Genetic diversity in European Pisum germplasm collections.

The distinctness of, and overlap between, pea genotypes held in several Pisum germplasm collections has been used to determine their relatedness and to test previous ideas about the genetic diversity of Pisum. Our characterisation of genetic diversity among 4,538 Pisum accessions held in 7 European Genebanks has identified sources of novel genetic variation, and both reinforces and refines previous interpretations of the overall structure of genetic diversity in Pisum. Molecular marker analysis was based upon the presence/absence of polymorphism of retrotransposon insertions scored by a high-throughput microarray and SSAP approaches. We conclude that the diversity of Pisum constitutes a broad continuum, with graded differentiation into sub-populations which display various degrees of distinctness. The most distinct genetic groups correspond to the named taxa while the cultivars and landraces of Pisum sativum can be divided into two broad types, one of which is strongly enriched for modern cultivars. The addition of germplasm sets from six European Genebanks, chosen to represent high diversity, to a single collection previously studied with these markers resulted in modest additions to the overall diversity observed, suggesting that the great majority of the total genetic diversity collected for the Pisum genus has now been described. Two interesting sources of novel genetic variation have been identified. Finally, we have proposed reference sets of core accessions with a range of sample sizes to represent Pisum diversity for the future study and exploitation by researchers and breeders.

The use of DNA markers to map anthelmintic resistance loci in an intraspecific cross of Haemonchus contortus.

The use of DNA markers to track the development of anthelmintic resistance in parasites of livestock would allow informed choices for the management of this important problem. We describe a genetic mapping approach for the discovery of DNA markers for anthelmintic resistance in Haemonchus contortus. We crossed a multi-drug resistant field isolate of H. contortus with a well-characterized laboratory strain susceptible to 4 drug classes. The F2 were separately selected with 5 anthelmintics from 4 drug classes, producing drug-resistant populations carrying gene variants derived from both the field isolate and the laboratory strain. Individual F2 worms were analysed using amplicon length polymorphisms (ALPs). We looked for field isolate alleles over- or under-represented in F2 populations compared to the unselected F2 and/or the laboratory strain. The data we obtained suggest that marker association can be used to link neutral markers with resistance, but also that more markers and perhaps more inbred laboratory strains would make the procedure more likely to succeed.

Genetic and phenotypic differences between isolates of Haemonchus contortus in Australia.

We believe this study is the first to consider the genetic and phenotypic divergence between isolates of Haemonchus contortus in Australia. Microsatellite markers have been used to investigate genetic divergence, whilst phenotypic divergence has been considered through individual worm morphology, isolate life history traits and the effect of isolates upon the host. The results are discussed in the context of the likely introduction of H. contortus to Australia, its recent isolation, and the characteristics of sheep and goat farming which might act to either isolate or distribute parasites. We conclude that there is significant observable genetic divergence between isolates of H. contortus in Australia. The divergence may have been under-estimated in this study due to a variety of factors. Phenotypic divergence is also observed, and potentially has significant implications for both economic losses due to haemonchosis on individual properties and for decisions regarding the regulation of stock movements in Australia.

Intensive rotational grazing assists control of gastrointestinal nematodosis of sheep in a cool temperate environment with summer-dominant rainfall.

While rotational grazing methods have an accepted role in the management of gastrointestinal nematodosis (GIN) of small ruminants in humid tropical regions, their efficacy and application in cool temperate regions is more controversial. This study evaluated GIN over 2 years in three classes of fine wool Merino sheep (lambs, hoggets and ewes) under three different sheep management systems in a cool tableland environment near Armidale NSW Australia (950m altitude, 30 degrees 31'S, 151 degrees 39'E). The management systems were High input (HI) with high fertiliser inputs, a target of 100% sown pasture, high stocking rate (13.4 dry sheep equivalents/ha) and relatively long grazing periods; Typical (TYP) New England management system with moderate fertiliser inputs and stocking rate (9.3DSE/ha) and relatively long grazing periods; and Intensive rotational grazing (IRG) with moderate fertiliser inputs and stocking rate (8.8DSE/ha) but very short (mean 5 days) grazing periods and long (mean 103 days) rest periods. Twenty sheep of each class in each management treatment were sampled monthly for faecal worm egg counts (WEC, followed by larval differentiation), and body weights with a blood sample taken for haematology every second month. The proportion of sheep with WEC above zero did not differ between management systems but the magnitude of WEC did, with sheep under IRG displaying lower mean WEC than those on the other treatments (IRG: 326, HI: 594, TYP: 536, eggs/g P<0.0001). This was despite a significantly longer mean interval between anthelmintic treatments (IRG: 144 days, HI: 77 days, TYP: 78 days, P<0.0001). The IRG management system also influenced the composition of the infections with sheep on this treatment having a significantly lower proportion of Haemonchus contortus in their faecal cultures (IRG: 59.7%, HI: 79.4%, TYP: 80.9%, P<0.05) and a significantly higher proportion of Trichostrongylus spp. Sheep on the IRG treatment also had a significantly higher haematocrit (HCT) than those on the other management systems. Despite the lower WEC and higher HCT, sheep under IRG also had significantly lower bodyweights and fleece weights overall, although this was only evident in sheep raised to adulthood prior to the experiment, not those raised during the 2-year experimental period. The results demonstrate that IRG systems with short grazing periods and long rest periods between grazing events can assist with control of GIN in cool temperate climates where H. contortus is the dominant parasite.

