F1 Calves Research Articles

Partial albinism (heterochromia irides) in Black Angus cattle

A new coat colour defect (heterochromia irides) is described in Black Angus cattle. The coat colour is brownish. The iris is light, two-coloured, with an outer faintly brown ring and an inner blue ring. The fundus of the eye is albinotic. The trait does not impair the ability to reproduce although photophobia is present. Gestation length and birth weights were not affected in F1 Hereford × Angus progeny. All progeny which resulted from this mating proved normal in every respect upon physical examination. The 52 normal F1 calves resulting from this mating suggest that this trait is transmitted as a simple autosomal recessive. Breeding an affected bull to three affected dams resulted in three affected calves (one female, two males). The F1 females resulting from similar matings must be considered viable commercial breeding cattle when due care is exercised in future sire selection.

Additive genetic and heterosis effects in crosses among cattle breeds of British, European and Zebu origin.

Breed and heterosis effects for maternal and calf components for weaning traits were measured in the progeny of Angus (A), Brahman (B) and Charolais (C) sires mated to A, B, C and reciprocal AB, AC and BC dams. Additive breed effects for the calf component for weaning weight were -3.0 +/- 3.2, -26.6 +/- 3.1 and 29.6 +/- 3.3 kg for A, B and C, respectively. Corresponding maternal breed effects were -1.7 +/- 2.4, 7.8 +/- 2.3 and -6.1 +/- 2.6 kilograms. Heterosis effects on weaning weight for the calf component were 21.2 +/- 3.6 for AB, 1.4 +/- 3.7 for AC and 16.5 +/- 3.4 for BC crosses, while heterosis levels for the maternal component were 28.9 +/- 2.7 for AB, 16.5 +/- 3.2 for AC and 18.7 +/- 2.9 kg for BC dams. The corresponding estimates for condition scores tended to parallel those for weaning weight. Approximate relative production efficiency rates were computed for the different mating groups as (calf weight divided by cow weight) x weaning rate. These values were .34 for purebred matings, .36 for purebred dams raising F1 calves, .40 for F1 cows raising backcross calves and .43 for F1 dams raising three breed crossbred calves.

Breed and heterosis effects of American Zebu cattle.

The Brahman (American Zebu) has been evaluated in numerous crossbreeding studies throughout the Southern United States. Brahman females producing straightbred calves have usually been found to have a lower calving percentage, calf survival rate and weaning rate than other contemporary straightbreds, although they have been reported to be superior or competitive in some studies. Birth weights of Brahman calves have been larger than those of Angus, smaller than Charolais and comparable to those of Herefords. Brahman steers generally have had lower postweaning daily gains, lower carcass grades, less backfat and higher Warner-Bratzler shear values than other contemporary straightbreds. Heterosis estimates for reproduction have been small and variable in producing F1 calves, but larger and positive for reproductive traits of F1 cows. Birth and weaning weight heterosis estimates averaged 3.3 and 21.7 kg for F1 calves and 1.9 and 31.1 kg for calves of F1 cows. Small and variable heterosis estimates have been found for all carcass traits.

Effective crossbreeding systems utilizing Zebu cattle.

The basic objectives and procedures for successful crossbreeding of beef cattle were considered, with special reference to the levels of realized hybrid vigor that might be anticipated for different crossbreeding programs involving the American Brahman (Z1) and European (Ej) breeds. Intralocus heterozygosis levels with respect to breed origin of genes (breed heterozygosis) were computed for various crossbreeding systems. These values were weighted by approximate relative F1 heterosis levels for different breed combinations (1.0 for Z1Ej and .3 for E1E2) to yield the estimated relative hybrid vigor levels for total performance in alternative crossbreeding systems. The estimated average maternal heterosis levels for the various systems, were respectively 0, 33, 67, 66, 50, 54 and 49% for production of F1 (EZ) calves, three-breed terminal cross calves, two-breed-of-sire (E1--Z1) rotation crosses, three-breed-of-sire (Z1--E1--E2) rotation crosses, two-breed (Z X E) synthetics, three-breed (Z1 X E1E2) synthetics and four-breed (Z1E1 X E2E3) synthetics. The respective values for calf heterosis levels were 50, 57, 67, 66, 50, 54 and 49%. Successful crossbreeding requires (1) the choice of appropriate breed combinations for the environment and production system management programs to support the increased production potential or crossbred cattle.