Conception rates to artificial insemination in primiparous, suckled cows exposed to the biostimulatory effect of bulls before and during a gonadotropin-releasing hormone-based estrus synchronization protocol1,2

Sexual stimulation as a luteolytic inductor in beef heifers

The objective was to determine if the introduction of androgenized steers or females in oestrus has luteolytic effects during the advanced luteal phase (Day 12-13 of the cycle, Day of ovulation = Day 0) in heifers by analysing the changes in corpus luteum (CL) size and perfused area together with progesterone (P4) secretion. Experiment 1 (EXP1) was carried out in May (autumn) with 12 Angus and Angus X Hereford heifers and experiment 2 (EXP2) in September (spring) with 20 heifers of the same breed. Procedures for both experiments were the same. Firstly, oestrus was synchronized in heifers, then, transrectal colour doppler ultrasonography was performed daily from Day 10 to Day 12 of the cycle in all animals. On Day 12 in the afternoon, animals were allocated to two experimental groups (control and biostimulated) and maintained separated (minimum distance: 1000 m) until the end of each experiment. In EXP1, two androgenized steers were introduced into the biostimulated group (BAS) and compared with unstimulated control group (CON1). In EXP2, 20 animals were separated into control group (CON2) and biostimulated group (BHE), in which 4 oestrous heifers were introduced on Day 12 in the afternoon, and 4 more on day 13. The oestrous heifers were injected with 2 mg i.m. of oestradiol benzoate every 12 h until the end of the experiment to maintain the receptiveness. In both experiments, from Day 13 until the day on which detectable luteal blood flow (irrigation) disappeared, colour doppler ultrasonography was performed every 12 h in both groups. Blood samples were collected from all heifers every 12 h from Day 10 to the day in which irrigation disappeared. In EXP1 there was no effect of treatment on CL volume. The BAS had less CL's perfused area than controls 0.09 ± 0.02 cm² vs 0.16 ± 0.02 cm², respectively (p = 0.015), less percentage of perfused area (2.4 ± 0.4% vs 4.2 ± 0.4%; p = 0,011), and lower progesterone (P4) concentration than CON1 (2.7 ± 1.0 ng/mL vs 5.8 ± 0.9 ng/mL respectively; p = 0.046). On Day 14.5 of the cycle, the BAS tended to have a lower concentration of P4 than the CON1 (p = 0.06) and on Days 15.5, 16, 16.5, 17, 17.5, 19.5 the P4 concentration was lower in BAS than in CON1 (p < 0.05). In EXP2 there were no treatment effects in any of the studied variables. Overall, it was concluded that the introduction of androgenized steers during heifers' advanced luteal phase of heifers advanced the luteolytic process. However, the introduction of oestrous heifers had no effect on luteal activity.

Occlusion of the corpus cavernosum penis in bulls intended for estrus detection: 18 cases (2002-2016)

OBJECTIVE To report surgical and long-term postoperative outcomes of bulls undergoing surgical occlusion of the corpus cavernosum penis (CCP) by acrylic injection and epididymectomy with or without penile fixation as preparation for use in estrus detection. DESIGN Retrospective case series. ANIMALS 18 client-owned bulls. PROCEDURES Medical records of bulls that underwent CCP occlusion between December 2002 and March 2016 were identified. Signalment, surgical data, and reported complications were recorded. Long-term (> 6 months after surgery) follow-up data were obtained from medical records or by telephone interview of bull owners with a questionnaire focused on postoperative outcome, use of the bull for estrus detection, and overall satisfaction with the procedure. RESULTS Intraoperative complications included difficulty isolating the penis, polymerization of the acrylic prior to injection, incomplete anesthesia of the surgical site, and fecal contamination of the site. Deposition of acrylic in an improper location led to urethral obstruction and euthanasia of 1 bull; another developed an abscess that was treated successfully. One bull was euthanized because of orchitis. Most (15/18) bulls were used for estrus detection (mean duration, 17.9 months). Libido was considered good or very good for 14 of 15 bulls; 1 was culled for loss of libido after 14 months. Ten of 12 bulls were reportedly unable to protrude the penis; 2 had or developed partial protrusion ability. Overall client satisfaction was high. CONCLUSIONS AND CLINICAL RELEVANCE In this population of healthy young bulls, CCP occlusion was generally well tolerated. Most bulls that underwent CCP occlusion (and epididymectomy with or without penile fixation) had adequate libido, and none were reported able to achieve intromission.

