Shortening the postpartum anoestrous interval in suckled crossbred dual purpose cows using progestagen intravaginal sponges plus eCG and PGF(2alpha).

One hundred and twenty-six suckled crossbred cows (Bos taurus x Bos indicus), with body condition score >or=3 (1-5 point scale), were employed in the present study to evaluate the effectiveness of intravaginal progestin-releasing sponges (IVS) for shortening anoestrous interval. Fifty-four cows were assigned to control group. Seventy-two cows were treated with IVS impregnated with 250 mg of medroxy-acetate-progesterone (MAP) as follows: day 0, IVS plus 5 mg of 17beta-E and 50 mg of MAP i.m.; day 6, 500 IU of equine chorionic gonadotropin and 25 mg prostaglandin F(2alpha) i.m.; day 8, IVS withdrawal and day 9, 1 mg 17beta-E i.m. Cows were also grouped according to postpartum days (dpp) at treatment: MAP <70 days (n = 25); control <70 days (n = 22); MAP >70 days (n = 47); control >70 days (n = 32). From IVS removal, cows were detected in oestrus and inseminated. Cows not detected in oestrus were timed artificial insemination 72 h after sponge removal. Treatment effect on oestrous rate (ER), conception rate (CR), pregnancy rate (PR) and treatment to conception intervals (TCI) and calving to conception intervals (CCI) were evaluated. The ER, CR and PR were analysed using PROC LOGISTIC, while TCI and CCI with PROC GLM of SAS. The groups MAP <70 days and MAP >70 days showed higher (p < 0.01) ER than control <70 days and control >70 days (84.0% and 76.6% vs 31.8% and 31.3% respectively). The PR was higher (p < 0.01) in MAP <70 days vs control <70 days (64.0% vs 22.7%) and also higher (p < 0.05) in MAP >70 days vs control <70 days (40.4% vs 18.8%). The TCI and CCI were shorter (p < 0.01) in MAP <70 days vs control <70 days (36.0 and 95.8 days; 95.3 and 158.6 days respectively). In conclusion, only cows treated with IVS before 70 dpp had a CCI shorter than 100 days, consequently this treatment shortened postpartum anoestrous interval in crossbred dual purpose cattle.

Treatment with an intravaginal progestagen and estradiol to prevent prolonged anestrus in crossbred zebu cows under tropical conditions.

To study the effectiveness of a treatment with an intravaginal progestagen in combination with estradiol-17beta (E-17beta) on estrus induction, prevention of prolonged anestrus and fertility in noncycling crossbred zebu cows, a trial was conducted in a farm in Zulia state, Venezuela. Fifty noncycling suckled crossbred cows (B. taurus x B. indicus) with 60 dpp were randomly allotted to one of the following treatments: MAP+E-17beta (n=22), intravaginal device (250 mg of MAP) during 7 days + 50 mg of MAP and 5 mg of E-17beta im (day 0) and 1.5 mg of E-17beta im (day 8) (Pregnaheat-E; VIATECA-Venezuela); CG (n=28), control group without hormonal treatment. The MAP+E-17beta group showed higher (P<0.05) estrus and synchronization rates (59.1 and 36.4 %) than CG (25.0 and 3.5 %). Cows receiving MAP had higher (P<0.05) overall pregnancy rate than CG (45.5 and 17.8 %, respectively). A decreased (P<0.05) anestrus rate was observed in MAP+E-17beta (31.8%) compared to CG (57.1%). Calving-conception interval was shorter (P<0.05) in MAP+E-17beta (132.5+/-16.8 days) than in CG (178.9+/-14.7 days). In conclusion, treatment with MAP+E-17beta at 60 days postpartum was effective to induce estrus, prevent prolonged anestrus, and reduce the calving-conception interval, improving reproductive performance in dual purpose crossbred Zebu cows.

Factors affecting fertility according to the postpartum period in crossbred dual-purpose suckling cows in the tropics.

To determine the relationship between first service conception rate (FSC) and the postpartum period (PP), 6160 calvings from 2250 crossbred dual-purpose cows were analysed. The effects of breed predominance (BT: Bos taurus and BI: Bos indicus), season of service (dry, intermediate and humid), parity (1 or 2 and more), agroecological region (Sub-humid and Dry Tropical Forest) and milk production were studied. The postpartum period was grouped according to the calving-first service interval as G1 < or = 60 days (n = 1889); G2 > 60 < or = 90 days (n = 1436); G3 > 90 < or = 120 days (n = 1030); and G4 > 120 days (n = 1805). Data were analysed by chi-squared test. The overall mean for FSC was 58.2% and was lower in G1 (p < 0.01). All PP showed a breed effect on FSC, with mean values of 61.6% and 53.3% for BI and BT, respectively. Season of service also affected FSC, which was significantly lower during the humid period: 51.2% versus 57.4% and 61.5% for the intermediate and dry periods (p < 0.01), respectively. Parity and environmental effects were not observed on FSC. Levels of milk yield did influence the FSC, which decreased from 66.7% and 61.0% for milk yields of < 1500 kg and between 1501 and 2000 kg to 46.0% in milk yields > 2000 kg (p < 0.01).

