Risk factors for mortality associated with respiratory disease among Menz and Horro sheep in Ethiopia.

A retrospective case-control study was conducted on 6718 sheep of two breeds (2772 Horro and 3946 Menz) on risk factors for mortality associated with respiratory disease (MARD) in Ethiopia, based on data collected between October 1993 and December 1997. Potential risk factors examined were breed, gender, age, month, and air temperatures.Fifty-four per cent of total deaths in the flock could be attributed to respiratory disease and the annual MARD rate ranged between 6.3 and 19.0%. There was significant breed (P<0.0001) and gender (P<0.0001) difference in MARD. The Horro breed had a higher (P<0.0001) annual MARD than the Menz breed (16.5+/-0.18 vs. 12.4+/-0.15%). A higher (P<0.0001) proportion of males suffered than females (15.1+/-0.23% vs. 13.8+/-0.13%). Age was also an important risk factor for MARD: there was a strong polynomial relationship (R(2)=0.91, P<0.0001) between MARD and age; the risk of being young if a sheep was a MARD case was high. MARD was high between October and March but relatively low between the months of April and September. There was a significant (P<0.05) negative cubic relationship (R(2)=0.49) between monthly MARD and monthly average minimum air temperatures. There was also a significant (P<0.01) positive exponential relationship (R(2)=0.61) between monthly MARD and average monthly daily deviation between maximum and minimum air temperatures. Timely health and management interventions focusing on these factors are necessary to alleviate losses from MARD. Understanding variations in MARD risk within a population can enhance early response to potential outbreaks, reducing losses.

Genital disorders, linear and testicular characteristics in Menz rams.

Clinical examination, bodily condition score (BCS), heart girth (HG), body length (BL), wither height (WH), and scrotal circumference (SC) were assessed on 486 mature Ethiopian Menz rams, on small farms, in local markets, and at the main abattoir in Addis Ababa from December 1994 to April 1995. Almost 27% of the rams were found to be unfit for breeding. Poor general condition, mainly in the form of respiratory disorders, was seen in 1.2% of the rams. Balanoposthitis, epididymitis and orchitis were the most common pathological conditions, affecting the external reproductive organs in 14.6%, 4.5% and 4.1% of the rams, respectively. Testicular calcification, cysts and testicular haemorrhagic lesions were detected in 4, 6 and 8, respectively, of the 60 rams examined at necropsy. The BCS, HG, BL and WH averaged 2.1 +/- 0.5, 67.7 +/- 5.0 cm, 60.1 +/- 4.5 cm and 60.1 +/- 4.3 cm, respectively. The mean SC was 25.5 +/- 3.9 cm and did not vary significantly with age (p > 0.05). Among the linear body measurements, the highest correlation was between BL and WH (r = 0.66). SC was found to be most closely correlated to HG (r = 0.46). More investigations into the relationship between the present findings and actual fertility, and on their practical application in the selection of rams for breeding is recommended.

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.

Fertility in zebu cattle (Bos indicus) after prostaglandin administration and artificial insemination.

A total of 137 cycling zebu cows, each receiving a single dose of prostaglandin PGF(2alpha)were used in an oestrus synchronization programme on three different farms. Of the cows on the three farms, 60.6 and 90.5% showed overt oestrus and luteolysis, respectively. Pregnancy rate to fixed time inseminations following single injection of PGF(2alpha)was 61.4% for farm 1, significantly higher than the values of 45.7 and 46.9% for farms 2 and 3, respectively. The pregnancy rates to second service of rebred cows were 53.3, 50.0 and 50.0% for the three farms, respectively, with no significant differences between each. Fertility classification of the cows based on progesterone (P(4)) concentration showed that 6.6% of cows on the three farms were incorrectly diagnosed as having corpora lutea; 2.9% of them had incomplete luteolysis and 5.1% may have lost their embryos between days 21 and 45 post-insemination. The pregnancy rate was 10% higher in the rainy season than in the dry season. Cows with body condition scores of 3 and 4 had a higher overall pregnancy rates than those with a body condition score of 2. The findings of this study further confirm the luteolytic efficacy of prostaglandin in inducing oestrus in zebu cattle and indicate that the nutritional status of the cows must be satisfactory before embarking on oestrus synchronization programmes.

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.

Semen characteristics of Ile-de-France rams of different age and physical condition.

