Effects of oestradiol cypionate on spontaneous and oxytocin-stimulated postpartum myometrial activity in the cow.

The effects of oestradiol cypionate (ECP) on spontaneous and oxytocin-induced postpartum myometrial activity were measured in four cows using strain gauge transducers (SGT). On the first day after parturition, prior to treatment with ECP, myometrial activity consisted mainly of single-peak contractions (mean frequency 9.6/h, mean duration 141.0s, the majority of the contractions being propagated in a tubocervical direction. Injection of ECP (5 mg i.m.) 18 h after parturition led to suppression of coordinated myometrial activity and the development of sustained low amplitude contractions of reduced frequency (mean 2.9/h, P less than 0.01) and increased duration (mean 422.2 s, P less than 0.05), with multiple superimposed small peaks. In addition, all parts of the uterus tended to contract simultaneously. These changes were apparent by 4 h after treatment and persisted until day 5 after parturition. Injection of oxytocin (25 USP units i.v.) at 24 h after parturition stimulated the reappearance of single-peak coordinated contractions. However, pretreatment with ECP did not enhance the myometrial response to oxytocin.

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.

Myometrial activity during natural and dexamethasone-induced parturition in the cow.

Myometrial activity was monitored during natural and dexamethasone-induced parturition in 8 Holstein dairy cattle, using strain gauge transducers. Four gauges were attached to the serosal surface of the gravid uterine horn, dividing it into thirds. Parturition was induced in 2 of 4 heifers and 2 of 4 cows (group 1); the remaining animals were allowed to calve spontaneously (group 2). Chains of low-amplitude contractions (repeated small deviations from base line) were detected before parturition was induced, and these were more common at distended parts of the uterus. Uncharacteristically sharp peaks followed by small rhythmic contractions, during preinduction recording, indicated that the myometrium was responsive to fetal movement even several days before parturition. By 18 hours before parturition, discrete single contractions appeared independently of contraction chains, and the first tubocervical peristaltic contraction waves were detected. The mean area under recorded contraction curves (uterine work) increased quadratically and the frequency of contractions decreased linearly from 12 hours before parturition to 2 hours after parturition. There was also an increase in the proportion of tubocervical waves over this period, and contraction chains were no longer present. During the second stage of labor, distended and undistended parts of the uterus were equally active, and forceful maternal straining was associated with larger sustained contractions. Fetal membrane rupture was accompanied by a doubling in the rate of passage of contraction waves along the length of the uterus. After the calf was expelled, contractions became extremely regular, and the majority progressed in a tubocervical direction.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Nature of early reproductive failure caused by bovine viral diarrhea virus.

A 2-part study was undertaken to determine the effect of bovine viral diarrhea (BVD) virus on fertilization and early development of embryos. In experiment 1, 10 seronegative cows were superovulated and artificially inseminated twice during estrus. After the second insemination, 5 of the cows received intrauterine infusion of BVD virus suspension. The other 5 cows received suspending medium only and served as controls. All 10 cows were slaughtered on day 3, and ova and embryos were collected for morphologic evaluation. A total of 49 and 52 ova and embryos were collected from the control and virus-treated cows, respectively. Among the ova and embryos collected from control cows, 81.6% were fertilized, whereas only 52% were fertilized in the virus-treated group. The statistically significant difference (P less than 0.01) indicated that the virus interferes with fertilization. In experiment 2, the protocol was identical except for slaughter on day 13. Seventy-nine ova and embryos were collected from the 6 control cows, and the 6 virus-treated cows yielded 59 ova and embryos. Of the total ova and embryos recovered on day 13, 88.6% and 50.8% were hatched and developing normally in the control and virus-treated groups, respectively. The difference was highly significant (P less than 0.001). Unfertilized ova and degenerating embryos could not be differentiated on the basis of morphologic appearance. The nearly identical percentages of unfertilized ova in experiment 1 and unhatched ova and embryos in experiment 2 strongly suggested that fertilization failure is the principal manifestation of the observed adverse effect of BVD virus infection.

Effects of intrauterine challenge with Leptospira interrogans serovar hardjo on fertility in cattle.

The purpose of this study was to determine the effects of Leptospira interrogans serovar hardio on fertility in cattle. Twenty seronegative mature dairy cows were assigned to two groups. Group I (challenged cows) was bred by a seronegative bull followed by intrauterine infusion (within 30 minutes) of Leptospira interrogans serovar hardjo. Group II was bred by the same bull followed by intrauterine infusion of 5 ml of sterile culture medium. Blood samples were collected at two-day intervals to monitor serum antibody titers. Daily blood cultures for 10 days and weekly urine cultures for five weeks were performed to monitor the animals for leptospiremia and leptospiuria. Cows were slaughtered 35 days post-breeding, and their reproductive tracts were examined. All animals remained clinically normal following intrauterine challenge. There was no difference in pregnancy rates (Group I, 7/10; Group II, 6/10). All embryos, reproductive tracts, and kidneys appeared normal. A microscopic agglutination test (MA) showed that 4 of 10 challenged cows developed serum antibody titers between 8 and 20 days after challenge. However, on the basis of the hamster passive protection test, all challenged cows had serum antibodies present. All blood and urine cultures were negative through the experimental period, as were the final kidney and uterine cultures. In a second experiment, six seronegative cows were infused with killed microorganisms immediately after insemination. Results of a microscopic agglutination test and a hamster passive protection test indicated that these cows did not develop humoral antibodies against serovar hardjo. These results indicated that intrauterine inoculation of Leptospira interrogans serovar hardjo (hamster-adapted strain) following breeding did not affect pregnancy rates despite an intrauterine challenge which caused the development of humoral antibodies.

Effect of bovine viral diarrhea virus on conception in cattle.

Sixty adult dairy cows were used to study the effect of bovine viral diarrhea (BVD) virus on conception when inoculated with the virus within 2 hours after breeding. Fifteen cows were assigned at random to each of 4 groups. Group I (control) cows were given 3 ml of diluent in the uterus; group II (seropositive) cows were given 3 ml of BVD virus in the uterus; group III (seronegative) cows were given 3 ml of BVD virus in the uterus; and group IV (seronegative) cows were given 3 ml of BVD virus orally and 3 ml intranasally. At 35 days after breeding, the cows were slaughtered, their reproductive tracts were recovered, and pregnancy rates were recorded. The pregnancy rates for groups I, II, III, and IV were 67%, 60%, 27%, and 67%, respectively. The group III pregnancy rate was significantly lower (P less than 0.05) than that for the control group. However, the similarity of rates for groups I, II, and IV indicates that BVD virus does not inhibit conception when cattle are infected by natural routes or when virus is infused into the uterus of seropositive cows at the time of breeding. These results indicate that BVD virus is not a major cause of repeat breedings in cattle.

Development of a cell culture line of bovine fetal endometrial cells.

Monolayers of bovine fetal endometrial cells were established as primary culture cells within 1 to 2 weeks. After the 2nd passage, these cells were inoculated with bovine viral diarrhea virus. Effects of the virus were observed each day with a light microscope. Specific cytopathic effects consisting of degeneration and sloughing of the cells and a well-defined pattern of cytoplasmic vacuolation were observed at 5 days after inoculation.