R.L. Baker

Between and within breed variation in lamb survival and the risk factors associated with major causes of mortality in indigenous Horro and Menz sheep in Ethiopia

Data collected on 3256 lambs born to Horro and Menz breed ewes single-sire mated to 71 rams at the International Livestock Research Institute (ILRI) Debre Berhan station between September 1992 and June 1996 were analysed for rates of survival and growth from birth to weaning. A significantly lower proportion of Menz lambs died before 1 year of age (28%) than the Horro lambs (59%). Least squares means for pre- and post-weaning mortality were 8.8 and 19.3%, respectively in Menz, and 25.3 and 34.2% for Horro sheep. Major causes of death were similar in Horro versus Menz lambs and were pneumonia (53 vs. 54%, respectively), digestive problems (14 vs. 12%), endoparasite infections (9 vs. 13%), starvation-mismothering-exposure (SME) complex (10 vs. 7%) and septicemia (3 vs. 2%). Relationships among causes of mortality with breed, birth weight (BWT), season of birth, parity, litter size and lamb health category (number of times a lamb was sick between birth and 1 year of age) were determined. The impact of these factors on mortality varied with lamb age. Lambs that were born with <2kg BWT had a greater risk of dying from any cause except pneumonia. But, even though Horro lambs were heavier than Menz at birth (2.4 vs. 2.1kg, respectively), twice as many died before 1 year of age. The cause of mortality was further influenced by season of birth, lamb sex and health category. In addition, sires were a significant source of variation for progeny survival at 6, 9 and 12 months of age, but not at the younger ages. The best and worst Horro ram sired progeny groups that had mortality rates up to 1 year of age of 22 vs. 80%, respectively. The same estimates in Menz rams were 11 and 48%, respectively. Reduced mortality rate would significantly increase lamb output. However, isolated efforts to solve this problem are likely to have limited impact. Instead, an integrated approach to minimise the impact of underlying factors is advocated. Farm (animal) management routines that could be introduced in the short or longer term are discussed.

Reproductive characteristics of Ethiopian highland sheep II. Genetic parameters of semen characteristics and their relationships with testicular measurements in ram lambs

A study was conducted to investigate the effect of season on, and to estimate heritabilities of, and genetic correlations among, semen and spermatozoa characteristics and the relationship of these characteristics with measures of testicular or scrotal size in 6-, 9- and 12-month old ram lambs of Menz and Horro sheep breeds indigenous to Ethiopian highlands. A total of 278 ram lambs with substantial pedigree information were involved in the study. There was improvement in all semen and spermatozoa traits with age, the means at 12 months being consistently superior to values at 6 and 9 months of age. There were no significant breed differences in any of the traits studied, except semen volume at 9 months (0.67, S.E. 0.07 for Horro versus 0.39, S.E. 0.05ml for Menz) and proportion of dead spermatozoa at 12 months (0.18, S.E. 0.03 versus 0.23, S.E. 0.02, respectively). Season was significant (p<0.05) for most of the traits studied, and differences were attributed primarily to nutrition. Semen collected in the wet season had higher spermatozoa concentration while samples collected in the dry season had higher proportion of abnormalities. After correcting for differences in total spermatozoa abnormalities, the wet season (of collection) had the highest spermatozoa output (volumexconcentration) in 12-month old ram lambs. Heritability estimates varied substantially in magnitude, ranging from zero to over 0.4. Traits with non-trivial heritability estimates were mass motility at 9 months (0.32, S.E. 0.11), individual motility at 9 months (0.32, S.E. 0.12) and at 12 months (0.16, S.E. 0.12) and proportion of abnormal spermatozoa at 9 months (0.35, S.E. 0.13). Genetic correlations among semen and spermatozoa characteristics, as well as correlations with testicular measurements, were medium to high and generally favourable, but were associated with large standard errors. The genetic correlations of scrotal circumference with semen volume (0.55, S.E. 0.11), mass motility (0.62, S.E. 0.20), individual motility (0.54, S.E. 0.12), concentration (0.25, S.E. 0.04) and proportion of abnormal spermatozoa (-0.75, S.E. 0.24) in 12-month old rams indicated that selection based on this trait, which is highly heritable and easy to measure and can be measured early in life, should have appreciable favourable correlated response in semen quality and spermatozoa production.