Exploiting the effect of dietary supplementation of small ruminants on resilience and resistance against gastrointestinal nematodes.

This paper focuses on targeted nutritional supplementation as a means to reduce the requirement for chemotherapeutic control of gastrointestinal nematode infection of small ruminants and considers the limitations to practical application. Supplementary feeding, particularly with additional dietary protein, can assist resilience to infection during times when metabolic resources are being directed towards dealing with the pathophysiological effects of infection and away from production of meat, milk and fibre. Substantial experimental evidence from studies of both sheep and goats supports this hypothesis particularly in relation to young lambs and kids after weaning and in ewes around parturition. In addition, nutritional supplementation frequently increases resistance to infection, as indicated by decreased faecal worm egg counts and worm burdens. As a result, supplementation has the potential to reduce the requirement for anthelmintic treatment. Practical application of this knowledge can, however, be quite complex in many small ruminant production systems. In general, strategic supplementation should target those times when nutrient requirements are greatest and provide those nutrients which are deficient whether protein, energy, minerals or trace elements. Complexity arises when we consider that nutrient requirements will differ between localities for different species and breed of host, at different stages of growth and reproduction, with differing seasonal availability of forage, with different species of nematodes and different levels of established infections and exposure to infective stages. As a starting point, the provision of nutrients to optimize rumen function and animal performance in the particular production system should assist in maintaining resilience to nematode infection. Provision of nutrients in excess of this requirement, if economically feasible, may yield further benefits in some situations and reduce the need for alternative control measures for gastrointestinal nematode parasites.

Excess heterozygosity contributes to genetic map expansion in pea recombinant inbred populations.

Several plant genetic maps presented in the literature are longer than expected from cytogenetic data. Here we compare F(2) and RI maps derived from a cross between the same two parental lines and show that excess heterozygosity contributes to map inflation. These maps have been constructed using a common set of dominant markers. Although not generally regarded as informative for F(2) mapping, these allowed rapid map construction, and the resulting data analysis has provided information not otherwise obvious when examining a population from only one generation. Segregation distortion, a common feature of most populations and marker systems, found in the F(2) but not the RI, has identified excess heterozygosity. A few markers with a deficiency of heterozygotes were found to map to linkage group V (chromosome 3), which is known to form rod bivalents in this cross. Although the final map length was longer for the F(2) population, the mapped order of markers was generally the same in the F(2) and RI maps. The data presented in this analysis reconcile much of the inconsistency between map length estimates from chiasma counts and genetic data.

Nodule-expressed Cyp15a cysteine protease genes map to syntenic genome regions in Pisum and Medicago spp.

PsCyp15a is a gene that encodes a vacuolar cysteine protease expressed in wilt-induced shoots of Pisum sativum (pea) and in root nodules. To further the understanding of nodular PsCyp15a expression, a region 5' to the coding sequence of the gene was cloned. Varying lengths of 5' untranslated sequence were fused with the uidA coding region and introduced from Agrobacterium rhizogenes into "hairy roots" of Vicia hirsuta. In this transgenic root nodulation assay, a promoter sequence of 900 bp was sufficient to give an expression pattern indistinguishable from that obtained in pea nodules by in situ hybridization. An orthologue of PsCyp15a was cloned from nodule mRNA of Medicago sativa and a corresponding gene identified in M. truncatula was also shown to express strongly in nodules. With molecular mapping techniques, it was demonstrated that these genes map to a syntenic genome location in pea and Medicago spp., but the map positions of the Cyp15a genes cannot be correlated with existing nodulation mutants.

