Losses over a 2-year period associated with fetal infection with the bovine viral diarrhea virus in a beef cow-calf herd in Saskatchewan

Modeling the Effect of Bovine Viral Diarrhea Virus in Australian Beef Herds

Bovine viral diarrhea virus (BVDV) is an economically important disease in Australian beef farming. The disease typically results in low-level production losses that can be difficult to detect for several years. Simulation modeling can be used to support the decision to control BVDV; however, current BVDV simulation models do not adequately reflect the extensive farming environment of Australian beef production. Therefore, the objective of this study was to develop a disease simulation model to explore the impact of BVDV on beef cattle production in south-east Australia. A dynamic, individual-based, stochastic, discrete-time simulation model was created to simulate within-herd transmission of BVDV in a seasonal, self-replacing beef herd. We used the model to simulate the effect of herd size and BVDV introduction time on disease transmission and assessed the short- and long-term impact of BVDV on production outputs that influence the economic performance of beef farms. We found that BVDV can become established in a herd after a single PI introduction in 60% of cases, most frequently associated with the breeding period. The initial impact of BVDV will be more severe in smaller herds, although self-elimination is more likely in small herds than in larger herds, in which there is a 23% chance that the virus can persist for >15 years following a single incursion in a herd with 800 breeders. The number and weight of steers sold was reduced in the presence of BVDV and the results demonstrated that repeat incursions exacerbate long-term production losses, even when annual losses appear marginal. This model reflects the short- and long-term production losses attributed to BVDV in beef herds in southeast Australia and provides a foundation from which the influence and economic utility of BVDV prevention in Australian beef herds can be assessed.

Seroprevalence of Bovine Viral Diarrhea Virus in Local Borana Cattle Breed and Camels (Camelus dromedarius) in Ethiopia

Background

Bovine viral diarrhea, caused by bovine viral diarrhea virus (BVDV), has been considered a disease of cattle but is now emerging in camels. In Ethiopia it has been detected in exotic and cross-bred dairy cattle but no information is available on its occurrence in indigenous cattle breeds and camels. This study was, therefore, conducted to estimate the prevalence of BVDV infection in indigenous Borana cattle and camels (Camelus dromedarius) in Moyale and Miesso pastoral districts.

Methodology

Serological investigation was carried out on 219 cattle from 44 herds and 137 camels from 11 herds in contact with the selected cattle herds in Boranara zone and 348 camels from 41 herds in Shinille zone. The sera samples were tested using a competitive enzyme lnked immunosorbent assay (c-ELISA) to detect antibodies against p80 protein of BVDV. In addition, all of the cattle sera were tested using antigen detection ELISA for identification of persistent infection.

Results

Among the 219 cattle tested, 177 (80.82%; 95% CI: 74.97–85.81) were found to be positive for antibodies against BVDV in Moyale district, Borena Zone. The prevalence varied among different age groups and parity. The highest prevalence was observed in cattle aged 8 years and older (84.0%; 95% CI: 69.6–98.4) and in primiparous cattle (85.5%; 95% CI: 76.2–94.8). Two of the 219 cattle tested (0.05%; 95% CI: 0.02–0.08) were found to be positive with antigen detection ELISA. In addition, out of a total of 137 camels tested, two (1.46%; 95% CI: 0.18–5.17) were found to be positive in this district. Among the 348 camels tested, eight (2.29%; 95% CI: 0.99–4.485) were found to be positive for antibodies against BVDV. In conclusion, this study revealed a high prevalence of infection in Borana cattle. In addition, it recorded the occurrence of infection with BVDV in camel herds. None of the camels tested positive for the antigen of BVDV using antigen ELISA.

