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PubMed2000

Molecular cloning and functional analysis of three type D endogenous retroviruses of sheep reveal a different cell tropism from that of the highly related exogenous jaagsiekte sheep retrovirus.

Integrated into the sheep genome are 15 to 20 copies of type D endogenous loci that are highly related to two exogenous oncogenic viruses, jaagsiekte sheep retrovirus (JSRV) and enzootic nasal tumor virus (ENTV). The exogenous viruses cause infectious neoplasms of the respiratory tract in small ruminants. In this study, we molecularly cloned three intact type D endogenous retroviruses of sheep (enJS56A1, enJS5F16, and enJS59A1; collectively called enJRSVs) and analyzed their genomic structures, their phylogenies with respect to their exogenous counterparts, their capacity to form viral particles, and the expression specificities of their long terminal repeats (LTRs). In addition, the pattern of expression of enJSRVs in vivo was studied by in situ hybridization. All of the three enJSRV proviruses had open reading frames for at least one of the structural genes. In particular, enJS56A1 had open reading frames for all structural genes, but it could not assemble viral particles when highly expressed in human 293T cells. We localized the defect for viral assembly in the first two-thirds of the gag gene by making a series of chimeras between enJS56A1 and the exogenous infectious molecular clone JSRV(21). Phylogenetic analysis distinguished five ovine type D retroviruses: enJSRV groups A and B, ENTV, and two exogenous JSRV groups (African versus United Kingdom/North America isolates). Transient transfection assays indicated that the LTRs of the three enJSRVs were not preferentially active in differentiated lung epithelial cells. This suggests that the pulmonary tropic JSRV developed from a type D retrovirus that did not have lung specificity. Consistent with this, in situ hybridization of a panel of normal ovine tissues revealed high expression of enJSRV mRNA in the luminal epithelium and glandular epithelium of the uterus; lower expression was localized in the lamina propria of the gut and in the bronchiolar epithelium of the lungs.

Amino Acid Sequence↗
PubMed1989

Regulation of expression of a sheep metallothionein 1a-sheep growth hormone fusion gene in transgenic mice.

Transgenic mice containing a sheep metallothionein 1a-sheep growth hormone fusion gene exhibited low, tissue-specific basal levels of transgene mRNA expression, resulting in slightly elevated levels of circulating growth hormone that did not lead to a detectable increase in growth. After zinc stimulation, high levels of transgene mRNA expression were induced in a number of tissues; these levels correlated with increased levels of circulating growth hormone, resulting in growth increases of up to 1.5 times the levels of controls and unstimulated transgenic mice. After removal of the zinc stimulus, transgene expression and circulating growth hormone concentrations returned to basal levels. Additional evidence from the pattern of developmental expression of the transgene suggests that zinc is the main regulator of this promoter in mice. The demonstrated regulation and low basal level of expression of the sheep metallothionein 1a promoter make it a candidate for use in other mouse transgenic studies and for use in transgenic livestock, in which regulation of expression is essential.

Animals↗
PubMed1990

Progesterone and oestrogen concentrations in plasma of Barbary sheep (aoudad, Ammotragus lervia) compared with those of domestic sheep and goats during pregnancy.

Steroid hormone concentrations have been measured in the peripheral plasma of 3 Barbary sheep over 3 breeding seasons. During pregnancy mean progesterone values rose initially and after a small decline between Days 30 and 50, increased again and remained between 17 and 28 nmol/l until the last 2 days of pregnancy. Oestradiol-17 beta reached a peak of about 300 pmol/l during mid-pregnancy, increasing to over 400 pmol/l in the last 5 days of pregnancy. Oestrone sulphate began to increase in concentration from about Day 40 of pregnancy and reached a peak of about 19 nmol/l by Day 120. Following a slight decrease from Day 130, there was a further rise in values just before parturition. Values for these steroids in the Barbary sheep studied were between those expected for domestic sheep and goats.

Animals↗
PubMed1993

Failure of sheep-goat hybrid conceptuses to develop to term in sheep-goat chimaeras.

