ALBERT

Description: SummaryData on gestation period of 701 indigenous East African and Galla does and pre- and postweaning growth of 810 pure-bred and cross-bred kids were analysed by least squares statistical analysis. Breeds of kids were East African, Galla, Toggenburg × East African, Toggenburg × Galla, Anglo-Nubian × East African and Anglo-Nubian × Galla. Average gestation length was 149 days and was significantly (P 〈 0·05) affected by type of birth of the kid, year–month of kidding, and age of dam. Does carrying twins had shorter gestation length than does carrying singles. Sex and breed of kid did not have significant effect on gestation length.Significant (P 〈 0·05) factors affecting birth weight, weight at 30, 60, 90, 120, 150, 210 and 270 days of age, and preweaning growth rate were breed and sex of kid, type of birth, year–month and age of dam. Male kids grew faster and were heavier than females. Kids born single were heavier and grew faster than twin-born kids. Kids from dams less than 3 years old weighed less than kids from older dams. Cross-bred kids had higher preweaning growth rates than indigenous pure-bred kids. The Anglo-Nubian × Galla cross was heaviest while the East African ranked lowest. The results point to importance of cross-breeding with temperate breeds to increase growth rates of indigenous goats. Comparison of Toggenburg and Anglo-Nubian sires for cross-breeding showed both buck breeds produced kids with roughly equal growth rates. Evaluation of indigenous Galla and East African dams for cross-breeding showed Galla dams produced heavier kids than East African but preweaning growth rates were not significantly different.

Description: SUMMARYBrody (1945) concluded that the inflection point of the growth curve of domestic animals coincides with the onset of puberty and is coupled with an increase in proportion of fat gain at that time. This purported coincidence of growth inflection and onset of puberty has been termed the ‘Brody Law’. Recent findings suggesting a pivotal role of body energy reserves, communicated by the metabolic hormone leptin, on the onset of puberty led to the hypothesis that sheep must reach the inflection point of growth (AIP) considerably before the onset of puberty (AOP). In order to test this hypothesis, growth curves were fitted for ewe lambs on different growth trajectories from two experiments. Both experiments examined the effect of growth trajectory on AOP in ewe lambs. One data set was developed in France with Merino sheep; the other came from two distinct genetic lines of Targhee sheep in the USA. The French experiment subjected ewe lambs to two different feeding levels, while the USA experiment compared two nutritional regimens differing in both energy and protein concentration.Several non-linear models described in the literature as potentially useful for modelling weight–age relationships were fitted. The Logistic function was identified as the superior model for all datasets. All animals in both experiments reached AIP considerably before AOP. AOP was defined using two criteria threshold levels of progesterone as AOP1 ⩾0·5 ng/ml and AOP2 ⩾1 ng/ml progesterone. For the USA data, multivariate analysis of AIP, AOP1 and AOP2 demonstrated that nutritional treatment was highly significant; this was also the case for the multivariate analysis of AIP, degree of maturity at AOP1 (DOM1) and DOM2. The correlation between AIP and DOM was highly negative. In contrast, the feeding treatment in the French experiments had no effect on any of the response variables except estimated mature weight. However, AIP was negatively correlated with DOM1 and DOM2. AOP was highly positively correlated with DOM. Most notably, AIP was not correlated with AOP1 or AOP2 in either experiment, and all animals reached AIP considerably before AOP1. These findings are consistent with the hypothesis that growing female sheep must reach a certain minimum level of body fatness before the onset of puberty. Genetic group and nutritional treatment significantly affect growth curve parameters; hence, the age at which this (currently unknown) level is reached must strongly depend on nutritional regimen. It is concluded that growth modelling per se cannot be used to infer onset of puberty, and that endocrine thresholds do not necessarily demarcate distinct phases of the growth curve.