Poll Dorset Research Articles

Genetical influence on histological structure and chemical composition of muscular tissue in sheep

The effect of different genotypes kept in the same feeding level on microstructure and chemical composition of muscular tissue (musculus longissimus dorsi) of sheep has studied. The study aims to see how the gene combination of different breeds influences the mentioned problem. It was revealed that sheep muscular tissue obtained by crossing the North-Caucasian breeds (NC) and Texel (T) was characterized by a larger quantity of muscular fibres by 4.73 % and 10.14% (P<0.05), and a smaller diameter by 5.65 % and 18.6% (P< 0.05), a higher evaluation of marbling by 5.2 and 8.3 points, less connective tissue content by 0.8 and 1.3 absolute percentage compared to thoroughbred North-Caucasian and from crossing North-Caucasian with Poll Dorset (PD). It showed that meat obtained from crossing animals of the T?NC variant is more delicate, succulent, and has a total higher quality and consumer properties. The results of different crossing indicate the reasonability to use morphological characteristics of muscular tissue on the histological level when the quality of sheep slaughtering performance had evaluated.

Desempenho de cruzamentos entre raças deslanadas localmente adaptadas e raças especializadas para produção de carne

Existem diversas opções de genética de ovinos para os sistemas de produção, desde recursos genéticos locais (geralmente adaptados as condições ambientais) até raças especializadas. O cruzamento é uma alternativa para explorar a heterose e complementariedade entre as raças. Este estudo avaliou oito grupos genéticos obtidos a partir do cruzamento entre Santa Inês (SI), Poll Dorset (PD), Dorper (DO), East Friesian (EF), Primera (PR), and White Dorper (WD). SI e PD foram usados com raças paternas e maternas, enquanto as demais foram usadas apenas como raças paternas. Quarenta e oito cordeiros foram avaliados para altura da cernelha, perímetro torácico, comprimento do corpo e da garupa e espessura da pele, bem como peso de carcaça fria e peso dos cortes comerciais como pescoço, fralda, paleta, pernil, costela e lombo. Os animais Santa Inês demoraram mais tempo para atingir o peso de abate (30 kg) que as cruzas com Dorper e Poll Dorset. Os animais 87PDSI, 75PDSI e DOPD apresentaram maior peso dos cortes comerciais e maior rendimento de carcaça. O uso da raça Santa Inês, uma raça localmente adaptada, como raça maternal em sistema de cruzamento apresentou resultados similares ao uso de Poll Dorset, uma raça especializada para produção de carne. Esses resultados destacam a utilidade dos recursos genéticos locais em sistema de produção intensivo. Poll Dorset é a raça paterna recomendada para o cruzamento com matrizes Santa Inês em sistema de produção intensivo.

Genome-wide linkage disequilibrium and genetic diversity in five populations of Australian domestic sheep

BackgroundKnowledge of the genetic structure and overall diversity of livestock species is important to maximise the potential of genome-wide association studies and genomic prediction. Commonly used measures such as linkage disequilibrium (LD), effective population size (Ne), heterozygosity, fixation index (FST) and runs of homozygosity (ROH) are widely used and help to improve our knowledge about genetic diversity in animal populations. The development of high-density single nucleotide polymorphism (SNP) arrays and the subsequent genotyping of large numbers of animals have greatly increased the accuracy of these population-based estimates.MethodsIn this study, we used the Illumina OvineSNP50 BeadChip array to estimate and compare LD (measured by r2 and D′), Ne, heterozygosity, FST and ROH in five Australian sheep populations: three pure breeds, i.e., Merino (MER), Border Leicester (BL), Poll Dorset (PD) and two crossbred populations i.e. F1 crosses of Merino and Border Leicester (MxB) and MxB crossed to Poll Dorset (MxBxP).ResultsCompared to other livestock species, the sheep populations that were analysed in this study had low levels of LD and high levels of genetic diversity. The rate of LD decay was greater in Merino than in the other pure breeds. Over short distances (<10 kb), the levels of LD were higher in BL and PD than in MER. Similarly, BL and PD had comparatively smaller Ne than MER. Observed heterozygosity in the pure breeds ranged from 0.3 in BL to 0.38 in MER. Genetic distances between breeds were modest compared to other livestock species (highest FST = 0.063) but the genetic diversity within breeds was high. Based on ROH, two chromosomal regions showed evidence of strong recent selection.ConclusionsThis study shows that there is a large range of genome diversity in Australian sheep breeds, especially in Merino sheep. The observed range of diversity will influence the design of genome-wide association studies and the results that can be obtained from them. This knowledge will also be useful to design reference populations for genomic prediction of breeding values in sheep.Electronic supplementary materialThe online version of this article (doi:10.1186/s12711-015-0169-6) contains supplementary material, which is available to authorized users.

