Border Leicester Research Articles

Dual energy X-ray absorptiometry (DXA) can be used to predict live animal and whole carcass composition of sheep

An Hologic QDR4500A dual energy X-ray absorptiometer (DXA) was used to measure live body composition in 15 second-cross wether lambs ((Border Leicester×Merino)×Poll Dorset) aged 6–8 months (17–50kg) and 13 mature ewes (composite terminal sire line based largely on Poll Dorset, White Suffolk and Texel breeds) (44–71kg). After slaughter, DXA scans were also performed on the whole carcasses. Values determined by DXA including total tissue mass (TTM), lean tissue mass (LTM), fat tissue mass (FTM) and bone mineral content (BMC) for the half carcass were evaluated by comparison with chemically determined composition. In the case of BMC the relationship was with chemically determined ash content. Live weight and chemically determined lean, fat and ash were strongly related to DXA-derived values for whole body TTM, LTM, FTM and BMC, respectively (R2=0.999, 0.988, 0.980 and 0.977, respectively). Carcass weight and chemically determined lean, fat and ash were strongly related to DXA-derived values for carcass TTM, LTM, FTM and BMC, respectively (R2=0.998, 0.984, 0.986 and 0.906, respectively). However, because DXA estimates were different from chemically determined values in this sample of carcasses, they needed to be adjusted with the use of appropriate regression equations to correct the in-built algorithms used to predict human body composition. These data demonstrate the efficacy of DXA as a non-destructive method for determining the composition of the whole body and carcasses of sheep.

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.

Validation of a short-term methane measurement using portable static chambers to estimate daily methane production in sheep

There is increasing demand for technologies to measure CH4 production (DMP) of ruminant livestock in inventory and mitigation research. Studies of genetic variation among animals in DMP require these emissions to be measured on thousands of animals which cannot be managed using traditional chamber studies. However, short-term emission measures have been reported to correlate well with DMP. Our study was conducted to determine the usefulness of 1 and 2h emission measures using chambers in predicting DMP. In our first experiment, Merino sheep (n=13) were measured for DMP over 22h using open circuit chambers. On two subsequent days, after overnight fasts, sheep were offered feed for 1h before return to the chambers for 2h and their CH4 production determined. DMP estimated from 22h measurements correlated moderately well with 2h emission measures (r2 of 0.42–0.48) and 1h measures (r2 of 0.39–0.43). In our second experiment, portable static chambers were designed for 1 and 2h CH4 emission measurements. The portable static chambers retained 98–99% of an injected tracer gas after 2h showing that gas leakage from the chamber was very low. With a sheep inside a portable static chamber, CO2 concentration reached 2.2×103ppmv after 2h, but sheep showed no discomfort and the partial pressure of O2 in their blood remained above 97% (i.e., safe for animal health). Our third experiment was to validate use of short-term emission measures from portable static chambers as predictors of DMP. Crossbred Dorset and Border Leicester and Merino ewes (n=40, LW 54±10.9kg) were measured for three 22h sessions in open circuit chambers, after which they were measured for 1h in portable static chambers. Open circuit chamber measurements had high repeatability (i.e., 0.88) and, excluding one sheep with inconsistent eating patterns, the correlation (r) between 1h portable static chamber measurements and average emissions in the open circuit chambers was 0.71. We conclude that 1 and 2h measures of CH4 output in portable static chambers are useful for determining genetic differences in CH4 production in groups of ruminants.This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

Ovelhas esquiladas e não esquiladas durante a gestação no Sul do Brasil: efeito na condição corporal e no peso ao nascer dos cordeiros

