19 September 1997

HIGH MERIT COW WELFARE

NOT BEING COMPROMISED

A three-year, £900,000 study of the welfare of high yielding dairy cows looks like concluding that the animals are not being compromised, provided management and feeding matches genetic potential. Allan Wright has been talking to the scientists involved in the research

THE public can be reassured that our top dairy cows are not being stressed any more than their more moderate counterparts. But those of the highest genetic merit are living closer to the edge and demand quality management to avoid being at risk, according to Dr John Oldham, head of genetics and behavioural sciences at the Scottish Agricultural College.

He heads the multi-centre research programme commissioned by the Scottish Office to study metabolic stress in high yielding cows. The project brings together the SAC and the Moredun, Hannah, and Roslin research institutes.

"Advances in dairy cow productivity have given rise to public concern that the cows are being pushed too hard so that their metabolic equilibrium may be compromised in some way. We are looking at genetic merit, various milk yields, physiological functions, immunity, reproduction, health, and the behaviour of cows to see if there is a justifiable foundation for concern," says Dr Oldham.

"The study is now into its final year and we are beginning to bring all the results together. The broad conclusions are that there are no harmful effects on cow welfare or health, that there is a small negative effect on reproduction, and that, while our evidence on disease is limited, it seems that high yielding cows do live closer to the edge," he says.

That final point has been shown in a trial using IBR vaccine in the four sections of the Langhill herd at Edinburgh.

"Control groups, those with average genetic merit, on both high and low input regimes, gave a good immune response to the vaccine. So did the high genetic merit group on the high input system, although it was slightly less than in the control groups.

"But there was a marked drop in the immune response from high merit cows on a low input diet. It is the first evidence I am aware of which suggests that genetically superior animals are at higher risk from disease," says Dr Oldham.

The technology will now be used to monitor successive lactations and see how the immunity progresses.

"We have seen similar results from trials on reproductive success and they also suggest that high merit cows are more at risk. When challenged they are less capable of mounting a response. If they were any closer to the edge then the results would be more extreme.

"Basically what we are saying is that high yielding cows need top line management and diets to match their potential. Any slackening of management could have harmful effects," says Dr Oldham.

He thinks the Langhill herd, with its high level of management, may mask greater variation in commercial herds.

"We have had access to data on health and reproduction from herds recorded by Scottish Livestock Services which have been very helpful. They show a genetic correlation between genetic merit and some disease markers like ketosis, which reinforces the need for high levels of management when dealing with high genetic merit animals," says Dr Oldham.

The final report from the complete study will be published next April.

BEHAVIOUR IS NO DIFFERENT

APART from obvious things like producing more milk and, therefore, spending more time eating, there are no significant differences in behaviour patterns between high yielding dairy cows and their less productive counterparts.

That is the conclusion from countless hours of monitoring behaviour in the two groups which has been done by Dr Birte Neilsen.

Reporting on her work, Dr Oldham said a lot of good science was based on confirming expectations and that was what had happened in this case.

"The cows do not rest any longer. But they do spend more time feeding, especially those on high forage diets. There are no extra needs to attend to on behaviour with high merit cows.

"It should also be remembered that cows do not have an extensive behavioural pattern, nothing like that exhibited by pigs. Nevertheless, it is reassuring to know that the cows normal behaviour is not being disrupted by high yields," said Dr Oldham.

LESS FERTILE, EXTRA OUTPUT

HIGH yielding cows do have a reduced rate of reproductive success compared with average yielders but the cost is well covered by the extra production.

That side of the work in the metabolic stress programme is being done by PhD student Jenny Pryce and the results will not only form part of the final report but will be among the things stemming from the project which will be incorporated in future versions of the breeding index ITEM.

"We have looked at record from Scottish Livestock Services and DAISY and, using PIN, have established that for each 100kg of extra production there is an extra 0.3 days in the calving interval. The cost of that is estimated at more than £1 but the margin on the extra milk has to be £10 so the net gain is substantial," says Ms Pryce.

"The genetic correlation for yield and calving index is quite high at 0.4, and it should be possible to select for animals which do not suffer an extended calving interval," she says.

But Dr Oldham is quick to point out that although selection may be possible, owners of high yielding cows should be asking what sort of calving interval is best for top animals.

"Getting them pregnant sharpens the milk curve and depresses yield. Dairy farmers with high genetic merit cows have to ask questions about the sensible length of lactation for these top yielding animals," he says.

Ms Pryce is also studying the correlation between somatic cell count and mastitis and has found it to be high. The theory is that although the heritability of mastitis is low, heritability of somatic cell count is 10 times higher and, therefore, a strong correlation between the two means that selection for mastitis resistance is possible.

"PTAs on somatic cell count are becoming available in sire records and we have been looking at data from Scottish Livestock Services to monitor how daughters of bulls with good PTAs for somatic cell count are performing in terms of mastitis control," says Ms Pryce.

COPE WELL WITH DEMAND

DAIRY cows are very forgiving and cope well with most of the demands placed on them, according to veterinary surgeon Dr David Logue from the Scottish Agricultural College.

His part in the metabolic stress study has been to monitor lameness and mastitis at the colleges Acrehead unit at Dumfries.

The herd there is split into 70 cows averaging 5500kg on a grass/clover diet supplemented with 0.25t of concentrates, and 70 being milked three-times-a day to average 8500kg from 1.5t of concentrates.

Dr Logue reports that there have been no significant differences between the two groups and he is satisfied that, provided management standards are high, there is no extra welfare burden being placed on the high yielding animals.

However, in another piece of research, Dr Peter Ball is beginning to suggest that high genetic merit animals geared to calving down at two years old may be sexually mature too early for their own good.

"We are in the very early stages of this work but there would appear to be a tendency for these heifers to start cycling earlier than normal and then to stop later in their development," says Dr Ball. It is a potential problem but it is too early to be definitive, he adds.

LOW YIELDERS NEED CARE

LOW genetic merit cows need just as much attention as their superior counterparts when being pushed to maximum yields, according to Dr Chris Knight from the Hannah Research Institute at Ayr.

His input to the metabolic stress programme has been to take groups of low and high genetic merit cows from the Langhill herd owned by the Scottish Agricultural College and from the Blythbank herd owned by the Roslin Institute and the push them as hard as possible using a wide variety of diets and treatments.

"Both low and high genetic merit groups increased output and there was clear evidence that both were operating close to their maximum levels. What we have found is that management has to be equally high for both levels of genetic merit when they are being pushed to the limit," says Dr Knight.

"It would be unsafe to assume that, under normal management, low genetic merit animals do not need the same high level of care. They are working as hard as they can and the simple advice is that all the cows in a herd require top level management when they are producing close to maximum yields," he says. &#42

Dr John Oldham… high yields no threat to cow health or welfare but top line management needed.

HIGH MERIT APPROACH

&#8226 No harmful effects on welfare.

&#8226 Small negative effect on fertility.

&#8226 At higher risk from disease.

&#8226 Need top line management.

Jenny Pryce… high yielding cows do have reduced fertility.

High yielding cows… health and welfare not compromised provided herd management matches genetic potential – but they do live closer to the edge.

FERTILITY FINDINGS

&#8226 Reduced reproductive success.

&#8226 For each extra 100kg milk, extra 0.3 days in the calving interval

&#8226 But cost covered by extra production.

&#8226 Selection for tighter calving interval should be possible.