The characteristics and causes of sheep losses in the Victorian Mallee

SUMMARY The extent and causes of sheep losses in the semi-arid Mallee region of north-western Victoria were assessed by interviewing the owners of 79 randomly selected farms running 241 flocks in 1987/88 and 245 flocks in 1988/89. Mean annual losses were higher in ram flocks (21%) than in ewe flocks (7%), in flocks of non-Merino sheep (rams 24%, ewes 11%, weaners 5%) than in Merino (rams 11%, ewes 6%, wethers 4%, weaners 4%) and in ewe flocks 3 or more years old (10%) than in young ewe flocks (3.5%). In flocks where losses exceeded 5%, the causes most often reported by farmers were blowfly strike (especially in Merino sheep and weaners), ewe losses in autumn close to lambing, and heliotrope (Heliotropium europaeum) poisoning. Heliotrope poisoning was considered by the authors to be the main reason for the higher losses in old ewes than in young ewes and in non-Merino sheep than in Merino sheep. Losses of ewes associated with pregnancy and lambing were considered by the authors to be often predisposed by liver damage caused by heliotrope poisoning, and high losses in non-Merino ram flocks were attributed to both heliotrope poisoning and their ability to escape through boundary fences. Reasons for continuing high losses due to enterotoxaemia are discussed. Losses due to gastro-intestinal parasites, footrot and foot abscess were low.     

Losses of adult sheep due to ovine Johne's disease in 12 infected flocks over a 3-year period

OBJECTIVE: To measure the biological and financial impact of ovine Johne's disease (OJD) mortalities on 12 infected flocks within the endemic area of southern New South Wales over a 3-year period. DESIGN AND POPULATION: An observational study was conducted over a 3-year period from 2002 to 2004 on sheep from 12 OJD-infected flocks from southern NSW. Flocks ranged from between 3,500 and 20,000 sheep. At the start of the study owner estimates of OJD mortality were 5% or greater. METHOD: Annual mortality rates were estimated from farm records provided by owners. The proportion of OJD mortalities was assessed after histological examination of tissues collected from dead and moribund sheep during 5-day necropsy inspections conducted in autumn, winter, spring and summer in 2002. The financial impact was estimated using a gross margin analysis for each of the three study years and by placing a financial value on the necropsied sheep. RESULTS: On the 12 farms, the average OJD mortality rate was 6.2% (range 2.1% to 17.5%) in 2002, 7.8% (range 1.8% to 14.6%) in 2003 and 6.4% (range 2% to 11.9%) in 2004. The average decrease in gross margin due to OJD infection on a farm in 2002 was 6.4% (range 2.2% to 15.4%), 8.5% (range 3.1% to 15.8%) in 2003 and 7.4% (range 1.5% to 15.4%) in 2004. This equates to an average reduction in annual income of $13,715 per farm per year. OJD losses accounted on average for two thirds of the total estimated financial loss associated with sheep deaths. CONCLUSION: This study demonstrates the significant biological and financial impact of OJD on sheep flocks. These findings are of relevance to all Australian sheep flocks infected or at risk of OJD infection.     

Maedi-visna impact on productivity in Quebec sheep flocks (Canada)

An epidemiological study was conducted to determine the impact of maedi-visna (MV) seropositivity on productivity in commercial sheep flocks of the province of Quebec, Canada. A total of 1734 ewes and 220 rams were selected randomly from 29 flocks distributed in the Bas-St-Laurent and Estrie regions. Serostatus was determined with an enzyme-linked immunosorbent assay (ELISA) using recombinant proteins.Flock-specific, animal-level seroprevalence varied from 3 to 70% (median=29%). Seroprevalence increased with age and size of the flock, and was higher in ewes relative to rams (but was not associated with body score). A decrease of 0.94 kg per lamb in weaning weight was seen only for lambs raised by seropositive ewes >/=4 years old, and seropositivity in ewes of any age was associated with an increase in 0-30 days lamb-mortality (OR: 1.65). The impact of MV infection on weaning weight and lamb mortality did not vary between flocks, and seropositivity in ewes was not associated with litter size or lamb's birth weight.     