No presente trabalho, foi testado o efeito da esquila pré-parto na condição corporal (BCS), no peso de cordeiros ao nascer e no seu desenvolvimento. O grupo experimental foi constituído de 64 ovelhas com 3 anos, cruzas Border Leicester x Texel (49-54 kg), encarneiradas em março, foram divididas, aos 74 dias de gestação, em dois grupos de 32 cada. As ovelhas foram mantidas em campo nativo, 5 ovelhas/ha, com disponibilidade aproximada de 800 kg/ha. Aos 74 dias de gestação, um grupo foi esquilado (S) e o outro foi mantido não esquilado (US). A BCS dos dois grupos foi avaliada no início do experimento (P74), P108 e P135 dias de gestação e aos 15 e 24 dias da lactação. Foi também coletado o peso dos cordeiros ao nascer e a duas e três semanas da lactação. Observou-se uma redução na BCS média das ovelhas, de ambos os grupos, durante a gestação e lactação. O grupo S experimentou uma redução significativamente mais severa (P < 0,05) na BCS. A BCS média desse grupo decresceu de 3,3 no dia P74 para 1,79 e 1,22 nos dias P135 e L24. No mesmo período, os valores da BCS média do grupo US foram de 3,11, 2,19 e 1,21. Ao nascer, o peso dos cordeiros, de ovelhas S foi 0,71 kg maior (P < 0,05) do que o dos cordeiros de ovelhas do grupo US. Não houve diferença entre o ganho de peso dos cordeiros dos dois grupos medido a duas e três semanas de vida. O aumento no peso ao nascer dos cordeiros produzido pela esquila das ovelhas durante a gestação, descrito nesse trabalho, poderá reduzir a mortalidade perinatal de cordeiros, especialmente em anos com escassez de pastagem que pode resultar em uma BCS crítica durante a gestação. Os resultados sugerem também que atenção especial deverá ser dada a BCS das ovelhas durante a gestação, prática que não é comum no Sul do Brasil.

Preliminary estimates of genetic parameters for carcass and meat quality traits in Australian sheep

Using performance from progeny born in 2007 and 2008 generated by the Information Nucleus program of the Cooperative Research Centre for Sheep Industry Innovation, preliminary estimates of heritability were obtained for a range of novel carcass and meat attributes of lamb relevant to consumers, including carcass characteristics, meat quality and nutritional value of lamb. Phenotypic and genetic correlations of live animal traits with carcass composition and meat quality traits were also estimated. The data were from progeny located at eight sites, sired by 183 rams from Merino, maternal and terminal meat breeds and were representative of the Merino, Border Leicester × Merino, Terminal × Merino and Terminal × Border Leicester-Merino production types of the Australian sheep industry. Data were available from 7176 lambs for weaning weight, 6771 lambs for ultrasound scanning and 4110 lambs for slaughter traits. For the novel meat quality traits, generally moderate to high heritability estimates were obtained for meat quality measures of shear force (0.27 aged 1 day, 0.38 aged 5 days), intramuscular fat (0.39), retail meat colour (range of 0.09 to 0.44) and myoglobin content (0.22). The nutritional value traits of omega-3 fatty acids and iron and zinc contents tended to have low to moderate heritabilities (0.11–0.37), although these were based on fewer records. Fresh meat colour traits were of low to moderate heritability (0.06–0.21) whereas measures of meat pH were of low heritability (~0.10). For the carcass traits, estimates of heritability were moderate to high for the various measures of carcass fat (0.18–0.50), muscle weight (0.22–0.35), meat yield (0.24–0.35), carcass muscle dimensions (0.25–0.34) and bone weight (0.27). Results indicate that for most lamb carcass and meat quality traits there is sufficient genetic variation for selection to alter successfully these characteristics. Additionally, most genetic correlations of live animal assessments of bodyweight, muscle and subcutaneous fat with the carcass and meat quality traits were favourable. Appropriate definition of breeding objectives and design of selection indexes should be able to account for the small unfavourable relationships that exist and achieve the desired outcomes from breeding programs.

Influence of finishing systems and sampling site on fatty acid composition and retail shelf-life of lamb