A breeding soundness examination (BSE) involving animal physical examination, scrotal circumference (SC) and semen evaluation was undertaken on 80 Ile-de-France rams at a government breeding farm, 32 km south-west of Casablanca (Morocco) from March to May 1988. A large percentage of rams (21.4%) was found to be unfit for breeding due to physical and genital abnormalities; 11 and 5% had disorders of the feet and respiratory system; upon genital palpation, 17.5, 13.8 and 7.5% of animals had orchitis, epididymitis and posthitis, respectively. The SC increased with age from 28.8+/-3.2 cm at

Plasma progesterone and blood metabolite profiles in post-partum small east African zebu cows.

Plasma progesterone profiles were used to monitor post-partum reproductive activity in 12 Small East African zebu (Bos indicus) cows allocated to either supplementary or no supplementary feeding (control) with continuous or restricted (twice daily) suckling regimes. Intact bulls were used for breeding. Blood samples were collected 3 times a week for 33 weeks to determine plasma progesterone levels. Weekly blood samples were also used to determine blood metabolite concentrations. Plasma progesterone levels remained below 1 ng/ml in all cows until week 12 post-partum. Only 5 cows showed ovarian activity over the 33 week period. Cows that cycled expressed irregular and short-lived progesterone rises (> 1 ng/ml) lasting 8 to 12 days prior to establishment of normal patterns of progesterone secretion where progesterone levels ranged from 8 to 10 ng/ml in cows with normal cycles. Plasma total protein, albumin, globulin, blood urea nitrogen and glucose levels varied over time without consistent trends, and were not influenced by either supplementary feeding of suckling regimes, nor differed between cyclic and acyclic cows. It was concluded that extended post-partum anoestrus, conception failure and early embryonic mortality were responsible for lowered reproductive efficiency in zebu cows. Blood metabolite concentrations were not good indicators of nutritional status and were not related to post-partum ovarian activity.

Seasonal variation in ovarian and oestrous activity of tropical Menz sheep as affected by plane of nutrition.

Forty-eight mature Ethiopian Menz ewes were used to investigate the effect of nutrition on oestrous and ovarian activity in tropical sheep. A control group was fed on hay alone and a high nutrition group received an additional 400 g per ewe per d of a concentrate feed providing 263 g crude protein/kg dry matter and 10.5 MJ metabolisable energy/kg dry matter. Half the ewes in each group interacted with harnessed vasectomized rams to detect oestrus, which was also verified by weekly plasma progesterone assays. Ram presence did not depress feed intake or liveweight gain (P > 0.05). The mean percentage of ewes showing oestrus at least once a month was very high (95%) and there was a marked reduction in sexual activity from June to September, the wet season. Only 79% of ewes cycled in August and the number of heats per ewe per month dropped to 1.3 during this wet season in contrast to 1.9 the rest of year. Ewes came into oestrus 21 times (range 18-23) a year with no significant effect of level of nutrition. Mean cycle duration was 17.9 +/- 8.7 d; 22% of cycles were short (< or = 13 d), 56% normal (14-19 d), 11% long (20-26 d), 8% silent or missed (27-40 d) and 3% represented anoestrus (> or = 40 d) with no major difference due to nutrition level. Individual animal progesterone profiles revealed that ewes failing to show oestrus had experienced increased silent ovulations. Forty percent of undetected heats were from the same animals. We concluded that, although Menz ewes are year-round breeders, they experience an apparent reduction in sexual activity from June to September, which appears to be independent of the level of nutrition, but might influence their breeding activity and flock production.

Seasonal influences on gonadal and extragonadal sperm reserves in Small East African zebu (Bos indicus) bulls in Ethiopia.

Body weight and scrotal circumference (SC) data were taken ante mortem and genitalia collected after slaughter from Small East African zebu (SEAZ) bulls slaughtered during the wet (n = 46) and the dry (n = 53) seasons. Bulls slaughtered during the wet season were significantly heavier (47 kg) and had significantly larger SC measurements (3.3 cm) than those slaughtered during the dry season. Mean (+/- s.e.m.) paired testes weights were 233.7 +/- 13.8 and 292.8 +/- 11.3 g and epididymal weights 26.8 +/- 0.9 and 35.9 +/- 1.1 g in bulls slaughtered during the dry and wet seasons, respectively. Daily sperm production rates and epididymal sperm reserves were 2.2 +/- 0.1 x 10(9) and 3.0 +/- 0.1 x 10(9); and 16.1 +/- 0.3 x 10(9) and 17.6 +/- 0.4 x 10(9) in bulls slaughtered during the dry and wet seasons, respectively. These differences were significant. It was concluded that season affected reproductive capacity of zebu bulls probably due to variations in the quality and quantity of nutrition. However, the confounding effects of ambient temperature and nutrition on reproductive capacity of zebu bulls in tropical regions need further examinations.