Six hybrid pregnancies were established: three in sheep-goat chimaeras, one in a sheep-(sheep-goat)hybrid chimaera and two in does. Pregnancies were monitored weekly by ultrasonography and peripheral concentrations of pregnancy specific protein B (PSPB) were measured. Placental development as detected by ultrasonography appeared to be slower in hybrid-in-goat pregnancies than in hybrid-in-chimaera pregnancies, although this difference was not reflected in PSPB concentrations. Time of fetal death could not be predicted from PSPB concentrations. Chimaeras appeared to carry hybrid pregnancies longer than ewes and does usually carry hybrid pregnancies, but none was carried to term.

Animals↗
PubMed1979

Sulfur and methionine metabolism in sheep. II. Quantitative estimates of sulfur metabolism in the sheep's stomach.

The metabolism of dietary and supplemental DL-methionine sulfur in the stomach of sheep was studied in two experiments. In both experiments sheep were fed a 50 : 50 oaten chaff: lucerne chaff ration at two levels of intake, and some animals received intraruminal infusions of DL-methionine. In experiment 2 increasing dry matter intake (DMI) increased first approximations of total, neutral, protein and reducible sulfur flows and also sulfide sulfur flow from the reticulo-rumen. Increased DMI (from 500 to 1000 g/day) also resulted in greater true flows of total (2207 v. 1104 mg/day), neutral (1867 v. 1043 mg/day) and protein (893 v. 482 mg/day) sulfur at the duodenum. Two flow diagrams of sulfur metabolism in the compartments of the ruminant stomach were developed from the data of experiment 2. Fluid flows of sulfur in experiment 1 were used to supplement the data of experiment 2 in developing the balance models. The two models represent the extremes of dietary and supplemental sulfur metabolism in the sheep's stomach under the conditions of experiment 2, and they are discussed in relation to previous research on sulfur metabolism in the stomach.

Animals↗
PubMed1976

Volatile fatty acid metabolism in sheep. 1. Average daily volatile fatty acid production in the rumen of sheep fed lucerne hay.

Changes in the total concentration of the volatile fatty acid (VFA) pool in the rumen were followed over a 24 hour period in 2 groups of sheep, 1 fed at 08h00 and the other twice daily at 08h00 and 20h00. Although similar maximum (143 and 147 meq/1) and average (100, 3 and 102, 1 meq/1) levels were found in the 12 and 24 h groups respectively, the twice daily feeding regimen resulted in a lower variation (S.D.=17, 0 meq/1 and 28, 9 meq/1 respectively). It was concluded from changes in the percentage molar composition of the VFA pool over the same period that the other of VFA absorption from the rumen was propionate greater than acetate greater than butyrate for both groups, but that the differences were less marked for the twice daily fed sheep. Long term infusions of 14C labelled acetic, propionic and butyric acids into the rumen of sheep fed a total of 1 600 g lucerne hay twice daily (08h00 and 20h00), gave an average net total VFA production rate of 4,52+/-1,01 moles/800 g/12 hours irrespective of the acid infused. The net individual turnover rates for acetic (2,81 moles/12 h), propionic acid (0,82 moles/12 h) and butyric acid (0,55 moles/12 h), derived by the subtraction of the inter-conversion factors from the gross production rates of the acids, and expressed as the percentage contribution of each acid to the total net VFA turnover (acetic=62%, propionic=18% and butyric=12%) closely resembled the percentage molar composition of the VFA pool in the rumen (acetic=60%, propionic=23% and butyric=12%). The total net VFA production was found to be directly proportional to the total VFA concentration in the rumen (correlation coefficient=0,83), and the relationships can be described by the equation y=0,034 x + 0,16 where y=VFA production in moles/12 hour and x=VFA concentration in meq/1. A specific VFA production rate of 0,85 moles per 100 g digestible organic matter was calculated from the average daily VFA production rate and the composition of the lucerne hay.

Acetates↗
PubMed2002

Nairobi sheep disease virus, an important tick-borne pathogen of sheep and goats in Africa, is also present in Asia.