Thirty 7-month-old crossbred lambs (Poll Dorset × Border Leicester × Merino) finished over 5 weeks on either low quality pasture or grain-with-hay on a farm in southern Victoria were assessed for carcass parameters, muscle fat composition and retail colour stability. Lambs on the grain diet had a mix of barley grain (80%) and lentils (20%) at 800 g/head.day (air-dry basis ~ad libitum) with cape weed (Arctotheca calendula) hay available at all times. Lambs under grazing had predominantly rye grass (Lolium perenne) and barley grass (Hordeum leporinum) available ad libitum. Carcass weight tended to be higher (P = 0.14) in grain-fed lambs than in grass-fed lambs, but fatness indicated by GR (total muscle + fat tissue thickness at 11 cm from midline) did not differ between feeding systems. Fatty acid composition was determined in the loin from the forequarter (M. longissimus thoracis) and lumbar (M. longissimus lumborum) regions and from the leg region (M. semimembranosus). This showed that grain-finished lamb had higher muscle fat (P < 0.001) and omega-6 fatty acid (P < 0.001) content. Alpha-linolenic acid, eicosapentaenoic acid (EPA) or total omega-3 fat did not differ (P > 0.05) between feeding groups. Saturated fatty acids were greater (P < 0.01) in both loin sampling sites than the leg. The levels of EPA, docosahexaenoic acid and docosapentaenoic acid were lower (P < 0.01) in the forequarter (9%) or lumbar (11%) sites than the leg sampling site. The distribution pattern of fatty acids across the three sampling sites did not differ between feed types. Retail colour stability determined over 4 days of display (only performed in muscle from the lumbar site), evaluated by the redness (HunterLab a*-value) and metmyoglobin formation (reflectance ratio at 630 : 580-nm wavelengths) was superior for grass-fed lamb compared with short-term grain-finished lamb. The results demonstrate that the health claimable omega-3 fat mainly EPA or total omega-3 fat content in lamb was not altered by short-term grain finishing compared with lamb finished under pasture grazing conditions.

Bioeconomic modelling to identify the relative importance of a range of critical control points for prime lamb production systems in south-west Victoria

Whole-farm decision making is complex as many factors influence the profitability of pasture-based lamb production systems and other influences such as skills and attitudes also affect the behaviours of individual farmers. In this paper we used bioeconomic modelling to identify the relative importance of manipulating components of lamb production systems in south-west Victoria and quantified their likely impacts on whole-farm profitability. Four lamb production systems that varied in relation to the genotype of the ewes and the time of sale of the lambs were examined in the analysis. Two ‘systems’ were based on first-cross Border Leicester × Merino ewes that were mated to a terminal sire and the lambs were either sold as finished slaughter lambs at 45 kg liveweight or as stores at weaning at 30 kg liveweight. The other two ‘systems’ were based on a self-replacing composite breed (Romney × Coopworth base) and the lambs were sold as finished slaughter lambs or stores. Based on the assumptions used the analysis highlighted that the potential economic gain per unit change was high for several factors examined and the relative importance of these critical control points differed between production systems. Matching lamb turn-off (finished or store) to existing ewe genotype improved profitability by more than $100/ha or 50% and optimising pasture utilisation was also important regardless of production system. A 20% increase in pasture utilisation up to the optimum increased whole-farm profit by more than $100/ha. The impacts of improving pasture growth just after the break of season and through early winter on whole-farm profit were even greater. An extra 20 kg of pasture growth per day at this time of the year is potentially worth about $200/ha due to increases in whole-farm stocking rate. Extra pasture growth in early summer also has significant value for later lambing flocks. When farmers have optimised these factors the second-order control points were cost of replacement ewes for the first-cross system, age at first mating and reproduction efficiency in adult ewes. The management and production factors that will provide the greatest return on effort for individual farmers will depend on the potential economic gain per unit change in the target factor, their current management and production levels and the ease with which the management change or increase in production potential can be achieved in the farming system.

Introduction of meat sheep breeds in extensive systems of Patagonia: Lamb growth and survival1