Influence of diet type on the kinetic disposition of fenbendazole in cattle and buffalo.

The plasma concentration profiles of fenbendazole (FBZ), FBZ-sulphoxide and FBZ-sulphone were measured following intraruminal administration of FBZ at 7.5 mg kg-1 body weight in cattle and buffalo offered 3 different diets: 100% dry mature sorghum hay, 100% green Pennisetum spp. and a 50:50 mix of these 2 diets. Changing the diet from dry to green fodder resulted in significantly lower systemic availability of FBZ and its metabolites in both species. Buffalo had a lower systemic availability of the drug than cattle on the dry diet and the difference between species increased when the diet included green fodder. It is suggested that decreased transit time of digesta on the green fodder reduced systemic concentrations by reducing the time available for gastrointestinal absorption of the drug.

Biological control of field infections of nematode parasites of young sheep with Duddingtonia flagrans and effects of spore intake on efficacy.

A field study was undertaken to determine the effects of feeding Duddingtonia flagrans to young Merino sheep on pasture. A total of 60 mixed sex lambs 4-5 months old were divided into six even groups on the basis of liveweight. On Monday to Friday, each week for 6 months, three groups were offered barley grains on which D. flagrans had been cultured while the other three groups remained untreated. Every 4 weeks liveweights were recorded and faecal samples collected for nematode egg count estimation. Feeding D. flagrans reduced faecal egg counts and tended to improve liveweight gains, but considerable differences were observed between groups within treatment. These differences are thought to result from variations between the groups in consumption of the treated barley with the "best" consumers showing the greater effects of treatment.

The effects of urea supplementation on production and parasitological responses of sheep infected with Haemonchus contortus and Trichostrongylus colubriformis.

Merino wether lambs were individually confined and fed a basal diet of oaten chaff containing essential minerals which was untreated or contained 3% urea. Within each dietary group animals were orally infected with either 200 H. contortus (H), 1000 T. colubriformis (T) or both species (H + T) thrice weekly or remained uninfected (C). Weight gain, wool production, and parasite burden were measured over a 19-week period. Sheep on the diet containing urea gained more weight, consumed more feed and grew more wool of higher fibre diameter than their counterparts given no urea. On both diets uninfected sheep consumed more feed than infected sheep and the sheep given no urea and infected with both H and T worm species consumed the least feed. Parasitised sheep gained less weight than uninfected control sheep. Sheep with urea in their diet had lower faecal egg counts when infected with H alone or with H and T but there was no effect of urea on egg count of sheep infected with T alone. In contrast, T numbers after slaughter were reduced in sheep fed diets containing urea whereas H numbers were not affected by diet. It was concluded that supplementation with urea can increase resilience to parasitism thereby improving production and also enhance resistance mechanisms against worms in young sheep on low quality roughage diets. These responses can be partly attributed to stimulation of feed intake, presumably due to enhanced ruminal digestion, but also to elevated rumen NH3-N levels which would be expected to have increased rumen microbial protein synthesis and availability to the intestines.

The potential of nematophagous fungi to control the free-living stages of nematode parasites of sheep: feeding and block studies with Duddingtonia flagrans.

A series of feeding trials was conducted with penned sheep harboring Trichostrongylus colubriformis infections. They were offered barley grains supporting the growth of the nematophagous fungus Duddingtonia flagrans. It was shown that as little as 5g of grain/sheep per day was sufficient to virtually eliminate larval numbers from faecal culture. This effect persisted for the time that the fungal grains were fed, and for up to 2 days following cessation of feeding this material. Macerated fungal grains were also incorporated into a range of feed block formulations. In all these, D. flagrans was found to survive the manufacturing process and resulted in significant reductions in larval numbers in faecal cultures set up during the feeding period to sheep. This was observed even for sheep that showed only modest and irregular block consumption. These studies demonstrate that supplementary feeding or block administration offer potential deployment options for D. flagrans as a means of biological control of nematode parasites of livestock.

Enhancing immunity to nematode parasites in single-bearing Merino ewes through nutrition and genetic selection.