Reproductive characteristics of Ethiopian highland sheep. I. Genetic parameters of testicular measurements in ram lambs and relationship with age at puberty in ewe lambs.

A study was conducted to estimate heritabilities of, and genetic correlations among, body weight (WT) and testicular measurements - scrotal circumference (SC), testicular diameter (TD), testicular length (TL) and epididymal diameter (ED) - in ram lambs between 6, 9 and 12 months old, and relationship of the testicular traits with age at puberty in ewe lambs (AP). Two fat-tailed sheep breeds, the Horro and Menz, indigenous to the Ethiopian highlands were studied. Experimental lambs were produced by mating 250 oestrus-synchronized ewes of each breed to 10 sires in a single-sire mating system over three mating periods which produced, for this study, a total of 361 ram lambs and 148 ewe lambs, with substantial pedigree information, in two dry seasons (October/November 1992 and 1993) and one wet season (June/July 1993). Mean AP was 322.7 days. Breed was not significant (P0.05) for all testicular measurements, except ED at 9 months for which the Horro had a higher (P<0.01) value (20.6, s.e. 0.38 versus 19.3 s.e. 0.30). Horro ewe lambs had their first oestrus 28 days earlier (P<0.05) than the Menz. Heritability estimates were obtained from a sire model (M1) and from an individual animal model with additive direct and maternal effects (M2). The maternal effect was not fitted in M2 for AP. Repeatability and heritability estimates were also obtained by analysing records at the three ages in a repeated measures model (M3). M1 and M2 heritability estimates were generally low to moderate but were associated with large standard errors. Heritability estimates for testicular measurements were generally similar to those for WT. Among the testicular measurements, SC had the highest heritability estimates at 6 (0.45, s.e. 0.24 for M1) and at 12 months (0.41, s.e. 0.21 and 0.41, s.e. 0.20 for M1 and M2, respectively). Model 3 heritability estimates were 0.29 (s.e. 0.14), 0.24 (s.e. 0.12), 0.09 (s.e. 0.07), 0.11 (s.e. 0.08) and 0.12 (s.e. 0.08) for WT, SC, TD, TL and ED, respectively. Only repeatability estimates for WT (0.34, s.e. 0.02) and SC (0.25, s.e. 0.03) were significant. Heritability of AP was estimated at 0.16 (s.e. 0.21) by M1 and 0.14 (s.e. 0.19) by M2. Genetic correlations of AP with testicular measurements, especially with SC (-0.57, s.e. 0.38 and -0.78, s.e. 0.33, at 9 and 12 months, respectively) and TD (-0.72, s.e. 0.33 and -0.83, s.e. 0.48), were desirable and generally high. Adjustment of testicular measurements for liveweight consistently resulted in a reduction in estimates of heritability and genetic correlations. SC was suggested as the most appropriate selection candidate for the genetic improvement of both male and female reproductive performance in these breeds.

Effects of breed and dietary protein supplementation on the responses to gastrointestinal nematode infections in Ethiopian sheep

