Fourteen pairs of monozygous twin cows of mixed ages were used to determine the effect of underfeeding from the 3rd to the 8th week inclusive after calving on milk and butterfat production and on the composition of the milk.Those cows which were well fed over the 6-week period produced more milk and a larger weight of butterfat than their sisters which had been poorly fed. The milk from the well-fed cows had a lower percentage of butterfat, but higher percentages of solids-not-fat and total protein, than the milk from the poorly fed cows.The complete lactation averages failed to show statistical significant differences in all characteristics except in the case of solids-not-fat percentage. The mean difference between the two groups for solidsnot-fat was found to be highly significant.In general, the results support the conclusions of other workers, that underfeeding dairy cows may depress the solids-not-fat content of the milk.It appeared that differences between the two groups in butterfat percentage over the 6-week experimental feeding period were strongly correlated with differences in weight changes and that the small amount of variance associated with milk yield differences was not significant.

Genetic transformation for egg and feather colour hs been obtained in the whole animal, chicken, by the use of irradiated male gametes. In this technique recipient females are first inseminated with irradiated semen from the donor and 24 h later are reinseminated with unirradiated, normal semen of the recipient strain. The transformed progeny are identical to the female strain but for one or a few genes derived from the irradiated semen. The expression of the transferred gene is irregular and may occur either in the first generation, after insemination with irradiated semen, or may occur in the following backcross generation. It is suggested that integration of a normally recessive, transferred gene at non-homologous sites in the recipient chromosomes might affect not only its regularity of expression but also its dominance relationship with the original maternal gene, "releasing" it from the dominance of the latter. The technique potentially offers a rapid method of improving an already established strain of an animal.

The nutritional value of two recently developed New Zealand cultivars of triticale, 'Aranui' and 'Karere', was determined by chemical analysis of the grain and by animal feeding studies. Four trials were carried out using rats to determine protein quality, apparent digestibility of protein and amino acids, apparent digestible energy (ADE) and apparent metabolisable energy (AME), and the capacity of triticale to support growth of rats followed by postmortem examination of the carcasses. Pigs were used to determine ADE and AME, and cockerels were used to determine true metabolisable energy (TME). Protein quality, as assessed by amino acid analysis (i.e., amino acid score) and determined by the rat bioassay procedure of relative protein value (RPV), was not different between cultivars. Rat ileal apparent digestibilities of amino acids were also not different between cultivars except for methionine and arginine. The ADE and AME bioassays using the rat and pig, and the TME bioassay using the cockerel, all showed a higher content of DE and ME in 'Karere'. 'Aranui' and 'Karere' supported similar rates of liveweight gain of rats given diets containing the same levels of crude protein. Postmortem examination of the carcasses showed no gross differences in the appearance of tissues and organs of rats fed triticale and control (lactalbumin) diets. The crude protein content of the two samples of triticale used in the evaluation was higher in 'Karere'. Five additional pairs of triticale samples from other localities showed a consistently higher level of crude protein in 'Karere'. From a nutritional standpoint, 'Karere' was the preferred cultivar because of a higher crude protein, DE, and ME content. The nutritional parameters determined with triticale were compared with corresponding literature or measured values for barley and bread wheat.

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1. Seven sets of monozygous twins were kept under the same open-grazing conditions for one year. Milks were analysed for fat, solids-not-fat, lactose and total protein contents, and butterfats were isolated at fortnightly intervals for estimation of iodine value, refractive index, softening point, saponification value, Reichert value, carotene content and vitamin A content. The results are presented both graphically and statistically.2. Consistent differences in body weights of the cows of a twin set did not render the twin set unsuitable for use in experimental work on causes of changes in milk yield, fat yield, milk composition or butterfat characteristics.3. The advantages of monozygous twins over unrelated cows was shown: (a) by the close general correspondence of the within-twin-set results as compared with the between-twin-set results throughout the period of the trial; (b) by the similarity in the forms of the curves for the different sets of twins; (c) by the marked similarity of the reaction of the cows of a twin set to change in environmental conditions—this applied particularly for butterfat characteristics such as iodine value and refractive index; (d) by the ‘twin efficiency values’ for butterfat properties computed from the whole-lactation weighted means, viz. iodine value, 7·8; saponification value, 3·4; Reichert value, 5·5; carotene content, 7·8; vitamin A content, 1·7; and vitamin A potency, 2·5.4. There were wide differences in the degree of approach to ‘identicality’ with different sets of twins. The cows in two of the sets showed a consistently close within-twin-set relationship for all characteristics studied.