The effectiveness of protein supplementation and genetic selection to enhance the resistance of periparturient Merino ewes to infection from gastrointestinal parasites was tested in a replicated grazing experiment. One hundred and twenty ewes from lines selected for increased resistance (R) to Haemonchus contortus or at random (C) were subjected to one of the three supplement groups that provided 0 or 250 g per day cottonseed meal for 5 weeks prior to, or for 6 weeks after the start of lambing. Faecal egg counts (FEC) of R ewes were consistently lower than those of C ewes but both groups exhibited a periparturient rise in FEC. Supplementation during the pre-partum period reduced FEC and increased ewe body weight gain. The benefits of pre-partum supplementation in reducing FEC continued to be apparent up to 10 weeks after supplementation ceased. There was a strong suggestion that the benefits to parasite resistance from protein supplementation were greatest in C ewes. Wool growth rates (15%) and birth weights (5%) were greater for C ewes but differences between the lines for lamb body weight had disappeared by day 97. The greatest benefit to resistance from protein supplementation was observed when ewes were experiencing a loss of maternal body weight. Conversely, no benefits to resistance were observed when ewes had moderate (78-107 g per day) rates of maternal weight gain. These results suggest that increased resistance as a result of protein supplementation is dependent on the prevailing supply and demand for scarce nutrients such as metabolisable protein (MP). Both genetic selection and protein nutrition are effective strategies to enhance host resistance to nematode infection during the periparturient period.

Regulation of the resistance to nematode parasites of single- and twin-bearing Merino ewes through nutrition and genetic selection.

Periparturient Merino ewes obtained from lines of sheep that had been selected either for increased resistance to Haemonchus contortus (R) or at random (C) were supplemented, while grazing at pasture, with either nil or 250 g/day cottonseed meal (CSM) for the 6 weeks prior to or the 6 weeks after the start of parturition. Ewes from both supplement groups had lower (mean 66% reduction) faecal egg counts (FECs) during the postpartum period and this coincided with a period of maternal body weight loss. Factors which increased the rate of maternal body weight loss, such as pregnancy and lactation status, also increased FEC. Evidence is presented that the magnitude of the periparturient rise (PPR) in FEC in grazing ewes will be greatest during periods of maternal weight loss and at these times supplementation to increase metabolisable protein (MP) supply will be most effective in increasing resistance to nematode parasites. The resistance of R ewes to nematode parasites was greater than that of C ewes throughout the experiment and was sufficiently low such that anthelmintic treatment in a commercial environment may not have been required. Irrespective of actual FEC, ewes from all treatment combinations exhibited a PPR in FEC. Reduced FEC of R ewes resulted in reduced apparent pasture larval contamination after 18 weeks of continuous grazing but supplementation was ineffective in this regard. It is suggested that integrated parasite management (IPM) programs for periparturient ewes should make use of both protein supplementation and genetic selection to increase worm resistance and reduce dependency on anthelmintics for worm control.

Effectiveness of copper oxide wire particles for Haemonchus contortus control in sheep.

OBJECTIVE: To assess the efficacy of copper oxide wire particles (COWP) for the control of H contortus infections in grazing sheep. PROCEDURE: In experiment 1, 40 worm-free Merino hoggets (11 to 12 months of age) were divided into four equal groups and allocated to separate 0.8 ha pasture plots. Two groups then received 2.5 g COWP whereas the other two groups were untreated. From 1 week after COWP treatment all lambs received a weekly infection of 2000 H contortus larvae. At week 8, six sheep from the untreated group were then allocated to two groups and treated with either 2.5 or 5.0 g of COWP to establish therapeutic efficacy of treatment. Experiment 2 followed a similar protocol but was conducted with 40 worm-free Merino lambs (3 to 4 months of age) and no assessment of therapeutic efficacy was made. RESULTS: In experiment 1 no significant difference in faecal worm egg counts was observed between treatments and faecal worm egg counts remained less than 3000 epg in all animals. Total worm counts were reduced by 37% by COWP treatment (P = 0.055). Both 2.5 g and 5.0 g doses of COWP at 8 weeks of infection reduced faecal worm egg counts by > 85% with the higher dose giving an earlier response to treatment. In experiment 2, faecal worm egg counts at 4 and 6 weeks were reduced by more than 90% in the COWP treated lambs and worm numbers were 54% lower after 6 weeks when all remaining untreated lambs had to be treated for haemonchosis. Mean faecal worm egg counts in the COWP lambs remained below 3500 epg and clinical disease did not develop in the majority of lambs before the end of the experiment at 10 weeks. CONCLUSION: Treatment with COWPs appears to have the potential to reduce establishment and worm fecundity of Haemonchus spp for an extended period and may offer livestock producers a supplementary means of reducing larval contamination of pasture particularly in areas where anthelmintic resistance is a problem and copper supplementation is likely to be beneficial.

