Summary
It is known that muscle growth can be accelerated, fat deposition reduced, and feed efficiency improved, by synthetic B-agonist drugs such as clenbuterol. In principle, Bagonists could be used to improve the efficiency of cattle production, but as they are feed additives, this would only be practical in intensive systems. Furthermore, the use of such compounds could present a risk to the consumer, as they are capable of leaving tissue residues which are heat-stable and orally active in humans.
MRC-funded research into the mechanism of action of B-agonists, has identified a receptor in muscle through which the effects of drugs like clenbuterol are mediated (the B2-adrenoceptor). It was also shown that a small part of this natural B-receptor protein can be used as the basis for a vaccine, which can be injected into cattle to cause them to produce B-receptor antibodies. Such antibodies have been purified from the blood of treated cattle, and shown to cause 'clenbuterol-like' effects when tested in laboratory animals, or on isolated pieces of bovine muscle. Unlike B-agonist drugs, however, the antibodies are not heat stable, not orally active, and unlikely to accumulate in animal tissues.
Thus, it is conceivable to devise a vaccine treatment that would improve the efficiency of cattle growth, be convenient for use in grazing livestock, and present no risk to human health. This project evaluated a prototype B-receptor vaccine in live cattle, in order to determine whether B-receptor antibodies could be generated in sufficient amounts to have 'clenbuterol-like' effects on the growth or blood chemistry of the animal. To provide an additional stimulus to the immune system, the B-receptor antigen was given in combination with an adjuvant mixture. Several different adjuvants were tested, to identify the most potent one that would be acceptable for use in a commercial situation. Finally, because the B-receptor antigen is difficult to make and to purify, various fragments of it were investigated in the hope of finding one that would cause a similar effect, while being easier and less expensive to make.