Abstract The effects of breed and dietary protein supplementation on the development of resistance and resilience to gastrointestinal nematode parasites (endoparasites) were examined in artificially infected Horro and Menz lambs from 4 to 12 months of age. The factorial design involved two breeds, two infection treatments (infected vs non-infected) and three dietary protein treatments (hay and wheat bran (basal diet), hay plus molasses urea block (MUB), hay plus cotton seed cake (CSC)). At the start of the study, 152 weaner lambs (103 Menz and 49 Horro) were assigned to the 12 treatment combinations each in a separate pen. Endoparasite challenge involved three infection periods (primary, secondary and tertiary) each separated by an anthelmintic treatment. The first two infections were with Haemonchus contortus, while the third infection was a mixed infection of H. contortus, Longistrongylus elongata and Trichostrongylus colubriformis. During the entire study, infected lambs gained significantly less weight and had a lower blood packed cell volume (PCV) than the non-infected lambs. Protein supplementation of lambs with CSC resulted in lower faecal egg counts (FEC) and higher PCV and growth rates than lambs fed the basal diet. In the first two infection periods there was no significant effect of infections in lambs supplemented with MUB, probably due to low intake of MUB. In the tertiary infection period MUB was fed ad libitum which resulted in MUB-supplemented lambs having significantly higher PCV than lambs on the basal diet, with CSC-supplemented lambs intermediate. During the primary infection, naive Horro lambs had a significantly lower FEC than Menz lambs, but there was no significant breed difference for PCV. In the secondary infection period there was no significant breed difference for FEC or PCV in infected lambs. However, during the tertiary infection, while there was no significant breed difference for FEC, the Menz had a significantly higher PCV than Horro irrespective of infection status. At the end of the tertiary infection, the Menz lambs (n=26) had significantly lower adult worm burdens for H. contortus and L. elongata than Horro lambs (n=18), but there was no significant difference between the breeds for T. colubriformis worm burdens. Both the worm count and PCV data suggest that Menz lambs acquire the ability to resist and tolerate endoparasite infections better than the Horro lambs.

Reproductive performance and productivity of Menz and Horro sheep lambing in the wet and dry seasons in the highlands of Ethiopia

Abstract Ewe reproduction and productivity were studied in the highlands of Ethiopia in Horro and Menz ewes mated to lamb in both the wet and dry seasons from June 1992 to May 1997. The data included a total of 4890 mating records of which 2516 were Menz ewes and 2374 Horro ewes, with 2360 matings in the wet season and 2530 in the dry season. Menz sheep had a significantly higher ( P P In the first 3 years of the study (1992–1995), oestrous synchronisation was used at each mating. Oestrus was synchronised with intravaginal sponges containing 40xa0mg flugestone acetate (FGA). Most of the ewes (83%) came in oestrus after hormonal treatment and out of these 81% were synchronised and mated within 5 days after sponge removal. The percentage of ewes synchronised was 10% higher after treatment in the wet season than in the dry season ( P P

Assessment of natural Ixodid tick infestations in sheep

Abstract Assessment of adult female tick burden was performed on 160, 151 and 150 yearling sheep in coastal Kenya at the end of three consecutive infestation periods, respectively. The main attachment sites of fully engorged female ticks were ears, head, body sides, perianal and scrotal/udder regions. Averaged over the three sampling periods, 87% of the ticks counted were on the ears. The correlation between tick count on the ears and total body tick count was high (0.97). The average repeatability for two recorders of tick counts on the ears and the whole body was similar and high (0.95 and 0.93, respectively). The results suggest that ear tick count is a good indicator of tick burden on sheep exposed to natural tick challenge consisting predominantly of Rhipicephalus appendiculatus and R. evertsi.

Effects of non-genetic factors on responses to gastro-intestinal nematode infections in Ethiopian sheep

The effects of non-genetic factors on responses to gastrointestinal nematode infections were examined in artificially infected indigenous Horro and Menz lambs in the central highlands of Ethiopia. The experiment involved lambs of two sexes, infection and monitoring regimens (3 levels), dam parity (4 levels) and birth types (2 levels). A total of 152 weaner lambs (103 Menz and 49 Horro) were used. Endoparasite challenge involved three infection periods (primary, secondary and tertiary) each separated by an anthelmintic treatment. Data were collected on faecal egg counts (FEC), packed cell volume (PCV), worm count, and weight gain. Female lambs were found to harbor lower numbers of T. colubriformis counts and had lower (pu2009<u20090.01) FEC in tertiary infection compared to males. Younger animals were more susceptible to the nematode infections than older animals as measured by all the parameters studied (pu2009<u20090.01). Twins had higher FEC in both secondary and tertiary infections compared to singles. Lambs born to dams of first parity had higher PCV and lower FEC values during the tertiary infection compared to other parities. These results would be used as basic information in designing a more rational control strategy and should also help to advise on better management care for less resistant sheep.