Genotype effects on lamb growth, survival, and commercial finishing were estimated in a 5-yr study aimed at assessing potential benefits from introducing meat breeds into extensive sheep systems of northeastern Patagonia. Five ram [Corriedale: CO; Border Leicester: BL; Ile de France: IF; Texel: TX; and synthetic CRIII (25% Merino, 37.5% IF, 37.5% TX)] and 5 dam (CO; synthetic CRIII; BLCO: BL x CO; IFCO: IF x CO; and TXCO: TX x CO) genotypes were represented in the study. Data were collected from 1,426 born and 1,258 weaned lambs of 9 resulting genotypes (CO x CO, BL x CO, IF x CO, TX x CO, CRIII x CO, CRIII x BLCO, CRIII x IFCO, CRIII x TXCO, and CRIII x CRIII). Birth weight was recorded on all lambs; subsequently, BW and BCS (scale 1 to 5) were recorded at regular intervals until weaning. Body weights were adjusted to 60 and 90 (weaning) d of age, and ADG were calculated from the adjusted BW for the periods 0 to 60 d and 60 to 90 d; BCS was adjusted to 90 d. Survival to weaning and percentage of lambs reaching commercial finishing (BW >or= 23 kg and BCS >or= 2.5 points) were also recorded. Significant (P < 0.05) genotype x litter size interactions were detected for birth weight and ADG 60 to 90 d. With the exception of CRIII x CO, crossbred and synthetic genotypes presented greater (P < 0.05) ADG 0 to 60 d and BW at 60 and 90 d than CO x CO lambs. Second cross lambs reared as singles presented greater ADG 60 to 90 d (P < 0.05) than BL x CO, TX x CO, and CRIII x CO, but less (P < 0.05) ADG 60 to 90 d, and no differences were observed for twins. The IF x CO, CRIII x BLCO, CRIII x IFCO, and CRIII x CRIII genotypes showed greater BCS at 90 d (P < 0.05) than CO x CO. The probability of greater commercial finishing for crossbred and synthetic genotypes relative to CO x CO was at least 79%. Probabilities of greater survival to weaning in CO x CO and CRIII x BLCO lambs relative to IF x CO, TX x CO, CRIII x CO, and CRIII x CRIII lambs were greater than 81%. Results indicate significant improvements in lamb BW and saleable lambs from the introduction of meat genotypes. Among the terminal sire breeds evaluated, BL and IF would produce the greatest impact. Differential nutritional management of pregnant ewes carrying twins and of twin lambs beyond 60 d should be implemented to mitigate litter size x genotype interactions constraining growth potential benefits, which may be critical for northeastern Patagonia conditions.

Irradiation Enhances the Efficiency of Testicular Germ Cell Transplantation in Sheep

Testis germ cell transplantation in livestock has the potential for production of transgenic genotypes and for use as an alternative to artificial insemination in animal breeding systems. In a pilot experiment, we investigated a workable protocol for testis germ cell transplantation in sheep, including donor cell isolation, rete testis injection, and microsatellite detection of donor spermatozoa in recipient semen. In a second experiment, the effect of depletion of endogenous stem cells with a single irradiation dose of 9 Gy (n = 5) or 15 Gy (n = 5) on the outcome of germ cell transplantation was investigated. Irradiation of recipient testes with a single dose of 15 Gy, followed by transplantation 6 wk after depletion, may be most advantageous because it resulted in all recipients (five of five) producing donor-derived spermatozoa, while the 9-Gy and control groups had limited success rates (two of five and one of three, respectively). Using microsatellite markers to detect the presence of donor DNA, 10 rams were identified that produced spermatozoa of donor origin. The proportion of donor DNA was between 1% and 30% of total ejaculate DNA. When three of these positive rams were used in breeding experiments, four donor-derived offspring (four of 50 [8% of progeny])resulted from a recipient in Merino to Merino transplantation. Six lambs (six of 41 [15% of progeny]) were sired by donor-derived Border Leicester sperm produced in a Merino recipient ram; however, no donor-derived offspring were detected among 34 progeny from a second Border Leicester to Merino combination. These results confirm that preparation of recipient animals with a correct dose of irradiation not only enhances the success rate of the transplantation procedure but also increases the proportion of donor spermatozoa in recipient semen. This study represents the first report of the production of live progeny following testis germ cell transplantation using irradiated recipients in a livestock species.

Polyunsaturated fats in meat from Merino, first- and second-cross sheep slaughtered as yearlings

