Getting Livestock Vaccines Past a Maternal Block

Use of a virus linked to the common cold is among the novel approaches Agricultural Research Service (ARS) scientists in Iowa are using to bypass maternal defenses that thwart vaccination of very young livestock.

Maternal antibodies are crucial to the offspring of animals such as cattle and swine, which are born with no protective antibodies of their own. These young get their immunity to disease from suckling colostrum, a protective substance in their mother's milk, during the first 24 to 36 hours after birth.

But these maternal antibodies also fight off virus strains that are placed in vaccines to initiate immunity against disease.

In one study, veterinary medical officers Ronald Wesley and Kelly Lager of the ARS National Animal Disease Center (NADC) in Ames immunized—against swine flu—recently born piglets that had suckled maternal influenza-fighting antibodies. They did this by getting the flu strain past the antibodies piggybacked aboard a genetically engineered virus made with weakened adenoviruses.

The ability of adenoviruses to infect cells makes them good conduits for carrying genetic material into animals. And since adenoviruses originate from humans—they can cause respiratory ailments such as the common cold, pneumonia and bronchitis in people—livestock have no maternal antibody resistance to them.

This is a potentially major breakthrough that may close a window of vulnerability during which the maternal antibodies' waning powers still repel vaccines but leave young animals open to contracting diseases.

In another project, testing led by NADC virologists Julia Ridpath and John Neill indicated that exposing suckling calves to bovine viral diarrhea virus (BVDV) generates a T-cell, or immune, response that will repel that virus. BVDV costs U.S. cattle producers millions of dollars in losses each year and induces diseases affecting animal reproduction and nutrition, milk output and digestive and respiratory function.

Read more about this research in the November/December 2006 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's principal scientific research agency.