S. Tembely

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.

The epidemiology of nematode infections in sheep in a cool tropical environment

The epidemiology of nematode infections in Menz sheep was studied in the highlands of Ethiopia at the International Livestock Research Institute (ILRI), Debre Berhan Research Station, using a series of tracer lambs grazing contaminated pasture for either 4, 16, 32 or 48 weeks from July 1992 to June 1994. The basic nematode seasonal infectivity pattern was expressed in terms of relative numbers of third-stage larvae (L3) available on pasture for different months. Data from faecal nematode egg counts, pasture larval recoveries and worm counts from the tracer lambs were used to investigate the infectivity pattern. Four nematode species of economic importance: Longistrongylus (Pseudomarshallagia) elongata, Trichostronglylus colubriformis, Haemonchus contortus, and Dictyocaulus filaria, were recovered from sheep. The largest numbers were recovered during the wet season (i.e. July to November) with peaks in late August and early September. During this 2 year study period, the seasonal pattern of sheep gastrointestinal nematodes was clearly defined. An important finding was that conditions during the short rainy season (i.e. March-May) were not conducive to the development and survival of nematode eggs and the free-living stages, hence little or no transmission occurred. Rainfall and humidity seemed to be the most important factors for the development of eggs and free-living stages. The period of acquisition of third-stage larvae from pasture was found to be relatively short, suggesting that a strategic control programme is feasible with minimal anthelmintic use. Results from the studies are discussed in relation to control strategies.

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.

Breed and season effects on the peri-parturient rise in nematode egg output in indigenous ewes in a cool tropical environment

A study was carried out at the International Livestock Research Institute (ILRI) Debre Berhan Research Station in Ethiopia from 1992 to 1995 to compare the peri-parturient rise (PPR) in faecal nematode egg counts (FEC) in ewes of two indigenous sheep breeds. A total of 1439 Menz and 1347 Horro ewes were single sire mated following oestrus synchronization to lamb in the wet and dry season. Three ewe treatment groups were constituted as mated/lactating/undrenched; mated/lactating/drenched; unmated/undrenched for three wet and three dry lambing seasons. All ewes grazed naturally contaminated pasture. Levels of faecal egg output were monitored at mating, 3 months after mating, 2 weeks before lambing, 4, 8 and 12 weeks post-lambing. A significant PPR in FEC occurred 2 weeks before lambing and peaked at 4 weeks post-parturition in ewes lambing just before the beginning of the dry season (October/November). There was no significant increase in FEC when lambing occurred before the onset of the long rainy season (May/June). The PPR in this study was associated with both lactation and seasonal availability of third-stage infective larvae on pasture. There was no consistent breed difference in FEC during the six sampling periods from mating to weaning. Faecal cultures and worm counts from both breeds confirmed the presence of Longistrongylus (Pseudomarshallagia) elongata, Trichostrongylus spp.and Haemonchus contortus. The role of the peri-parturient rise of FEC in ewes in gastrointestinal nematode transmission is discussed.

Effect of breed and season on production and response to infections with gastro-intestinal nematode parasites in sheep in the highlands of Ethiopia

The effects of breed (Menz and Horro), season (wet and dry), and the breed by season interaction on production and response to naturally acquired gastro-intestinal (GI) nematode parasite infections (predominantly Longistrongylus elongata and Trichostrongylus spp. and a small proportion of Haemonchus contortus) of lambs in the highlands of Ethiopia were investigated. A total of 2395 Menz and 1966 Horro lambs, born from five lambings in the wet season and five lambings in the dry season, were recorded in the study from birth to 12 months of age. These were the progeny of 43 Menz and 41 Horro rams. Horro lambs were significantly (P 0.001) packed cell volume (PCV) than the Horro lambs at 3 and 12 months of age, possibly indicating a better adaptation of the Menz to a high altitude environment. The Menz lambs had significantly (P<0.001) lower cumulative mortality (37%) to 12 months of age than the Horro (68%), principally due to better adaptation of the Menz to the study environment and not due to resistance to GI nematode parasites. Heritabilities for and genetic correlations among live weight (LWT), PCV and LFEC were estimated. Overall results showed that, in this environment, the Menz are more productive than the Horro.