This study examined the level of long chain omega-3 and omega-6 polyunsaturated fats, the ratio of polyunsaturated fat to saturated fat (PUFA/SFA) and the ratio of omega-6 to omega-3 ( n-6/ n-3) fat in sheep grown under grazing conditions in Australia. The sheep genotypes used were Poll Dorset growth × Border Leicester Merino (PDg × BLM), Poll Dorset growth × Merino (PDg × M), Poll Dorset muscling × Merino (PDm × M), Border Leicester × Merino (BL × M) and Merino × Merino (M × M). Loin muscles ( Longissimus lumborum) collected from 40 ewe and wether sheep slaughtered at 14 months of age were processed for fatty acid determination. After frozen storage, 20 g samples were minced and a 7 g homogenate was processed for muscle lipid extraction using a chloroform:methanol (2:1) procedure. There was an increase in PUFA/SFA as the proportion of Merino genetics increased in the progeny (second-cross < first-cross < Merino), but this was not shown in the n-6/ n-3 ratio. The PUFA/SFA trend appeared to be associated with an increase in the level of total polyunsaturated fats, but not a decrease in the level of total saturated fats. The results demonstrate that there is a need to improve the PUFA/SFA content in first- and second-cross animals which are mainly used for meat production in Australia so as to maintain the healthy lipids in meat. Nutritional manipulation through feeding systems or selection of sires for greater heritability of omega-3 fat deposition may be suitable pathways to elevate the ratio of polyunsaturated fatty acids, and in particular omega-3.

Carcass Composition of Crossbred and Straightbred Lambs Finished on a High Concentrate Diet

The body measurements and carcass composition of 35 Naeemi x Border Leicester Merino (NaeemixBLM) crossbred and 9 Naeemi straightbred lambs were investigated. The Naeemi lambs were, on average, 2 kg heavier and had the Body Conditioning Scores (BCS) that were 0.78 points lower and body lengths that were 10.2 cm shorter than the crossbred lambs. There were no significant differences between the genetic groups for (GR) or (BT) but crossbred lambs had significantly more kidney fat. They also had 5.5% higher dressing percentages and 14% higher carcass yields than the Naeemi lambs. Carcass moisture and protein were 6.3 and 1.6% higher and fat was 7.8% lower in the whole carcasses of th e Naeemi lambs than in those of the crossbred lambs. It is concluded that the Naeemi x BLM lambs produce heavier carcasses but also accumulate more carcass fat than straight Naeemi lambs.

Practice Tip: Treatment of entropion in newborn lambs

The condition is thought to have a hereditary c o m p o n e n t , p ro b a bly being transmitted as a dominant allele. It is seen commonly in the Border Leicester and Bluefaced Leicester breeds and their c ro s s b red prog e ny. Since a great pro p o rtion of crossbred ewes in the UK have these breeds in their p a re n t a g e, t h e re is a potential for congenital entropion to become increasingly common.

Genetic analysis of milk production and composition in crossbred ewes from different maternal genotypes

Milk production and milk composition were measured in 1056 crossbred ewes managed under pasture grazing in a lamb production system. Most ewes were milked on three occasions at ~3, 4 and 12 weeks of lactation. The ewes were the progeny of mainly Merino dams and 91 sires from several maternal crossing breeds including Border Leicester, East Friesian, Finnsheep and Coopworth. The ewes were born over 3 years and run at three sites where they were joined naturally to meat rams. Most of the ewes were first parity (autumn-joined at 7 months of age and spring-joined at 14–17 months of age), with the remainder second or third parity. The cohorts of ewes and sites were linked genetically by three common maternal sires. The 4-h oxytocin-induced milking procedure was used to estimate daily milk production and milk samples were analysed for composition (fat%, protein% and lactose%). Daily milk yield and milk composition traits were analysed using restricted maximum likelihood mixed models procedures. The sire breed of crossbred ewes was significant for milk yield (P &lt; 0.01), fat% (P &lt; 0.01) and lactose% (P &lt; 0.05). There was a significant (P &lt; 0.01) interaction of sire breed × days of lactation, mainly due to the relatively higher milk yield of the East Friesian and White Suffolk cross ewes compared with the other crosses, at the end of the lactation. The East Friesian cross ewes had lower milk fat% than the other cross ewes. Ewes suckling multiple lambs had 29% higher peak milk yield than those bearing and suckling single lambs (P &lt; 0.001). There was an increase in peak milk yield of the ewes from first to second parity, and third parity ewes had a greater decline to the end of lactation causing a significant interaction (P &lt; 0.001). The overall decline in milk yield from peak to late lactation was –21.2 ± 0.7 g/day. Separate analysis showed a significant increase in milk yield with ewe pre-joining weight (regression 6.1 ± 1.8 g/day.kg). The estimate of heritability for daily milk yield was 0.24 ± 0.04 at 90 days of lactation and 0.10 ± 0.02 at 21 days of lactation. The estimates of heritability for the milk composition traits were generally moderate. Estimates of genetic correlations between measurements early and late in the lactation for milk yield and most composition traits were high. The within ewe by stage variance component estimates of repeatability were moderate to high for milk yield, fat% and protein%, with lactose% being low.