Effect of acute bull exposure around the time of artificial insemination on serum oxytocin and progesterone concentrations and pregnancy rates in dairy cows

This study examined the effect of acute bull exposure around the time of artificial insemination (AI) on oxytocin and progesterone concentrations, and pregnancy rates in dairy cows. Ninety six dairy cows, stratified according to parity into primiparous and pluriparous, were divided into three groups; short bull exposure (SBE; 10 min, n = 32), long bull exposure (LBE; 4 h, n = 32) or no bull exposure (NBE; n = 32). On day 45 post-partum, all cows were treated with PGF2α on three occasions 11-14 days apart to synchronize oestrus. They were submitted to fixed time AI 80 h after the third PGF2α injection. Cows in the SBE and LBE groups were artificially inseminated 5 min after the introduction of the bull. From a subset of cows (n = 6 per group; three primiparous and three pluriparous), blood samples were collected once every 5 min starting 15 min before AI until 15 min after AI and analysed for oxytocin concentrations. Additional blood samples were collected for measurements of progesterone (P4) concentrations once daily for 4 days starting on the day of AI and once every 3 days thereafter until day 22. The effects of bull exposure, time, parity, difficulty of AI, and pregnancy on oxytocin and P4 concentrations were analysed using the mixed linear model procedure. Mean oxytocin concentrations or change in oxytocin concentrations after bull exposure or AI were not different among groups. Pregnancy rates for the NBE, SBE and LBE groups were 55.5%, 33.3% and 44.4%, respectively, and were not different among groups. In conclusion, acute bull exposure around the time of AI did not affect oxytocin and progesterone concentrations and did not improve pregnancy rates in dairy cattle under these farms conditions.

Exposure to androgenised steers did not improve the fertility obtained in progesterone-based fixed-timed artificial insemination programs in extensively managed cows and heifers

Biostimulation – the stimulation of females’ reproductive activity by the presence of males – has been used to stimulate postpartum rebreeding in cows, and to advance puberty in heifers. The objective of the present experiment was to determine whether previous exposure to androgenised steers improves conception rates after a progesterone-based fixed-timed artificial insemination program applied during spring. Three trials were carried out between October and January (spring–early summer) with a total of 903 Hereford and Hereford × Angus cows and heifers. All of the females were isolated from male contact (minimum distance = 4000 m) 3 months before the beginning of the experiments. While one group (EXP) in each trial was exposed to androgenised steers for 20 days, the other group (ISO) remained isolated from males (bulls, steers) during the experiment. In trial 1, 248 and 267 heifers were included in the EXP and ISO groups, respectively; in trial 2, 141 and 134 spring calving cows were used for the same treatments; and in trial 3, 53 and 60 autumn-calving cows were respectively included in the experimental groups. All animals were joined and a traditional progesterone-based fixed-timed artificial insemination program was applied to all of them. Pregnancy was determined 45–50 days after insemination with transrectal ultrasound. There were no differences between the EXP and ISO groups in any of the trials. The general conception rate was 54.6, 50.2 and 54.0% in trials 1, 2 and 3, respectively. Overall, it was concluded that exposition to androgenised steers does not improve the fertility obtained in progesterone-based fixed-timed artificial insemination programs in extensively managed cows and heifers.

Influence of a CIDR prior to bull breeding on pregnancy rates and subsequent calving distribution

We determined whether insertion of a CIDR for 7 days prior to the breeding season enhanced pregnancy rates and altered the date of conception in suckled beef cows mated naturally. Suckled beef cows (n=2033) from 15 locations were randomly assigned to one of two treatments: (1) cows received a CIDR 7 days prior to the breeding season for 7 days (CIDR; n=999); (2) cows received no treatment (Control; n=1034). On the first day of the breeding season bulls were introduced to herds at a rate of 15-25 cows per yearling bull or 20-30 cows per mature bull. Pregnancy status and the date of conception were determined via transrectal ultrasonography at 56 and 120 days after initiation of the breeding season. Overall pregnancy rates ranged from 59.3 to 98.9% among the 15 locations. The percentage of cows becoming pregnant during the first 30 days of the breeding season was similar between CIDR (68.2%) and Control (66.7%) cows, and overall pregnancy rates were similar between CIDR (88.9%) and Control (88.6%) cows. The average day of conception after initiation of the breeding season was shorter (P<0.01) for CIDR (20.1+/-0.8 days) compared to Control cows (23.2+/-0.8 days). Of cows conceiving during the breeding season, more (P<0.05) CIDR cows (35.9%) conceived during the first 10 days of the breeding season than Control cows (30.8%). Neither body condition score and nor parity affected pregnancy rates or days to conception, whereas pregnancy rates and days to conception were affected (P<0.01) by location and days postpartum. Days to conception were greater for cows that calved within 40 days (31.6+/-1.2 days) of initiation of the breeding season compared to cows calving between 40 and 50 days (25.3+/-1.2 days) prior to initiation of the breeding season, which were greater than those cows calving between 50-60 days (20.0+/-0.8 days) and 60-70 days (21.3+/-1.0 days) prior to initiation of the breeding season. Cows calving greater than 70 days (17.3+/-1.5 days) from initiation of the breeding season had the shortest interval to conception. We concluded that insertion of a CIDR prior to the breeding season failed to increase overall pregnancy rates, but did influence the average day of conception.