Nairobi sheep disease (NSD) virus is the prototype of the tick-borne NSD serogroup, genus Nairovirus, family Bunyaviridae. It is highly pathogenic for sheep and goats, causes disease in humans, and is widespread throughout East Africa. Ganjam virus has caused disease in goats and humans in India. Due to their occurrence on different continents and association with different ticks, these viruses were considered distinct despite serologic cross-reactivity. Their S RNA genome segments and encoded nucleocapsid proteins were found to be 1590 nucleotides and 482 amino acids in length and differed by only 10 and 3% at nucleotide and amino acid levels, respectively. Genetic and serologic data demonstrate that Ganjam virus is an Asian variant of NSD virus. These viruses were phylogenetically more closely related to Hazara virus than Dugbe virus.

Africa↗
PubMed2006

Expression of the jaagsiekte sheep retrovirus envelope glycoprotein is sufficient to induce lung tumors in sheep.

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary adenocarcinoma (OPA). The expression of the JSRV envelope (Env) alone is sufficient to transform a variety of cell lines in vitro and induce lung cancer in immunodeficient mice. In order to determine the role of the JSRV Env in OPA tumorigenesis in sheep, we derived a JSRV replication-defective virus (JS-RD) which expresses env under the control of its own long terminal repeat (LTR). JS-RD was produced by transiently transfecting 293T cells with a two plasmid system, involving (i) a packaging plasmid, with the putative JSRV packaging signal deleted, expressing the structural and enzymatic proteins Gag, Pro, and Pol, and (ii) a plasmid which expresses env in trans for JS-RD particles and provides the genomes necessary to deliver JSRV env upon infection. During the optimization of the JS-RD system we determined that both R-U5 (in the viral 5' LTR) and the env region are important for JSRV particle production. Two independent experimental transmission studies were carried out with newborn lambs. Four of five lambs inoculated with JS-RD showed OPA lesions in the lungs at various times between 4 and 12 months postinoculation. Abundant expression of JSRV Env was detected in tumor cells of JS-RD-infected animals and PCR assays confirmed the presence of the deleted JS-RD genome. These data strongly suggest that the JSRV Env functions as a dominant oncoprotein in the natural immunocompetent host and that JSRV can induce OPA in the absence of viral spread.

Adenocarcinoma↗
PubMed1992

Cellular immune responses in the skin of sheep infected with larvae of Lucilia cuprina, the sheep blowfly.

Cellular immune responses were observed in the skin of sheep after primary and secondary infection with sheep blowfly (Lucilia cuprina) larvae. Both primary and secondary infections resulted in a massive cellular infiltration within 48 h of wound initiation, with the majority of cells having the CD45 phenotype. Neutrophils comprised the major cell type at the skin surface. In the dermis, the number of CD4+ T helper, gamma delta-TCR+ cells and T19+ (CD4-, CD8-) T cells also increased significantly in skin during both primary and secondary infections compared with control sites. However, there was no significant difference in the numbers of these cells between primary and secondary infections. An increase in the expression of the CD1 antigen on Langerhans/dendritic cells was observed, along with an apparent increase in the number of these cells in secondary lesions, with the majority of the cells being concentrated in the upper dermis and epidermis. While there was no increase in mast cells, eosinophils increased significantly during infection compared with control sites. The cellular infiltration observed following primary and secondary infections suggests polyclonal activation of T cells and their selective recruitment to the lesion site.

Animals↗
PubMed1993

Effect of avermectin residues in sheep dung on mating of the Australian sheep blowfly Lucilia cuprina.