Comparison of manual assessments of ewe fat reserves for on-farm use

The two systems currently used in Australia for assessing the body reserves of live sheep (fat and condition scoring) were evaluated for their ability to quantify the range of scores within a mob and their ability to discriminate between sheep of varying fatness. Three ewe genotypes (fine Merino, medium Merino and first-cross Border Leicester × Merino) were independently assessed by four assessors experienced in each system (i.e. eight assessors). Twenty-four hours after assessment the ewes were slaughtered in a commercial abattoir and hot carcass measures of tissue depth at the GR site (thickness of tissue over the 12th rib, 110mm from the midline) taken to allow correlation with the assessed live scores. There was at least three times more phenotypic variation in fat score assessment compared with condition score as the fat score assessors used a wider range of scores. Despite this the average repeatability of fat scoring (0.73–0.85) was greater than condition scoring (0.64–0.84) particularly within the fine Merino genotype. Although there was a strong linear relationship between assessments of fat and condition scoring, the regression coefficients comparing the two scoring systems indicated a greater discrimination among animals on fat score across all three genotypes. Furthermore the fat scores had a significantly higher correlation with GR tissue depth measured on the carcass than condition scores. These data indicate that both systems will similarly assess the average body fat reserves of a mob or animals; however, fat scoring achieves greater discrimination when the goal is to identify individuals that are lower or higher than the mob average.

Linkage disequilibrium compared between five populations of domestic sheep

BackgroundThe success of genome-wide scans depends on the strength and magnitude of linkage disequilibrium (LD) present within the populations under investigation. High density SNP arrays are currently in development for the sheep genome, however little is known about the behaviour of LD in this livestock species. This study examined the behaviour of LD within five sheep populations using two LD metrics, D' and x2'. Four economically important Australian sheep flocks, three pure breeds (White Faced Suffolk, Poll Dorset, Merino) and a crossbred population (Merino × Border Leicester), along with an inbred Australian Merino museum flock were analysed.ResultsShort range LD (0 – 5 cM) was observed in all five populations, however the persistence with increasing distance and magnitude of LD varied considerably between populations. Average LD (x2') for markers spaced up to 20 cM exceeded the non-syntenic average within the White Faced Suffolk, Poll Dorset and Macarthur Merino. LD decayed faster within the Merino and Merino × Border Leicester, with LD below or consistent with observed background levels. Using marker-marker LD as a guide to the behaviour of marker-QTL LD, estimates of minimum marker spacing were made. For a 95% probability of detecting QTL, a microsatellite marker would be required every 0.1 – 2.5 centimorgans, depending on the population used.ConclusionSheep populations were selected which were inbred (Macarthur Merino), highly heterogeneous (Merino) or intermediate between these two extremes. This facilitated analysis and comparison of LD (x2') between populations. The strength and magnitude of LD was found to differ markedly between breeds and aligned closely with both observed levels of genetic diversity and expectations based on breed history. This confirmed that breed specific information is likely to be important for genome wide selection and during the design of successful genome scans where tens of thousands of markers will be required.

Irradiation Enhanced Efficiency of Testicular Germ Cell Transplantation in Sheep.