Genomic prediction of weight and wool traits in a multi-breed sheep population

The objective of this study was to predict the accuracy of genomic prediction for 26 traits, including weight, muscle, fat, and wool quantity and quality traits, in Australian sheep based on a large, multi-breed reference population. The reference population consisted of two research flocks, with the main breeds being Merino, Border Leicester (BL), Poll Dorset (PD), and White Suffolk (WS). The genomic estimated breeding value (GEBV) was based on GBLUP (genomic best linear unbiased prediction), applying a genomic relationship matrix calculated from the 50K Ovine SNP chip marker genotypes. The accuracy of GEBV was evaluated as the Pearson correlation coefficient between GEBV and accurate estimated breeding value based on progeny records in a set of genotyped industry animals. The accuracies of weight traits were relatively low to moderate in PD and WS breeds (0.11–0.27) and moderate to relatively high in BL and Merino (0.25–0.63). The accuracy of muscle and fat traits was moderate to relatively high across all breeds (between 0.21 and 0.55). The accuracy of GEBV of yearling and adult wool traits in Merino was, on average, high (0.33–0.75). The results showed the accuracy of genomic prediction depends on trait heritability and the effective size of the reference population, whereas the observed GEBV accuracies were more related to the breed proportions in the multi-breed reference population. No extra gain in within-breed GEBV accuracy was observed based on across breed information. More investigations are required to determine the precise effect of across-breed information on within-breed genomic prediction.

Accuracy of genotype imputation in sheep breeds

Although genomic selection offers the prospect of improving the rate of genetic gain in meat, wool and dairy sheep breeding programs, the key constraint is likely to be the cost of genotyping. Potentially, this constraint can be overcome by genotyping selection candidates for a low density (low cost) panel of SNPs with sparse genotype coverage, imputing a much higher density of SNP genotypes using a densely genotyped reference population. These imputed genotypes would then be used with a prediction equation to produce genomic estimated breeding values. In the future, it may also be desirable to impute very dense marker genotypes or even whole genome re-sequence data from moderate density SNP panels. Such a strategy could lead to an accurate prediction of genomic estimated breeding values across breeds, for example. We used genotypes from 48 640 (50K) SNPs genotyped in four sheep breeds to investigate both the accuracy of imputation of the 50K SNPs from low density SNP panels, as well as prospects for imputing very dense or whole genome re-sequence data from the 50K SNPs (by leaving out a small number of the 50K SNPs at random). Accuracy of imputation was low if the sparse panel had less than 5000 (5K) markers. Across breeds, it was clear that the accuracy of imputing from sparse marker panels to 50K was higher if the genetic diversity within a breed was lower, such that relationships among animals in that breed were higher. The accuracy of imputation from sparse genotypes to 50K genotypes was higher when the imputation was performed within breed rather than when pooling all the data, despite the fact that the pooled reference set was much larger. For Border Leicesters, Poll Dorsets and White Suffolks, 5K sparse genotypes were sufficient to impute 50K with 80% accuracy. For Merinos, the accuracy of imputing 50K from 5K was lower at 71%, despite a large number of animals with full genotypes (2215) being used as a reference. For all breeds, the relationship of individuals to the reference explained up to 64% of the variation in accuracy of imputation, demonstrating that accuracy of imputation can be increased if sires and other ancestors of the individuals to be imputed are included in the reference population. The accuracy of imputation could also be increased if pedigree information was available and was used in tracking inheritance of large chromosome segments within families. In our study, we only considered methods of imputation based on population-wide linkage disequilibrium (largely because the pedigree for some of the populations was incomplete). Finally, in the scenarios designed to mimic imputation of high density or whole genome re-sequence data from the 50K panel, the accuracy of imputation was much higher (86-96%). This is promising, suggesting that in silico genome re-sequencing is possible in sheep if a suitable pool of key ancestors is sequenced for each breed.

