Comparison of long-term CIDR-based protocols to synchronize estrus in beef heifers

Two experiments evaluated long-term controlled internal drug release (CIDR) insert-based protocols to synchronize estrus and compare differences in their potential ability to facilitate fixed-time artificial insemination (FTAI) in beef heifers. In Experiment 1 estrous cycling heifers (n = 85) were assigned to one of two treatments by age and body weight (BW). Heifers with T1 received a CIDR from days 0 to 14, gonadotropin releasing hormone (GnRH) on day 23, and prostaglandin F_2α (PG) on day 30. Heifers with T2 received a CIDR from days 2 to 16, GnRH on day 23, and PG on day 30. Ovaries were evaluated by ultrasonography on days 23 and 25 to determine ovulatory response to GnRH. In Experiment 2 heifers (n = 353) were assigned within reproductive tract scores by age and BW to one of four treatments. Heifers in T1 and T2 received the same treatments described in Experiment 1. Heifers in T3 and T4 received the same treatments as T1 and T2, respectively, minus the addition of GnRH. In Experiments 1 and 2, heifers were fitted with HeatWatch transmitters for estrous detection and AI was performed 12 h after estrus. In Experiment 1 heifers assigned to T1 had larger dominant follicles at GnRH compared to T2 (P < 0.01) but response to GnRH, estrous response after PG, mean interval to estrus, and variance for interval to estrus after PG did not differ (P > 0.10). AI conception and final pregnancy rate were similar (P > 0.50). In Experiment 2 estrous response after PG did not differ (P > 0.70). Differences in mean interval to estrus and variance for interval to estrus (P < 0.05) differed based on the three-way interaction of treatment length, GnRH, and estrous cyclicity status. AI conception and final pregnancy rates were similar (P > 0.10). In summary, the greater estrous response following PG and resulting AI conception and final pregnancy rates reported for heifers assigned to the two treatments in Experiment 1 and among the four treatments in Experiment 2 suggest that each of these long-term CIDR-based protocols was effective in synchronizing estrus in prepubertal and estrous cycling beef heifers. However, the three-way interaction involving treatment length, GnRH, and estrous cyclicity status in Experiment 2 clearly suggests that further evaluation of long-term CIDR-based protocols is required with and without the addition of GnRH and on the basis of estrous cyclicity status to determine the efficacy of these protocols for use in facilitating FTAI.     

Reproductive and metabolic hormones during estrus after fasting in Holstein heifers

The estrous cycles of 23 Holstein heifers were synchronized with three prostaglandin F₂α (PG) injections at 0600 h 11 d apart, designated as Days ?11, 0 and 11. Twelve of the animals were randomly assigned to receive no solid food (Group F) from Day 6 to 14, while the other animals remained on full feed to serve as controls (Group C). Jugular blood samples were collected at 6-h intervals beginning with PG injection at 0600 h on Day 0 until 1800 h on Day 4 and at 0600, 1200 and 1700 h on Day 8 through 10. Samples were collected again at 6-h intervals from PG Day 11 (0600 h) until 1800 h on Day 15. Period 1 was defined as those samples collected from Day 0 through 4.5, Period 2 from Day 7 through 10, Period 3 from Day 11 through 14.25, and Period 4 from Day 14.5 through 15. Plasma growth hormone concentrations were increased (P<0.01) in F as compared with C animals during Periods 2, 3 and 4. Plasma concentrations of prolactin (P<0.01) were decreased in F as compared with C animals during Periods 2 and 3. Plasma urea concentrations were increased (P<0.01) in F as compared with C animals during the first 3 d of the fast (Period 2) but were decreased (P<0.01) during the remainder of the experiment (Periods 3 and 4). Thus, fasting was effective in altering several metabolic parameters. Although plasma progesterone and luteinizing hormone (LH) concentrations remained similar (P>0.05) between F and C animals, plasma estradiol-17β concentrations decreased in F as compared with C animals during Periods 2, 3 and 4. No differences (P>0.05) between F and C animals were found in duration to LH peak after PG injection, estrous behavior, or pregnancy rates. Results from this study indicate that fasting reduced plasma estradiol-17β concentrations during estrus but did not alter occurrence of estrus or pregnancy rate.     

Ovulation and pregnancy outcomes in response to human chorionic gonadotropin before resynchronized ovulation in dairy cattle

