Risk factors associated with Neospora caninum seropositivity in randomly sampled Canadian dairy cows and herds

Our objective was to determine cow- and herd-level risk factors associated with seropositivity for Neospora caninum in a large number of randomly selected Canadian dairy herds, controlling for important confounding variables and co-infections with bovine leukemia virus (BLV), bovine viral diarrhea virus (BVDV) and Mycobacterium avium subspecies paratuberculosis (MAP). Serum samples were obtained from 30 randomly selected cows, where available, in 240 herds using monthly milk testing, within 6 of 10 provinces, and these samples were tested for antibodies against BLV, MAP and N. caninum using commercially available ELISA test kits. Five unvaccinated cattle >6 months old from each herd were tested for antibodies to BVDV using virus neutralization. Most herd-level predictors were obtained through personal interviews with questionnaires administrated to each farm manager. A mixed logistic-regression model was built using N. caninum serostatus at the cow-level as the outcome variable, with herd as a random effect and province as a fixed effect. A BLV seropositive cow was 1.50 times more likely to be seropositive for N. caninum than a BLV-seronegative cow, and this was the only cow-level variable to remain in the final model. Regarding herd-level variables, with “no on-farm dogs” as the baseline, “presence of dogs but not known to eat placentas and/or fetuses” increased the odds of seropositivity for N. caninum by a factor of 1.66. For “presence of dogs known to eat placentas and/or fetuses”, the odds ratio (OR) was 2.75, demonstrating a dose–response relationship. “Using embryo transfer” (OR = 0.69), “asking for a BVDV-negative test before introducing an animal” (OR = 0.30), “using monensin in dry cows” (OR = 0.71), and “heifers having nose-to-nose contact with calves” (OR = 0.73) were all dichotomous variables negatively associated with seropositivity for N. caninum. “Number of milk cows on the farm” (OR = 0.99), and “area (acres) used for forage production” (OR = 0.99) were continuous variables negatively associated with N. caninum seropositivity.     

Efficacy of a BVDV subunit vaccine produced in alfalfa transgenic plants

Bovine viral diarrhea virus (BVDV) is considered an important cause of economic loss within bovine herds worldwide. In Argentina, only the use of inactivated vaccines is allowed, however, the efficacy of inactivated BVDV vaccines is variable due to its low immunogenicity. The use of recombinant subunit vaccines has been proposed as an alternative to overcome this difficulty. Different studies on protection against BVDV infection have focused the E2 protein, supporting its putative use in subunit vaccines. Utilization of transgenic plants expressing recombinant antigens for the formulation of experimental vaccines represents an innovative and cost effective alternative to the classical fermentation systems.The aim of this work was to develop transgenic alfalfa plants (Medicago sativa, L.) expressing a truncated version of the structural protein E2 from BVDV fused to a molecule named APCH, that target to antigen presenting cells (APCH-tE2). The concentration of recombinant APCH-tE2 in alfalfa leaves was 1 μg/g at fresh weight and its expression remained stable after vegetative propagation. A methodology based an aqueous two phases system was standardized for concentration and partial purification of APCH-tE2 from alfalfa. Guinea pigs parentally immunized with leaf extracts developed high titers of neutralizing antibodies. In bovine, the APCH-tE2 subunit vaccine was able to induce BVDV-specific neutralizing antibodies. After challenge, bovines inoculated with 3 μg of APCH-tE2 produced in alfalfa transgenic plants showed complete virological protection.     

Systemic and local immune response in pigs intradermally and intramuscularly injected with inactivated Mycoplasma hyopneumoniae vaccines

