Chubby GM sheep produce more milk

The first research of its type in Australia has concluded that genetically modified sheep grow bigger and faster, produce double the amount of milk, can grow more wool, but require more care, reports the Commonwealth Scientific and research organisation in Australia (CSIRO).

The results of a three-year CSIRO​ Livestock Industries' research project show that although there is little commercial benefit in GM sheep at this stage, there could ultimately be a role but not until exhaustive evaluation is concluded.

"The potential benefits and limitations of this technology need to be properly evaluated, taking into account scientific data and community concerns,"​ said project leader, Dr. Norm Adams.

The project monitored generations of sheep genetically modified with an extra copy of growth hormone gene and found expression of the gene varied between sheep and in offspring. Growth hormone affects important characteristics of an animal's development, including growth rate and body fat.

The study found that these particular GM sheep required more attention than non-GM sheep. Excess growth hormone can cause the GM sheep's hooves to overgrow and so require regular clipping. GM sheep were also leaner, which can result in health problems, and some were susceptible to diabetes. Despite this, their overall mortality rate appears to vary little from normal farm sheep.

Dr. Adams reported that his research indicates the extra growth hormone gene affects sheep differently.

"GM merino sheep grew more wool, while the Poll Dorset breed grew less,"​ he said. "In some GM offspring the extra gene, although present, was silenced and not expressed."​

A sheep milk study revealed GM-growth hormone ewes experience a prolonged lactation period, producing on average twice the amount of milk as control sheep, and continued to produce milk after weaning. Sheep milk is used in the manufacture of some yoghurts and cheeses, not least in the much celebrated French cheese roquefort and the Greek cheese feta.

"The gross composition of the GM milk appears to be the same as normal sheep milk,"​ said Dr Adams. "The effect of extra growth hormone on sheep milk production was not unexpected - injecting growth hormone into lactating cows to make more milk is commonplace in the United States dairy industry."​

An unforeseen finding was that GM sheep indicated a lower tolerance to parasites than control sheep.

Dr. Adams commented that inserting an extra gene into a sheep's 45,000 genes was complex. "You could undoubtedly produce sheep with similar levels of growth hormone with conventional breeding techniques but it would take a long time,"​ he said. "This is nature speeded up."​

Dr. Adams said more research was required to understand the impact of an additional growth hormone gene over the lifespan of a GM sheep.

Approximately 100 sheep were involved in the study. The sheep were kept in a secured location in Western Australia, according to guidelines stipulated by the Commonwealth Office of the Gene Technology Regulator, CSIRO reports.

The original GM growth hormone sheep were produced at CSIRO's former research laboratory in Prospect, New South Wales.