We first determined a dose of human chorionic gonadotropin (hCG) sufficient to induce ovulation in lactating Holstein cows. Ovaries of 85 previously inseminated cows were mapped using transrectal ultrasonography 7 d before pregnancy diagnosis and assigned randomly to treatments of saline, 100 μg gonadotropin-releasing hormone (GnRH), or 500, 1000, 2000, or 3000 IU hCG. Appearance of new corpus luteum (CL) in response to ≥1000 IU hCG was similar to that for GnRH but greater (P < 0.001) than that for saline. Ovarian structures and serum progesterone then were monitored in 334 previously inseminated Holstein cows 0 and 7 d after treatment with GnRH, hCG (1000 IU), or saline. The incidence of ovulation was greater (P = 0.01) after GnRH than after saline in cows having pretreatment progesterone < 1 ng/mL, whereas in cows having progesterone ≥1 ng/mL, GnRH or hCG was more (P = 0.01) effective than saline, and hCG also differed from GnRH. Holstein cows of unknown pregnancy status in three herds were treated with either GnRH, hCG, or as controls to initiate an ovulation-resynchronization procedure 7 d before pregnancy diagnosis. In 1109 treated pregnant cows, pregnancy loss during 4 wk after treatment tended (P = 0.06) to be greater in those treated with hCG. Treated cows (n = 1343) diagnosed not pregnant were then given prostaglandin F_2α and inseminated and received GnRH 72 h later. A treatment by herd interaction (P = 0.06) resulted in more pregnancies after GnRH in two herds and after hCG in one herd compared with saline. We concluded that (1) ≥ 1000 IU hCG resulted in more CL than did treatment with saline, and the incidence of new CL after either GnRH or hCG depended on pretreatment progesterone status; (2) hCG tended to increase pregnancy loss in pregnant cows; and (3) pregnancies per artificial insemination after initiating resynchronization with either hCG or GnRH produced ambiguous results.     

Evaluation of the 5-day versus a modified 7-day CIDR breeding program in dairy heifers

Dairy heifers were used to compared the effects of two timed AI + controlled internal drug release (CIDR) protocols (5-day vs. a modified 7-day) on: (1) luteal regression to initiate a new ovarian follicular wave; (2) ovarian response to the initial GnRH injection; and (3) pregnancy outcomes. Holstein heifers (N = 543) were assigned randomly to two treatments: (1) 25 mg PGF_2α (im) and a CIDR insert on Day −7 followed by 100 μg of GnRH (GnRH-1) on Day −5 and 25 mg PGF_2α (im) at CIDR insert removal (7-day [7D]) on Day 0; or (2) 100 μg GnRH (GnRH-1) and insertion of a CIDR on Day −5 and 25 mg PGF_2α (im) at CIDR removal (5-day [5D]) on Day 0. Insemination with frozen-thawed conventional or gender-biased semen occurred after detected estrus from Days 0 to 2 or by appointment at 72 h after PGF_2α when a second 100-μg dose of GnRH was given. Blood was collected on Days −7, −5, 0, and 3 to determine concentrations of progesterone and incidence of luteolysis. Ovaries were scanned on Days −5 and 0. Luteolysis in the 7D treatment by 48 h after the initial PGF_2α was greater (P < 0.01) than what occurred spontaneously in the 5D treatment (36.2% vs. 19.7%, respectively). Incidence of ovulation after GnRH-1 on Day −5 was greater (P < 0.05) for 7D than for 5D heifers, but the proportion of heifers with an induced CL on Day 0 did not differ between treatments. Heifers inseminated after detected estrus (166/543, 30.6%) on Days 0, 1, and 2 had greater (P < 0.05) pregnancy per AI (P/AI) at 32 days post AI than after timed AI (38.2% vs. 28.3%) on Day 3. Pregnancy P/AI, however, was greater (P < 0.05) for 7D heifers inseminated at estrus (46.5%) than for 7D heifers receiving the timed AI (26.8%) and differed (P < 0.05) from all 5D heifers regardless of insemination time at estrus (30.5%) or at timed AI at 72 h (29.9%). At the Florida location in which conventional and sexed semen were used during two breeding clusters, P/AI using sexed semen (43.9%, N = 56) did not differ from that of conventional semen (21.2%, N = 50). Remaining replicates of sexed semen produced similar P/AI at the other two locations (sexed = 27.6%, N = 71; and sexed = 31.9%, N = 215). We concluded that the modified 7-day CO-Synch + CIDR program produced more P/AI in heifers inseminated at estrus than a standard 5-day CO-Synch + CIDR program, but when timed AI occurred at 72 h after PGF_2α and CIDR insert removal, P/AI did not differ between programs.     

Control of estrus and pregnancy in dairy heifers treated with Syncro-Mate-B

Control of estrus in dairy heifers with Syncro-Mate-B was evaluated in five experiments with a total of 393 Holstein heifers. Estradiol-17β at implant removal or gonadotropin releasing hormone 40 hr after implant removal did not cause any beneficial effect on fertility. In heifers implanted on selected days of the estrous cycle, 88.3% of heifers treated with SMB only were in estrus within 5 days of implant removal and fertility was not significantly different from that of control heifers. In heifers implanted at random stages of the estrous cycle, estrus occurred within 5 days of implant removal in 88.7% of 159 SMB treated heifers. First service conception rates (heifers pregnant of heifers inseminated) and pregnancy rates (heifers pregnant of heifers assigned) were 72.7% and 60.8% for heifers inseminated 8 to 16 hr after estrus within 5 days of implant removal, 55.0% and 55.0% for heifers inseminated 48 hr after implant removal without regard to estrus and 71.6% and 67.1% for control heifers inseminated over a 25 day period.     