Improvement of reproductive performance in crossbred zebu anestrous primiparous cows by treatment with norgestomet implants or 96 h calf removal.

The aim of the present study was to compare the effect of norgestomet implants (NI) and calf removal (CR) for 96 h on estrus induction and first service fertility in crossbred zebu primiparous anestrous cows after 120 days postpartum. A total of 152 cows in a tropical environment were allotted to three experimental groups: CR for 96 h (n = 51), NI for 9 days plus 500 IU of PMSG at implant removal (n = 51) and a control group (CG) without treatment (n = 50). Estrous rate (%) and mean interval to first estrus (days) were 50.9 and 26.3+/-6.8; 60.7 and 13.8+/-6.8; 16.0% and 61.8+/-5.9 days for groups CR, NI and CG, respectively. CR and NI were statistically similar, however, both groups were different (P < 0.01) when compared with CG. Calving interval to first service and to conception were: CR: 151.2+/-8.4 and 157.8+/-21.4; NI: 145.2+/-8.5 and 150.9+/-21.3; CG: 186.8+/-7.3 and 201.0+/-18.5. A difference (P < 0.01) was found in both intervals when comparing the CR and NI with CG, with longer intervals for cows in the CG group. First service conception rates were 61.5, 67.7 and 62.5% for groups CR, NI and CG, respectively, and were not different (P > 0.05). These results demonstrate the efficacy of NI + PMSG or temporary CR for 96 h in inducing a fertile estrus and shortening the interval to estrus and to conception in primiparous crossbred anestrous zebu cows in the tropics.

Bull effect on the reproductive performance of mature and first calf-suckled Zebu cows in the tropics.

This experiment was designed to determine if continuous bull exposure of heifers 2 wk post partum to a first calf (30 to 36 m old) or mature (42 to 72 m old) Zebú Brahman suckled cows reduces the interval to first estrus and the number of days open. Post partum first calf cows were randomly assigned to be exposed continuously to epidectomized bulls with surgical ablation of the dorsal ligament of the penis (Group 35 FBE, n = 25) or not exposed to bulls (Group FNE, n = 22). Post partum mature cows were likewise assigned to be continuously exposed (Group MBE, n = 24) or not exposed to bulls (Group MNE, n = 25). Milk samples were collected twice a week for progesterone assays to determine resumption of ovarian cyclic activity. All the cows were artificially inseminated for 120 d while in their respective treatment groups. The first postpartum estrus percentages were 60 < 90 d, 24.4%; and > 90 d, 33.7%. The interval to first estrus f-or Groups FBE and FNE was 75.4 and 104.2 d, respectively, and differed significantly (P < 0.01). For Groups MBE and MNE the interval to first estrus was 76.3 and 95.0 d, respectively (P < 0.05). The number of open days for Groups FBE and FNE was 77.3 and 114.9, respectively (P < 0.01); while for Groups MBE and MNE it was 73.0 and 98.6 d, respectively (P < 0.01). The results of the present study indicate that introduction of bulls to first calving cows or mature Zebú Brahman cows after parturition provides a practical and economical option for reducing the extended post partum anestrus interval and days open under tropical conditions.

Factors affecting postpartum ovarian activity in crossbred primiparous tropical heifers.

The relationship between postpartum ovarian activity and a total of 9 variables was studied in a dry tropical environment. Primiparous cows (n=61) that had shown no peripartum abnormalities, and were not suckled but milked twice daily, were used in the study. Independent variables included crossbreeding, sex of the calf, season, body condition, weight of cow at calving, age of dam at calving, uterine involution, calf weight and accumulated milk yield. Diet was a controlled variable. Dependent variables were first estrus postpartum and/or first milk progesterone elevation prior to first estrus. A bull fitted with a chin ball marker was used to detect first estrus postpartum, while ovarian structures were palpated per rectum once a week. Progesterone was measured by RIA in milk samples collected twice weekly. First postpartum estrus was detected at 56 +/- 32 days postpartum, a first milk progesterone elevation was observed in 50.8% of cows at 42 +/- 27 days. Cows calving in the dry season had longer intervals and those who calved males had shorter postpartum intervals. Accumulated milk yield affected both intervals significatly (p < 0.01). Weight, age and uterine involution were asociated with first milk progesterone elevation, while crossbreeding, weight at calving and weight postpartum change were associated with the dependent variables.

Patency of the cervical canal in cross-bred female Zebu x Brown Swiss selected for non-surgical recovery or transfer of embryos.

A test to evaluate the degree of patency of the cervical canal was carried out on 260 Zebu x Brown Swiss cows and heifers that were assigned for non-surgical recovery or transfer of embryos. A total of 204 females (78.5%) were found to have a patent cervix (P <0.05), compared with 56 (21.5%) which had a blockage or obstruction when an attempt was made to pass a catheter through the cervical canal or the "cervical knot" of the purebred and cross-bred Zebu cows. A smaller percentage (12.89%) of non-patent cervices (P <0.05) were detected in multiparas, compared with 25 and 27.5% in primiparas and nullipara, respectively. The test for cervical patency is carried out on Bos indicus cattle to screen the animals before non-surgical embryo transfer manipulations and to attain better results in the application of non-surgical recovery and transfer of embryos.

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.