Calf

Inactivation of bovine leukemia virus in bovine colostrum by spray-drying treatment

Alvaro Garcia

Enzootic bovine leukosis is caused by a retrovirus known as the bovine leukemia virus (BLV). There have been attempts in Europe to eradicate the disease by culling with Denmark and the United Kingdom having been successful.

According to the USDA, and due to its endemic nature, testing and culling seropositive animals may not be such a cost-effective control method compared with preventing its transmission. In the US this disease continues to be prevalent with more than 80% of dairy operations testing positive.

In South America it is also prevalent with around 10% of newborn calves infected, particularly during the first 24 months of life, and reaching almost 50% before first calving. Losses are also the result of up to 5% cow deaths related to a BLV-associated lymphosarcoma, with reported profit losses of more than $5,000 per animal.

Some experiments have demonstrated the presence of BLV in colostrum that helps prevent neonatal infection, others however, have also detected the virus and confirmed its infectivity by oral consumption. This has led to controversy as of the importance of colostrum as a source of protection against the disease.

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Control of bovine leukosis in dairy farms

Control of bovine leukosis in dairy farms

Nuria García

Bovine leukosis (BL) is a lifelong disease of dairy cattle caused by the bovine leukosis virus. Although most infections appear to be subclinical, a proportion of cows over 3 years old (30 – 50%) develop persistent lymphocytosis, and a smaller percentage (5%) develop malignant tumors (lymphosarcomas) in various internal organs. It has been reported this disease can reduce milk production (up to 1000 kg/lactation), cow fertility, and longevity due to premature death of cows. Moreover, it produces economic losses associated with condemnation of carcasses after slaughter.

As a result of decades of systematic control and eradication programs, BL has been successfully controlled and eradicated from many countries (some countries in the European Union, Australia, New Zealand…); however, BL is common in North American dairy cattle. Recent surveys indicate that 89% of US dairy farms had cattle seropositive for BL. Similarly, in a 2015 study from Canada, 78% of 315 surveyed dairy herds from 7 provinces had antibodies to BL.

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