The inheritance of liability to epistaxis in the southern African Thoroughbred

This study was carried out to estimate the heritability of liability to epistaxis in the southern African Thoroughbred population. Data of all horses that suffered epistaxis while racing in southern Africa and Mauritius from 1986 to 2002 and involving 1252 bleeders were analysed. Pedigree data covering the period 1960-1986 was used as required to calculate the incidence of bleeding amongst ancestors of the post-1986 era. Only pedigrees of horses that raced were included in this study as it was not possible to predict whether non-runners would have bled had they raced. Consequently all non-runners and also those that raced overseas in countries where bleeding occurrence was not recorded, were excluded. The heritability of liability method as described by Falconer (1989) was used to estimate the relative importance of heredity and environment. For the period investigated, the population incidence for epistaxis in southern African horses was 2.1%. The estimation of heritability of liability showed that 1st-degree relatives had a figure of 55.4%. Second-degree relatives had a heritability of 41.3% and 3rd-degree relatives came in at 30.4%. The heritability of liability shown in this study could be regarded as being at the lower end of the range but could be appreciably higher. The data depict horses that bled almost exclusively on race days, as only a small percentage (approximately 5%) was reported as having bled during exercise. Accordingly, the full extent of epistaxis amongst racing Thoroughbreds in southern Africa is difficult to gauge. It is clear that epistaxis in the racing Thoroughbred has a strong genetic basis. It is suggested that horses showing frankbleeding from the nostrils after racing or exercise be suspended, and not used for breeding purposes. This should result in relatively fast progress being made towards eradicating this costly scourge of the modern Thoroughbred racehorse.

Epistaxis related to exercise-induced pulmonary haemorrhage in south African Thoroughbreds

This study investigated if environmental factors had an effect on the incidence of epistaxis related to exercise-induced pulmonary haemorrhage (EIPH) among racehorses in southern Africa. Data covering the period 1986-2001 and involving 778 532 race runs were analysed. This included the following information: date of race, age, sex, name of breeder, trainer, distance, jockey, state of going, weight carried, racing centre and altitude. Veterinarians employed by the Jockey Club suspended officially entered horses that presented with epistaxis (frank bleeding from the nostrils) after racing. On-course endoscopy is not performed as a standard practice at any southern African racetrack. Epistaxis was identified in 1287 horses (0.165%). More horses presented with EIPH-related epistaxis (a) at sea level, (b) from May to October, (c) when older (> 3 years), (d) after 1995, (e) on Fridays and Sundays, and (f) more in geldings than in mares or entire males. No association could be established between epistaxis and breeder, trainer, distance run, jockey, state of going and weight carried. It is concluded that the frequency of EIPH-related epistaxis is associated with altitude, winter and spring, sex and age. It is suggested that racing at lower altitudes may increase the probability of exercise-induced pulmonary haemorrhage.

Genetic variances for liveweight and fleece traits in Merino, Dohne Merino and South African Meat Merino sheep

(Co)variance estimates for weaning weight, yearling liveweight, clean fleece weight and fibre diameter at yearling age were obtained for Merino, Dohne Merino and South African Meat Merino flocks maintained on the same property. Direct additive genetic variances for weaning weight [expressed as a ratio of the total phenotypic variance (h2, direct heritability)] were estimated at 0.15 for Merinos, 0.21 for Dohne Merinos and 0.32 for South African Meat Merinos. Corresponding maternal variance ratios (m2, including direct maternal variance and permanent environmental maternal variance) were estimated at 0.15, 0.30 and 0.24, respectively. The correlation between direct and maternal variance ratios was high and negative in Dohne Merinos and South African Meat Merinos (–0.72 and –0.53, respectively). Direct heritability estimates for yearling liveweight were 0.30 for Merinos, 0.33 for Dohne Merinos and 0.45 for South African Meat Merinos. Corresponding maternal variance ratios were only significant in the latter 2 breeds, amounting to 0.13 in Dohne Merinos and 0.12 in South African Meat Merinos. For yearling clean fleece weight, h2 and m2 were estimated at 0.28 and 0.12, respectively, for both Merinos and Dohne Merinos. In the case of South African Meat Merinos, only the h2 estimate was significant, at 0.68. Maternal variance ratios for yearling fibre diameter were not significant in any of the breeds, while h2 ranged from 0.58 in Merinos to 0.75 in South African Meat Merinos. Selection progress for yearling traits seems likely in all breeds, depending on the breeding objectives being strived for.