Causes of neonatal calf diarrhea and mortality in pasture-based dairy herds in Uruguay: a farm-matched case-control study

Neonatal calf diarrhea (NCD) and mortality cause significant losses to the dairy industry. The preweaning dairy calf mortality risk in Uruguay is high (15.2%); however, causes for these losses are largely unknown. This study aimed to assess whether various pathogens were associated with NCD and death in Uruguayan dairy calves and whether these infections, diarrhea, or deaths were associated with the failure of transfer of passive immunity (FTPI). Contemporary diarrheic (n = 264,) and non-diarrheic (n = 271) 1- to 30-day-old calves from 27 farms were sampled. Feces were analyzed by antigen-capture ELISA for Cryptosporidium spp., rotavirus, bovine coronavirus, and Escherichia coli F5+, RT-PCR for bovine astrovirus (BoAstV), and bacterial cultures for Salmonella enterica. Blood/serum was analyzed by RT-PCR or antigen-capture ELISA for bovine viral diarrhea virus (BVDV). Serum of ≤ 8-day-old calves (n = 95) was assessed by refractometry to determine the concention of serum total proteins (STP) as an indicator of FTPI. Whether the sampled calves died before weaning was recorded. At least one pathogen was detected in 65.4% of the calves, and this percentage was significantly higher in diarrheic (83.7%) versus non-diarrheic (47.6%) calves. Unlike the other pathogens, Cryptosporidium spp. and rotavirus were associated with NCD. Diarrheic calves, calves infected with any of the pathogens, and calves infected with rotavirus had significantly lower concentrations of STP. Diarrheic calves had higher chances of dying before weaning than non-diarrheic calves. Diarrheic calves infected with S. enterica were at increased risk of mortality. Controlling NCD, salmonellosis, cryptosporidiosis, and rotavirus infections, and improving colostrum management practices would help to reduce calf morbi-mortality in dairy farms in Uruguay.

Review and critical discussion of assumptions and modelling options to study the spread of the bovine viral diarrhoea virus (BVDV) within a cattle herd

Relevance of epidemiological models depends on assumptions on the population structure and dynamics, on the biology of the host-parasite interaction, and on mathematical modelling. In this paper we reviewed published models of the bovine viral diarrhoea virus (BVDV) spread within a herd. Modelling options and assumptions on herd dynamics and BVDV transmission were discussed. A cattle herd is a population with a controlled size. Animals are separated into subgroups according to their age or their physiological status inducing heterogeneity of horizontal transmission. Complexity of models results from: (1) horizontal and vertical virus transmission, (2) birth of persistently infected animals, (3) excretion by transiently and persistently infected animals. Areas where there was a lack of knowledge were identified. Assumptions on the force of infection used to model the horizontal virus transmission were presented and discussed. We proposed possible ways of improving models (e.g. force of infection, validation) and essential model features for further BVDV models.

Mechanism of action of a pestivirus antiviral compound

We report here the discovery of a small molecule inhibitor of pestivirus replication. The compound, designated VP32947, inhibits the replication of bovine viral diarrhea virus (BVDV) in cell culture at a 50% inhibitory concentration of approximately 20 nM. VP32947 inhibits both cytopathic and noncytopathic pestiviruses, including isolates of BVDV-1, BVDV-2, border disease virus, and classical swine fever virus. However, the compound shows no activity against viruses from unrelated virus groups. Time of drug addition studies indicated that VP32947 acts after virus adsorption and penetration and before virus assembly and release. Analysis of viral macromolecular synthesis showed VP32947 had no effect on viral protein synthesis or polyprotein processing but did inhibit viral RNA synthesis. To identify the molecular target of VP32947, we isolated drug-resistant (DR) variants of BVDV-1 in cell culture. Sequence analysis of the complete genomic RNA of two DR variants revealed a single common amino acid change located within the coding region of the NS5B protein, the viral RNA-dependent RNA polymerase. When this single amino acid change was introduced into an infectious clone of drug-sensitive wild-type (WT) BVDV-1, replication of the resulting virus was resistant to VP32947. The RNA-dependent RNA polymerase activity of the NS5B proteins derived from WT and DR viruses expressed and purified from recombinant baculovirus-infected insect cells confirmed the drug sensitivity of the WT enzyme and the drug resistance of the DR enzyme. This work formally validates NS5B as a target for antiviral drug discovery and development. The utility of VP32947 and similar compounds for the control of pestivirus diseases, and for hepatitis C virus drug discovery efforts, is discussed.

The water intake of ewes

1. Two experiments were carried out with non-pregnant ewes in which individual drymatter intake (DMI) and total water intake (TWI) were measured. TWI was closely correlated with DMI; TWI/unit DMI was higher for silage than for cubed dried grass and with both foods water intakes were higher than with long hay.