Early cycle FSH-p priming as a prelude to superovulating gonadotropin administration in ewes and heifers

The effect of an exogenous FSH treatment in the periovulatory, post-LH surge period on superovulatory response in the subsequent cycle of ewes and heifers was investigated. Thirty-five ewes were synchronized with progestagen pessaries and pregnant mares serum gonadotropin. The day following the onset of estrus (Day 1) 17 ewes received one intramuscular injection of 5 mg follicle stimulating hormone of porcine origin (FSH-p). All 35 ewes received another progestagen pessary on Day 1 and were superovulated with horse anterior pituitary extract (HAP). The ewes were bred and embryos collected 6 days following the onset of estrus. Early cycle FSH-p administration did not increase the subsequent ovulation rate (6.5 vs. 8.4 for controls, n.s.). Recovery rate for the FSH-p treated animals was higher (78.5% vs. 49.3%; P<0.05) as was fertilization rate (100% vs. 62.4%; P<0.05). The final result was a mean of 4.4 transferable embryos per ewe treated among the FSH-p boosted ewes and 2.6 transferable embryos per ewe treated among the control ewes.Twenty-nine heifers were brought into estrus with one 500-μg injection of prostaglandin F_2α (PG). Twelve of the 29 heifers were given one intramuscular injection of 10 mg FSH-p on either Day 2 or 3 (Day 1 is the day following the onset of estrus). All heifers were superovulated starting on Day 11–16, over a 4-day period using a decreasing dosage of FSH-p. Prostaglandin was administered at the time of the fifth superovulatory FSH-p injection and the heifers were bred by artificial insemination. Ova were recovered between 2 and 4.5 days following the onset of estrus. There was no effect on ovulation rate due to the interval from FSH-p priming to the day of superovulatory FSH-p initiation. The proportion of heifers that ovulated when given a FSH-p injection early in the cycle was higher than in the control group (94% vs. 68%; P<0.05). The primed heifers had a higher number of ovulations than did the control heifers (16.3 vs. 6.2; P<0.01). The effect of higher ovulation rate carried through all parameters measured, so that the FSH-p primed heifers also had a higher number of fertilized ova than the controls (10.7 vs. 3.9; P<0.05), indicating that there was no significant deterioration in ovum quality due to the FSH-p priming. The results show that FSH-p improved superovulatory efficiency in both sheep and cattle.     

Effect of progesterone concentrations,follicle diameter,timing of artificial insemination,and ovulatory stimulus on pregnancy rate to synchronized artificial insemination in postpubertal Nellore heifers

Two experiments were designed to evaluate the effects of treatments with low versus high serum progesterone (P₄) concentrations on factors associated with pregnancy success in postpubertal Nellore heifers submitted to either conventional or fixed timed artificial insemination (FTAI). Heifers were synchronized with a new controlled internal drug release device (CIDR; 1.9 g of P₄ [CIDR1]) or a CIDR previously used for 18 days (CIDR3) plus 2 mg of estradiol (E₂) benzoate on Day 0 and 12.5 mg of prostaglandin F2α on Day 7. In experiment 1 (n = 723), CIDR were removed on Day 7 or 9 and heifers were inseminated after estrus detection. In experiment 2 (n = 1083), CIDR were all removed on Day 9 and FTAI was performed either 48 hours later in heifers that received E₂ cypionate (ECP) on Day 9 (0.5 mg; E48) or 54 or 72 hours later in conjunction with administration of GnRH (100 μg; G54 or G72). Synchronization with CIDR1 resulted in greater serum P₄ concentrations and smaller follicle diameters on Days 7 and 9 in both experiments. In experiment 1, treatment with CIDR for 9 days decreased the interval from CIDR removal to estrus (Day 7, 3.76 ± 0.08 days vs. Day 9, 2.90 ± 0.07; P < 0.01) and improved conception (Day 7, 57.1% vs. Day 9, 65.8%; P = 0.05) and pregnancy rates (Day 7, 37.6% vs. Day 9, 45.3%; P = 0.04). In experiment 2, treatment with ECP improved (P < 0.01) the proportion of heifers in estrus (E48, 40.9%^a; G54, 17.1%^c; and G72, 32.0%^b), but the pregnancy rate was not affected (P = 0.64) by treatments (E48, 38.8%; G54, 35.5%; G72, 37.5%). Synchronization with CIDR3 increased follicle diameter at FTAI (CIDR1, 11.07 ± 0.10 vs. CIDR3, 11.61 ± 0.10 mm; P < 0.01), ovulation rate (CIDR1, 82.8% vs. CIDR3, 88.0%; P < 0.01) and did not affect conception (CIDR1, 42.2 vs. CIDR3, 45.1%; P = 0.38) or pregnancy rates (CIDR1, 34.7 vs. CIDR3, 39.4%; P = 0.11). In conclusion, length of treatment with P₄ affected the fertility of heifers bred based on estrus detection. When the heifers were submitted to FTAI protocol, follicle diameter at FTAI (≤10.7 mm, 23.6%; 10.8–15.7 mm, 51.5%; ≥15.8 mm, 30.0%; P < 0.01) was the main factor that affected conception and pregnancy rates.     

