BREEDING OF LIVESTOCK

New Zealand Herald, Volume LXXII, Issue 22030, 9 February 1935, Page 22

BREEDING OF LIVESTOCK

HEREDITARY FEATURES " REVERSION " IN OFFSPRING THEORY OF TELEGONY BY H.B.T. No. 11. The conjugation of the chromosomes, discussed in the previous article, seems sometimes to afford an opportunity for long-separated particles to reconibine, or possibly the spermatozoon merely stimulates the ovum to growth without participating in the building of the new individual. In either case the Jesuit is that from mixed types pure and it may be remote types are reproduced. For example, when two varieties of pigeons—say an Archangel and nn Owl —are crossed, and their hybrids bred with a third variety—say a white Fantail—the colour, make and habits closely agree with those of the common ancestor of all domesticated pigeons, the wild rock pigeon. On the other hand, many reversions, the result of crossing, follow the socalled Mendelian laws, that is, 25 per cent of the progeny are apparently of puro sire strain or breed, 25 per cent are pure dam, and the balance are hybrids which, when inter-bred, give progeny types in the same proportions. Pre-Natal Influence While it is evident that from the stage of fertilisation and division of the ovum onward the ova or spermati/zoa reserved for future propagation are not visibly influenced by the subsequent development or acquired characteristics of the parents, it is not so certain that the developing ovum cannot be influenced in its characteristics by environment or accidents which may affect the mother's health or nervous system. This is generally referred to as "pre-natal influence," a very debatable subject, notwithstanding criticism of the theory. The first recorded instance of apparent pre-natal influence in livestock breeding is found in the 30th chapter and 87th verse of Genesis. Jacob took peeled and mottled rods of poplar, hazel and chestnut, and set them ' in .the watering troughs that the sheep, cattle and goats might be influenced to bear a preponderance of parti-coloured offspring. This experiment to have been satisfactory, but it cannot be said that tho same principle has since been employed with practical or advantageous results. Characteristics ol Offspring In Baxter's Library of Agricultural and Horticultural Knowledge, published in 1834, the author quotes several cases, apparently authentic, of cows bearing calves unlike either the purebred mothers or their sires, but like other emasculated or female stock with which they had been grazing. I have been shown in recent years a number of calves which were born with irregularities in the shape of their ears. These, with little imagination, might be construed as tho' earmark of -the sire, a bull had a very distinctive identification mark. The noted authority J. Arthur Thomson. M.A., late Professor of Natural History at Aberdeen University, refuses "to commit himself on this subject, although he asks: "Is there any evidence that the vivid sense impressions of a pregnant mother may so affect the unborn offspring that structural changes result , which have some correspondence with the maternal experience?" Another factor which may conceivably influence the development of the ova comes under the heading of "telegony" or "infection." It has long been held by some experienced breeders that the progeny of a given mating may resemble in one or more features the sire with which the female was previously mated, rather than their actual parents. J. Cossar Ewart,- M.D., F.R.S., and other modern authorities refuse to accept the possibility of ".telegony." but Darwin, Agassiz, Carpenter and others were inclined to believe in the "infection" theory, and even Weismann admitted that the widespread belief "may be justifiable and founded on fact." Apparent Case of Telegony My own experience has led to the belief that "infection" occurs, at any rate at rare intervals. In 1932 I mated a Black Cocker spaniel bitch, the descendant of a long line of all-black Cockers, with a prepotent Blue Cocker dog. The puppies, nine in number, were, with one exception, "blues," marked very much like their sire. The one exception was a pure black. Six months later the same bitch was mated with a Cocker dog of pure black strain, Of eight puppies, the two first to be born were blues marked exactly like those of the previous litter. The balance of the litter were pure blacks. The only conclusion possible, was that tho bitch had been "infected."

It seems possible that sperm from a vigorous and prepotent sire might, by way of the Fallopian tubes, reach unripe ova, and penetrating them, set up a state of suspended fertility, which, when the ova ripen and are shed, results in immediate fertility. In the instance recorded, both the blue puppies were weakly and died soon after birth. Results of In-Breeding

When the male and female germ cells are produced by closely-related members of a long-established in-bred race, there is little -variation of a retrogressive kind, and a similarly small amount of progressive variation unless intelligent selection is undertaken by the breeder. This is probably because the male and female germ cells have great affinity for each other and blend completely to form what is called the "zygote," or fertilised ovum.

On the other hand, when two germ cells from individuals belonging to distinct races or breeds which have been living under different conditions for generations come into contact there may be only just sufficient affinity to produce fertilisation. The male germ may merely stimulate the subtle changes which eventually lead to the formation of a new individual, without, in a real and full sense, blending with"the female germ cell.

When there is reversion to a remote ancestor, it may not bo due to the germ cells containing chromosomes which are an exact reproduction of those of the ancestor restored, but rather to thg fact that the ancestral germ is more prepotent than the germ of the more recent ancestors.