The application of germ cell transplantation technology in livestock to produce individuals containing donor-origin sperm has great potential to replace traditional artificial insemination in animal breeding systems. However, current obstacles to this strategy are the low success rate of transplantation with a corresponding small proportion of donor spermatozoa in the recipient's semen. In rodents, the deletion of endogenous testicular stem cells by irradiation or chemotherapy drugs is a prerequisite for successful transplantation. However, until now there has been little information in the literature with regard to the beneficial effects of the preparation of recipients in germ cell transplantation in livestock animals. In the present study, we have investigated the effect of different doses of irradiation on the outcome of germ cell transplantation in sheep. Prepubertal Merino ram lambs with a scrotal circumference (SC) ranging from 21-28cm were irradiated with 9 and 15 Grays (Gy). The size of the SC decreased rapidly following irradiation in both groups with a greater reduction with 15 Gy. Donor testicular cells were enzymatically isolated from 5 cross-bred and 1 Border Leicester ram with SC from 18.5-25cm and injected into both testes of 13 recipient rams (n=3, non-irradiated control) at 6 weeks of post irradiation. In order to investigate the functionality of the irradiated recipient testes, semen was collected from all recipients following 3 months of post transplantation over a period of 10 months. The percentages of donor DNA were tested by microsatellite markers. One out of 3 (33%), 2/5 (40%) and 5/5 (100%) recipients tested positive for donor DNA in the control, 9 Gy and 15 Gy groups, respectively, indicating that irradiation of recipient testis with a single dose of 15 Gy significantly increased the success rate of germ cell transplantation. Interestingly, one ram in the control group tested positive for donor DNA at 18 weeks post transplantation but from 26 weeks onwards this ram tested negative. The highest percentage (30%) of donor origin sperm was identified in a 15Gy treated ram. One positive ram was obtained from the cross breed transplantation, where 10% of Border Leicester DNA was found in the semen of a Merino recipient from the 15 Gy group. Our results demonstrated that 1) the preparation of recipient's testis with irradiation not only enhances the efficiency of germ cell transplantation but also increase the proportion of donor sperm in recipient semen 2) homologous testicular germ cell transplantation in sheep is feasible and the resultant recipients are capable of producing sperm of donor origin.

Inhibition of nitric oxide release pre-slaughter increases post-mortem glycolysis and improves tenderness in ovine muscles

The aim of this experiment was to determine the effect of inhibiting the release of nitric oxide (NO) pre-slaughter in lambs on post-slaughter muscle metabolism and meat quality. Exercise was used as a positive control as NO is known to be released in skeletal muscle during exercise. Forty Border Leicester×Merino lambs were assigned to the treatments L-NAME (NO synthase inhibitor) infusion (0mg/kg vs. 30mg/kg, 135min pre-slaughter) and exercise (none vs. 15min immediately pre-slaughter). The inhibition of NO release using L-NAME reduced Warner–Bratzler shear force (WBSF) in the longissimus thoracis et lumborum (LTL) after 3days of ageing, while the Semimembranosous (SM) was unaffected. Inhibition of NO release with L-NAME resulted in altered glucose metabolism as indicated by reduced plasma glucose pre-slaughter particularly in exercised lambs, reduced LTL and SM glycogen of non-exercised lambs post-slaughter and increased SM lactate in exercised lambs post-slaughter. In conclusion, inhibition of NO Synthase with L-NAME pre-slaughter increases post-mortem glycolysis and improves tenderness in the loin muscle.

Intramuscular fat levels in sheep muscle during growth

A 5 × 4 factorial experiment was designed in which lambs representing five genotypes were slaughtered at four ages (110, 236, 412 and 662 days of age). The genotypes represented were Poll Dorsetgrowth × Border Leicester Merino, Poll Dorsetgrowth × Merino, Poll Dorsetmuscling × Merino, Merino × Merino and Border Leicester × Merino. Both sexes (ewes and wethers) were represented for each genotype and slaughter age combination. In total, 595 animals were slaughtered and the carcass composition and intramuscular fat were measured. Carcass composition [fat, ash and protein (lean)] was determined by dual energy X-ray absorptiometry, with the intramuscular fat percentage determined using near-infrared spectroscopy following removal and weighing of the entire longissimus thoracis et lumborum (LL) muscle. Analysis revealed that the proportion of intramusular fat in the loin relative to total carcass fat decreases as animals mature, thus indicating that intramusular fat deposition occurs early in the maturation of sheep. Furthermore, as animals became heavier and older the accretion rate of intramuscular fat in the LL muscle slowed down. Both genotype (P &lt; 0.05) and sex (P &lt; 0.001) were found to impact on this pattern, with Border Leicester × Merino animals exhibiting the largest increase in intramuscular fat proportion in the LL muscle (4.92 and 5.50% at 22 months of age for ewes and wethers, respectively). The Poll Dorsetgrowth × Border Leicester Merino animals were found to have the greatest absolute levels of intramuscular fat in the whole LL muscle (80.95 and 97.60 g at maturity for ewes and wethers, respectively). The amount of intramuscular fat significantly increased as the sheep became older and fatter; however, these differences were quantitatively small. As such, finishing prime lambs to high levels of total carcass fatness would have little effect on any eating quality benefits associated with increased intramuscular fat proportion.