Normal or induced secretory patterns of luteinising hormone and follicle-stimulating hormone in anoestrous gonadotrophin-releasing hormone-immunised and cyclic control heifers

The objective was to determine the effect of gonadotrophin-releasing hormone (GnRH), GnRH analogue (GnRH-A) or oestradiol administration on luteinising hormone (LH) and follicle-stimulating hormone (FSH) release in GnRH-immunised anoestrous and control cyclic heifers. Thirty-two heifers (477 ± 7.1 kg) were immunised against either human serum albumin (HSA; controls; n = 8), or a HSAGnRH conjugate. On day 70 after primary immunisation, control heifers (n = 4 per treatment; day 3 of cycle) received either (a) 2.5 μg GnRH or (b) 2.5 μg of GnRH-A (Buserelin®) and GnRH-immunised heifers (blocked by GnRH antibody titre; n = 6 per treatment) received either (c) saline, (d) 2.5 μg GnRH, (e) 25 μg GnRH or (f) 2.5 μg GnRH-A, intravenously. On day 105, 1 mg oestradiol was injected (intramuscularly) into control (n = 6) and GnRH-immunised anoestrous heifers with either low (13.4 ± 1.9% binding at 1:640; n = 6) or high GnRH antibody titres (33.4 ± 4.8% binding; n = 6). Data were analysed by ANOVA. Mean plasma LH and FSH concentrations on day 69 were higher (P < 0.05) in control than in GnRH-immunised heifers (3.1 ± 0.16 vs. 2.5 ± 0.12 ng LH ml⁻¹ and 22.5 ± 0.73 vs. 17.1 ± 0.64 ng FSH ml⁻¹, respectively). The number of LH pulses was higher (P < 0.05) in control than in GnRH-immunised heifers on day 69 (3.4 ± 0.45 and 1.0 ± 0.26 pulses per 6 h, respectively). On day 70, 2.5 μg GnRH increased (P < 0.05) LH concentrations in control but not in GnRH-immunised heifers, while both 25 μg GnRH and 2.5 μg GnRH-A increased (P < 0.05) LH concentrations in GnRH-immunised heifers, and 2.5 μg GnRH-A increased LH in controls. FSH was increased (P < 0.05) in GnRH-immunised heifers following 25 μg GnRH and 2.5 μg GnRH-A. Oestradiol challenge increased (P < 0.05) LH concentrations during the 13–24 h period after challenge with a greater (P < 0.05) increase in control than in GnRH-immunised heifers. FSH concentrations were decreased (P < 0.05) for at least 30 h after oestradiol challenge. In conclusion, GnRH immunisation decreased LH pulsatility and mean LH and FSH concentrations. GnRH antibodies neutralised low doses of GnRH (2.5 μg), but not high doses of GnRH (25 μg) and GnRH-A (2.5 μg). GnRH immunisation decreased the rise in LH concentrations following oestradiol challenge.     

Peripheral progesterone levels in pregnant and non-pregnant heifers following use of HCG.

Progesterone concentration in jugular blood of bred beef heifers was determined on days 9 and 16 in two trials. Human chorionic gonadotrophin (HCG) was administered to some of the heifers in each trial in an attempt to improve pregnancy percentage.In Trial 1, 183 heifers were divided into a control group and three groups of animals which were subjected to a 9-day estrous synchronization treatment prior to breeding. The treatment consisted of an ear implant containing 17 α acetoxy-11-beta-methyl 17 nor preg 4-ene 3, 20 dione (norgestomet) left in place for 9 days and an injection of 5 mg estradiol valerate (EV) and 3 mg of norgestomet given at the time of implantation. The heifers in one group received .25 mg estradiol-17β at time of implant removal; heifers in the 2nd group received 1500 IU of HCG in 5% beeswax and 95% sesame oil at breeding time, while heifers in the 3rd group received a placebo injection containing 5% beeswax and 95% sesame oil at breeding time. No differences in serum levels of progesterone were observed (P>0.5) between treatments or between pregnant and non-pregnant heifers on day 9 or 16 (P>.05). Pregnancy percentage in heifers receiving HCG was similar to that noted in the control heifers or the placebo injected heifers while injection of estradiol 17β decreased the proportion of heifers which became pregnant.In trial 2, 58 heifers which had been bred 1 or 2 times without becoming pregnant were divided into a control group and a group in which heifers received 1000 IU of HCG 96 hr. after observed estrus. In heifers receiving HCG, serum levels of progesterone were higher (P<.01), on day 9 and 16 post estrus than in controls but no difference in serum progesterone was noted (P>.05) between pregnant and non-pregnant heifers on day 9 or 16. The proportion pregnant did not differ (P>.05) between heifers receiving HCG and control heifers.     

