Abstract:
Data are presented on the growth of range cattle over a period of four years in a semi-arid region of South Africa. A total of 176 half-bred animals of five different breeds are included in this study.
The data consist of live weights taken at bi-monthly intervals of all animals, and linear body measurements taken at bi-monthly intervals for a period of 28 months for three different age groups.
Growth in weight is strictly seasonal from weaning to maturity. These seasonal fluctuations are shown to be closely allied to monthly rainfall. The bulk of the annual precipitation occurs from November to February and the period of greatest relative growth in weight lags approximately three months behind the period of heaviest precipitation.
The greatest increase in body weight occurs from January to March and the periods of smallest increase or greatest loss in weight occur from July to September. Body measurements are also influenced by seasonal changes but to a lesser extent than body weight. The following measurements are least affected: height at withers, height over hips, body length, depth of chest and depth of flank. The measurements markedly influenced by season of the year are length of pelvis, width at hooks, width at thurls, width of loin and width of chest.
Significant differences between the sexes exist from birth, males being heavier than females. Sex differences in body measurements are not so marked, especially in the earlier age groups. When maturity is approached the steers exceed the heifers to a marked degree in all body measurements except those of the pelvic region.
The breeds may be divided into two classes in respect to weight and size, Herefords and Sussex comprising one class and Aberdeen-Angus and Afrikander constituting another. The animals of the first class exceed those of the second class in weight and most body measurements. The Shorthorns occupy an intermediate position and the peculiar behaviour of this breed is discussed.
The Afrikanders proved to have greater wither height and hip height than all other breeds.
The relative importance of genetic and environmental factors on the growth of the animals is discussed.
It is shown that the variance in height at withers in this population is approximately three-fourths genetic and one-fourth environmental in origin. In width at thurls and width at hooks more than 60 per cent of the variance is genetic. The variance in body length and live weight is accounted for equally by genetic and environmental factors. In all chest measurements the variance appear to be only slightly hereditary.
It is shown that the factor of nutrition plays a very important role in the growth of range cattle under the conditions of this experiment.
It is not possible to determine from this study whether permanent stunting results from inadequate nutrition but it is concluded that growth is retarded and maturity delayed.