The systemic and respiratory local immune response induced by the intradermal administration of a commercial inactivated Mycoplasma hyopneumoniae whole-cell vaccine (Porcilis^® MHYO ID ONCE – MSD AH) in comparison with two commercial vaccines administered via the intramuscular route and a negative control (adjuvant only) was investigated. Forty conventional M. hyopneumoniae-free pigs were randomly assigned to four groups (ten animals each): Group A = intradermal administration of the test vaccine by using the needle-less IDAL^® vaccinator at a dose of 0.2 ml; Group B = intramuscular administration of a commercially available vaccine (vaccine B); Group C = intramuscular administration of the adjuvant only (2 ml of X-solve adjuvant); Group D = intramuscular administration of a commercially available vaccine (vaccine D). Pigs were vaccinated at 28 days of age. Blood and bronchoalveolar lavage (BAL) fluid samples were collected at vaccination (blood only), 4 and 8 weeks post-vaccination. Serum and BAL fluid were tested for the presence of antibodies by ELISA test. Peripheral blood monomorphonuclear cells (PBMC) were isolated to quantify the number of IFN-γ secreting cells by ELISpot. Moreover, cytokine gene expression from the BAL fluid was performed. Total antibodies against M. hyopneumoniae and specific IgG were detected in serum of intradermally and intramuscularly (vaccine B only) vaccinated pigs at 4 and 8 weeks post-vaccination. M. hyopneumoniae specific IgA were detected in BAL fluid from vaccinated animals (Groups A and B) but not from controls and animals vaccinated with the bacterin D (p < 0.05). Significantly higher gene expression of IL-10 was observed in the BAL fluid at week 8 post-vaccination in the intradermally vaccinated pigs (p < 0.05). The results support that the intradermal administration of an adjuvanted bacterin induces both systemic and mucosal immune responses. Moreover, the intramuscularly administered commercial vaccines each had a different ability to stimulate the immune response both systemically and locally.     

Antibody responses to inactivated vaccines and natural infection in cattle using bovine viral diarrhoea virus ELISA kits: Assessment of potential to differentiate infected and vaccinated animals

Bovine viral diarrhoea virus (BVDV) is one of the most common and economically important viral infections of cattle. As vaccination is common in most European countries, differentiation between infected and vaccinated animals is one of the key challenges facing BVDV eradication campaigns. This study was designed to compare the ability of commercial ELISA kits to differentiate antibodies generated following vaccination with four different commercial inactivated BVDV vaccines from antibodies generated following challenge with virulent BVDV. Although none of the tested vaccine–ELISA combinations was able to differentiate an infected from a vaccinated animal (DIVA) at the individual animal level, p80 blocking ELISAs, in combination with inactivated BVDV vaccines, may have some value under certain circumstances at herd level. In most cases, antibody responses to BVDV vaccines cannot be clearly distinguished from responses seen in the early phase of natural infection. No commercial BVD vaccine showed true marker qualities for DIVA using p80 blocking ELISAs.     

The live attenuated bovine viral diarrhea virus components of a multi-valent vaccine confer protection against fetal infection

Fetal infection with bovine virus diarrhea virus (BVDV) causes severe economic loss and virus spread in cattle. This study investigated the ability of modified live BVDV I and II components of a commercially available modified live virus (MLV) vaccine (Breed-Back FP 10, Boehringer Ingelheim Vetmedica Inc.) to prevent fetal infection and abortion, and therefore the birth of persistently infected animals. Heifers immunized with vaccine 4-8 weeks before insemination showed no adverse effects. All vaccinated animals had seroconverted to BVDV 4 weeks after immunization. Pregnant heifers were divided into two vaccination and two control groups and challenged with type I or II BVDV on days 60-90 of gestation. Seroconversion, clinical signs, immunosuppression, viremia, mortality, abortion rate, and fetal infection were studied. Post-challenge, 6/11 (type I challenged) and 8/11 (type II challenged) vaccinated heifers were free from clinical signs of BVD. Post-challenge clinical signs noted in the vaccinated groups were mild to moderate, while all unvaccinated controls had clinical signs ranging from moderate to severe. Viremia was not detected post-challenge in any of the vaccinated heifers. However, 100% of the controls were BVDV viremic on at least 1 day post-challenge. One of 22 vaccinated heifers had transient leukopenia, whereas 2/8 and 6/7 unvaccinated heifers in control groups I and II, respectively, had transient leukopenia. Type II BVDV infection led to abortion or death in 86% of unvaccinated heifers. The corresponding vaccinated group showed no deaths or abortions. All control group fetuses were infected with BVDV. The test vaccine gave 91% (type I BVDV challenged) and 100% (type II BVDV challenged) protection from fetal infection. This vaccine is safe and effective against fetal infection, abortion (type II BVDV) and the birth of persistently infected animals.     

