best chance to protect the calf from disease. Scours due to these disease agents are common components of “scours shots” administered to pregnant cows and heifers in late gestation.

When abomasal bloat/enterotoxemia (presumably due to Clostridium perfringens Type A) occurs in calves during the first 2 months of life, dam vaccination with the stand-alone Type A vaccine makes

sense. In herds with undifferentiated respiratory disease in young calves, early vaccination with intranasal vaccines (in light of the evidence of their effectiveness) is a probably a better way to address this problem compared with late gestation dam vaccination.

Of course, calf health is greatly aided by many non-vaccine factors in an operation, such as calving area hygiene, trace mineral and vitamin supplementation for the dam in late gestation, and taking steps to reduce dystocia. When these factors are optimized, any young calf vaccine program can look very good. On the other hand, when these actions fall short, an appropriate vaccine program can fail miserably.

These factors, along with a realistic assessment of calf health risks with a veterinarian – and using the right vaccine strategy when it makes sense – can properly boost the calf’s immune system to meet the challenges of pathogen exposure during its first weeks of life.