Prevalence of the causes of fleece derangement among sheep flocks in New South Wales

SUMMARY An investigation of sheep flocks with unknown histories of fleece derangement, selected at random from the main sheep raising areas of New South Wales, showed that Psorergates ovis was present in 53 of the 177 flocks surveyed and In 162 of the 3495 sheep examined. Of the single causes of fleece derangement, the most prevalent was grass seed contamination (15.7%) followed by Infestation with sheep body lice, Bovicola ovis, (14.7%) and Infestation with Itch mite (7.8%). The prevalence of fleece derangement was significantly higher on sheep In which lice were the only ectoparasites found than on those In which Itch mites were the only ectoparasites present. The greatest prevalence of P ovis was In flocks In the Young, Yass, Mudgee and Tenterfield districts. In most affected flocks, more than one potential cause of fleece derangement was present. Itch mite Infestation was more prevalent in flocks that received no treatment for ectoparasites than in those that had been treated in the year preceding the survey. Our results did not support a commonly held belief among farmers that arsenical compounds control Infestations of Itch mites more effectively than other types of pesticides. There was no significant difference in prevalence of fleece derangement between flocks treated with different pesticide groups and those that received no treatment, but mean fleece derangement score was significantly lower in sheep treated with organophosphates than in untreated sheep. Infestations of lice were significantly more prevalent in sheep from flocks treated with synthetic pyrethroids than from those treated with organophosphates or those that received no treatment.     

The seroprevalence of Toxoplasma gondii in Ontario sheep flocks

In a random sample of 103 sheep farms in Ontario, 99% of the farms had some sheep serologically positive for Toxoplasma gondii, based on an enzymelinked immunosorbent assay (ELISA). The percent of sheep affected within farms ranged from 3.8% to 97.8%, with an average flock prevalence of 57.6%. When farm management variables were considered in a multivariate analysis, significantly lower rates of serologically positive sheep were associated with neutering of female cats and clipping of ewes' perineums before lambing; significantly higher prevalence rates were found on farms where sheep were purchased from other flocks, pigs were raised on the same farm, sheep shared pasture with other animals, flowing water was available at pasture, and pastured replacements had access to housing. As well, in univariate analyses, higher prevalence was positively associated with an increasing number of cat litters born over the previous two years and offering creep feed or forage to lambs, and inversely with the amount of labor expended on sheep rearing.     

Ulcerative vulvitis and balanitis in sheep flocks

Outbreaks of ulcerative vulvitis and balanitis occurred in three commercial sheep flocks in England and Wales. Between 29 and 44 per cent of the ewes were affected; most of the lesions resolved in three weeks. Pathogens such as mycoplasmas, which have previously been associated with these conditions, were not detected despite using improved laboratory techniques. In one of the flocks, ovine herpesvirus type 2 was detected by pcr in the blood of two acutely affected ewes, from the vulval ulcers of one of them, and from the penis of an affected ram.     

Persistence of granulocytic Ehrlichia infection during wintertime in two sheep flocks in Norway

Granulocytic Ehrlichia infection in sheep is common in Norway in areas with Ixodes ricinus. In this study, 2 sheep flocks that had been grazing on I. ricinus infested pastures the previous season, were blood sampled after being housed indoors for nearly 6 months during wintertime. Thirty animals from each flock were examined for granulocytic Ehrlichia infection in the peripheral blood by blood inoculation studies, stained blood smear evaluation, polymerase chain reaction (PCR) analysis and serology (IFA-antibodies). The animals were sampled twice within a three-week period, the first time before and the second time after lambing. Two sheep in one flock were found Ehrlichia positive by both blood smear evaluation and PCR before lambing, and 3 sheep were found positive after lambing; 2 by blood smear examination and 3 by PCR. In the other flock, no sheep was found infected before lambing, but 2 ewes were found positive after lambing by both blood smear evaluation and PCR. In the first flock, 87% of the animals were found seropositive before lambing, and the mean antibody titre (log10 +/- SD) to E. equi was 2.45 +/- 0.401. In the second flock, 40% were found seropositive before lambing, and the mean antibody titre was 1.93 +/- 0.260. Seroprevalence and mean antibody titre in these 2 flocks were significantly different (p < 0.001). The present study indicates that sheep may be a reservoir host for granulocytic Ehrlichia infection from one grazing season to the next under natural conditions in Norway.     