Supplementation with Whole Sunflower Seeds Before Artificial Insemination in Beef Heifers

The objective of this study was to evaluate synchronization and pregnancy rates of beef heifers supplemented with 0.91 kg of whole sunflower seeds for 0, 30, or 60 d before AI. Beef heifers from four locations (n = 1,014) were assigned by BW to treatment (within location) and randomly to AI sire. Heifers at Location 1 (n = 176; mean BW = 332 kg) received either 0- or 60-d sunflower seed treatments. Heifers at Location 2 (n = 397; mean BW = 334 kg) were fed sunflower seeds for 0, 30, or 60 d. Heifers at Locations 3 (n = 211; mean BW = 345 kg) and 4 (n = 230; mean BW = 343 kg) received 0- or 30-d sunflower seed treatments. Within location, diets were formulated to be isocaloric and isonitrogenous. All heifers received melengesterol acetate (0.5 mg/d per head) for 14 d followed 19 d later by an injection of prostaglandin F_2a (PGF) (25 mg). Heifers were bred by AI according to the AM/PM rule except on d 3 when all heifers that had not exhibited estrus were artificially inseminated in mass. Neither 72-h estrous response nor pregnancy rate was affected (P>0.10) by 30- or 60-d sunflower feeding. In summary, feeding 0.91 kg of whole sunflower seeds for either 30 or 60 d before AI did not improve estrous response or pregnancy rate when compared with controls.     

Neospora caninum DNA detection by TaqMan real-time PCR assay in experimentally infected pregnant heifers

Neosporosis has been considered the main cause of abortion between the first and the second trimester of pregnancy in cattle. Therefore, the objective of this study was to identify the presence of Neospora caninum DNA obtained from experimental models based on the evaluation of different areas of the fetal nervous system and organs from heifers previously inoculated with NC-1 after or before insemination. This study was performed with Hereford × Nelore (n = 29) heifers and all animals were considered free of diseases at the beginning of the experiment. All animals were bred by fixed-time artificial insemination (TAI) and allocated as follows: (a) seronegative heifers subjected to TAI (TAI, n = 9), (b) heifers infected with N. caninun 60 days prior to TAI (NC-1 + TAI, n = 9), and (c) heifers submitted to TAI and infected with N. caninum 60 days later (TAI + NC-1, n = 11). The pregnancy was confirmed by transrectal ultrasonography 35 days after TAI and evaluated every 30 days until the end of gestation. Fetuses were collected surgically at 170 days of gestation, and immediately necropsied to remove tissues aseptically. Samples of the central nervous system (CNS), heart, kidney, lung, liver, skeletal muscle and caruncle were collected for DNA extraction. Days of gestation at abortion and interval from abortion to first insemination were examined by Student's t-test. At 35 days of gestation the pregnancy rates in the group NC-1 + TAI (4/9, 44.4%) was lower than in the control group (8/9, 88.8%, P < 0.05). At 60 days, the pregnancy rates in the NC-1 + TAI group (0/4, 0%) was lower compared to TAI + NC-1 (5/7, 71.4%) and control (6/8, 75.0%) groups (P < 0.05). Animals from the group NC-1 + TAI were re-inseminated 60 days after the first TAI. After pregnancy losses throughout the study, 5 animals (TAI), 3 animals (NC-1 + TAI) and 5 animals (TAI + NC-1) maintained pregnancy until 170 days of gestation. TaqMan RT-PCR demonstrated the presence of N. caninum DNA in the medulla and right posterior cortex in 3 out of 5 fetuses from the TAI + NC-1 group. We concluded that heifers infected after TAI had a higher incidence of the parasite at the fetus CNS. Identification of N. caninum by TaqMan RT-PCR would assist in the investigation of infection and in the evaluation of vaccines or therapeutic drugs to control neosporosis in cattle.     