Diverse lamb genotypes 4. Predicting the yield of saleable meat and high value trimmed cuts from carcass measurements

To determine how current predictors of carcass and cut yield perform in the Australian lamb industry a large study was undertaken using diverse genotypes. Carcass measurements and yield data were obtained for 591 lambs representing two sexes (cryptorchids, ewes). The lambs were sired by a selection of Texel (T), Poll Dorset (PD), Border Leicester (BL) and Merino (M) rams crossed with Border Leicester×Merino (BLM) and Merino (M) ewes giving six genotypes (T×BLM, PD×BLM, T×M, PD×M, BL×M, M×M). The percentage yield of saleable meat, hindquarter, loin and a range of trimmed cuts were predicted using models based on hot carcass weight, EUROP conformation score, m. longissimus thoracis et lumborum area (LL area) in combination with three different measures of carcass fatness: (1) the depth of muscle and fat tissue from the surface of the carcass to the lateral surface of 12th rib, 110 mm from the midline (GR); (2) fat depth over the LL at the deepest part of the muscle (FATC); and (3) fat depth at the 5th rib, 110 mm from the midline (FAT5). FAT5 was identified as the most accurate and robust (stable) fat measurement for the prediction of saleable meat yield in a production system based on diverse genotypes. Using GR as a fatness measurement led to overestimation of fatness level and underestimation of yield in T sired lambs. Conformation score after carcass weight and any of the fat measurements improved ( P<0.01) the prediction of the yield of saleable meat, hindquarter, loin and all trimmed lamb cuts with the exception of the ribloin (rack). LL area added significantly ( P<0.01) to the prediction of the yield of saleable meat, hindquarter and trimmed lamb cuts, but not for the midloin and neck fillet at a constant carcass weight and fatness. Large proportions of the variation in all yields were unaccounted for, even after the inclusion of either conformation or LL area. Predictions based on carcass weight and any of the three different fat measurements were not very accurate. Although the addition of LL area as a predictor significantly ( P<0.01) increased the accuracy of the predictions the results suggest that the current description system for lamb carcases in Australia needs to be re-examined.

Diverse lamb genotypes. 3. Eating quality and the relationship between its objective measurement and sensory assessment

The effect of genotype on eating quality was evaluated on m. Longissimus thoracis et lumborum (LTL) muscle of 60 lambs. The lambs were sired by a selection of Texel (T), Poll Dorset (PD), Border Leicester (BL) and Merino (M) rams, crossed with Border Leicester x Merino (BLM) and Merino (M) ewes giving six genotypes (TxBLM, PDxBLM, TxM, PDxM, BLxM and MxM). The relationships between sensory panel assessment of eating quality attributes and pH, cooking loss and shear force were also investigated. No significant differences were observed between genotypes for panel assessment of tenderness, juiciness, aroma liking, aroma strength, flavour liking, overall acceptability and rating. MxM lambs had a significantly ( P<0.05) higher flavour strength than BLxM lambs. pH was a poor indicator of any eating quality attributes, except aroma strength ( r=0.3, P<0.05). Warner Bratzler shear force value (WB) and tenderness showed a significant ( P<0.001) negative correlation (−0.7). Tenderness, flavour and juiciness were the most important sensory attributes, explaining 86.5% of the total variation in overall acceptability.

Diverse lamb genotypes—1. Yield of saleable cuts and meat in the carcass and the prediction of yield