Relationship of testicular growth and size to age, body weight and onset of puberty in Menz ram lambs.

Scrotal circumference as an index of testes size, along with body weight, wither height, heart girth and body condition score were measured fortnightly for 114 Menz ram lambs from weaning (91+/-7 SD days) until puberty, which was defined as age at first collection of an ejaculate with 50 x 10(6) spermatozoa and 10% motility. The animals were maintained on poor (n=28), low (n=29), medium (n=29) or high (n=28) levels of nutrition through grazing and supplementation. Further, half the lambs in each group were drenched for endoparasites. Daily gains in live weight, wither height, heart girth and scrotal circumference were 48.5+/-1.6 g, 0.05+/-0.01 cm, 0.07+/-0.01 cm and 0.07+/-0.03 cm, respectively for the period from weaning to puberty and varied with level of nutrition (P<0.05 to 0.001) but not with drenching or its interaction with nutrition level (P>0.10). Scrotal circumference increased linearly and was strongly correlated with age, body weight, wither height, and heart girth (r = 0.83 to 0.85, P<0.001), and lamb weight could be predicted by the equation: 6.35 + 0.53 scrotal circumference (R(2) = 0.73). Mean age, body weight and condition score at puberty were 288+/-6 days, 19.3+/-0.4 kg and 2.6+/-0.06, respectively, and varied due to season of birth, level of nutrition and weaning weight (P<0.01 to 0.001). The nutrition level also influenced (P<0.001) scrotal circumference at puberty, averaging 21.5+/-0.3 cm. It was concluded that postweaning nutrition management had a strong influence on lamb weight gain, which in turn was related to testicular growth and puberty onset in Menz ram lambs. The suitability of scrotal size measurement as a criterion for early selection of tropical ram lambs is emphasised.

Effect of the method of estrus synchronization and PMSG dosage on estrus and twinning in Ethiopian Menze sheep.

Mature, cyclic Ethiopian Menze ewes (n=72) were used in this study. They were divided into 6 equal groups in a 2x3 factorial experimental design. Estrus and ovulation were synchronized in all ewes using either 2 dosages of prostaglandin F2 alpha 12 days apart (n=36) or intravaginal progestogen sponges for an equal length of time (n=36). At sponge removal or at the second prostaglandin injection, equal groups of ewes were injected with either 0, 200, or 300 IU of PMSG. Prostaglandin-synchronized ewes exhibit estrus significantly earlier (P=0.025) than the progestogen-synchronized group. Although PMSG treatment increased twinning rates and therefore total number of lambs born, the differences between groups did not reach significant levels (P>0.10).

Effects of supplementary feeding and suckling intensity on postpartum reproductive performance of small East African Zebu cows.

Small East African Zebu cows (n = 120) which calved during the dry season were used to determine the effects of postpartum nutritional supplementation and suckling intensity on body weight, body condition score, reproductive performance and on calf mortality and preweaning growth performance. Cows were allocated based on calving body weight to either receive a supplementary feed of molasses blocks containing 10% urea or to serve as controls and to be grazed only. Within nutritional groups, cows were further assigned either to continuous suckling or to restricted suckling twice daily. Intact bulls were introduced 21 days after the first cow had calved, and data were collected for 8 months. Calving body weight and body condition score of dams ranged from 186 to 192 kg and from 3.8 to 4.2 and did not differ among the treatment groups. Supplementary feeding significantly (P<0.05) reduced calf mortality from 40 to 20%, while restricted suckling reduced mortality by 13% from 36 to 23%. Body weight and body condition score did not vary between groups during the supplementation period. Over the 8-month period, 65% of supplemented and 53% of control cows exhibited estrus (P>0.05). A significantly (P<0.05) karger percentage of restricted suckled cows showed estrus than of continuously suckled cows (74 vs 42%). The postpartum estrus interval was shorter by 54 days in supplemented than in control cows and by 13 days in restricted than in continuously suckled cows. The pregnancy rate was higher in supplemented than in control cows (37 vs 33%; P>0.05) and in restricted than in continuously suckled (46 vs 22%; P>0.05) cows.

Nutritional influences on growth and onset of puberty in Boran and Boran x Friesian bulls in Ethiopia.