Effects of diet and species on the pharmacokinetics of fenbendazole in cattle.

The plasma concentration profiles of fenbendazole (FBZ), FBZ-sulphoxide (OFZ) and FBZ-sulphone were measured following intraruminal administration of FBZ at 7.5 mg/kg bodyweight in Bos taurus and B. indicus cattle offered three different diets: 100% wheaten chaff, 100% lucerne, and a 50:50 mix of these two diets. No differences between the species were apparent except for a longer time to peak plasma concentration for OFZ in the B. taurus steers fed 100% wheaten chaff. Cattle fed wheaten chaff alone gave greater areas under the concentration-time curve and longer persistence for all metabolites than when the same cattle were fed the other diets. It is concluded that the reduced rate of passage of digesta on lower-quality fibrous diets allows greater time for absorption of FBZ and its metabolites from the gut, thereby increasing systemic availability.

The effect of peri-parturient anthelmintic treatment on the productivity of dairy cattle in subtropical western India.

Trials with fenbendazole (Panacur, Hoechst India Ltd) were carried out on two commercial farms in subtropical western India to study the response and economics of nematode treatment in adult dairy cows. Milk yield, lactation length, time to first oestrus and worm egg output were monitored in treated and control groups. Treatment reduced the egg count considerably. Treated cows produced 142 litres more milk over 100 days (p < 0.05), with extension of lactation length and advancement of time to first oestrus. The economic gain in terms of milk yield far outweighed the cost of anthelmintic used.

Comparative pharmacokinetics of fenbendazole in buffalo and cattle.

Swamp buffalo (Bubalus bubalis) and Droughtmaster cattle (Bos indicus x B. taurus), fitted with gastrointestinal cannulae, were dosed intraruminally with fenbendazole at 7.5 mg/kg liveweight, together with a chromium oxide capsule and a pulse dose of NaCoEDTA, to estimate the flow dynamics of the digesta in the rumen and duodenum. The concentrations of fenbendazole (FBZ) metabolites were measured in plasma and duodenal fluid collected over 120 h. In plasma, significantly lower peak concentrations and earlier disappearance of FBZ and its sulphoxide (OFZ) metabolite were observed in buffalo, which considerably reduced systemic availability in comparison with cattle. The availability of OFZ in the duodenal fluid of buffalo was significantly lower, whereas FBZ disposition was similar to that in cattle. The turnover rate of fluid in the rumen was higher in buffalo than in cattle, while the flow parameters for other digesta were similar in the two species. It is concluded that the decreased absorption of drug in buffalo was attributable to the shorter residence time of the dose in the rumen, and probably in the entire gastrointestinal tract. This may reduce the efficacy of treatment and indicate the need for higher dose rates for benzimidazole anthelmintics in buffalo than in cattle.

A comparison of plasma metabolite levels in goats and sheep during continuous low-level administration of fenbendazole.

Plasma levels of fenbendazole (FBZ) and its sulphoxide (OFZ) and sulphone (FBZ.SO2) metabolites were measured in goats and sheep during low-level administration of FBZ given by intraruminal infusion or formulated into a urea-molasses feed supplement block (UMB). In experiment 1, 6 goats and 6 sheep were offered UMB containing 0.5 g FBZ/kg (MUMB) and individual block consumption was measured daily for 18 days. In experiment 2, some of the same animals (n = 4 for each species) received FBZ by intraruminal infusion at 1, 1.5 and 3 mg/kg liveweight per day for 7 days at each dosage. FBZ, OFZ and FBZ.SO2 levels were determined in plasma collected every 3 days in experiment 1 and on days 4, 5 and 6 of each infusion period in experiment 2. In both experiments, higher equilibrium levels were observed for the three metabolites in sheep than in goats. Significant linear relationships were observed between the daily FBZ dosages and the plasma levels of the three metabolites in both species. The regression coefficients were significantly higher in sheep than in goats for FBZ and OFZ but not for FBZ.SO2, and they were also significantly higher during MUMB administration than during infusion for all three metabolites in both species. FBZ is a suitable anthelmintic for incorporation into a MUMB formulation for use in livestock production systems where responses to molasses urea supplementation have been demonstrated and gastrointestinal parasitism impairs productivity. The results indicate that target dose rates for goats should be 0.75 mg/kg per day compared with 0.5 mg/kg per day for sheep.

Role of host and environment in mediating reduced gastrointestinal nematode infections in sheep due to intensive rotational grazing.