Carcass measurements and composition data were obtained for 591 lambs representing two sexes (307 cryptorchid males, 284 ewes). The lambs were sired by a selection of Texel (T), Poll Dorset (PD), Border Leicester (BL) and Merino (M) rams, crossed with Border Leicester × Merino (BLM) and Merino (M) ewes giving 6 genotypes (T × ELM, PD × BLM, T × M, PD × M, BL × M, M × M). m × M carcasses were significantly ( p < 0.05) leaner than all other genotypes as measured by GR at a common weight, except for ewe carcasses where they were not significantly leaner than T × M carcasses. There was no difference in GR between Texel and Poll Dorset sired carcasses. The BL × M and PD × BLM carcasses were the fattest at the 5th rib. M × M lambs produced the lightest carcasses in each sex. Genotype differences were found for conformation using the EUROP scoring system. M×M lambs had a greater proportion ( p < 0.001) of poorer scores particularly compared to PD × BLM and T × BLM carcasses. Analysis of Texel and Poll Dorset sired carcasses showed that the Texel cross had a better conformation than Poll Dorset cross amongst both sexes. BLM dams produced carcasses with a superior conformation compared to Merino dams ( p < 0.001) in both sexes. BL × M carcasses had a significantly ( p < 0.05) smaller M. longissimus thoracis et lumborum area (LL area) than other genotypes, except for M × M ewe carcasses. Texel sired ewe carcasses had a larger LL area ( p < 0.05) than those sired by Poll Dorsets, but there was no significant difference for the heavier cryptorchid carcasses. Saleable meat yield for the BL × M carcasses of both sexes was significantly less ( p < 0.001) than all other genotypes. M × M carcasses of both sexes produced similar amounts of saleable product to second cross carcasses with the T × M carcasses being superior, resulting in a significant sire breed effect. Texel sired carcasses produced more product than Poll Dorset carcasses. Year had a significant ( p < 0.05) effect on all carcass measures and saleable meat yield. Genotype had a significant ( p < 0.05) effect on the proportion of each cut except for the neck from cryptorchids and neck fillet from ewes. Texel sired genotypes had significantly ( p < 0.05) heavier weights for the hindleg and forequarter cuts than those sired by Poll Dorsets. For the BL × M and m × M genotypes, some of the hindleg cuts, such as the topside and silverside weighed less than other genotypes. The boneless loins from the Poll Dorset genotypes were the heaviest, resulting in a significant ( p < 0.05) sire breed effect, with all other genotypes being similar. Models were developed to estimate the yield of cuts and saleable meat using hot carcass weight, GR and other variables. The amount of variation in yield explained by hot carcass weight and GR ranged from r 2 = 0.06 to 0.23. Inclusion of LL area increased the r 2 values up to 0.39. Inclusion of both genotype and year significantly ( p < 0.05) improved the prediction of yield, with year contributing the most. The addition of sex had no effect on the prediction of yield.

Diverse lamb genotypes—2. Meat pH, colour and tenderness

The effect of genotype on meat ultimate pH, colour and tenderness was studied in 3 experiments involving 436 lambs. The lambs were sired by a selection of Texel (T), Poll Dorset (PD), Border Leicester (BL) and Merino (M) rams, crossed with Border Leicester × Merino (BLM) and Merino (M) ewes giving 6 genotypes (T × BLM, PD × BLM, T × M, PD × M, BLM and M × M). In experiment 1, pH data were obtained for 4 muscles ( M. Semimembranosus (SM), M. Biceps femoris M. Semitendinosus and M. Longissimius thoracis et lumborum (LL)) from 198 carcasses representing two sexes (104 cryptorchid males, 94 ewes). There were significant differences for pH between genotypes in both sex groups. BL × M and M × M lambs tended to have higher pH values than the other genotypes. In experiment 2, meat pH, colour using a chromameter, and tenderness data were obtained for 186 lambs representing two sexes (101 cryptorchid males, 85 ewes). There were few significant differences between genotypes for the various meat quality traits amongst the ewes. The PD × BLM ewes had a significantly lower ( p < 0.05) pH than the BL × M ewes for the LL and SM muscles. The BL × M crypt orchids had a higher LL muscle pH ( p < 0.05) than the PD × BLM cryptorchids with other genotypes being intermediate. There were no significant differences between the genotypes for muscle shear force values. Within experiment 2, LL samples were taken from an additional 52 cryptorchid carcasses these being from 3 specific Poll Dorset sires (experiment 3). One of these sires (sire 3) was suspected of carrying a gene for increased muscling. Sire had a significant effect ( p < 0.05) on shear force values, cooking loss and L ∗ colour values, but not a ∗ or b ∗ colour values or pH. Sire 3 progeny had significantly ( p < 0.001) tougher LL muscles than those from the other 2 sires. Sire 3 also had the lowest L ∗ values, but was intermediate for cooking loss. There was no significant sire effect on LL area at the same carcass weight, but boneless loins from the progeny of Sire 3 were significantly ( p < 0.05) heavier. In a fourth experiment, meat colour was measured at three sites (LL, diaphragm and M. Obliquus externus abdominis) on 86 cryptorchid carcasses 24 hr post-mortem. There was little association between L ∗, a ∗ and b ∗ values measured at the different sites.

Scrapie-free Merino and Poll Dorset sheep from Australia and New Zealand have normal frequencies of scrapie-susceptible PrP genotypes.