Twenty-seven Boran and 37 Boran x Friesian crossbred bulls were weaned at 6 months of age and randomly assigned to either a dry season supplementary feed containing 16% crude protein or control groups. Data were collected on body weight, wither height and scrotal circumference (SC) at monthly intervals. Bulls were also challenged with 100 mug of gonadotropin releasing hormone (GnRH) at 2-month intervals and plasma testosterone responses were determined. Semen was collected at monthly intervals by electroejaculation. Post weaning average daily weight gain was significantly (P<0.001) higher in supplemented than in control groups (302 vs 208 g/day). Scrotal circumference growth rates were also significantly (P<0.001) higher in supplemented than in control bulls (0.38 vs 0.31 mm/day). Bulls fed supplemented diets were younger (430 vs 473 days; P<0.001) and heavier (217 vs 203 kg; P<0.05) and had better semen quality at puberty than the control bulls. There was a trend for larger SC at puberty in supplemented than in control bulls (P=0.06). There were no significant differences in wither height or in testosterone response to GnRH at puberty between supplemented and control bulls. Body and SC growth rates to puberty for Boran and Boran x Friesian bulls were 189 and 321 g/day (P<0.001) and 0.27 and 0.42 mm/day (P<0.01), respectively. Boran bulls were older (513 vs 406 days; P<0.01) and lighter (201 vs 215 kg; P<0.05), and had smaller SC (23.9 vs 26 cm; P<0.01) at puberty than Boran x Friesian bulls. Testosterone responses to GnRH increased (P<0.001) with age and were significantly higher (P<0.05) in supplemented and in Boran x Friesian bulls than in control and Boran bulls. Wither height, testosterone response to GnRH and semen quality at puberty did not differ between breeds. Dry season supplementation improved growth rate and enhanced sexual development and maturity in both Boran and Boran x Friesian bulls, and would be a useful management strategy for enhancing fertility in bulls in the tropics.

Effects of dry season nutritional supplementation on growth, onset of puberty and subsequent fertility in Boran and Boran x Friesian heifers in Ethiopia.

Shortly after weaning at 8 months of age, 43 Boran and 46 Boran x Friesian crossbred heifers were randomly divided to either receive a supplementary feed containing 16% crude protein during the dry season or to serve as controls. Heifers were examined monthly, and data on body weight, wither height and body condition score were recorded. Ovarian size and structures were determined per rectum and heifers were kept under continuous observation for standing estrus. Blood samples were collected at 10-day intervals every month for determination of plasma progesterone levels. All heifers were exposed to intact bulls for 4 months after they attained 18 months of age. Average daily weight gain to puberty was significantly (P<0.01) higher in heifers given supplementation than in the controls (360 vs 326 g/day). The average daily weight gain in Boran heifers (296 g/day) was significantly (P<0.01) lower than in crossbred (392 g/day) heifers. Mean age at puberty differed significantly (P<0.001) between heifers given supplementation (573 days) and the controls (627 days). Boran heifers attained puberty at a significantly later age (660 vs 540 days; P<0.001) than crossbred heifers. Body weight at puberty did not differ between supplemented and control heifers (226 vs 222 kg); while the difference between Boran and crossbred heifers was significant (216 vs 232 kg; P<0.01). Pelvic size and body condition score were not influenced by supplementation but differed significantly between genotypes. Pregnancy rate after 4 months of breeding was higher in supplemented (79%) than in control (64%) heifers. Boran heifers had a significantly (P<0.001) lower pregnancy rate than crossbred heifers (52 vs 91%). Mean age and body weight at conception were not affected by supplementation but differed significantly (P<0.05) between genotypes. The results indicate that prepubertal supplementary feeding during the dry season increased growth rate, reduced age at puberty and improved fertility in both Boran and Boran x Friesian heifers.

Studies on the reproductive performance of Ethiopian sheep by means of an enzyme immunoassay technique; a review.

Measurement of the concentration of hormones associated with reproductive function in female animals can aid in the evaluation of their reproductive status. In particular, from the point of view of production, determination of the concentration of circulatory progesterone can aid in the correct assessment of ewes. Many investigators have used radioimmunoassay for this purpose, but the enzyme-linked immunosorbent assay (ELISA) is equally reliable, quicker and cheaper. This report reviews the use of the ELISA in Ethiopian Menz sheep. Progesterone profiles in Ethiopian Menz sheep during pubertal development, the oestrous cycle, pregnancy and post-partum anoestrus were similar to those of temperate breeds. The practical applications of progesterone determination to sheep production and the requirement for the correct handling of samples are emphasized.