Effects of Lactation and Prenatal Androgenization on the Performance,Carcass Composition,and Longissimus Muscle Sensory Characteristics of Heifers in the Single-Calf Heifer System

Two experiments were conducted to evaluate feedlot performance, lactational characteristics, and carcass composition and quality of heifers and the performance of their calves in a single-calf heifer (SCH) system. In Exp. 1, 13 [10 lactating (L) and 3 nonlactating (NL)] prenatally androgenized (PA) heifers, born to cows implanted with testosterone propionate (TP) and 19 (13 L and 6 NL) control (C) heifers, born to nonimplanted cows, were used. Heifers were calved and the pairs were placed in feedlot pens to evaluate the effects of PA on feedlot performance and lactation. Heifers were fed an 85% concentrate diet and fed to a compositional endpoint of 1.1 cm of subcutaneous fat cover, at which point calves were weaned and heifers slaughtered approximately 12 h later. The NL heifers consumed 17.0% less (P<0.01) dry matter and were 30.8% more (P<0.01) efficient in feed conversion. When calf performance was included, overall feed efficiency of L heifers was 26.9% greater (P<0.05; 0.151 vs 0.119) than that of the NL feedlot heifers. Prenatal androgenization had no effect on heifer performance. Four percent fat-corrected milk yield averaged 7.79 and 5.62 kg/d for PA and C heifers, respectively. The NL heifers had 11.0% greater (P<0.01) marbling score and yield grades were 3.77 and 3.03 (P<0.05) for NL and L heifers, respectively. Livers (P<0.01) and kidneys (P<0.05) as a percentage of shrunk weight were heavier for L heifers than for NL heifers. Two carcasses were classified as hard-boned (C-maturity) and 74% received a USDA Choice grade. The L heifers tended (P<0.10) to have lower taste panel tenderness scores; however, shearforce was similar (P=0.81) for L and NL heifers. In Exp. 2, 24 Angus × Holstein heifers were utilized in the single-calf heifer system, similar to Exp. 1. Calves were weaned from their dam between d 64 and 89 postpartum. Heifers that had their calves early weaned (EW) gained 44.2% faster (P<0.01) and consumed 10.8% less (P<0.05) DM than L heifers. The EW heifers were 60.0% more (P<0.01) efficient than L heifers. However, when calf performance was included with heifer performance, L heifers were 23.7% more (P<0.05) efficient than EW heifers. The EW heifers had 18.9% heavier (P<0.01) hot carcasses than L heifers. Backfat thickness was 1.07 and 0.66 cm (P<0.01) for the EW and L heifers.     

A vaccine formulation combining rhoptry proteins NcROP40 and NcROP2 improves pup survival in a pregnant mouse model of neosporosis

Currently there are no effective vaccines for the control of bovine neosporosis. During the last years several subunit vaccines based on immunodominant antigens and other proteins involved in adhesion, invasion and intracellular proliferation of Neospora caninum have been evaluated as targets for vaccine development in experimental mouse infection models. Among them, the rhoptry antigen NcROP2 and the immunodominant NcGRA7 protein have been assessed with varying results. Recent studies have shown that another rhoptry component, NcROP40, and NcNTPase, a putative dense granule antigen, exhibit higher expression levels in tachyzoites of virulent N. caninum isolates, suggesting that these could be potential vaccine candidates to limit the effects of infection. In the present work, the safety and efficacy of these recombinant antigens formulated in Quil-A adjuvant as monovalent vaccines or pair-wise combinations (rNcROP40 + rNcROP2 and rNcGRA7 + rNcNTPase) were evaluated in a pregnant mouse model of neosporosis. All the vaccine formulations elicited a specific immune response against their respective native proteins after immunization. Mice vaccinated with rNcROP40 and rNcROP2 alone or in combination produced the highest levels of IFN-γ and exhibited low parasite burdens and low IgG antibody levels after the challenge. In addition, most of the vaccine formulations were able to increase the median survival time in the offspring. However, pup survival only ensued in the groups vaccinated with rNcROP40 + rNcROP2 (16.2%) and rNcROP2 (6.3%). Interestingly, vertical transmission was not observed in those survivor pups immunized with rNcROP40 + rNcROP2, as shown by PCR analyses. These results show a partial protection against N. caninum infection after vaccination with rNcROP40 + rNcROP2, suggesting a synergistic effect of the two recombinant rhoptry antigens.     

