SASKATOON – Turning bull calves into steers in the future could be as easy as giving them a needle.
Just as producers routinely vaccinate against diseases like IBR, so they could also inject against the hormone that causes puberty in bull calves, said Andrew Van Kessel, animal scientist with the University of Saskatchewan’s animal biotechnology centre.
Castrating by vaccination offers the advantages of surgical castration like inducing sterility so matings can be controlled, aiding handling by reducing aggressive behavior and limiting the incidence of dark-colored meat, Van Kessel said.
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It also diffuses criticism from animal rights’ activists and reduces the risk of infection posed by surgical castration.
But there are other advantages to castrating by vaccine.
While dressing percentages between carcasses from bulls, steers and “immunocastrates” vary little, the retail yield of meat from immune (vaccinated) castrates is better than steers, but not quite as good as bulls. Backfat is noticeably reduced when compared to steers, average daily gain in the feedlot increases, and the immunocastrates finish sooner.
That’s because the vaccine that castrates the animals doesn’t entirely shut off production of testosterone. The hormone that’s left is enough to stimulate better gains and meat yield normally associated with feeding bulls. Tenderness, however, isn’t quite as good as in meat from steers.
Van Kessel said the idea of vaccinating for castration has been around since biotechnology first hit the scene in the early 1980s.
But there are several challenges to vaccinating against a hormone which only recent advances in the field have been able to solve.
“Hormones are poorly immunogenic,” he told the recent Saskatchewan Beef Symposium.
The hormone in the vaccine, called gonadotropin releasing hormone, needs to be piggybacked by another substance, usually foreign to the animal, that can stimulate its immune system. And an adjuvant, a substance to assist the vaccine, is needed to improve the animal’s response.
“The formulation of the hormone, carrier and adjuvant is empirical,” Van Kessel said. “It’s probably more witchcraft than science.”
Once the vaccine is designed, the next challenge is to test how it actually works, which not only can vary among individual animals, but among species. A vaccine that works in cattle won’t necessarily work in pigs, he said.
A big obstacle to getting the vaccine on the market is perfecting its response.
A vaccine needs to work in at least 90 percent of cases, Van Kessel said. The one he and partners Mark Redmond and Bernard Laarveld have formulated is working nearly 100 percent of the time in their experiments.