As natural scrapie occurs only in sheep of specific PrP genotypes, one proposed aetiology was that scrapie is simply a genetic disease. However, Cheviot and Suffolk sheep of scrapie-susceptible genotypes are found in Australia and New Zealand, both generally accepted to be scrapie-free countries. A study of more common Australia and New Zealand sheep breeds (Merinos and Poll Dorsets) was carried out in order to obtain more generally applicable estimates of Australia and New Zealand sheep PrP genotype frequencies. We have confirmed that animals of highly susceptible PrP genotypes are found in Australia and New Zealand. Interestingly, the Poll Dorset sheep, although born in New Zealand, were brought to the UK as young adult animals and subsequently remained free of clinical scrapie despite 21% of the sheep having scrapie-susceptible genotypes. These results have implications for the genetic control of occurrence of the equivalent human diseases.

Differences in composition, muscularity, muscle:bone ratio and cut dimensions between six lamb genotypes

Carcass measurements and composition data were obtained for 198 lambs representing two sexes (104 cryptorchids, 94 ewes). Dorsal images of 166 of the carcasses were obtained on the slaughter chain using a video camera. The lambs were sired by a selection of Poll Dorset (PD), Texel (T), Border Leicester (BL) and Merino (M) rams, born to Border Leicester × Merino (BLM) and Merino (M) ewes giving 6 genotypes (PD × BLM, T × BLM, PD × M, T × M, BL × M, M × M). From the right hindleg and chump, the following muscles were dissected and weighed: semimembranosus, adductor femoris, semitendinosus, biceps femoris, and quadriceps femoris. The femur was weighed, the length measured and a muscularity value calculated as described by Purchas, et al. (1991, Meat Sci., 30, 181). Merino cryptorchid lambs were significantly ( P < 0.05) leaner, as measured by GR tissue depth (for explanation, see MATERIALS AND METHODS) adjusted to a mean carcass weight of 24.2 kg, than BL × M lambs, but there was no difference between genotypes within the ewe group (mean carcass weight of 17.1 kg). Genotype differences were found for conformation using the EUROP scoring system. Merino lambs had a greater proportion ( P < 0.001) of poorer scores, particularly compared to PD × BLM and T × BLM carcasses. The BL × M carcasses had a significantly ( P < 0.05) smaller m. longissimus thoracis et lumborum area than other genotypes with no difference between carcasses of T and PD sires. Muscularity values for the BL × M and M lambs were significantly ( P < 0.05) lower than the other crosses but not different from each other. Carcasses from T sires had significantly ( P < 0.05) higher muscularity values than those from PD sires. A negative association ( r = −0.56) was found between EUROP scores and muscularity when carcass differences were adjusted for, but significant differences between genotypes for muscularity were not necessarily carried through to differences in EUROP conformation score. BL × M carcasses had the lowest muscle:bone ratio and T × M the highest with M carcasses having similar ratios to carcasses from PD-sired lambs. Only small differences were found between genotypes for composition of the hindleg, the exception being BL × M carcasses of both sexes which were significantly ( P < 0.05) fatter than T × BLM, T × M and PD × M carcasses. Carcasses from T sires had significantly ( P < 0.05) more muscle in the hindleg than carcasses from PD sires, with the differences being greater in the heavier cryptorchids (1.8%) than the ewes (1.1%). There was no consistent effect of genotype on the cross-sectional areas of the round and topside cuts within either sex. Differences between genotypes for the proportion of the carcass attributed to the round were small and only for BL × M ewe carcasses was this cut significantly lighter ( P < 0.05) than from all other genotypes, except the PD × BLM carcasses. This trend was similar for the topside and silverside cuts. A moderate correlation ( r = 0.46; P < 0.001) was found between muscularity values determined by dissection and those predicted using the equations of Hopkins et al. (1996, Proc. Aust. Soc. Anim. Prod., 21, 181) based on carcass width measurements taken from video images.