Validation of betapropiolactone (BPL) as an inactivant for infectious bovine rhinotracheitis (IBR) virus

Infectious bovine rhinotracheitis (IBR) virus causes vulvovaginitis, abortion and respiratory disease in cows and heifers. Betapropiolactone (BPL) is a disinfectant, effective against bacteria, fungi and viruses. It is also used to prepare inactivated vaccines because it destroys the nucleic acid core of viruses but does not damage the capsid. For the validation of BPL when used as an inactivant, it is more important to assure the quality of inactivating agent and the validity of the inactivation process. In the present study, the inactivation kinetics of IBR virus was determined with different concentration of BPL (1:250, 1:500, 1:1000, 1:1500, 1:2000 and 1:2500) at 4 and 37 °C. The result indicated that the BPL at 4 °C was able to inactivate the IBR virus within 4, 5 and 12 h with the concentration of 1:250, 1:500 and 1:1000, respectively. BPL at 37 °C was able to inactivate virus within 30 min with the concentration of 1:250. BPL with the concentration of 1:500 and 1:1000 were able to inactivate the virus within 120 min at 37 °C. Based on the kinetic study seven formulations were prepared and a sero conversion study of IBR inactivated vaccine was carried out. Serological response in animals to different formulations did not differ significantly (P > 0.05).     

Hypothalamic deafferentation in prepuberal beef heifers: Effects of gonadotropin-releasing hormone and estradiol benzoate on luteinizing hormone secretion

Hypothalamic control of luteinizing hormone (LH) secretion was investigated in crossbred beef heifer calves by comparing anterior (AHD), posterior (PHD), and complete (CHD) hypothalamic deafferentation with sham operated controls (SOC). Heifers (n = 16) were fitted with an indwelling jugular catheter for 6 days before cranial surgery, and assigned randomly to treatments. Blood for radioimmunoassay of LH was collected sequentially at 15-min intervals during an 8-h period on days ? 1 before and day 6 after hypothalamic deafferentation or sham operation. On the day of surgery, blood samples were collected sequentially at 15-min intervals 2 h before induction of anesthesia and throughout surgery and early recovery. Seven months after hypothalamic deafferentation, all experimental and sham operated heifers were ovariectomized and treated with vegetable oil (i.m.) plus saline (i.v.), vegetable oil plus gonadotropin releasing hormone (GnRH), estradiol benzoate (EB, 1 mg) in vegetable oil. After ovariectomy basal plasma concentrations of LH increased (P < 0.01) compared with the low circulating hormone levels before ovariectomy. The amplitude of LH response to GnRH was greater (P < 0.01) in CHD and PHD when compared with SOC and AHD heifers. Injection of EB failed to induce a LH surge in CHD and PHD 900–1100 min later when compared with the robust response seen in SOC and AHD heifers. Injection of EB plus GnRH elicited LH release in all deafferentated and sham operated heifers. These results indicate a transient change in LH secretion after AHD or CHD in prepuberal heifers with intact ovaries. After OVX, the integrity of the neural connection of the posterior hypothalamus is required for EB-induced LH release in beef heifers.     

Safety of a modified-live combination vaccine against respiratory and reproductive diseases in pregnant cows

A combination vaccine (Bovi-Shield FP4 + L5, Pfizer Animal Health) containing modified-live virus (MLV) components against bovine herpesvirus-1 (BHV-1), bovine viral diarrhea virus BVDV), parainfluenza virus-3 (PI3), bovine respiratory syncytial virus (BRSV), and inactivated cultures of Leptospira canicola, grippotyphosa, hardjo, icterohaemorrhagiae, and pomona was evaluated for safety in pregnant beef and dairy animals. Heifers vaccinated prebreeding with the minimum immunizing dose (lowest antigen level initiating immunizing effects) of the vaccine's MLV BHV-1 or BVDV components and during pregnancy (approximately 200 days of gestation) with vaccine containing 10x doses of the same BHV-1 and BVDV components delivered live, healthy calves that were determined to be serologically negative (titer less than 1:2) for neutralizing antibodies to BHV-1 and BVDV prior to nursing. Additionally, in three field safety studies, previously vaccinated cows and heifers that received a field dose (vaccine containing antigen levels required for commercial sale of the MLV combination vaccine during either the first, second, or third trimester of pregnancy had abortion rates similar to those of pregnant cows and heifers vaccinated during the same stage of pregnancy with sterile water diluent.     