Ovine toxoplasmosis: Seroconversion during pregnancy and lamb birth rate in Uruguayan sheep flocks

Specific anti-Toxoplasma gondii antibodies were analyzed by latex agglutination during the 5 months of pregnancy in the serum of sheep from two flocks in the Uruguayan north-west: one flock (79 sheep) kept under an intensive management system and the other (494 sheep) kept under an extensive management system. Titers obtained using the latex test correlated with those obtained by indirect immunofluorescence. Pregnancy was confirmed by laparoscopy in all sheep from the smaller flock and by determination of serum progesterone levels in the seroconverted sheep from the larger flock. The percentage of sheep originally exhibiting significant serum levels of anti-T. gondii anti-bodies (13.9% in the smaller flock and 28.5% in the larger one) as well as the observed levels of seroconversion (22.8% and 7.7%, respectively), indicated a high prevalence of this infection in the north-west of Uruguay. In addition, birth rates of seroconverted sheep in the larger flock were significantly different from those of non-seroconverted animals. These results, although preliminary, suggest that Toxoplasma infection would produce considerable economic losses in extensive ovine production in Uruguay.     

Toxoplasmosis and other causes of abortions in sheep from north central United States

Between 1983 and 1989, we examined 1,201 aborted fetuses and dead lambs from the north central United States. Toxoplasmosis was diagnosed in 17.5%, campylobacteriosis in 9.9%, chlamydiosis in 4.7%, and miscellaneous infections in 15.1%. Inflammatory lesions suggestive of infectious causes were seen in 13%. Noninfectious causes were identified in 6.1%, and a diagnosis was not reached in 33.3%. An agglutination test was used to detect Toxoplasma gondii-specific antibodies in ovine fluids. Toxoplasma gondii antibodies were detected in 223 of 1,064 (20.9%) fluids from fetuses and dead lambs. Of 201 seropostive (greater than or equal to 16) fetuses and lambs, T gondii antibody titers (reciprocal) were 16 (21 fetuses and lambs), 32 (10 fetuses and lambs), 64 (2 fetuses and lambs), 128 (7 fetuses and lambs), 256 (9 fetuses and lambs), 512 (5 fetuses and lambs), 1,024 (15 fetuses and lambs), 2,048 (13 fetuses and lambs), 4,096 (13 fetuses and lambs), 8,196 (13 fetuses and lambs), 16,392 (19 fetuses and lambs), and greater than or equal to 32,784 (74 fetuses and lambs).     

The estimated prevalence of Johne's disease infected sheep flocks in Australia

OBJECTIVE: To estimate the likely geographical distribution and flock-prevalence of ovine Johne's disease (OJD) in Australia. DESIGN: A cross-sectional study design was used. PROCEDURE: The results of abattoir surveillance for OJD carried out during 2000 were analysed to estimate the prevalence of infected flocks in three regions of New South Wales and in other States. A Bayesian approach was used to adjust apparent prevalence estimates for the assumed flock-sensitivity and flock-specificity of abattoir surveillance, and to allow for uncertainty about the true values of these measures. RESULTS: The 95% probability limits for flock-prevalence at 31 December 2000 were 0.04%-1.5%, 8%-15% and 29%-39% for low, moderate and high prevalence regions of New South Wales respectively. The other States generally had an upper 97.5% probability limit of about 1% or less. Based on these estimates about 6 to 10% of flocks in New South Wales and 2.4 to 4.4% of flocks Australia-wide are likely to be infected. CONCLUSION: This study suggests that OJD has a highly clustered distribution in Australia, and provides estimates of the prevalence of infected flocks by State or region. Based on this analysis there were probably between 2000 and 3700 infected flocks in Australia at 31 December 2000, with more than 80% of these in a relatively small geographic area of central and southern New South Wales. Some States, such as Queensland and Western Australia, may have a prevalence equal or close to 0%, however the technique used was unable to demonstrate the absence of infection in these States with the intensity of surveillance undertaken to date.     

