70 Discussion 



DISCUSSION 



Benjamin: The improvement in average lifespan in the more 

 recent groups you mentioned was very much smaller than in the 

 cattle in earlier years. Is there some sort of resistance to increasing 

 the lifespan or is there some other factor involved ? 



Hartwig: The overall tendency was towards an increased lifespan, 

 and the smaller increment there is not significant. 



Bourliere : Is there any correlation between the average lifespan of 

 the different breeds of cows and their weight ? 



Hartwig: The lighter cattle live longer than the heavy ones. 



Danielli: Have you any data for highland cattle living in the 

 lowlands, and vice versa ? 



Hartwig: There is the example that when cows were exported to 

 Africa the highland cows adapted themselves better to those condi- 

 tions than the lowland ones. 



Kershaw: When were these cattle exported ? 



Hartwig: At the end of the 1920's. 



Kershaw: In that case there is a complicating factor, because I 

 have seen their progeny in the Cameroons and they are remarkably 

 resistant to sleeping sickness. 



Danielli: To what extent is this increase in average age due to 

 better veterinary services? 



Hartwig: That is too complex to answer and I am unable to 

 decide the cause of it. 



Danielli: Unless one has some idea of the extent to which some 

 specific disorders have been suppressed by veterinary work, it is 

 very difficult to evaluate the data at all. 



Hartwig: The veterinarians claim that they helped towards this 

 increase, but on the other hand the breeders say it is due to their 

 work. 



Comfort: Has it been possible, in your data on horses, to compute 

 lifespans or life-tables in the same sort of way as I have done, on the 

 basis of age-specific natural death rates allowing for the animals 

 lost or culled ? 



Hartwig: Yes, that has been done. 



Comfort: The agricultural lifespans are a very different matter 

 indeed from those of horses, which are kept to advanced ages. I am 

 sure these cows would live a great deal longer if they were not 

 culled. 



Hartwig: I agree with you. 



Comfort: It would be very useful if we could get a good life-table 

 for one of the heavy breeds for comparison with thoroughbreds. 