The impact of dystocia on dairy calf health,welfare, performance and survival

Up to one-third of dairy calves are born after dystocia and this is a major cause of calf mortality. This study investigated the neonatal physiology, survival, health and subsequent growth of dairy calves following dystocia and is the first longitudinal study to analyse multiple effects and to look beyond the perinatal period.A total of 455 live born Holstein calves (N: No assistance, n = 360; FN: Farmer assistance but normally presented calf, n = 82; FM: Farmer assistance of malpresented calf, n = 13) were followed from birth to first service (heifers) or until leaving the farm (bulls). Compared to N calves, FN and FM animals had higher salivary cortisol concentrations at day 1 (P < 0.001) and FN calves had lower passive immune transfer (P = 0.03). Dystocia had no biologically significant impact on rectal temperature throughout the first 4 days (P > 0.05). During the first 60 days, FM calves had a higher proportion of days with non-routine health treatments (P < 0.05) and, by the time of weaning, mortality in FN and FM heifers was higher than in N calves (2.8×; P < 0.01). However, in surviving calves, growth to first service was not affected by dystocia category (P > 0.05).Calves which survive dystocia experience lower passive immunity transfer, higher mortality and higher indicators of physiological stress. Such calves have poorer welfare in the neonatal period and possibly beyond. Strategies need to be implemented to improve the subsequent health and welfare of such calves and to lower the incidence of dystocia.     

Cattle Grazing Distribution and Efficacy of Strategic Mineral Mix Placement in Tropical Brazilian Pastures

A study was conducted in Brazil to identify factors affecting grazing distribution of yearling Nelore cross heifers and to evaluate the efficacy of placement of a salt–mineral mix away from water to improve uniformity of grazing. Two pastures (25 ha and 42 ha) were evaluated for four 15-d sessions. Mineral mix was placed 590 m to 780 m from water during two sessions and at water for two sessions. Stubble heights were measured at the beginning and end of each session in 1-ha subunits of each pasture. Cattle locations were recorded on day 13 and 14 of each session by horseback observers. Heifers avoided areas with a preponderance of forbs and taller grass (P < 0.001). For the first 15 days of the study cattle avoided subunits farther from water. Thereafter, horizontal distance from water had no affect on grazing use (P > 0.10). Stubble height reduction was more uniform (P < 0.05) when the mineral mix was at water compared to away from water. In contrast, heifers spent less time farther from water when mineral mix was placed at water (P = 0.02) based on visual observations. Strategic placement of a salt–mineral mix away from water does not appear to be a reliable tool to improve cattle grazing distribution in humid tropical pastures from 25 ha to 45 ha in size.     

Evaluation of Three Estrous Synchronization Protocols in Beef Heifers

Objectives of this study were to evaluate synchronization, conception, and pregnancy rates of heifers synchronized with melengestrol acetate (MGA)-prostaglandin F_2α (PGF_2α,), Select Synch, or Select Synch preceded by MGA (MGA-Select Synch). Heifers in the MGA-PGF_2α group (n = 209; BW = 378 kg) received MGA (0.5 mg/ d per heifer) for 14 d and PGF_2α (25 mg) 19 d later. Select Synch heifers (n = 213; BW = 374 kg) received gonadotropin-releasing hormone (GnRH; 100 μg) followed by PGF_2α (25 mg) 7 d later. The MGA-Select Synch heifers (n = 210; BW = 373 kg) were fed MGA (0.5 mg/d per heifer) for 7 d, GnRH (100 μg) the day following the last MGA feeding, and PGF_2α (25 mg) 7 d after GnRH. More (P<0.01) heifers were in estrus 1 to 4 d before PGF2a administration in both the Select Synch (20%) and MGA-Select Synch (24%) groups than in the MGA-PGF_2α (4%) group. Pregnancy rates for heifers in estrus early (d 1 to 4 before PGF_2α) were greater (P<0.05) for both Select Synch (55%) and MGA-Select Synch (63%) compared with MGA-PGF_2α heifers (18%). Synchronization rate (detected after PGF_2α) was greater (P<0.01) for MGA-PGF_2α heifers (86%) compared with Select Synch (66%) and MGA-Select Synch (68%) heifers; however, conception rate did not differ (P=0.13) and averaged 72, 63, and 62% for MGA-PGF_2α, Select Synch, and MGA-Select Synch heifers, respectively. Select Synch (52%), MGA-Select Synch (58%), and MGA-PGF_2α protocols (61%) provided similar (P=0.18) overall AI pregnancy rates; however, more heifers were in estrus before PGF_2α administration in protocols using GnRH.     