Fibre metrology and physical characteristics of lambskins from large Merino and crossbred lambs

Summary. Two hundred and eighty-three lambskins were derived from the progeny of Merino (M), Texel (T), Poll Dorset (PD) and Border Leicester (BL) sires individually mated to Merino and Border Leicester × Merino (BLM) ewes giving 6 genotypes (M × M, T × M, PD × M, BL × M, T × BLM and PD × BLM). The lambs were shorn at 14 weeks and slaughtered (about 20 weeks later) at minimum carcass weights of 18 and 22 kg for ewe and cryptorchid sexes respectively. The ewe lambskins were fellmongered and the pelts processed to nappa, while the cryptorchids were processed to wool-on tannage. Comparative information on fibre metrology, skin mensuration, physical strength of the leather and commercial utility was collected. Skins from all genotypes had a surface area &gt;0.75 m2 and satisfactory physical properties. Pinhole was common amongst all genotypes, whereas ribbyness was largely a Merino trait. Ribbyness was associated with more frequent scarring from shearing damage and processing, indicating that Merino skins are least desirable for production of lamb nappa. The fine diameter and low medullation of Merino wool differed from all the other genotypes whose wool can be classed as industrial. After trimming to a 25 mm nap, lambskins of all genotypes were suitable for wool-on leather products. Skins from well managed lambs of all genotypes would be suitable as wool-on skins.

The association of a codon 136 PrP gene variant with the occurrence of natural scrapie.

Incidence of both experimental and natural scrapie in sheep has been associated with polymorphisms of the PrP gene. In case/control studies the PrP allele which encodes valine at codon 136 (Val136) is found in 96-100% of naturally infected scrapie sheep of Shetland, Scottish Halfbred and Blue du Maine breeds. In contrast, in healthy animals from the same flocks, the most frequent allele encodes Ala136 (91-100% of sheep). However Val136 does not correlate with incidence of scrapie in two other flocks--Poll Dorsets and Suffolks--and there may therefore be breed differences in PrP genotypes affected by scrapie.

Effects of season and testosterone treatment on gonadotrophin secretion and pituitary responsiveness to gonadotrophin-releasing hormone in castrated Romney and Poll Dorset rams.

In castrated rams (Romney and Poll Dorset, n = 8 for each breed), inhibition by testosterone treatment (administered via Silastic capsules) of luteinizing hormone (LH) pulse frequency, basal and mean LH concentrations, mean follicle-stimulating hormone (FSH) concentration, and the peak and total LH responses to exogenous gonadotrophin-releasing hormone (GnRH) were significantly (P less than 0.01) greater during the nonbreeding than during the breeding season. Poll Dorset rams were less sensitive to testosterone treatment than Romney rams. In rams not receiving testosterone treatment, LH pulse frequency was significantly (P less than 0.05) lower during the nonbreeding season than during the breeding season in the Romneys (15.8 +/- 0.9 versus 12.0 +/- 0.4 pulses in 8 h), but not in the Poll Dorsets (13.6 +/- 1.2 versus 12.8 +/- 0.8 pulses in 8 h). It is concluded that, in rams, season influences gonadotrophin secretion through a steroid-independent effect (directly on hypothalamic GnRH secretion) and a steroid-dependent effect (indirectly on the sensitivity of the hypothalamo-pituitary axis to the negative feedback of testosterone). The magnitude of these effects appears to be related to the seasonality of the breed.

Estimating carcass weight from liveweight in lambs

Dressing percentage of 922 second-cross lambs rose as liveweight and fatness increased. Lambs weighing 35 kg and sired by Poll Dorset (PD) and Suffolk rams had dressing percentages of 44.7 and 43.4%, respectively. For PD sired lambs weighing 35 kg and fatscore 2 and 4, the dressing percentage increased from 44 to 49.7%, respectively. There was no significant difference between ewe and wether PD sired lambs for carcass weight/liveweight relationships with both groups having similar levels of fatness. Carpetwool lambs (114) had lower dressing percentages than second cross lambs. In contrast to second cross lambs the dressing percentage of carpetwool lambs decreased with increases in liveweight.

Seasonality of ovulation and estrus, and the ram effect in poll dorset ewes

The effects of month on the proportion of Poll Dorset ewes expressing estrus and ovulating and on their ovulation rate when continually exposed to vasectomised rams and the effects of isolating the ewes from rams in winter/early spring were examined during 15 months in New South Wales, Australia. The percentage of ewes ovulating and their ovulation rate varied from 23% and 1.10 in November to an average of 99% and 1.85 in April and June, and the proportion of ewes expressing estrus followed a similar trend. Some ewes (6.8%) ovulated throughout the 15 months, and the average breeding season was 294 (SE = 6.1) days. Isolating ewes from rams in late winter/early spring significantly decreased the proportion of ewes ovulating from September to November, increased the proportion in December, but did not significantly alter ovulation rate. The variability in reproductive measures during spring offers scope for selection; with the ram effect, improvements in spring joining results from Dorset ewes are possible.

