How selective breeding can change behaviour patterns - Veterinary Practice
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How selective breeding can change behaviour patterns

JOHN BONNER presents a further report on the UFAW seminar on Darwinian selection and selective breeding

NEIGHBOURLINESS is an inheritable trait that can be selected for in-breeding programmes to improve economic performance in the livestock industry, according to a leading Dutch agricultural scientist.

Dr Bas Rodenburg of the University of Wageningen told the UFAW meeting in June – entitled Darwinian selection, selective breeding and the welfare of animals – that the selection of breeding stock should not concentrate solely on production characteristics such as improved daily weight gain or increased milk yield. If that is the only consideration, it can have adverse consequences for the welfare of individual animals and limit the performance of the whole herd or flock.

Results from studies originally carried out in Japanese quail but since confirmed in more conventional agricultural species have shown that breeding exclusively from the most productive individuals can select for increased aggression which results in higher rates of injury and deaths. However, choosing more amiable animals can reduce fighting and cannibalism and improve the overall performance of the group.

Mortality increase

The quail studies were carried out by Bill Muir from the department of animal science at Purdue University, Indiana, who produced a four-fold increase in mortality by selecting fast growing aggressive individuals.

Other groups have carried out similar work in laying hens. Choosing birds from lines with low rates of feather plucking created pacific poultry which were less sensitive to the stresses of group housing. “Group selection for low mortality leads to animals that are less fearful, more social and more active in a range of behavioural tests,” said Dr Rodenburg.

His studies on pigs have shown that selecting for social effects does influence performance but that the situation was more complex than in birds. Those pigs which were expected to have a positive impact on their herd mates were actually found to get into more fights than those with a “low social breeding value”, when groups of pigs were mixed together for the first time.

However, these same animals were found to be less aggressive after being group housed for six weeks and so it appears that their beneficial effects on the growth of their herd-mates is the result of an inherited capacity to rapidly form stable social groups, he suggested.

Realistic goal

Techniques which show what proportion of the variation within a population in a particular characteristic is due to genetic factors have been developed. These show that in many cases it is a realistic goal to attempt to select for a desired behavioural trait.

But it is generally more challenging to select for behavioural characteristics than for standard production parameters because it is difficult and time-consuming to reliably measure those behaviours in the large numbers of animals needed for a breeding programme, noted Dr Rick D’Eath from the Scottish Agricultural Colleges, Edinburgh.

Danish researchers are working to produce farmed mink which are less fearful and easier to handle than normal animals. Similar projects are being conducted in Limousin cattle to reduce aggression towards humans and in Suffolk sheep to improve maternal behaviour. But if they become more widely used, these methods would need to be carefully monitored as they could possibly result in serious welfare problems.

“We could end up by adapting animals to suit poor management systems which are seen by the public to be ethically undesirable such as battery cages,” he warned. Two particular dangers would be the creation of unreactive zombie-like creatures or excessively stoical animals that show no behavioural signs of poor welfare while still experiencing significant suffering.

In the meantime, however, it is vital to use improved selection methods to choose traits which will remedy the serious welfare issues that have arisen because of the narrow focus on production parameters, according to Professor Donald Broom of the Cambridge veterinary school.

Worst problems

He believed that high-yielding dairy cattle suffered the worst welfare problems of any European animal. Conditions such as lameness, mastitis and reproductive problems were a direct result of a highly successful campaign to boost milk production, with yields doubling over the past 40 years to around 10,000 litres per year.

About half of this improvement has been due to genetic factors and so an equally effective campaign needs to be launched to increase genetic resistance to these conditions. Unless this issue is addressed urgently, the general public may well begin to lose its appetite for dairy products, he warned.

There was even a possibility of farmers being prosecuted under the new animal welfare legislation for tolerating the unacceptably high incidence of disease seen in the industry.

Prof. Broom acknowledged that dairy farmers were facing significant financial pressures because of the low prices being paid by the supermarkets for their milk. So he argued that the responsibility for improving the situation should largely rest with retailers who should be prepared to pay more for milk produced to high welfare standards.

Just how effective marketing initiatives can be in bringing about improvements in animal welfare was explained by Marc Cooper from the RCSPCA farm animals department. He showed how the society’s Freedom Food campaign is being used to reduce the burden of diseases like chronic leg disorders, ascites and sudden death syndrome in broiler chickens.

Eat to death

These are a direct result of selecting for rapid growth which has reduced the time taken by producers to raise chickens to slaughter weight from about 84 days in 1956 to about 32 days in 2007.

This fast growth results in even greater welfare problems in the broiler breeding sector where birds live longer and would eat themselves to death if provided with food ad libitum. So the birds have to be restricted to eating no more than 50% of the food they would choose to eat and spend their whole lives hungry, frustrated and stressed, he said.

Following discussions with breeding companies, the RSPCA set a maximum daily weight gain of 45g/day for flocks included in its scheme, compared with the 56g/day achievable by the industry in 2007. At the time, only one of the three main companies had a commercial strain that would qualify under these rules but the other two have since developed suitable strains.

Studies on the first of these slower growing strains have confirmed that it produces significantly fewer diseased birds.

Closer attention

The higher welfare standards associated with the scheme have been welcomed by the general public. In 2006, 25 million birds or 3% of the UK market were sold under the Freedom Food label, rising to 44 million in the following year and 55 million in 2008.

Scientists will get better results if they pay closer attention to animal welfare concerns when carrying out studies involving laboratory mice, Professor Jane Hurst, a researcher at the Liverpool veterinary school, told the meeting.

Handling mice in the manner recommended in all the standard textbooks on laboratory animal care can actually cause them acute stress which may be responsible for some of the unexplained variation that often occurs in experimental results, she said.

Prof. Hurst’s group has been investigating the genetics and behavioural ecology of the laboratory mouse in an effort to identify those factors that determine their welfare. They have found that picking up mice by the base of the tail is much more distressing than is commonly supposed.

The experience causes subtle but long-lasting signs of anxiety which are difficult to detect because of the changes wrought by domestication on mouse behaviour.

Laboratory mice do not display the normal jumping and flight responses of their wild ancestors. But that does not mean that they have fully adapted to human contact. However, the negative effects of handling can be much reduced if the mouse is trapped in the laboratory technician’s cupped hand or captured by trapping them in a pipe which can be blocked at each end and lifted out of the cage.

Aversion to capture

Once the mice have become accustomed to the experience they may even actively seek out contact with the handler and they can be manipulated for routine examinations by being held by the tail – it is only the act of capture that they find aversive, she explained.

The main focus of the Liverpool research is on the genes coding for the major urinary protein complex that is used as the basis for social communication in this species.

Generations of inbreeding have denuded this region of the mouse genome of much of the variety seen in wild cousins and the homogeneity of the resulting urinary odours is the reason why laboratory mice can be kept at high population densities with so little social strife.

The work has also shown that all laboratory mice strains are hybrids of three separate subspecies of Mus musculus, but the evidence from mitochondrial DNA suggests that they can all trace their ancestry back to a single individual female, she said.

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