Dorper Breed Research Articles

Ultrasonographic Fetal Sex Identification in Pregnant Sheep Derived from Natural Mating and Embryo Transfer

The objective of this study was to identify the migration period of the genital tubercle and the period of visualization of external genital structures in fetuses of the Dorper breed of sheep derived from natural mating and from fresh, frozen and vitrified embryo transfer. Transrectal ultrasound was performed using a double-frequency linear transducer (6.0 and 8.0 MHz) to monitor 130 ewe fetuses distributed in the four treatments regarding embryo origin. The accuracy of the ultrasound was 100% in this experiment. The fetuses originated from controlled natural mating (NM) and from fresh (FrE), frozen (FE) and vitrified (VE) embryo transfer, with embryos collected 7 days after breeding. Migration of the genital tubercle occurred earlier (P<0.05) in NM (42.21+/-2.86 days) than in FrE (43.98+/-3.00 days), FE (44.97+/-1.83 days) and VE (44.58+/-1.97 days). Visualization of the scrotal bag, prepuce and vulva occurred, respectively, earlier (P<0.05) in NM (45.22+/-1.25, 45.95+/-1.53 and 45.01+/-1.03 days) than in FrE (48.91+/-1.92, 48.52+/-1.41 and 47.41+/-1.41 days), FE (49.97+/-1.08, 49.18+/-2.00 and 47.64+/-1.82 days) and VE (50.12+/-1.66, 49.27+/-1.61 and 47.93+/-1.92 days). The results show that fetal sexing can be accomplished from the 50th day onward in fetuses produced by natural mating and from the 55th day onward in fetuses derived from fresh, frozen and vitrified embryos. It can also be concluded that real-time ultrasonography is a reliable tool for fetal sex determination in sheep taking into account both the location of the genital tubercle and the identification of external genital structures.

Ulcerative balanitis and vulvitis of Dorper sheep in South Africa : a study on its aetiology and clinical features

Ovine ulcerative balanitis and vulvitis in sheep of the Dorper breed has been observed in South Africa since 1979. Its aetiology has not been conclusively resolved, and there is some discrepancy in descriptions of its clinical features. In order to identify the pathogenic micro-organism/s that contribute to the occurrence of the disease, the microflora in the genital tracts of both clinically healthy and affected sheep were isolated and compared. Bacteriological examination of materials from affected and unaffected sheep resulted in the isolation of Arcanobacterium pyogenes from 44.2% and 17.2% of them respectively. This difference is statistically significant (P < 0.01). Seventy-four per cent of the isolates originated from severe clinical cases. Mycoplasmas were isolated from 49.3% of 116 clinically normal sheep and 78.2% of 104 affected sheep. There were significant differences in their rates of isolation in clinical groups (P < 0.05). Of all the mycoplasma isolates, Mycoplasma mycoides mycoides large colony variant (MmmLC) was isolated from 61.5% of clinically diseased sheep while 6.0% of the isolates were from apparently healthy animals (P < 0.05). The study threw light on the prevalence of mycoplasmas in the genital tract of apparently healthy sheep and, at the same time the identity of the mycoplasma pathogen associated with ulcerative balanitis and vulvitis was revealed. The findings of this investigation therefore confirmed the involvement of mycoplasma, particularly that of MmmLC large colony, in the disease in Dorper sheep in South Africa, and it was concluded that this microorganism is an important pathogen of balanitis and vulvitis in them. The study furthermore demonstrated a probable synergism between A. pyogenes and MmmLC. Finding these 2 organisms together occurred 53.4 times more frequently in the affected sheep than in the unaffected, which emphasises the probable multifactorial nature of the disease. The association between age and the presence of clinical signs was statistically significant. It was found that young sheep were more likely to have lesions than adult sheep. Clinical observations showed that the typical ulceration appears to be confined to the glans penis and lips of the vulva; no ulceration was observed on the shaft of the penis and prepuce or vaginal vestibule. In uncomplicated cases inflammation of the prepuce and vaginal vestibule is not a regular feature of the disease. Therefore the names ulcerative balanitis and vulvitis most accurately describe the nature of the disease in South Africa.

Voluntary intake of maize stover supplemented by urea lick in dorper and local Malawi sheep.