DEVELOPMENT AND SURVIVAL OF INFECTIVE LARVAE OF NEMATODE PARASITES OF SHEEP ON PASTURE IN A COOL TROPICAL ENVIRONMENT

The development and survival of nematode parasites of sheep were studied in a cool tropical environment of the highlands of Ethiopia on 24 plots serially contaminated with Haemonchus contortus, Longistrongylus elongata and Trichostrongylus colubriformis eggs over a period of 2 consecutive years from June 1993 to May 1995. The availability of infective larvae was monitored by monthly pasture sampling and larvae recovery. Infective larvae were recovered from the herbage collected from the plots contaminated in June, July, August, September and October of both years. The longevity of infective larvae varied between two and six weeks when eggs were deposited on pasture in June and October, respectively. During the dry and short rainy season (November through May), eggs failed to develop into L3 stage. It is suggested that the long period (7 to 8 months) of lack of development of trichostrongylid infective larvae on the pasture can be efficiently used in a strategic treatment programme to interrupt transmission of H. contortus, L. elongata and T. colubriformis in sheep in this environment.

Effect of molasses-urea-block (MUB) on dry matter intake, growth, reproductive performance and control of gastrointestinal nematode infection of grazing Menz ram lambs

Abstract The effect of urea-molasses feed-supplement blocks (MUB) on feed utilisation and the inclusion of anthelmintic medication into the blocks at strategic times to control nematode parasites was studied in lambs grazed on low quality tropical pasture. 120 Menz ram lambs of 5–7 months of age were divided into six groups for methods of treatment against internal parasites and urea molasses supplementation. The benzimidazole anthelmintic fenbendazole was administered at the rate of 10 mg kg−1 liveweight as a drench or via medicated MUB. Animals grazed in two lots during the day and had access to grass hay in night pens ad libitum. Groups 1–3 comprised a non-supplemented (NOSUP) lot that only grazed while groups 4–6 consumed, in addition, an average of 80 g per head per day of molasses-urea-block (SUPP) supplement. The MUB supplement was provided daily for nine months but medicated MUB was used only for strategic prophylactic treatment against nematodes. SUPP animals had higher daily DM intakes (568 ±11 versus 532 ± 11 g DM per head per day, P 0.05). Testicular growth increased faster during the first 3 months to highest values of 26.9 ± 0.3 and 25.3 ± 0.3 cm, respectively in SUPP and NOSUP animals (P

Effect of experimental fascioliasis on feed intake, nitrogen retention and body weight changes in open and pregnant Menz sheep

The effect of a sub-clinical fascioliasis infection on feed intake, OM digestibility (OMD), N retention (NRET), rate of BW changes and lamb birth weight was studied in 23 open and 17 pregnant Menz ewes. The infection was imposed by oral dosing with Fasciola hepatica in pregnant and open ewes. All ewes were assigned to four treatment groups: pregnant infected (PI), pregnant non-infected (PC), open infected (OI) and open non-infected (OC). The infected ewes became anaemic from Week 8 post-infection (p.i.) and F. hepatica eggs were first observed in the faeces from Week 11 p.i. During two NRET trials (at Weeks 7 and 13 p.i.) OM intake (OMI) and digestibility coefficients were not affected by subclinical fascioliasis. All parasitized ewes voided higher urinary N, resulting in lower NRET at 8 weeks p.i. Infected ewes also had lower weight gains than control ewes. Lambs from infected dams weighed less at birth than lambs from control dams (P < 0.05). It was concluded that under the conditions of the present experiment, although subclinical fascioliasis did not affect feed intake or digestibility coefficients, it did reduce the rates of live weight changes, NRET, and lamb birth weight. Consequently, it reduced the overall productivity of infected ewes.