2. Twelve ewes were fed on silage and twelve on hay from the 9th to the 19th week of pregnancy. TWI/unit DMI of each feed doubled during this period. Another twenty-four ewes were fed on silage from the 14th to the 20th week of pregnancy. TWI/unit DMI was positively related to litter size.

3. Fifteen ewes were fed on hay from the 4th week of pregnancy until the 7th week of lactation. Milk yield was estimated weekly. Six non-pregnant ewes were controls. TWI/unit DMI for the seven twin-bearing and the nine single-bearing ewes in the last 4 and 3 weeks of pregnancy respectively was significantly higher than that of the six non-pregnant ewes. In the control group TWI/unit DMI was closely related to environmental temperature. In the first 4 weeks of lactation TWI/unit DMI was greater than the sum of TWI/unit DMI of the non-pregnant ewes plus the water in the milk.

4. The results supplement those used by the Agricultural Research Council (1965) to assess the water requirements of sheep.

EFFECTS OF LOW FLUCTUATING TEMPERATURES ON FARM ANIMALS: IV. INFLUENCE OF TEMPERATURE ON MILK YIELD AND MILK COMPOSITION

Changes in milk yield and milk composition from mature Holstein-Friesian cows managed under low fluctuating environmental temperatures have been presented. The experiment conducted at the University of Saskatchewan, Saskatoon, lasted for 106 days during the winter of 1956–57. Loafing barn temperatures, measured continuously in degree-hours per day (d-h/day) ranged from 110 to 1202 and daily minimum ambient air temperature (DMAAT) varied from −5° to 38°F.As temperature decreased below 25°F., daily yield of milk decreased significantly. Milk yield was unaffected by d-h/day at mean temperatures over 25°F. (600 d-h/day) and on days colder than 600 d-h/day the temperature effect on milk yield was curvilinear. The rate of decline in milk yield (pounds) was four times greater on days when DMAAT was below 10°F. than on days when DMAAT was above 10°F. While DMAAT had a significant effect on milk total-solids percentage and a highly significant negative effect on crude protein yield, the effect of d-h/day on these two factors was not significant. Neither DMAAT nor d-h/day had a significant effect on butterfat yield and percentage, fat-corrected milk yield, total-solids yield, solids-not-fat yield and percentage, or crude protein percentage.Stage of lactation had a significant effect on all characteristics studied except butterfat percentage.Under conditions of declining lactation and a high, variable plane of nutrition, cows that had been subjected to gradually cooling variable low temperatures were influenced by low daily minimum temperatures (DMAAT) to a greater degree than low mean daily temperatures (d-h/day).

EFFECTS OF LOW FLUCTUATING TEMPERATURES ON FARM ANIMALS.: III. INFLUENCE OF AMBIENT AIR TEMPERATURE ON FEED INTAKE OF LACTATING HOLSTEIN-FRIESIAN COWS

This report presents effects of low temperatures on the feed consumption and efficiency of milk production of six mature, lactating, Holstein-Friesian cows that were confined in stanchions for three fortnightly experimental periods during which ambient temperatures measured in degree-hours per day (d-h/day) ranged from 110 to 1152 and daily minimum ambient air temperature (DMAAT) varied from 0° to 38°F. Applying results obtained, it was calculated that as temperatures decreased, i.e., d-h/day increased from 100 to 1200 and DMAAT decreased from 40° to 0°F, average daily intakes of total dry matter, hay, and gross and digestible Calories increased approximately 6.4 lb., 5.3 lb., 13 Therms and 9 Therms, respectively. Each of these increases was statistically significant at the 1 per cent level. Reductions in temperature also decreased gross and net caloric efficiencies of milk production approximately 10 and 8.5 per cent, respectively. These decreases were significant at the 2 per cent level. No correlation was evident between crude protein utilization and temperature.Results indicated that thermal stress was not overcome adequately by supplementary hay intake alone and that appetite stimulation by low temperatures had a carry-over effect continuing at least 24 hours. For continued efficient milk production during winters where low ambient temperatures are prevalent these results suggest it is necessary to provide some form of building insulation, ambient heat and/or provide a high energy supplement to otherwise adequate production rations.