Ten Dorper (16.0 to 37.0 kg) and Local (12.0 to 28.5kg) rams were used to determine the voluntary intake, digestibility, nitrogen retention of maize stover and live weight change. Dietary treatments were maize stover offered to meet the requirement for maintenance with urea lick, 1.5 or 2 times maintenance with urea lick. Stover stems had higher fibre content (78.5 % NDF) and lower content of nitrogen (0.34 %) and metabolizable energy than leaves. The sheep consumed leaves and rejected all stems. Intake of maize stover increased (P < 0.001) with increasing level of feed offered above maintenance. Sheep offered stover at 1.5 times maintenance had highest intake of stover (24.7 g/kg body weight) and nitrogen (1.5 % feed intake). There were no differences in intake between levels higher than maintenance. Digestibility was highest (P < 0.01) for sheep offered stover at 1.5 times maintenance. Higher nitrogen intake of stover diet increased digestibility and intake of dry matter owing to the stimulation of microbial activity. Liveweight gain was higher (P < 0.05) for sheep offered stover at 1.5 times maintenance (52 g/day) reflecting high intake, while sheep offered stover at maintenance lost weight (-105 g/day). Metabolizable energy intake increased with increasing total dry matter intake. Nitrogen balance was positive for diets with nitrogen intake of more than 1 % of feed intake. Nitrogen retention increased with high nitrogen intake. Breeds did not differ in voluntary intake. Dorper sheep had higher digestibility, higher nitrogen retention and gained more weight than local sheep (P < 0.001). It was concluded that for sheep fed low quality maize stover, voluntary intake, digestibility, nitrogen retention and liveweight gain increased by offering greater amounts of stover with high nitrogen intake (1 % feed intake). Differences in digestibility suggest that the Dorper breed could be a valuable resource for sheep production even in areas where low quality maize stover limit the use of European breeds.UNISWA Jnl of Agric Vol 8 1999: pp 44-49

Breed and environmental influences on weaner lamb production in Zimbabwe

Performance of the Dorper and Mutton Merino breeds and their crosses was assessed from 1,305 ewe and 1,453 lamb records from six lambing seasons. Dorper and Mutton Merino were mated in all combinations under an accelerated lambing system and crossbred females were mated to Suffolk rams. The Dorper and Mutton Merino breeds were not significantly different for fertility, pre-weaning lamb growth and survival. Suffolk sired lambs from crossbred ewes grew rapidly and were heaviest at birth and at weaning. They also survived better than lambs from the other breeding groups and this contributed to the higher weaning rate (P less than 0.05) in crossbred ewes. Weight of weaned lambs per ewe exposed to the ram per season was 12% higher (P less than 0.05) in the Dorper than the Mutton Merino ewes. However lifetime production was 28% higher (P less than 0.01) in Mutton Merino ewes due to significantly superior longevity. Crossbred ewes were highly productive. Individual heterosis was not significant but estimates were positive for most traits. Growth rate and survival of lambs increased as age of dam increased to 48 and 40 months respectively. Lambs born to previously non-lactating ewes were heavier and survived better than lambs born to ewes lactating in the previous season. Lambs born and reared as singles were 25% heavier at birth (P less than 0.001) and 52% heavier at weaning (P less than 0.001) than those born and reared as twins. Male lambs grew faster and were 7% heavier at weaning than females (P less than 0.001).

Influence of Municipal Abattoir Conditions and Animal-related Factors on Avoidance-related Behaviour, Bleeding Times at Slaughter and the Quality of Lamb Meat.

The objective of this study was to determine the effect of municipal abattoir conditions and animal factors on avoidance-related behaviour (AB) of sheep at slaughter, bleeding times (BT) and mutton quality. The behaviour of 66 castrates and 19 ewes of different age categories was observed at three stages of slaughter. Higher behaviour scores indicated higher levels of AB. Time intervals between the start of blood flow and the time the flow changed from a constant stream into drips were recorded as BT. Thirty two meat samples were obtained to measure quality variables. These were colour (L*, a* and b*), pH24, temperature, cooking loss (CL) and tenderness. Correlations were determined between BT and meat quality variables. Animal behaviour at slaughter differed with breed, gender and age group. Avoidance behaviour was higher in the Dorper breed than in both the Merino breed and their crosses. It was also higher in younger (<10 months) lambs than in older sheep. Castrates were more aggressive or in panic than ewes. Castrates had longer (72.6±0.53 s) BT than the ewes (63.6±2.82 s). Ewes had higher CL (39.8±1.04%) values than castrates (35.1±0.95%). Meat from castrates was tougher (32.6±1.95 N) than the meat from ewes (24.3±1.16 N). There were no significant correlations obtained between BT and meat quality variables. It can therefore be concluded that abattoir conditions, breed, age and gender had an effect on AB at slaughter. Gender had an effect on BT and mutton quality.