That's because the many strains or serotypes of the virus can quickly develop resistance to a virus-oriented vaccine. This problem wouldn't occur with a vaccine targeted to the gnat's salivary- gland proteins. Countries without the disease won't accept some American livestock exports. Calves castrated at birth suffer less stress than calves castrated at six months of age. Colostrum is high-protein milk that's produced by the mother for a few days after giving birth.
Colostrum contains many antibodies and increases the calves' resistance to disease.
Weaning is a stressful time for calves. That stress can be heightened by production practices such as castration. Animals are castrated primarily to reduce the danger of handling males, who are often aggressive, if they're allowed to reach sexual maturity uncastrated. Castration also improves the taste and tenderness of beef. Meat from uncastrated cattle can be tougher and may carry an unpleasant odor.