Pregnancy rate in peripuberal beef heifers following treatment with syncro-mate-B and gonadotropin releasing-hormone

A study was conducted to evaluate the effectiveness of treatment with Syncro-Mate-B (SMB) and gonadotropin releasing-hormone (GnRH) on inducing a fertile estrus and/or ovulation in peripuberal beef heifers. Two hundred and twenty-three, 13 to 15 month peripuberal beef heifers, primarily of Angus or Simmental breeding, were alternately allotted by weight and age within breed to a non-treated control group (C) and three groups which received the SMB treatment regime. Treated groups differed in that one group was inseminated approximately 12 hr after detected in estrus (T) while two other groups were inseminated at a fixed time after implant removal (T-G-I42, T-I48). Heifers in group T-G-I42 received 125 mug GnRH at 30 hr, and were inseminated 42 hr after implant removal. The remaining group of SMB-treated heifers received no additional hormone therapy but were inseminated 48 hr after implant removal (T-I48). Age had no significant effect on estrous response or pregnancy rate nor were there significant age by weight interactions on these parameters. Weight was a significant source of variation on interval from start of breeding to pregnancy (P<.01) and the effect on interval to estrus approached statistical significance (P<.0.9). In control heifers, increased weight had a positive effect on estrous response during the first 21 days of breeding (P<.05). Conversely, weight had no effect on estrous response during the 5-day synchronized period in heifers treated with SMB and observed for estrus (group T). Cumulative estrous response in control heifers was 10, 47, 48 and 55% in 5, 21, 27 and 45 days of breeding, respectively. Cumulative estrous response in SMB-treated heifers obsrved for estrus (group T) was 88, 91, 91 and 91% in 5, 21, 27 and 45 days of breeding, respectively. Pregnancy rate after 5 days of breeding was 9, 27, 18 and 30% for heifers in groups C, T, T-G-I42 and T-I48, respectively. Pregnancy rate after 21 days of breeding for heirfers in groups C, T, T-G-I42 and T-I48, respectively, was 33, 38, 21 and 41%; after 27 days of breeding was 36, 43, 40 and 48%; after 45 days of breeding was 48, 61, 51 and 69% and after the total 88-day breeding season was 59, 68, 71 and 72%. While a large percentage of peripuberal beef heifers with adequate age but insufficient weight were induced into estrus with the SMB treatment, pregnancy rates were low. Timed insemination programs with or without GnRH do not appear to be effective in improving pregnancy response in non-cyclic beef heifers.     

Effects of the reproductive status in Zebu heifers on the immunoglobulin M and G levels in bovine Trypanosoma vivax infection

Immunoglobulin M and G levels in bovine Trypanosoma vivax infection were compared in non-pregnant, first, second and third trimester pregnant heifers. All the infected heifers showed a significant rise in IgM levels when compared to the non-infected controls. 7–8 fold increases were recorded. There were however differences in the rate of increases and ability to maintain peak level response (P <0.01) between the groups. Infected pregnant heifers in the first and second trimester responded better than infected non-pregnant and infected heifers in the third trimester pregnancy. In all the groups, the differences between the infected and control heifers were highly significant (P <0.001). The IgG levels showed a similar pattern of increases in infected heifers though response was gradual. In the different groups 1.4–2.5-fold increases were recorded. These were significantly different from levels in the control (P <0.01). Again, pregnant heifers responded better than non-pregnant heifers except those in the third trimester pregnancy. The results correlated with the observation that given the same conditions, clinical manifestation of T. vivax infection is more severe in non-pregnant than in pregnant heifers except those in advanced pregnancy.     

Endogenous hormone response and fertility in dairy heifers after treatment with Lutalyse and GnRH

Fifty-five dairy heifers were given two injections of Lutalyse 11 days apart. Twenty-one of the heifers were also given an injection of GnRH 48 hr after the second Lutalyse injection (Group G). Of the remaining 34 animals, 19 were randomly allotted to be inseminated 12 hr after observed estrus following Lutalyse (Group E), while 15 were inseminated 80 hr after the second Lutalyse injection (Group P). The intervals from second Lutalyse injection to occurrence of both estrus and peak gonadotropin concentrations were variable among animals receiving only Lutalyse. GnRH injections reduced variation (P<.01) in the interval from second Lutalyse injection to occurrence of peak gonadotropin concentrations, but did not improve fertility. Pregnancy rates did not differ (P>.05) among treatment groups. The failure of GnRH administration following Lutalyse to improve pregnancy rates indicates that GnRH administration followed by insemination 12 hr later is not effective in increasing pregnancy rates above those attained in animals inseminated at either 12 hr post estrus or 80 hr after second Lutalyse injection.     