The acute effect of bull presence on plasma profiles of luteinizing hormone in postpartum, anoestrous dairy cows

The objective of this study was to investigate whether bull exposure affects LH profiles in postpartum, anoestrous dairy cows. Eight cows between 10 and 17 days after parturition were used. On Day 1, blood samples were taken at 10 min intervals for 8 h. On Day 2, blood sampling continued at 10 min intervals and after 2 h a bull was introduced behind a fence, and blood sampling continued for another 8 h. Time of resumption of luteal activity was between 25 and more than 80 days after parturition for these animals and was not related (P>0.1) with frequency of LH pulses, amplitude of pulses and basal LH concentration on either Day 1 or Day 2. In 6 of the 8 cows, average and basal LH concentration were greater (P<0.001) during the 8 h of bull presence (0.56 +/- 0.33 and 0.39 +/- 0.26 ng/ml, respectively) compared to the 8 h without a bull (0.50 +/- 0.30 and 0.35 +/- 0.24 ng/ml, respectively). Pulse amplitude did not differ (P=0.85) between Day 2 (0.45 +/- 0.24 ng/ml) or Day 1 (0.45 +/- 0.14 ng/ml). LH pulse frequency was greater (P<0.1) on Day 2 (5.3 pulses/8h) compared to the Day 1 (4.6 pulses/8h). In conclusion, fenceline bull exposure early postpartum seems to have an acute effect on LH-release in anoestrous dairy cows. Whether sustained bull exposure can hasten first ovulation after calving through an effect on LH release in dairy cows is an interesting area of research.

Putative urinary pheromone of bulls involved with breeding performance of primiparous beef cows in a progestin-based estrous synchronization protocol1

The objective of this study was to determine if factors associated with the biostimulatory effect of bulls alter breeding performance of primiparous, suckled beef cows using a progestin-based estrous synchronization protocol. We tested the hypotheses that the estrous synchronization response and AI pregnancy rates differ among cows exposed to bulls, continuously exposed to bull urine, and exposed to fence-line contact with bulls or cows not exposed to bulls or bull urine. Data were collected from 3 experiments performed over consecutive years. Cows were assigned to the following treatments: bull exposure (BE; n = 26) or no bull exposure (NB; n = 25) in Exp. 1, bull urine exposure (BUE; n = 19) or steer urine exposure (SUE; n = 19) in Exp. 2, and fence-line contact with bulls (BFL; n = 26) or no bull exposure (NB; n = 26) in Exp. 3. Synchronization protocols in each experiment included the use of a controlled internal drug release device (d -10), PGF(2alpha) (d -3), and GnRH and fixed-time AI (TAI; d 0). Cows that were observed in estrus by 60 h after PGF(2alpha) were inseminated 12 h later. Cows not observed in estrus by 60 h after PGF(2alpha) were TAI at 72 h and given GnRH (100 mug). Pregnancy was determined by ultrasonography 35 d after TAI. In Exp. 1, 2, and 3, cows were exposed directly to bulls, bull urine, or bull fence-line contact for 35, 64, and 42 d, respectively. Data were analyzed between treatments within each experiment. The proportion of estrous cycling cows did not differ between treatments at the beginning of each experiment; however, more (P < 0.05) BE and BFL cows were estrous cycling at the beginning of the estrous synchronization protocol than NB cows in Exp. 1 and 3. The proportion of cows that showed estrus and interval to estrus after PGF(2alpha) did not differ between treatments in Exp. 1 and 3. However, in Exp. 2, more BUE cows tended (P = 0.09) to have shorter intervals to estrus and to exhibit estrus after PGF(2alpha) than SUE cows. Overall, AI pregnancy rates were greater (P < 0.05) for BE and BUE cows than for NB and SUE cows in Exp. 1 and 2, respectively. There was no difference in AI pregnancy rates between BFL and NB cows in Exp. 3. The presence of bulls and exposure to bull urine appeared to improve breeding performance of primiparous beef cows using a progestin-based estrous synchronization protocol, whereas fence-line bull exposure was insufficient to cause this biostimulatory effect. We propose that a novel urinary pheromone of bulls may be responsible for the enhancement of fertility in the primiparous, postpartum cow.