Male and female Lucilia cuprina adults were separated after emergence and then fed either dung excreted from sheep after an oral treatment with ivermectin (Ivomec) or non-treated sheep dung. Fresh dung (non-treated or ivermectin-treated) was collected daily and fed to adults for 6 days after drenching. After this feeding period, males and females from each feeding treatment were paired and all aspects of mating behaviour recorded. Feeding on avermectin residues by adults had a significant effect on two components of mating: (1) males fed on ivermectin-treated dung directed less mating attempts at females compared with males fed on non-treated dung; (2) mating duration by males fed on ivermectin-treated dung was longer compared with males fed on non-treated dung. There was no significant difference in the level of sexual receptivity (percentage mating) between females fed on either ivermectin-treated dung or non-treated dung, although subsequent oviposition by females fed ivermectin-treated dung was significantly delayed. Both female and male mortality was significantly greater when feeding on ivermectin-treated dung compared with non-treated dung. The effects on mating, when coupled with the deleterious effects on ovarian development and adult mortality, demonstrate the potential for avermectin usage in a control strategy against L. cuprina.

Animals↗
PubMed2006

Texel sheep are more resistant to natural nematode challenge than Suffolk sheep based on faecal egg count and nematode burden.

Limited information is available on differences between sheep breeds with respect to helminth resistance under temperate conditions. The present study was designed to confirm and extend preliminary findings on observed breed differences in resistance to naturally acquired gastrointestinal nematodes in Suffolk and Texel sheep. Three trials were carried out. In trial 1 (1999-2003) lambs co-grazed from birth were faecal sampled at various time points up to 17 weeks of age. Worm burden was assessed at 17 weeks of age from a minimum of six lambs per breed in each of the 3 years. In trial 2, faecal egg count (FEC) was determined on six farms with co-grazed Suffolk and Texel purebred lambs. In trial 3 (2001-2003), ewes were faecal sampled at winter housing. In all three trials, an influence of breed on resistance to naturally acquired trichostrongyle infection was demonstrated. In trial 1, significantly higher FEC and worm burden was observed in Suffolk compared with Texel lambs following natural challenge. In trial 2, FEC recorded in lambs from six farms confirmed the breed differences previously observed. A breed difference in resistance to GI parasites was also observed in older ewes. In both breeds, an age effect on the FEC was observed with younger ewes having greater FEC than older ewes.

Age Factors↗
PubMed1996

The development of cockle, a sheep pelt defect, in relation to size of infestation and time of exposure to Bovicola ovis, the sheep-biting louse.

Groups of ten louse-naive lambs were infested with one, ten or 100 female Bovicola ovis and killed 84 days later when an examination of their pelts was made to detect cockle. In a second experiment groups of ten lambs were infested with ten or 100 female B. ovis and groups of lambs were killed every fortnight up to 84 days post-infestation. The pelts were examined in order to detect the earliest time at which cockle could be detected following a louse infestation. Cockle is a nodular condition of the skin arising in response to infestation with B. ovis and is possibly a hypersensitivity on the part of some sheep to antigens of louse origin. In the first experiment cockle did not develop in lambs that had remained louse free or which had been initially infested with one louse. However, five of ten lambs that had been infested with ten lice and all lambs that had been infested with 100 lice developed cockle. In general cockle severity was positively related to the size of the terminal louse population. Group mean louse counts only slightly exceeded the initial infestation in the lambs infested with either ten or 100 lice, and were less than the initial infestation in lambs given only one louse. In the second experiment cockle was first seen 54 days post-infestation, but only in sheep infested initially with 100 lice.

Animals↗
PubMed1978

A survey of Nairobi sheep disease antibody in sheep and goats, wild ruminants and rodents within Kenya.

The distribution of antibody to Nairobi sheep disease in sheep and goats in Kenya was found to coincide closely with that of the tick, Rhipicephalus appendiculatus. The proportions of a population in an enzootic area with antibody was similar in the different age groups. No antibody to the virus was found in rodent sera and while some low titres were found in some wild ruminant sera, these were considered to be most likely cross reactions with antibody to related viruses.

Animal Population Groups↗
PubMed1978

Nairobi sheep disease in Kenya. The isolation of virus from sheep and goats, ticks and possible maintenance hosts.

