704. The properties of New Zealand butters and butterfats: V. Milks and butterfats from monozygotic twin cows

Abstract

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.

Sources of variation in the fatty acid composition of milk fat from monozygous twin cattle housed indoors

“…The highly significant within-twin set variation was quite unexpected and differs from available information on sources of variation of milk fat properties in twin experiments. McDowall and Patchell (1958) present uniformity data on properties of 3-day composite samples of butterfat collected fortnightly from seven sets of grazing twins over a complete lactation. Under these management and sampling conditions, variation due to differences between twin sets was substantially greater than that due to differences within sets for all parameters examined.…”

“…There is no published information on the sources of variation in milk fat fatty acid composition except that which can be inferred from studies of long-term variation in butterfat characteristics (McDowall and Patchell 1958) where differences between sets of monozygous twins were much greater than differences between members within twin sets for all parameters examined. McDowall and Patchell's data were obtained from samples bulked over 3-day collections throughout the lactation, but we required data on variations in the proportion of fatty acids during short sampling periods for use in the design of short-term nutrition experiments.…”