Seronegative conversion in four Neospora caninum-infected cows, with a low rate of transplacental transmission.

Four Neospora-seropositive pregnant cows (prebreeding indirect fluorescent antibody (IFA) titers between 1:400 and 1:1600) were confined and observed until parturition. All cows gave birth to normal calves. Selected tissues were tested for NC by histopathology, immunohistochemical (IHC) and polymerase chain reaction (PCR). Parasite isolation was attempted in vero cell cultures. At parturition, all cows were seronegative at 1:200 and two of four cows had a titer of 1:100 when further tested. Three of four calves were not infected, as determined by negative results of precolostral serology (1:25 cut-off), histopathology, IHC and PCR. One calf was congenitally infected, as shown by the presence of a thick-walled cyst labelled by IHC in its brain, positive PCR of brain and a precolostral IFA titer of 1:100. It was concluded that NC antibody titers may drop or convert to seronegative status in chronically infected cows by the time of parturition and this finding in four of four cows indicates that this could be a common occurrence. Similarly, the finding of an infected calf with a low antibody titer indicates that precolostral serology may not be a fool-proof means of identifying calves with congenital Neospora caninum infections. These findings call into question conclusions of other studies that have estimated rates of congenital transmission of this parasite based on serological tests at calving. This study is the first confirmed report of congenital NC infection in a calf in Thailand.

Neospora caninum seroprevalence in dairy cattle in central Thailand.

The seroprevalence, in dairy cattle, of antibodies to Neospora caninum, the relationship between seropositivity and age (heifer versus cow), the relationship of herd infection with herd size and the relationship of herd infection with the presence of dogs on the farm were studied. The study involved 549 cows and 82 dogs in 59 dairy herds in Nakhon Pathom, Thailand. A competitive enzyme-linked immunosorbent assay (cELISA) with NC-specific monoclonal antibody was used to detect the NC antibodies in the sera. Individual and herd seroprevalence of NC were 5.5% (30/549) and 34% (20/59), respectively. No significant relationships between NC seropositivity with the age of the cows (heifer versus cow; P > 0.05) and between herd infection and the presence of dogs on the farm (P > 0.05) were found. Herd size significantly affected herd infection (P < 0.05) with higher infection in large than small herds (> or = 21 versus < or = 20 cows). Of 12 cows with a history of abortion, one was seropositive to NC. The seroprevalence of NC antibodies in dogs was 1.2% (1/82). This is the first NC seroprevalence study in dogs in Thailand. It was concluded that Neospora infection was more common at the herd level rather than the individual level in Thailand and the presence of dogs on the farm was not related to the level of herd infection. Caution should be taken in the interpretation of serological tests from the farm dogs.

Early embryonic development in Thai swamp buffalo (Bubalus bubalis ).

A total of 33 nonsurgical embryo collections was carried out to investigate early embryo development in Thai swamp buffalo. Collections were performed on Days 5.5, 6.0, 6.5, 7.0 and 7.5. The different stages of embryo development on these days were the 16-cell stage, compact morula, blastocyst, hatched blastocyst and hatched expanding blastocyst, respectively. In addition, some degenerating embryos and unfertilized ova were also recovered. A higher recovery rate was obtained with single embryo collection after natural estrus than after induced estrus or superovulation, 78% (7 9 ) vs 46% (6 13 ) vs 54.5% (6 11 ), respectively. A higher percentage of normal embryos was also obtained with single embryo collection after either natural or induced estrus than after superovulation, 71% (5 7 ), 83% (5 6 ) and 38% (6 16 ), respectively.

Fertility of cows challenged with a cytopathic strain of Bovine Viral Diarrhea virus during an outbreak of spontaneous infection with a noncytopathic strain.

During an attempt to accumulate 40 Bovine Viral Diarrhea virus (BVDV) seronegative cows for breeding and for intramuscular infection on Day 21 of gestation, a persistently infected cow was inadvertently included among the first group of seronegative animals assembled. This animal proceeded to infect all seronegative animals added to the experimental herd. Since the addition of cows was gradual and they were bred as they arrived, a group of cows was bred before they seroconverted, another group was inseminated during seroconversion and a third group was seropositive when bred. First service conception rates were 22.2, 44.4 and 78.6%, respectively. The difference between 22.2 and 78.6% conception rates was significant (P < 0.05). Thirty cows were diagnosed pregnant at 21 d after service on the basis of nonreturn to estrus, presence of a palpable corpus luteum and high serum progesterone concentration. Seventeen of these received cytopathic BVDV intramuscularly and 13 cows served as controls. All control cows and 9 of 17 (52.9%) virus-treated cows had normal fetuses and placentas at slaughter on Day 70. Six pregnancies were lost between 23 and 33 d after insemination and two were lost between 35 and 40 d after insemination. Noncytopathic BVDV was demonstrated in all eight of these cows either in the buffy coat or in tissues, despite the presence of serum neutralizing antibodies.

Prevalence of antibodies to specific infectious agents in bovine fetuses from a slaughterhouse in Minnesota.

Sera from 486 bovine fetuses, approximately 60 to 270 days of gestation, were collected at slaughter and tested for the presence of immunoglobulins (Ig). One hundred ten (27%) of the sera were positive for IgG and/or IgM. The earliest age at which fetuses tested positive for IgM and IgG was estimated to be 100 and 120 days, respectively. Ig concentration increased with increased age of the fetus. Sera that were positive for Ig were tested for the presence of specific antibodies to five different infectious agents. Bovine parvovirus antibodies were found in 99 of 110 sera (90%) by hemagglutination inhibition (HI) test. However, only 35 (31.8%) of these sera were positive by serum neutralization (SN) test. Antibodies to parainfluenza-3 virus were detected in 30 sera (27%) by HI test and in 20 sera (18%) by SN test. Five (4%) sera contained SN antibodies to bovine viral diarrhea virus. Only one (0.9%) serum sample contained SN antibodies to infectious bovine rhinotracheitis virus. None of the sera had antibodies against five Leptospira spp. Results of this study suggest that bovine parvovirus may be a potential cause of reproductive problems in cattle.