Evaluation of fetal protection against experimental infection with type 1 and type 2 bovine viral diarrhea virus after vaccination of the dam with a bivalent modified-live virus vaccine

OBJECTIVE: To evaluate the efficacy of a modified-live virus (MLV) combination vaccine containing type 1 and type 2 bovine viral diarrhea virus (BVDV) in providing fetal protection against challenge with heterologous type 1 and type 2 BVDV. DESIGN: Prospective study. ANIMALS: 55 heifers. PROCEDURE: Heifers were vaccinated with a commercial MLV combination vaccine or given a sham vaccine (sterile water) and bred 47 to 53 days later. Heifers were challenged with type 1 or type 2 BVDV on days 75 to 79 of gestation. Clinical signs of BVDV infection, presence of viremia, and WBC count were assessed for 14 days after challenge. Fetuses were collected on days 152 to 156 of gestation, and virus isolation was attempted from fetal tissues. RESULTS: Type 1 BVDV was not isolated in any fetuses from vaccinated heifers and was isolated in all fetuses from nonvaccinated heifers challenged with type 1 BVDV. Type 2 BVDV was isolated in 1 fetus from a vaccinated heifer and all fetuses from nonvaccinated heifers challenged with type 2 BVDV. CONCLUSIONS AND CLINICAL RELEVANCE: A commercial MLV combination vaccine containing type 1 and type 2 BVDV given to the dam prior to breeding protected 100% of fetuses against type 1 BVDV infection and 95% of fetuses against type 2 BVDV infection. Use of a bivalent MLV vaccine in combination with a comprehensive BVDV control program should result in decreased incidence of persistent infection in calves and therefore minimize the risk of BVDV infection in the herd.     

Prevention of persistent infection in calves by vaccination of dams with noncytopathic type-1 modified-live bovine viral diarrhea virus prior to breeding

OBJECTIVE: To determine the ability of a modified-live virus (MLV) bovine viral diarrhea virus (BVDV) type 1 (BVDV1) vaccine administered to heifers prior to breeding to stimulate protective immunity that would block transmission of virulent heterologous BVDV during gestation, thus preventing persistent infection of a fetus. ANIMAL: 40 crossbred Angus heifers that were 15 to 18 months old and seronegative for BVDV and 36 calves born to those heifers. PROCEDURE: Heifers were randomly assigned to control (n = 13) or vaccinated (27) groups. The control group was administered a multivalent vaccine where-in the BVDV component had been omitted. The vaccinated heifers were administered a single dose of vaccine (IM or SC) containing MLV BVDV1 (WRL strain). All vaccinated and control heifers were maintained in pastures and exposed to BVDV-negative bulls 21 days later. Thirty-five heifers were confirmed pregnant and were challenge exposed at 55 to 100 days of gestation by IV administration of virulent BVDV1 (7443 strain). RESULTS: All control heifers were viremic following challenge exposure, and calves born to control heifers were persistently infected with BVDV. Viremia was not detected in the vaccinated heifers, and 92% of calves born to vaccinated heifers were not persistently infected with BVDV. CONCLUSIONS AND CLINICAL RELEVANCE: These results document that vaccination with BVDV1 strain WRL protects fetuses from infection with heterologous virulent BVDV1.