Identical Twin Calves for Research

New Zealand Journal of Agriculture, Volume 81, Issue 1, 15 July 1950, Page 11

Identical Twin Calves for Research

TDENTICAL twin calves will again be required this season to “®" enable special research work to be carried out at the Department of Agriculture Animal Research Stations at Ruakura and Wallaceville. Through the co-operation of farmers in the South Auckland district, 35 sets of heifers were collected last year. As a still greater number is required this season, it has been decided to attempt to locate twins for a limited period in July and August in Northland and Taranaki.

ORDINARY or fraternal twins develop from two different eggs fertilised by two different sperms and are no more alike than full brothers or full sisters. It has been calculated that approximately 90 per cent, of all cattle twins are fraternal. This type of twinning depends at. least to a certain degree on inherited factors, as shown partly by the well-known fact that twinning tends to “run in families” and partly by the differences in twinning rate recorded in various breeds of cattle. Breed Twinning rate Per cent. Frieslans .. .. .. .. 3.5 Ayrshire . . .. .. .. 1.8 Jersey .. .. .. .. 1.0 Beef breeds .. .. .. 0.5 The sex combinations of fraternal twins show approximately the following relationship:— . Bull-bull Bull-helfer Heifer-heifer Per cent. Per cent. Per cent. 25 50 25 A peculiarity in cattle twins not shared by twins of any other species is that in most cases they have a common or intermingled blood system leading to their mother’s placenta which makes blood interchange between the unborn twins possible. This is the mechanism that underlies the condition known as the “free-mar-tin”; that is a twin heifer which can never breed. Free-martins are always co-twins to bulls, and the explanation for their occurrence is as follows: The sexual organs of the bull twin mature earlier than those of the heifer twin and begin to secrete hormones at a fairly early stage of pregnancy. Because of the common blood system

these hormones circulate in the heifer calf and suppress the development of her sexual organs. A heifer of this type will never show heat. About 10 per cent, of all cattle twins have separate blood systems, which explains why occasionally a heifer calf born co-twin to a bull will be a breeder. However, as it is very difficult to distinguish between a free-martin and a normal heifer calf, it is only under exceptional circumstances that a heifer born as twin to a bull is worth keeping. Bull twins always are fertile whether born twin to heifers or bulls. A heifer calf which is co-twin to another heifer naturally is also normal. Identical Triplets Twins are called identical if they have developed from one egg fertilised by one sperm; such animals have exactly the same inheritance and so must be similar in most respects. Triplets, quadruplets, and even quintuplets may develop in this manner. However, in cattle such multiple births are exceedingly rare. It has been calculated' that identical triplet heifers occur only once in every 4,000,000 calvings. In the 6 years of twin collection work Ruakura has located 2 sets of these rarities. Illustrated is a set of pedigree Jersey triplets born this year in the herd of Mr. Wm. S. McEwen, of Tamahere. As far as is known identical twinning does not depend on inheritance. In nearly 250 calvings at Ruakura identical twins have not yet been borne by identical twin cows. Recognition of Identical Twins Identical, twins are always of the same sex, but in addition they must be very similar in other respects such as size, head shape, hair whorls, coat

colour, body conformation, and pigmentation of mouth, tongue,- muzzle, ears, and hooves. In examination for recognition of identical twins the calves’ heads should be. held together and each point examined separately. As experience has shown that identical twins show no differences in coat colour and colour distribution, great importance must be attached to these features. Any colour differences will show up more easily if a finger is pushed against the grain of the hair so that the undercoat can be seen. Hair whorls are usually found on the forehead, poll, back, and often above the eyes, and should generally be of approximately the same shape and in the same position on both calves. The calves should be turned on their backs and their bellies examined, as colour differences not previously . noticed often show up there. Little attention should be paid to differences in white spotting. Collection and Payment Farmers south of Auckland who believe they have a set of identical twin calves are asked to advise Ruakura Animal Research Station, Private Bag, Hamilton, by letter or. by telephone (4790 Hamilton). Taranaki and Northland farmers should advise the Department of Agriculture in New Plymouth and Whangarei respectively. Farmers advising Ruakura by letter should give their exact and full, address (district, road, and telephone number), as much valuable time may be wasted in trying to find the farm if an inadequate address is given. As soon as possible after receipt of advice an officer of the Station will visit the farm and inspect the calves. Those judged to be identical will be bought at £2 10s. a head plus Is. 6d. a head pel' day up to 10 days of age to cover the cost of rearing. Older calves will be bought by arrangement. The Station prefers to take over the calves when they are about a fortnight old. In Taranaki and Northland it will be possible to inspect twins only about once every 8 days, beginning from the last week in July. Only identical heifer twins are required this year. / • <

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