Epidemiological modelling of chlamydial abortion in sheep flocks

Chlamydophila (C.) abortus, responsible for chlamydial abortion (commonly known as Enzootic Abortion of Ewes [EAE]), causes major financial losses to the sheep industry worldwide. There remain many uncertainties surrounding the epidemiology of EAE. The aim of this study was to construct an epidemiological model to simulate EAE based on current knowledge of the disease, and in doing so, identify knowledge gaps that need to be addressed through further research. Key parameters that impact upon the development of the disease, such as the rate of contact between na?ve ewes and infected material, are defined. Sensitivity analysis was undertaken for parameter values that are unknown to explore their impact upon the pattern of disease. The simulated results show the importance of the transmission rate (i.e. contact) and the number of infected replacements introduced at the start of an outbreak. Depending upon the rate of transmission, the year in which the peak number of affected ewes occurs and the number of years over which a high number of animals are affected varies. This suggests that a better understanding of the underlying processes that drive transmission of C. abortus is needed. Furthermore, if infected ewes could be identified prior to parturition, when they shed the organism in large numbers, the impact of EAE on sheep flocks could be greatly reduced.     

The extent and cause of perinatal lamb mortality in 3 flocks of Merino sheep

Autopsies were performed on lamb carcases from 2 groups of Merino ewes lambing in paddocks in spring 1978 and from 1 group lambing in pens in 1980 in southwest Queensland. These showed that the main causes of death were starvation due to failure of the lamb to obtain milk, problems at parturition causing death during or shortly after birth and, in some cases, predation. The majority of lambs died within 1 week of birth with the highest mortalities occurring in the lighter lambs. In the pen study, mean birth weight of lambs that died was 3.0 (s.d. = +/- 0.5) kg. The mean daily weight loss of lambs that died of starvation in the pens was 0.22 kg and the mean loss to autopsy was 0.35 kg. In the pen study, there were more lamb deaths, deaths from starvation, mismothering and desertion in each of 2 groups fed a below maintenance ration than in an above maintenance group. More lambs died and more lamb deaths were due to starvation in a group with unsound udders than in a sound udder group. The results are similar to those found by workers investigating perinatal lamb mortality in other areas. Their significance is discussed in relation to Merino sheep flocks in southwestern Queensland.     