We have previously reported marked reductions in faecal worm egg counts (WECs) and drenching frequency in sheep on an intensive rotational grazing system (IRG) in a cool temperate environment with summer-dominant rainfall. These experiments were designed to determine the role of the host and environmental factors in mediating this. The role of host factors was investigated by administering a fixed larval challenge in each of the 4 seasons of the year to groups of 20 young sheep on three different management systems, including IRG. This comprised a mixed larval challenge containing infective larvae of Haemonchus contortus and Trichostrongylus colubriformis 7 days after short-acting anthelmintic treatment. A range of measurements was then made up to day 35 post-challenge. The role of environmental factors was determined by assessing pasture infectivity in four seasons using faecal worm egg counts (WECs) and pooled faecal culture of worm-free tracer sheep. The management systems were high input (HI) with high fertiliser inputs high stocking rate and relatively long grazing periods; typical New England management system (TYP) with moderate fertiliser inputs and stocking rate and relatively long grazing periods and; Intensive rotational grazing (IRG) with moderate fertiliser inputs and stocking rate but very short (mean 5 days) grazing periods and long (mean 103 days) rest periods. IRG sheep had higher mean WEC at 28 and 35 days after fixed larval challenge than HI and TYP sheep in spring (IRG: 9500 ± 1000; HI: 4000 ± 1000; TYP: 7200 ± 1000 eggs/g, P<0.01) and summer (IRG: 8400 ± 750; HI: 5300 ± 800; TYP: 4400 ± 700 eggs/g; P<0.001) and also had lower live weights during these seasons. There was no difference in WEC after the autumn challenge (IRG: 5100 ± 450 HI: 4500 ± 450; TYP: 4200 ± 450 eggs/g; P ≈ 0.36) but IRG had lower WEC than TYP following the winter challenge (IRG: 2900 ± 400; HI: 2300 ± 400; TYP: 4300 ± 400 eggs/g, P<0.01). The tracer sheep (used to determine pasture infectivity) on IRG had significantly lower WECs during winter, spring and summer than those under the other management systems. Faecal culture and larval differentiation revealed that faeces from tracers on IRG contained significantly lower proportions of H. contortus and significantly higher proportions of Trichostrongylus spp. and Teladorsagia circumcincta than faeces from tracers on the HI and TYP treatments. Thus, when IRG was most efficacious for worm control, during spring and summer when short graze and long rest periods were maintained, sheep on this system exhibited greater susceptibility to larval challenge while tracer sheep indicated lower pasture infectivity. This demonstrates that the effects of IRG on WEC are mediated by reduced larval challenge rather than increased host resistance to infection.

The effect of combination treatment with trenbolone acetate and estradiol-17ß on skeletal muscle expression and plasma concentrations of oxytocin in sheep.

Implantation of trenbolone acetate (TBA) in conjunction with estradiol-17ß (E(2)) increases growth, feed conversion efficiency, and carcass leanness in cattle. Our previous study in Brahman steers suggested that the neuropeptide hormone oxytocin (OXT) may be involved in increasing muscle growth after TBA-E(2) treatment. The present study aimed to determine whether OXT mRNA expression in the longissimus muscle (LM) is also up-regulated in TBA-E(2-)implanted wethers as has been found in steers. Real-time quantitative PCR was used to measure the expression of the gene encoding the OXT precursor, three genes with increased expression in the LM muscle of TBA-E(2)-treated steers, MYOD1 (muscle transcription factor), GREB1 (growth regulation by estrogen in breast cancer 1), and WISP2 (Wnt-1 inducible signaling pathway protein 2), and two genes encoding IGF pathway proteins, IGF1, IGFR, in the LM of both untreated and TBA-E(2)-treated wethers. The expression of OXT mRNA in wethers that received the TBA-E(2) treatment was increased ~4.4-fold (P = 0.01). TBA-E(2) treatment also induced a 2.3-fold increase in circulating OXT (P = 0.001). These data, together with the observation that untreated wethers had much higher baseline concentrations of circulating OXT than previously observed in steers, suggest that wethers and steers have quite different OXT hormone systems. TBA-E(2) treatment had no effect on the expression of IGF1, IGFR, and the muscle regulatory gene MYOD1 mRNA levels in wethers (P ≥ 0.15), but there was an increase in the expression of the two growth-related genes, GREB1 (P = 0.001) and WISP2 (P = 0.04). Both genes are common gene targets for both the estrogen and androgen signaling pathways. Consequently, their actions may contribute to the positive interaction between TBA and E(2) on additive improvements on muscle growth.