The use of estradiol and/or GnRH in a two-dose PGF protocol for breeding management of beef heifers

The objective was to determine reproductive performance following AI in beef heifers given estradiol to synchronize ovarian follicular wave emergence and estradiol or GnRH to synchronize ovulation in a two-dose PGF-based protocol. In Experiment 1, 561 cycling (confirmed by ultrasonography), Angus heifers received 500 microg cloprostenol, i.m. (PGF) twice, 14 days apart (days 0 and 14) and were equally allocated to four groups in a 2 x 2 factorial design. On Day 7, heifers received either 2 mg estradiol benzoate (EB) and 50 mg progesterone (P), i.m. in oil (EBP group) or no treatment (NT group). Half the heifers in each group received 1mg EB, i.m. in oil on Day 15 (24h after the second PGF treatment) with TAI 28 h later (52 h after PGF), and the other half received 100 microg GnRH, i.m. on Day 17 (72 h after PGF) concurrent with TAI. All heifers were observed for estrus twice daily from days 13 to 17; those detected in estrus more than 16 h before scheduled TAI were inseminated 4-16 h later and considered nonpregnant to TAI. Overall pregnancy rate (approximately 35 days after AI) was higher in heifers that received EBP than those that did not (61.6% versus 48.2%, respectively; P < 0.002); but was lower in heifers that received EB after PGF than those that received GnRH (50.0% versus 59.8%; P < 0.02). Although estrus was detected prior to TAI in 77 of 279 heifers (27.6%) treated with EBP (presumably due to induced luteolysis), they were inseminated and 53.2% became pregnant. Overall pregnancy rates were 51.4, 68.3, 45.0, and 55.0% in the NT/GnRH, EBP/GnRH, NT/EB, and EBP/EB groups, respectively (P < 0.05). In Experiment 2, 401 cycling, Angus heifers were used. The design was identical to Experiment 1, except that 1.5mg estradiol-17beta (E-17beta) plus 50mg progesterone (E-17betaP) and 1mg E-17beta were used in lieu of EBP and EB, respectively. All heifers receiving E-17beta 24h after the second injection of PGF (NT/E-17beta and E-17betaP/E-17beta) were TAI 28 h later without estrus detection, i.e. 52 h after PGF. Heifers in the other two groups received 100 microg GnRH, i.m. 72 h after PGF and were concurrently TAI; heifers in these two groups that were detected in estrus prior to this time were inseminated 4-12h later and considered nonpregnant to TAI. Estrus rate during the first 72 h after the second PGF treatment was higher (P < 0.05) in the E-17betaP/GnRH group (45.0%; n = 100) than in the NT/GnRH group (16.0%; n = 100), but conception rate following estrus detection and AI was not different (mean, 57.4%; P = 0.50). Overall pregnancy rate was not significantly different among groups (mean, 46.9%; P = 0.32). In summary, the use of EB or E-17beta to synchronize follicular wave emergence and estradiol or GnRH to synchronize ovulation in a two-dose, PGF-based protocol resulted in acceptable fertility to TAI. However, when 2mg EB was used to synchronize follicular wave emergence, early estrus occurred in approximately 28% of heifers, necessitating additional estrus detection. A combination of estrus detection and timed-AI in a two-dose PGF protocol resulted in highly acceptable pregnancy rates.     

Factors influencing estrus and conception in dairy heifers after prostaglandin F2-alpha

The influence of interval between insemination (AI) and estrus on subsequent fertility of PGF(2alpha)-treated (two injections of 25 mg, 11 days apart) heifers was assessed in two experiments. In Experiment I, 240 heifers were allotted to Control (AI 8 to 16 hr after estrus detection), PGF(2alpha)-E (AI 8 to 16 hr after estrus within five days of second PGF(2alpha)) or PGF(2alpha)-T (AI 80 hr after second PGF(2alpha)). In Experiment II, 130 heifers were assigned to control (AI as before) or PGF(2alpha) (AI 72 or 80 hr after second PGF(2alpha)) with half the PGF(2alpha) heifers receiving 100 mug GnRH 72 hr after first PGF(2alpha). Heifers of both experiments that were bred at a predetermined time were arrayed by interval from AI to estrus. Conception rates of heifers detected in estrus from 32 hr before AI to 24 hr after AI did not differ (x(2)=3.35, df=5, P>0.5). The percentage of GnRH-treated heifers in estrus within five days (81.8%) was not (P>0.75) greater than those not receiving GnRH (77.3%) but they had higher (P<0.05) serum progesterone (P(4)) concentration at second PGF(2alpha) (3.17 vs 2.41 ng/ml). When P(4) values were arrayed for both groups at 1 ng intervals, the percentage of heifers exhibiting estrus increased with increasing P(4) level (P<0.05).     

A two injection schedule with prostaglandin F2alpha for the regulation of the ovulatory cycle of cattle

Thirty randomly cycling Holstein heifers were given two injections of prostaglandin F_2α 10 days apart, to determine whether this treatment would cause most of the animals to show estrus shortly after the second injection. Twenty-five of the 30 heifers (83%) were in estrus and inseminated 2 to 4 days following the second injection and 10 of the 25 (40%) were pregnant at 60 days post insemination. Thirteen of 15 control heifers (87%) were detected in estrus over a 3 week period and seven of the 13 (54%) were pregnant at 60 days. Chi square analysis indicated that the proportion of animals showing estrus and subsequent pregnancy in the treated and in the control groups were not significantly different. The two injection system may have commercial application for the regulation of the ovulatory cycle of cattle.     

