DISEASE AND DEFECTS AND THEIR ERADICATION.

Otago Witness, Issue 2811, 29 January 1908, Page 6

DISEASE AND DEFECTS AND THEIR ERADICATION.

In the view of some authorities "disease" includes unsoundness; but the general view is that disease is more or less constitutional or hereditary, while unsoundness is acquired in the individual, and should not be hereditary. The Mendelian theory, which is at piesent so much discussed, lays it down that inheritance of, or rather predisposition to, disease on one hand and .resistance to disease on the other are subject to the same principles of heredity as any other characteristics. Thus, as long as two susceptible forms ar© bred together the disease will be present in all their progeny. Unsoundness is a more difficult question to deal with. Broadly speaking, it is the result of artificial conditions to which animals are subjected, wi'd animals thus being never unsound. It is acquired, and is not. or should not, be hereditary. /Yet there may be an hereditary .predisposition which will render an animal susceptible to influences which may cause unsoundness. Such an animal may escape these influences and remain absolutely sound all its life, but the latent predisposition will remain, and may be handed on to the next generation. It is, -therefore, of importance for injtending breeders, tp look back to the (parents of the \anxmal in question to make sure that it is iree from detrimental hereditary tendencies. A show animal which has never done_ real work is especially {Laager oxtSj as is its case the

weakness may be very great, and will be transmitted in proportionate intensity to the progeny. The Eojal Oommiision on horse-breeding, many years ago, declared that the only true test of the soundness and other qualities was actxaal test — in the case of the thoroughbred the racecourse and the winning post. The same principle must be extended to other clas&es of stock — those which most completely fulfil their functions are those which are most free from unsoundness and disease. The Mendelian system is the best guide to the breeding out of disease — in which predisposition to unsoundness is included. As is summarised in the discussion of the system, no matter whether the predisposition to contract a definite parasitical disease or an actual Tinsoundness is in question, either can easily be bred out by attention to these principles. The defective animal must be mated with one absolutely free (and its parents also) from the same predisposition. The defect may be ' dominant, in which case it will be found iepfil' the progeny; but on in-breeding" them -.the breeder can feel certain tEat about 26 pet cent, of the second generation will come" free from the weakness, and that such will be pure in this respect, and will never' reproduce the disease as long as , they are 'not mated with animals possessing it.- 'If, -on 'the other hand, the defect is recessive (does not appear in the progeny of the first generation), then the breeder may be certain that about 25 per cent, of the -second in-bred generation will possess it in its fullest hereditary intensity, and he will do well to weed out of his stud, herd, or flock all those individuals which come with it.