Genetic distance between the Australian Merino and the Poll Dorset Sheep

SUMMARYMerinos (189) and Poll Dorsets (106) were compared for genetic variation at 30 loci for blood proteins. ‘Malic enzyme’ and NADH diaphorase I polymorphism occur in Merinos but not in Poll Dorsets, whereas both breeds are polymorphic for haemoglobin, erythrocyte X-protein, serum esterase, catalase and transferrin, although the breeds differ in the presence or absence of certain rare transferrin variants. Poll Dorsets but not Merinos have genetic variation of erythrocyte pyruvate kinase at low gene frequencies; Merinos but not Poll Dorsets have genetic variation of two erythrocyte Gly-Leu peptidases, glucosephosphate isomerase, superoxide dismutase, and NADH diaphorase II, all at low gene frequencies (P&lt; 0·05).Using Masatoshi Nei's (1972, 1976) standard genetic distance, over all 30 loci, to calculate the time of divergence of the two breeds, we obtainedt= 69700 years – whereas sheep are believed to have been domesticated by man for not more than 11000 years, and ancestors of the British breeds and of the Merino have probably not been separated for more than 2000 years. Several possible explanations for this discrepancy are discussed, including the accuracy of the coefficient of codon change (α), changes in population size and structure, selection, and additional hybridization in the ancestry of the Merino.

Production of lamb with poly-unsaturated depot fats (from feeding a dietary supplement of formaldehyde-treated ground sunflower seed)

Abstract Eight Coopworth and eight Poll Dorset ewe lambs were used in two experiments respectively to determine how quickly the animals adapted to feedlot from grass pasture, and warmed to being fed a supplement of ground sunflower seed treated with formaldehyde so that the oil (70% linoleic acid) resisted biohydrogenation in the rumen. It was found that the level of linoleic acid in the perirenal fat of Coopworth lambs increased from 3 to 14% in a period of 40 days when they consumed an average of 100 g lipid/head daily and that of the Poll Dorset lambs increased from 4 to 25% in 30 days. Coopworths were fed 60% effectively protected supplement and Poll Dorsets 80% protected. Tasting tests showed that meat containing elevated levels of linoleic acid had a bland, pork-like flavour and a sweet, lingering odour-note on cooking. Only at the highest levels of poly-unsaturation ( > 20 %) did the meat have an oily taste; this was particularly apparent with the hot joint.

TRAUMATIC EPIDIDYMITIS OF DORSET HORN AND POLL DORSET RAMS

Australian Veterinary JournalVolume 43, Issue 3 p. 99-101 TRAUMATIC EPIDIDYMITIS OF DORSET HORN AND POLL DORSET RAMS M. F. Pulsford B.V.Sc., H.D.A., M. F. Pulsford B.V.Sc., H.D.A. *Department of Agruculture Adelaide, South AustraliaSearch for more papers by this authorB. C. Eastick B.V.Sc., R.D.A., B. C. Eastick B.V.Sc., R.D.A. †Bright Street, Wilaston, South AustraliaSearch for more papers by this authorK. H. Clapp M.Sc., K. H. Clapp M.Sc. ‡Institute of Medical & Veterinary science, Adelaide, South Australia, now Queen Elizabeth Hospital, Wood-ville South AustraliaSearch for more papers by this authorR. Roterts R.D.A., R. Roterts R.D.A. *Department of Agruculture Adelaide, South AustraliaSearch for more papers by this author M. F. Pulsford B.V.Sc., H.D.A., M. F. Pulsford B.V.Sc., H.D.A. *Department of Agruculture Adelaide, South AustraliaSearch for more papers by this authorB. C. Eastick B.V.Sc., R.D.A., B. C. Eastick B.V.Sc., R.D.A. †Bright Street, Wilaston, South AustraliaSearch for more papers by this authorK. H. Clapp M.Sc., K. H. Clapp M.Sc. ‡Institute of Medical & Veterinary science, Adelaide, South Australia, now Queen Elizabeth Hospital, Wood-ville South AustraliaSearch for more papers by this authorR. Roterts R.D.A., R. Roterts R.D.A. *Department of Agruculture Adelaide, South AustraliaSearch for more papers by this author First published: March 1967 https://doi.org/10.1111/j.1751-0813.1967.tb08893.xCitations: 3 AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume43, Issue3March 1967Pages 99-101 RelatedInformation