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Red Maasai and Dorper sheep were evaluated for their resistance to gastro-intestinal (GI) nematode parasites (predominantly Haemonchus contortus), productivity and productive efficiency (assessed on a metabolizable energy basis) in experiments undertaken at the Kenyan coast (sub-humid environment) and the Kenya highlands (semi-arid environment). In both ewes and lambs there were few significant genotype by environment (G X E) interactions for either resistance (assessed by faecal egg counts-FEC) or resilience (assessed by blood packed red cell volume-PCV) to GI nematodes. Red Maasai sheep were consistently more resistant (low FEC) and more resilient (high PCV) than Dorper sheep. However, there were significant G X £ interactions for ewe reproductive performance and for ewe and lamb mortality rates and live weights. These interactions were due to very poor performance of the Dorper compared to the Red Maasai in the sub-humid coastal environment and to the much improved performance of the Dorper in the semi-arid environment. When these component traits were combined into estimates of flock productivity and productive efficiency there were highly significant GXE interactions with the Red Maasai sheep being considerably more efficient than Dorper sheep in the sub-humid environment, while in the semi-arid environment there was a negligible breed difference in productive efficiency. The results are discussed in terms of breeding strategies for smallholder farmers and pastoralists managing sheep in low-input systems in sub-humid and semi-arid environments.

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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.

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