1. The formation of a herd of Northern Frontier Zebus for genetical research has been described.2. Details are given of the system of mating used and the type of management adopted.Thanks are due to Dr J. W. B. King of the Animal Breeding Research Organization, Edinburgh, for his advice, to Mr M. A. Witcomb for taking the photographs, and to the Directors of the East African Veterinary Research Organization and the East African Agriculture and Forestry Research Organisation for their encouragement.

1. The estimation of milk yield in a herd of suckled zebu cattle has been described.2. Milk yield was found to be relatively stable when compared with weight at calving and subsequent live-weight change.3. Under constant conditions, there was a negative correlation between milk yield and live-weight change in the cows, compared with a positive correlation when both characters were affected by seasonal changes.4. Variation in milk yield was reflected in the growth rate of the calves, but considerably greater quantities of milk were required to increase growth without the aid of extra grass.5. It was concluded that, under the present conditions, calf growth rate could be increased more efficiently by the improvement of nutrition than by selection for high milk yield in the dams.

Observations were made of the ages at first appearance of each pair of permanent incisors ('eruption age'), and the time from first appearance to full eruption of each pair ('eruption period'), for Large East African Zebu cattle (Boran). For females the eruption ages were found to be 108-5 + 9-9 weeks, 137-2 + 12-9, 165-7 ± 15-8, and 200-9 + 18-2 for incisor pairs one to four respectively; for steers the figures were 104-3 + 7-9, 130-3 ±10-6, 154-6 ±13-2, and 180-9 ±14-0; and for bulls 103-3 ±8-6, 127-6 ±11-2, 151-0+12-9, and 181-2 ±15-7. Females were significantly different from steers (P < 0-01), but steers not significantly different from bulls, for all four incisor pairs.The distributions of eruption ages for each sex and pair can be considered as Normal for statistical purposes. There is a tendency for eruption to be asymmetrical after the first pair, with the right tooth preceding the left.Correlations of eruption ages between adjacent pairs are of the order of 0-80 for all pairs and sexes; they decrease progressively as pairs intervene to 0-55 for the first and fourth pairs. Partial correlations approach zero when any intermediate pair is held constant. These results indicate that the whole eruption process is highly interdependent.Evaluation of age grouping and estimations from the presence of incisors showed that this technique, although limited on its own, is still the best developmental trait for ageing. A steer with one incisor pair present had a probability of 0-108 of being the same age or older than one with two pairs. The ages of steers with one and two incisor pairs present were 115-7 ± 12-05 and 140-7 ± 14-27 weeks respectively.Heritabilities of eruption age, for the various incisor pairs, varied between 0-91 ± 0-33 and 0-43 ± 0-25 for females, and 0-87 ± 0-37 and 0-11 ± 0-59 for steers.Sources of environmental variation examined were variation between and within years, both of which were of the same order and a very small proportion of the total variation. The maternal environment had a small effect, probably specifically associated with milk consumption, which had a correlation of -0-22 for females and -0-12 for steers (P < 0-01) with the eruption age of the first incisor pair.Eruption periods for females were 5-1 + 2-8 weeks, 5-7 + 3-8, 6-8 ±4-5, and 8-8 + 5-6 for pairs one to four respectively; for steers 4-6 ± 2-6, 4-9 ± 2-9, 5-6 ± 3-8, 7-2 + 5-3; and for bulls 4-9 + 2-2, 4-8 + 2-7, 5-7 ± 3-8, 6-0 + 3-3. Females were significantly slower than steers (P < 0-05) for the first three incisor pairs only, while steers did not differ significantly from bulls for any pair.The distribution of eruption periods was positively skewed, and the correlations between pairs ranged between 0-0 and 0-35. Correlations of eruption ages and periods within incisor pairs lay between 0-50 and 0-95.

A 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.TMTT?r»T)TTPTTO' Nr arise from the widespread use of the chronology of incisor eruption for determining the age of rumiThe first of these two papers described the nants. Probably the major instance of this is with chronology of permanent incisor eruption and carcass grading systems that put a premium on examined the sources of variation. Another matter reaching a certain stage of development before a of considerable interest but for which there is little particular stage in the eruption process: it is information at present, is the relations that exist assumed that eruption solely measures chronobetween the eruption pattern and body growth and logical age, and that any correlated effects with development. In addition to the need to clarify carcass composition are negligible, but this has not these relations in order to understand more fully been confirmed, the eruption process, there are the implications that Studies of the relations with body growth have

Lactating Boran type zebu cows had high haemoglobin levels during the week after calving, after which these levels dropped sharply and then continued to decline more gradually until their calves were weaned. Some recovery was made during the subsequent dry period.Cows fed 1 oz. dicalcium phosphate daily were constantly lower in blood haemoglobin level than their controls, and significantly so between the 14th and 20th weeks of the lactation. No differences were observed in weekly weight changes or in estimated milk yields.Calf haemoglobins decreased gradually with age until relatively adult levels were reached at about a year of age. Initial content during the week of birth was lower than at a few weeks old. There was no difference in the blood haemoglobins of calves suckling on treated and untreated cows.Individual variation was high in all groups. Some implications of seasonal effects and altitude are discussed.