POULTRY farmers can stop dosing their birds with antibiotics. Researchers in Wisconsin have developed an alternative to the controversial practice of adding antibiotics to feed to make poultry grow quickly: adding antibodies against appetite-suppressing neurotransmitters and a fatty acid first isolated from hamburgers.
Antibiotics work as growth promoters because, by knocking out bacteria, they help prevent stimulation of the immune system. When a bird's immune system is stimulated by infection, immune cells release chemical messengers such as interleukin-1 or tumour necrosis factor. These cause muscle wasting and also cause the release of peptide neurotransmitters that suppress appetite.
"Chickens respond to immune stimulants much the way we do to flu," says Mark Cook of the University of Wisconsin in Madison. "They don't want to eat, their muscles begin to break down and they lose weight."
But the wholesale use of antibiotics could have serious consequences. The European Union has already banned the use of five antibiotics as growth promoters, fearing that they could encourage the spread of resistance to drugs used against dangerous human pathogens.
Cook's approach is based on antibodies that block the actions of the appetite-suppressing neurotransmitter peptides, which are produced in the gut. To make the antibodies, they inject chickens with small fragments of the peptides attached to larger carrier molecules. The birds secrete antibodies against the neurotransmitters, which are incorporated into the yolks of their eggs. DCV of Wilmington, Delaware has developed a way of harvesting the yolk without denaturing the antibodies. The yolk is then powdered and added to chicken feed in small quantities.
The antibody supplements produce growth gains similar to those given by antibiotics. "We're getting a 3 to 5 per cent improvement in growth," says Cook.
His team is also working on another feed additive, called conjugated linoleic acid (CLA). This fatty acid is produced by bacteria that live in the guts of ruminants, such as cows and sheep. It is found in ground beef and is thought to have anticancer properties. CLA also increases growth rates in chickens, by blocking the chemical messengers that cause muscle wasting.
DCV is preparing to launch the antibody additive, called Ovation, in the US and will be conducting European trials early this year. Meanwhile, Conlinco of Detroit Lakes, Minnesota, is planning to market CLA supplements.Matt Walker
Clones may not grow old before their time
SIX calves from Connecticut, cloning's latest stars, should finally answer the question of whether clones age prematurely.
Dolly the sheep, the first animal to be cloned from an adult cell, appears healthy so far. But there are signs that the wear and tear accumulated by that donor cell could make her age before her time: Dolly's chromosomes are shorter than normal sheep of the same age, which is a sign of cellular ageing (New Scientist, 29 May 1999, p 12).
Even if Dolly dies young, however, it might just be that longevity doesn't run in her family. Since Dolly's relatives aren't around, Jerry Yang at the University of Connecticut in Storrs and his colleagues are studying the way clones age more precisely. To see how cellular ageing might affect ageing of animals cloned from the cells, they took cells from the ear of a 17-year-old bull and allowed them to divide in culture for differing periods of time.
Some cells divided five times, others as many as 30 times. "Each division is like ageing the cells about one year," says Yang. So by comparing animals cloned from cells cultured for varying periods, it should be possible to tell if older cells yield clones that age faster.
Because the breed of bull used by Yang typically lives to about 25 years old, he suspected that the oldest cells wouldn't be useful for cloning. But they actually seemed to work better. Only 30 per cent of embryos produced from cells that had divided 10 times established pregnancies, compared with 64 per cent for cells that had divided 20 times. And although the number of pregnancies that went to term was small, these tended to be from cells cultured for longer. "Getting healthy births from such old cells suggests that ageing might not be as big a concern as we thought," says Jim Robl of the University of Massachusetts at Amherst, who also works on cow cloning.
Yang intends to monitor the calves, looking for signs of accelerated ageing such as chromosome shortening and declining immunity. "These bulls will be watched closely day and night the rest of their lives," he says.
Author: Philip Cohen
New Scientist issue 15th January 2000
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