Abortion after PGF2α in heifers with multiple pregnancies following superovulation with FSH and PGF2α

Multiple ovulations were induced with follicle stimulating hormone and estrus was synchronized with prostaglandin F_2α (PGF_2α) in 23 Holstein heifers. In 19 heifers which responded to the treatments, an average of 1.8 corpora lutea were formed after the induced estrus and 6 of 19 heifers conceived (total of ten fetuses at 39 days gestation) to artificial insemination at 60 and 84 hr after the PGF_2α injection. Injection of 33 mg PGF_2α Tham salt into the six pregnant heifers on day 40 of gestation caused abortion between 54 and 66 hr after treatment in all heifers.     

Comparison of controlled internal drug release device and melengesterol acetate as progestin sources in an estrous synchronization protocol for beef heifers

The objectives of this experiment were to compare estrous synchronization responses and AI pregnancy rates of beef heifers using protocols that included either CIDR or MGA as the progestin source. The hypotheses tested were that: (1) estrous synchronization responses after (a) progestin removal, and (b) PGF(2alpha); and, (2) AI pregnancy rates, do not differ between heifers synchronized with either progestin source. At the start of the experiment (Day 0) in both years, heifers were assigned randomly to receive, MGA supplement for 14 days (MGA-treated; n=79) or CIDR for 14 days (CIDR-treated; n=77). On Day 14 progestin was removed and heifers were observed for estrus up to and after PGF(2alpha) on Days 31 and 33 for CIDR-treated and MGA-treated heifers, respectively. Heifers that exhibited estrus within 60h after PGF(2alpha) were inseminated by AI 12h later; the remaining heifers were inseminated at 72h after PGF(2alpha) and given GnRH (100mug). More (P<0.05) CIDR-treated heifers exhibited estrus within 120h after progestin removal than MGA-treated heifers. Intervals to estrus after progestin removal were shorter (P<0.05) for CIDR-treated heifers than MGA-treated heifers. More (P<0.05) CIDR-treated heifers exhibited estrus and were inseminated within 60h after PGF(2alpha) than MGA-treated heifers. Pregnancy rates did not differ (P>0.10) between MGA-treated (66%) and CIDR-treated (62%) heifers. In conclusion, the use of CIDR as a progestin source in a 14-day progestin, PGF(2alpha), and timed AI and GnRH estrous synchronization protocol was as effective as the use of MGA to synchronize estrus and generate AI pregnancies in beef heifers.     

Effects of naloxone and animal temperament on serum luteinizing hormone and cortisol concentrations in seasonally anestrous Brahman heifers

The effect of endogenous opioid peptides (EOP) and individual animal temperament on serum luteinizing hormone (LH) were investigated in seasonally anestrous Brahman heifers (n = 24). Animals that had shown behavioral estrus in previous months but that had not returned to estrus for at least 30 d were selected. The heifers were ranked by temperament (tame = 1, normal = 2, wild = 3) and randomly allotted into three groups. Blood was collected from one heifer of each group per day. Blood samples were taken via jugular cannula every 15 min for 6 h and every 30 min for another 4 h. After the first hour of sampling, the heifers received intravenous saline (SAL, n = 8); naloxone (LN, 0.5 mg/kg i.v., n = 8); or naloxone (HN, 1.0 mg/kg i.v., n = 8). Three hours after naloxone treatment, each heifer was given gonadotropin releasing hormone (GnRH, 100 mug i.m.). All samples were processed to yield serum and were assayed for LH by radioimmunoassay (RIA). Hourly samples were assayed for cortisol by RIA. The area under the LH curve 60 min postnaloxone treatment was higher in LN and HN than in SAL (57.0 and 40.8 vs 6.1 units; P<0.01); and the area under the 180 min postnaloxone curve remained higher in LN than in SAL (106.2 vs 35.1 units; P<0.05). Cortisol concentrations 60 min postnaloxone administration were above prenaloxone levels(38.2 vs 26.7 ng/ml; P<0.0002). Temperament scores of heifers were positively correlated with cortisol release. The area under the cortisol curve had a negative correlation with mean LH. Serum LH concentrations appear to be suppressed by EOP in seasonally anestrous Brahman heifers, and EOP appear to reduce serum cortisol concentrations. Excitable heifers had higher concentrations of serum cortisol, which negatively affected serum LH concentrations.     