Nairobi sheep disease was seen principally upon movement of susceptible animals into the enzootic areas. This occurred most frequently for marketing purposes near the main centres of population. Other outbreaks followed local breakdowns in tick control measures. The disease did not occur in epizootic form during the period under consideration. Nairobi sheep disease was isolated from pools of Rhipicephalus appendiculatus but not from many pools of other tick species. No virus was isolated from the blood or tissues of a range of wild ruminants and rodents.

Animals↗
PubMed1986

Survey of anthelmintic resistance in Western Australian sheep flocks. 2. Relationship with sheep management and parasite control practices.

Owners of 116 farms, whose flocks had been tested for anthelmintic resistance, were interviewed to determine their use of various sheep management and parasite control practices and their knowledge and adoption of recommended procedures for the prevention and control of resistance. Farmers knowledge of current recommendations related mainly to changing drenches and drench groups. Other aspects of the recommended program including reduction of drenching frequency and the use of alternative management strategies were not considered as important by farmers. For most questions a high proportion of farmers (greater than 20%) had no opinion. Associations between various strategies for nematode control and resistance of Trichostrongylus and Teladorsagia to thiabendazole and levamisole were examined. These relationships differed between anthelmintics and nematode genera. A number of factors were related to resistance of one or both nematode genera to one or both anthelmintic groups. These factors included flock size, percentage of ewes in the flock, cattle number, main sheep production activity, grazing strategy, frequency of drenching, changes in the frequency of drenching, number of summer drenches and the method of estimating dose rates. It was concluded that the methods employed to control anthelmintic resistance may vary with the nematode, its resistance status and the anthelmintic to which it is exposed. Modifications to the previously recommended program have been proposed which incorporate selection of the anthelmintic to be used following a test for anthelmintic resistance.

Animal Husbandry↗
PubMed1984

Control of sheep scab and other sheep ectoparasites with propetamphos.

Propetamphos is a new organophosphorous compound with broad spectrum acaricidal and insecticidal activity. Dip wash concentrations of 100 to 200 ppm protect sheep against field challenge for approximately 10 weeks for blowflies, 16 weeks for lice and keds and six weeks for ticks. During laboratory and field trial studies a wash concentration of 125 ppm propetamphos eradicated sheep scab and protected from reinfestation for over four weeks.

Animals↗
PubMed1991

Failure of a single treatment with ivermectin to control sheep scab (Psoroptes ovis) on artificially infested sheep.

Ivermectin at 200 micrograms/kg bodyweight given either as a single subcutaneous injection or as an oral drench failed to eradicate Psoroptes ovis from artificially infested sheep. The oral drench reduced the mite populations by 43 per cent within 24 hours but no further significant decline was recorded over 38 days. The subcutaneous injection reduced the mite populations by 90 per cent after 10 days but live P ovis were present on all the treated animals 84 days after treatment. The efficacy of treatment was less the higher the initial mite burden. The injection had no effect on clinical sheep scab, and the disease continued to progress despite the mite mortality.

Administration, Cutaneous↗
PubMed2000

Radiocaesium variability within sheep flocks: determination of 137Cs intake in free-ranging sheep.

A study is described in which 137Cs intake by free-ranging sheep was estimated at two farms in the area of west Cumbria (northwest England) which received some of the highest amounts of fallout from the Chernobyl accident within the United Kingdom. The faecal excretion of 137Cs was estimated from faecal 137Cs activity concentrations and the use of intraruminal controlled release devices containing Cr2O3 to determine faecal dry matter output. The intake of 137Cs was estimated by assuming an apparent absorption coefficient appropriate to the herbage grazed. The methodology has the advantage that sampling of herbage representative of that ingested by study animals is not required. Caesium-137 dietary intake explained >60% of the observed variability in the 137Cs activity concentration determined in the muscle of sheep. Resultant transfer coefficient (Ff) values to describe the transfer of 137Cs from the diet to muscle were in agreement with previously reported values. At one farm, there was a positive correlation between the 137Cs activity concentration in muscle and Ff whilst at the other farm there was a negative correlation between Ff and 137Cs dietary intake. Potential reasons for these observations are discussed.

Animals↗