H—29

Uniformity Trials: Milk-production. —Nine sets of twins calved sufficiently close together to provide data on the uniformity of twins in respect to milk and butterfat production. The records, reduced, where necessary, to a standard lactation length of 255 days, are given in the following table, and show how closely identical twins resemble each other in milk-production :

The figures for variance ratio give an indication of the superiority of identical twins for research work- —for example, in an experiment involving butterfat yields the results from one pair of identical twins would be approximately as valuable as those from two groups of 109 cows each. Grazing Behaviour.—As the grazing behaviour of dairy cattle is a factor of considerable importance in dairy-cow production in New Zealand, the usefulness of twins for grazing-behaviour studies has been measured. Twins were found to be much more alike than non-twins in respect of grazing-time, loafing-time, lying-time, the distances walked, number of defaecations and micturations, and number of drinks. During the present season studies have also been made of the relation of weather, production level, stage of lactation, season, and nutritional level to grazing behaviour. Growth. —Growth trials involving 42 sets of twins reared under the same conditions show that identical twins grow much more uniformly than other calves and that for growth during the first year of life they may be considered approximately twenty-five times more useful than other calves. Quantitative Relationship of Pasture and Pasture plus Concentrates to Butterfat2>roduction. —In this project identical twins are being used to compare the butterfatproducing quantities of two levels of pasture and to assess the effect of feeding concentrates to the cows fed at the higher level. Small areas are enclosed in wire-netting frames during the grazing periods, and at the end of these the pasture in the frames is clipped to the level of the grazed pasture and from the weight of clippings the amount eaten is estimated. The composition and digestibility of the clippings are also estimated. Efforts are being made to calculate intake by the use of indigestible markers, such as

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Twin No. Milk Yield. Butterfat Yield. Test. Casein Yield. Casein. T. 1 T. 2 T. 3 T. 4 T. 11 T. 12 T. 13 T. 14 T. 17 T. 18 T. 23 T. 24 T. 27 T. 28 T. 29 T. 30 T. 31 T. 32 Variance ratio * lb. 5,042 5,275 4,032 4,157 3,833 3,621 3,943 4,085 5,781 5,623 200 127 4,120 4,100 5,205 5,695 349 363 lb. 266 278 240 248 222 216 212 211 323 315 11 5 216 221 242 245 17 17 Per Cent. 5-3 5-3 6-0 6-0 5-8 6-0 5-4 5-2 5-6 5-6 5-3 5-4 ' 4-7 4-3 lb. 141 144 105 110 99 93 98 98 154 149 6-5 3-6 109 109 129 135 9-0 9-0 Per Cent. 2-8 2-7 2-6 2-6 2-6 . 2-6 2-5 2-4 2-7 2-6 2-6 2-7 2-5 2-4 45 109 31 101 21 * T. 23 and T. 24 and T. 31 and T. 32 have been omitted from these calculations, as their inclusion would overemphasize the relative usefulness of twins.