Genotype and age effects on sheep meat production. 5. Lean meat and fat content in the carcasses of Australian sheep genotypes at 20-, 30- and 40-kg carcass weights

Lean meat and fat content of Australian sheep genotypes were compared at 20-, 30- and 40-kg carcass weights. Sheep comprised Poll Dorsetgrowth × Border Leicester Merino (PDg × BLM), Poll Dorsetgrowth × Merino (PDg × M), Poll Dorsetmuscling × Merino (PDm × M), Border Leicester × Merino (BL × M) and Merino × Merino (M × M) genotypes. Lambs were raised as a mixed flock under grazing and slaughtered at 4, 8, 14 and 22 months of age with each slaughter time involving ~150 mixed sex animals. At 24 h after slaughter, chilled carcasses were halved along the backbone and the right sides were used for determination of lean, fat and ash percentages using dual energy X-ray absorptiometry. Within a particular age group and genotype, animals growing at faster rates and reaching heavier carcass weights had lower carcass lean meat content than slower growing animals. Merino carcasses weighing 20 and 30 kg had similar levels of lean meat to PD × M genotypes, which was greater than that from the BL × M genotype. Second-cross PD × BLM carcasses weighing 20 kg at 4 months and 30 kg at 8 months had similar carcass fat and lean percentages to 20-kg Merino carcasses at 8 months and first-cross PD × M carcasses weighing 30 kg at 14 months, respectively. At 40-kg carcass weight, 22-month-old Merinos had similar levels of leanness to carcasses from 22-month-old PD × M animals and carcasses from 14-month-old second-cross PD × BLM animals. Carcass lean meat content decreased with increasing carcass weight and first- cross BL × M animals had the lowest carcass lean across all weight categories. There was a major acceleration in carcass fatness between 14 and 22 months associated with a reduction in muscle deposition. Results indicate that age of the animal should be taken into account when carcass lean and fat contents are compared at a particular carcass weight. Merinos will achieve weight/composition specifications at least equally well to crossbreds but will take longer with a likely increase in production costs.

251. Production of donor-derived live lambs following testis germ cell transplantation

Testes germ cell transplantation in livestock has the potential for amplification of transgenic genotypes and for use as an alternative to artificial insemination. This study investigated a workable protocol for testis germ cell transplantation in sheep between animals of the same breed and different breeds. Testes of two groups of recipients at the stage of pre-pubertal (transition from gonocytes to spermatogonia, n = 2) or peri-pubertal (spermatogenesis initiated, n = 2) were treated with a single dose of 9 grey (Gy) or 15 Gy with a 6MV photon beam irradiation, respectively. In the first experiment, using pre-pubertal irradiated animals, testis germ cell transplantation between the same breed was performed at 16 weeks post irradiation. The left testes of recipient rams were injected with donor cells labelled with fluorescent dye PHK26, while the right testes were given unlabelled cells. The left testes of recipients were removed by castration after 2 weeks following transplantation to evaluate the location of the transferred cells, while the right testes were kept in place for long-term assessment of sperm output. In cryosections of the left testes, PKH26 positive cells were found both on the basement membrane as single cells or in the interstitial area. In the second experiment, animals irradiated at the peri-pubertal stage, received donor cells at 5 weeks post irradiation and animals were kept intact for semen production. For a period of two years after transplantation, semen samples were collected routinely from two groups of rams and analysed using microsatellite markers. Two recipients (50%) demonstrated the presence of donor DNA in their ejaculates. In order to investigate the fertility of the donor-origin sperm in recipient ejaculates, 99 ewes were artificially inseminated with semen from two positive rams. Four lambs (8%) have been identified as being sired by donor-derived sperm produced in the recipient ram that received a Merino to Merino transplantation, while no donor-derived offspring was obtained from the recipient with Border Leicester to Merino transplantation. This study represents the first report of the production of live progeny following testis germ cell transplantation in sheep.