Studies of the permanent incisor eruption, and body development, of the Large East African Zebu (Boran): 2. Relations of incisor eruption with body growth, body development, and carcass composition

Abstract

SUMMARYA comparison was made of the growth curves for early and late eruptors (steers whose eruption age of the first incisor pair was less than the mean, and greater than the mean respectively). From birth to 195 weeks early eruptors were consistently heavier than late eruptors (P < 0·01) by approximately 4% of the overall mean body weight. Growth was linear from birth up to 126 weeks of age, and the variability increased markedly from about 60 weeks of age.The average daily gain from birth to 195 weeks was 341 g. Linear growth-rates for consecutive stages within this period were generally faster for early eruptors, with the differences ranging between 4 and 6% of the mean for periods exceeding 60 weeks. Comparison of these differences showed that linear growth-rates were only significantly different for growth periods of approximately 120 weeks and longer. When the specific growth-rates were compared no differences were significant.The differences between the growth rates of fast and slow eruptors (steers whose eruption period was less than the mean, and greater than the mean respectively) were not significant, both for linear and specific growth rates.Early eruptors had larger heads (head length x head width) relative to body weight (P < 0·05), indicating eruption at an earlier stage of body development. Also early eruptors had longer narrower heads, suggesting slower maturation rates.Partial correlations between eruption age and head length varied from 0·37 to 0·74 (P < 0·01) showing a close relation with stage of head development. Partial correlations with other measures of skeletal development showed that they were of negligible importance relative to head development.Relations between eruption age of the first incisor pair and six measures of carcass composition were negligible, as none of the partial regression coefficients was significant.