Dear Sir

I thank you sincerely for your prompt and great kindness, and return the letter, which I have been very glad to see and have had copied.² The increase is more rapid than I anticipated; but it seems rather conjectural; I had hoped that in so interesting a case some exact record had been kept. The number of births or calves reared till they followed their mothers would perhaps have been best datum. From Mr. Hardy’s letter I infer then 10 must be annually born to make up the deaths from various causes.³ In Paraguay, Azara states that in a herd of 4000 from 1000 to 1300 are reared, but then though they do not kill calves, but castrate the young bulls, no doubt the oxen would be killed earlier than the cows, so that the herd would contain probably more of the female sex, than the herd at Chillingham.⁴

There is not apparently any record, whether more young Bulls are killed than cows. If you should continue to keep notes on this interesting subject, which you have so well illustrated, it would be worth while to have the date of the last killed owing to the number exceeding 50, until one has to be killed from number exceeding 70. I am surprised that Lord Tankerville does not have exact record kept of deaths and sexes and Births, after a dozen years it would be an interesting statistical record to the naturalist and agriculturalist.

With my cordial thanks for your kindness, I beg leave to remain, Dear Sir, | Yours faithfully and obliged | Charles Darwin.