A comparative assessment of Dorper sheep in different production environments and systems

Performance of Dorper sheep was compared to other breeds in pure and cross-breeding evaluations under different production systems. The number of ewes lambed per ewe joint (E(L)/E(J)) varied for the Dorper from 0.68 to 0.91 (average 0.81) and for other breeds and crosses from 0.65 to 0.91 (average 0.82). Average litter size (L(B)/lambing) varied from 1.02 to 1.52 (average 1.28) and from 1.02 to 1.70 (average 1.30) for the two groups, respectively. In general, the Afrino and Finnish composite lines were more prolific than the Dorper. Post-weaning mortality rates in Kenya were high (49%) among Dorper lambs compared to the local Red Maaisai breed, owing to a high susceptibility to gastrointestinal parasites. Average weaning weights (WW) (100 days) were 12.4% heavier in the Dorper than in the breeds it was compared to, but 31.7% heavier than the woolled breeds. Total WW and efficiency of Dorper and Dorper crosses were higher than Merino, Afrino, Döhne merino, South African Mutton Merino, but lower than in Finnish Landrace composite lines. Both Dorper and Dorper cross-breeds reached target slaughter weight of approx. 40kg earlier than Merino, Afrino, Suffolk and Ile de France crosses. Average daily gain to slaughter was 44% higher in the Dorper than the average of the groups it was compared to. It is concluded that the Dorper was superior in reproductive and growth traits to woolled and other indigenous breeds. However, there is a lack of information on the performance of the Dorper in cross-breeding systems.

Animal x testing environment interaction on postweaning liveweight gains of young bulls

Postweaning liveweight gain records of 1610 young bulls obtained both in feedlot and under pasture were used to estimate (co)variance components using a multivariate restricted maximum likelihood analysis. The pedigree file included 3477 animals. Heritability estimates for liveweights and gain in both environments correspond to most previously reported estimates. The genetic correlation of gain between the 2 environments was -0·12, suggesting a large genotype testing environment interaction and re-ranking of animal breeding values across environments. Results of this analysis suggest the need for environment-specific breeding values for postweaning gain.

The effect of melatonin treatment on reproductive efficiency in an accelerated lambing system

A trial, which involved 917 ewes, was conducted to examine whether reproductive traits could be improved in an accelerated lambing system with 3 lambing seasons per year by subcutaneous melatonin treatment. Fertility (ewes lambed per ewes put to the ram), litter size and the interval between melatonin application date and lambing date were not affected by treatment. However, in the first lambing season (15 February to 15 March), fertility was 16% higher in melatonin-treated ewes compared to untreated ewes (P > 0.05). Season or month of application therefore seems to be an important factor with regard to the response. It is concluded that melatonin treatment in accelerated lambing systems is further complicated by the presence of pregnant and lactating ewes, which makes the value of commercial use thereof doubtful.

The influence of body mass and condition on ovulation rate in polyandroalbumin immunized S A mutton Merino ewes

Two groups of 40 S A Mutton merino ewes were used to determine the effect of body mass and condition score on the response of immunisation against androstenedione. The effect of immunisation was significant (P less than 0.05) on ovulation rate (1.64 for non-immunised and 2.08 for immunised ewes) and higher body mass and condition scores acted complimentary to the effect of immunisation. The ovulation rate in control ewes was more closely related to condition score (r = 0.511) and body mass (r = 0.600) at the end of the experimental period than in the immunised ewe group (r = 0.302 and 0.235).