Dairy Pipeline: February 2004
Extension Area Dairy Agent,
This month brought more disturbing news about milk pay prices, and it is important to control costs as much as possible. However, I caution dairy producers to not cut corners when it comes to herd health, particularly young stock vaccinations. The most important diseases to vaccinate young dairy calves (besides Brucellosis and other veterinarian administered vaccines) are IBR, BVD (Types I & II), PI3, and BRSV. Recently, I was asked about calves that just weren't as healthy as they could be. The calves were well fed and cared for but when I questioned the owner about their vaccination program, it became apparent that no program existed in between vet visits. There isn't enough room here to go into all calfhood illnesses, so let's concentrate on one illness that is easily treated yet highly virulent. The calves I observed had classic signs on BRSV or Bovine Respiratory Syncytial Virus. Calves with BRSV generally have dry, hacking coughs. These calves may also have eye and nasal discharges and symptoms of pneumonia. Left untreated they are very susceptible to colds, pneumonia, and other respiratory illness. BRSV attacks the papillae or hair like lining of the air passages leading to the lungs. The papillae act as miniature brooms that "sweep" foreign material from the lungs toward the mouth and nose. BRSV doesn't affect the calf as an infection like pneumonia; rather it attacks and destroys the papillae, making it difficult for the calf to clear its air passages. The result is a coughing calf that truly can't catch its breath. According to Purdue University's Disease Diagnosis Laboratory, BRSV has been recognized as a pathogen in cattle since 1970. The presence of this virus in cattle herds is recognized worldwide. In the United States antibody prevalence has been reported to 65% to 81% in the cattle population. Cattle most susceptible are beef calves six weeks to 13 months of age and dairy calves two weeks to nine months. In younger calves mortality rates are increased by secondary bacterial infections. Infections with BRSV have been implicated as the initiating cause of shipping fever and other respiratory disease complexes again because the animal has no defense against the introduction of pathogens. Humans can also carry Syncytial Virus so limit young calves exposure to young children. Prevention is the key to dealing with BRSV infections. Good husbandry and well-ventilated housing is mandatory for the prevention of all respiratory diseases, but vaccination is necessary to prevent BRSV infections. Both modified live vaccines and inactivated vaccines are available. Both types have pros and cons. Modified live vaccines tend to stimulate stronger neutralizing antibodies responses. Both modified live and inactivated vaccines stimulate non-neutralizing antibody and prime T cells in calves.