Effects of resynchronization strategies for lactating Holstein cows on pattern of reinsemination, fertility, and economic outcome

The objectives were to evaluate the pattern of re-insemination, pregnancy outcomes to re-insemination in estrus and at fixed time, and economic outcomes of lactating Holstein cows submitted to three resynchronization protocols. Cows were enrolled in the Experiment at 32 ± 3 d after pre-enrollment Artificial Insemination (AI), 7 d before pregnancy diagnosis, and randomly assigned to three resynchronization protocols. All cows diagnosed not pregnant at 39 ± 3 d after pre-enrollment AI were submitted to the Cosynch72 (Day 0 GnRH, Day 7 prostaglandin F_2α, and Day 10 GnRH and fixed time AI). Cows assigned to the control treatment received no further treatment, cows assigned to the GGPG treatment received a GnRH injection on Day −7, and cows assigned to the CIDR treatment received a controlled internal drug release (CIDR) insert containing 1.38 g of progesterone from Days 0-7. Cows observed in estrus were re-inseminated on the same day. Pregnancy was diagnosed at 39 ± 3 and 67 ± 3 d after re-insemination. Costs of the resynchronization protocols were calculated for individual cows enrolled in the study and pregnancies generated were given a value of $275. The GGPG treatment resulted in the slowest (P ≤ 0.06) rate of re-insemination. Overall pregnancy per AI (P/AI) at 39 ± 3 (P = 0.50) and 67 ± 3 (P = 0.49) d after re-insemination were not affected by treatment. Although cost of the control protocol was (P < 0.01) the smallest, return per cow resynchronized was (P < 0.01) greater for GGPG and CIDR protocols. We concluded that presynchronizing the estrous cycle of cows with GnRH or treating cows with a CIDR insert during resynchronization altered the pattern of re-insemination and improved the economic return of resynchronized cows.     

Resynchronization of previously timed-inseminated beef heifers with progestins

The objective was to determine the efficacy of a previously used CIDR or melengestrol acetate (MGA; 0.5mg/head/day) for resynchronization of estrus in beef heifers not pregnant to timed-AI (TAI). In three experiments and a field trial, heifers were reinseminated 6-12 h after first detection of estrus. Pregnancy diagnosis was done from approximately 25-43 days after either TAI or reinsemination. In Experiment 1, 79 heifers received a once-used CIDR from 13 to 20 days after TAI and 80 heifers were untreated controls. For these two groups, there were 34 and 35 heifers, respectively, not pregnant to TAI; median +/- S.E. intervals from TAI to onset of estrus were 22 +/- 0.2 days versus 20 +/- 0.6 days (P < 0.001); estrus rates were 70.6% versus 85.7% (P = 0.1); conception rates were 62.5% versus 76.7% (P < 0.3); and pregnancy rates were 44.1% versus 65.7% (P = 0.07), for CIDR and untreated (control) groups, respectively. In Experiment 2, heifers (n = 651) were TAI (Day 0) and 13 days later randomly assigned to one of seven groups (n = 93 per group) to receive a once-used CIDR (three groups; Days 13-20), MGA (three groups; Days 13-19), or no treatment (control group). Groups given a CIDR or MGA also received: no further treatment (CIDR or MGA alone); 1.5mg estradiol-17beta (E-17beta) and 50 mg progesterone (P4) in 2 mL canola oil on Day 13; or E-17beta and P4 on Day 13 and 0.5 mg E-17beta on Day 21 (24 h after CIDR removal or 48 h after the last feeding of MGA). Pregnancy rate to TAI was lowest (P < 0.05) for the group given a CIDR plus E-17beta and P4 on Day 13 and E-17beta on Day 21. Variability in return to estrus was greater (P < 0.001) in the control and MGA groups than in CIDR groups. Conception and pregnancy rates in heifers given a CIDR (65.1 and 61.4%) were higher (P<0.01) than those fed MGA (49.6 and 40.4%), but not different from controls (62.2 and 54.9%, respectively). In Experiment 3, 616 heifers received a once- or twice-used CIDR for 7 days, beginning 13+/-1 days after TAI, with or without a concurrent injection of 150 mg of P4 (2 x 2 factorial design). Pregnancy rate to TAI was 47.2%. In heifers that returned to estrus, there was no significant difference between a once- or twice-used CIDR for rates of estrus (68.8%, P < 0.3), conception (65.9%, P < 0.6) and pregnancy (45.3%, P < 0.8). Injecting progesterone at CIDR insertion increased the median interval from CIDR removal to onset of estrus (P < 0.05) and reduced rates of estrus (63.8% versus 73.8%, P<0.05), conception (60.5% versus 70.6%, P = 0.1) and pregnancy (38.6% versus 52.2%, P < 0.02). In a field trial, 983 heifers received a once-used CIDR for 7 days, beginning 13 +/- 1 days after TAI. Pregnancy rate to TAI was 55.2%. The median (and mode) of the interval from CIDR removal to estrus was 2.5 days. Estrus, conception and pregnancy rates were 78.2, 70.3 and 55.0% (overall pregnancy rate to TAI and rebreeding, 78.7%). In summary, a once- or twice-used CIDR for 7 days, starting 13 +/- 1 days after TAI resulted in the majority of nonpregnant heifers detected in estrus over a 4-day interval, with acceptable conception rates; however, injecting progesterone at CIDR insertion significantly reduced both estrus and pregnancy rates, and estradiol treatment after CIDR removal was associated with a decreased pregnancy rate to TAI. Fertility was higher in heifers resynchronized with a once-used CIDR than with MGA.