Effect of nutrition and endoparasitic treatment on growth, onset of puberty and reproductive activity in Menz ewe lambs.

Ewe lambs of the Ethiopian Menz breed were assigned at weaning (90+/-3 days) to four levels of nutrition (poor, low, medium and high) to achieve different premating growth rates with or without treatment for endoparasites. A concentrate mixture providing 2.5 Mcal/kg dry matter (DM) metabolizable energy and 15.2 g/kg DM digestible protein was used. Improved nutrition increased lamb postweaning average daily weight gain up to puberty by 6 to 26 g/day and the conception rate to first estrus by 9 to 16% while it reduced the mortality rate by 24 to 31% and age at first lambing by 2 to 5 months. Lambs reached puberty (age at first estrus) at 16.9+/-0.1 kg (+/-SEM) or 60% of mature body weight and 350+/-12 days of age. The onset of puberty was advanced by weaning weight (P<0.05), itself being well correlated with birth weight (r = 0.51, P<0.001), and by level of nutrition (high=299+/-19, medium=301+/-18, low=383+/-23 and poor=454+/-31 days, P<0.001) through enhanced growth rate (r = -0.82, P<0.001). No independent effect of drenching for endoparasites on pubertal development was observed (P>0.05), but its interaction with season-of-birth improved the growth of lambs born during the period of short rains (P<0.05). Overall mean litter size at first lambing was 1.07; the twinning rate was 6.5% and the birth weight was 1.9+/-0.1 kg. Up to 13.4% of newborn lambs, averaging 1.3+/-0.6 kg, died on the day of parturition. The results indicate that improved growth rate and body weight, resulting from better postweaning nutrition, affects the attainment of puberty in Menz ewe lambs. Mitigation of nutrition stress and endoparasitic infection depending on season-of-birth would thus increase the annual reproductive rate of breeding ewes and flock productivity.

A quantitative histological study of testicular and epididymal development in Boran and Boran x Friesian bulls in Ethiopia.

Quantitative histological techniques were used to characterize the pattern of testicular and epididymal development in 42 Boran and 49 Boran x Friesian bulls aged between 6 and 23 mo. Bulls were divided into five age groups having four-month intervals. Between 6 and 23 mo of age, body weight increased from 124 to 293 kg and 179 to 267 kg (P<0.01) in Boran and Boran x Friesian bulls, respectively. Scrotal circumference measurements increased from 6 to 23 mo by 10.2 and 8.9 cm in Boran and Boran x Friesian bulls. Paired testes weight increased significantly (P<0.001) over the same period from 29 to 304 g and 59 to 291 g in Boran and Boran x Friesian bulls, respectively. Both caput and cauda epididymal segment weights also increased significantly (P<0.001) with age. There were significant (P<0.05) genotype differences in seminiferous tubule diameter, which increased by 137 and 90 microm with increasing age in Boran and Boran x Friesian bulls, respectively. Patent seminiferous tubules were first observed at 206 and 188 d of age in Boran and Boran x Friesian bulls, respectively. The appearance of elongated spermatids and spermatozoa in the seminiferous tubules and epididymal tubules occurred at later ages in Boran than in Boran x Friesian bulls.

Influence of suckling and continuous cow-calf association on the resumption of post-partum ovarian function in Bos indicus cows monitored by plasma progesterone profiles.

The effect of suckling on post-partum ovarian function was monitored by weekly plasma progesterone determinations using enzyme immunoassay in 16 Small East African Zebu (Bos indicus) cows maintained with a fertile bull. Five cows continuously suckled their calves (COS), but starting 30 d after calving 6 cows remained with their calves which were prevented from suckling using nose plates (NOS) while 5 calves were separated and penned (PEN). The mean (+/- SE) interval from calving to first behavioural oestrus was 81 +/- 11 d and was significantly (P less than 0.001) shorter for PEN (43 +/- 10 d) than NOS (72 +/- 9 d) or COS cows (133 +/- 11 d). COS cows nonetheless weaned heavier (P less than 0.001) calves at 5 months. Ovarian activity determined by plasma progesterone levels greater than or equal to 1.3 ng/ml indicated that "silent ovulation" was initiated in 44% of cows by 40 +/- 6 d post-partum. The results indicate that continuous suckling or constant cow-calf interaction extend the post-partum anoestrous interval in Ethiopian Zebu cows. However, early-weaned calves or those on restricted suckling would need extra nutritional supplementation to ensure continued growth.