HEREDITARY INFLUENCE ON THE HORSE

Manawatu Times, Volume LIV, Issue 6954, 6 July 1929, Page 4

HEREDITARY INFLUENCE ON THE HORSE

Veterinary Opinion POINTS OP INTEREST FOR HORSE BREEDERS Tie following is tie concluding portion of tie address on tie iorsc given by Mr. J. M. McLinden, M.R.C.V.S., lecturer in veterinary science, during tie Winter Show. In this portion ie deals with unsoundness from the hereditary aspect. _ ' Realising and acknowledging tie damage which has Men done in years gone by, legislation is to be found in different countries which is directed against tie use of sires affected with diseases. Using tio sire from the customary aspect in breeding, it will be agreed that he is a very important factor. One frequently hears the saying that the dairy bull is half the herd. Bo that the correct proportion or not, it is apparent that the sire is related to all his progeny whilst the dam may have very little, if any, to the remainder of the progeny. If a sine should possess what is called an inherited disease, that sire will influence all his progeny, to a greater oh lesser extent with the same disease. It might quite easily happen than an animal may never show symptoms of an inherited disease which may have been quite apparent in the sire. That is not. to say the factors for that, disease are not lying there latent or inactive aDd ready to reappear in the next generation.

In order to aid you in forming the picture w 7 hich is wanted of how a factor, or let us say, an influence can be dormant, take the example of the purebred black cow to a purebred black ball, the progeny of which may have a red coat. . Such an occurrence is woll known. Or put it this way. Most will have heard the saying that certain diseases jump a generation. The two examples are totally different, no doubt, in their method of working, but they will aid you in following what is meant, when it is said that an hereditary disease may be lying dormant, giving no cause for suspicion, yet reappearing in the offspring. But all the blame is not being laid against the sire. The male and female are both required to reproduce their kind. It should.be obvious they both contribute something to the formation of the new individual. Now wo want to know what it is they contribute. The female produces from her ovaries what is known as an ova or egg. The male produces from iiis testes little bodies called spermatoza. The male element, as we will call it, has the power of movement. The female element has the power to attract it. In the mare it is usual to find only one element being formed at a time, whilst the male produces many. OrJy one, however, is required to unite with the female element in order to render her pregnant. These little cells ere very complicated little structures, as we shall see.

Development of the Cell. When you look at some stalwart policeman, do you realise that he was once a lifctlo cell! Ho was. This little cell after fertilisation divides itself into two, these two into four, and so on, until his body was finally built up of myriads of little cells. The sarnie occurs with the horse and the maTC. They develop in the very same way. Scientists have found that this, dividing business is no mere slicing in . two. No, when a cell commences to divide there is a dense little body in its centre (nucleus) and this body changes its appearance and looks very much like a twisted piece of thread (chromatin). Next it is observed to divide up into a number of small pieces (ehromasomes), the number depending on the species of animal. These small pieces split, the halves moving in opposite directions to either extremity. At this stage the coll bogins to divide and when done these small pieces Tun together forming a new dark mass, as seen in the original cell. But with the cells of rc-production this does not take place. The small pieces do not split in two. Supposing 40 such, pieces existed: twenty move to one and twenty to the other, i.e., neglecting a special sex, one which has been observed. So in reproductive cells there is only one half the number compared with the original cell. This applies both to male and female reproductive cells. When they combine these small pieces pair themselves, restoring the original number, and division goes on as originally described. It is the little thread-like pieces of material which carry all the hereditary characters. As they have a different history from the cells of the body any influence these may have on the reproductive cells must bo indirect. Slow Process.

. Knowing then how the male and female contribute towards the new generation, by eliminating the undesirable males it means that we greatly reduce the numbers of undesirables produced annually. To eliminate hereditary unsoundness by such a method it will therefore be a slow and long process. It will require a careful scrutiny of ail sires before they be granted a license. In conclusion let me make one plea. Remember the veterinarian applies his experience, and it is gained, amongst disease, to the animal before him and endeavours to form an unbiased opinion, or should do, irrespective of whose feelings he may hurt even if he has the painful duty of rejecting a valuable animal.