Epidemiological survey of cestode-larva disease in Greek sheep flocks

The epidemiological status of hydatidosis, cysticercosis, and gid in sheep and the production practices of sheep farmers that increase the risk of exposure of sheep to infecting agents of these diseases were investigated in Thessaly, central Greece during 2002-2006. A total of 700 hoggets (sheep up to the age of 1 year) and 1500 adult sheep were examined randomly at an abattoir survey and the prevalences of hydatidosis and cysticercosis were found 39.32% and 29.41%, respectively. Hoggets had significantly lower prevalences of hydatidosis and cysticercosis compared to adult sheep (p<0.001). The distribution of parasitic cysts showed an overdispersion pattern mostly in the hogget population. The proportion of fertile hydatid cysts was significantly higher in hoggets compared to adult sheep (p<0.001). A cohort of 74 sheep flocks was observed during the same period in a prospective survey to assess the incidence of gid. A total of 57 sheep belonging to 15 flocks (20.27% of investigated flocks) developed clinical signs of gid at an annual rate of 11.40+/-4.77 (95% C.I.). In the infected flocks there were 3.80+/-0.92 (95% C.I.) gid cases per flock. The mean age of onset of clinical signs for all sheep was 11.86+/-1.33 months (95% C.I.) (range 5-22 months) while for hoggets was 8.48+/-0.73 (95% C.I.) (range 5-12 months) and for adult sheep 17.23+/-1.42 (95% C.I.) (range 13-22 months). A significant difference was observed in the prevalence of unilateral blindness between hoggets (31.42%) and adult sheep (4.54%) (p<0.05). The most common production practices identified in a questionnaire survey of sheep farmers that may increase the risk of exposure of sheep to hydatidosis, cysticercosis, and gid were the improper disposal of dead animals, the access of farm dogs to offal of slaughtered sheep, the carelessness of farmers to treat farm dogs with anthelmintics, and the grazing of flocks in fields where stray dogs have free access.     

Endemic sheep scab: risk factors and the behaviour of upland sheep flocks

Since the deregulation of sheep scab in 1992, the number of scab outbreaks per year in the UK has increased rapidly; there has been an estimated 60-fold increase in outbreak incidence between 1992 and 2007. How best to focus management or eradication efforts has therefore been an issue of ongoing debate. Previous work has shown that scab outbreaks occur repeatedly on some farms whereas others never or rarely experience outbreaks. Here, to consider why this pattern occurs, and to quantify the risk of scab associated with different husbandry practices, face-to-face interviews with farmers at 16, randomly selected, repeat-outbreak farms and 16 matched farms with no or little history of scab over the previous 10 years, were used to identify associated risk factors. This showed that farms using common grazing were at significantly higher risk of infestation than farms not using common grazing, as were farms that had direct contact with neighbours' sheep and that had neighbours with scab. To further demonstrate the risk of common grazing, a survey of sheep on one common in south Wales showed that there was significant mixing of sheep from three farms, highlighting the potential for scab transmission between flocks. Common grazing, associated with upland regions, would appear to be the largest single obstacle to effective national scab control in the UK. The results suggest that a cost-effective approach to scab control may be to consider upland and lowland farms as separate epidemiological systems, with upland regions requiring a co-ordinated, systematic approach to achieve any significant management of the problem. In contrast, on lowland farms outbreaks are already largely contained effectively through good biosecurity and treated on a case-by-case basis if they occur.     

Diagnosis and control of neonatal losses in sheep

Perinatal mortality is affected by a variety of management factors and disease processes that create significant losses for the sheep industry. Annual production losses prior to weaning include roughly 15% to 20% of the lamb crop. The majority of these perinatal losses occur during the prenatal, natal, and early postnatal periods, with the predominant wave of mortality occurring during the first several days following birth. Causes of perinatal mortality may vary between flocks and between geographic areas; however, four dominant categories of lamb loss consistently surface: (1) abortions; (2) hypothermia, starvation, and exposure; (3) pneumonia; and (4) stillbirth and dystocia. They account for roughly 50% to 75% of all documented perinatal losses. Veterinarians and producers need to work together to document the type of losses that occur in a given flock and then design economic prevention programs that address these problems. In most cases, traditional prevention programs will need to be replaced by a comprehensive management scheme addressing nutrition, genetics, housing, marketing, lambing husbandry, and labor.     

The seroprevalence of coxiellosis (Q fever) in Ontario sheep flocks.

A serological survey for Coxiella burnetii was undertaken on a randomly selected population of 103 Ontario sheep flocks. Twenty-two flocks had at least one positive ewe; seven flocks had two or more reactors. The positive flocks were geographically clustered northwest of Guelph. Crutch-clipping of the ewe's wool prior to lambing, and total confinement housing at lambing in winter and spring seemed to lower the probability of seroreactivity of the flock (p less than 0.05). The study suggests that sheep are not a major reservoir for Coxiella burnetii in Ontario.