Postpartum subestrus in dairy cows: comparison of treatment with prostaglandin F2 alpha or GnRH + prostaglandin F2 alpha + GnRH

Two experiments (Experiment 1, 185 cows in 1996/97; Experiment 2, 168 cows in 1997/98) were conducted with Prim Holstein dairy cattle in the Mayenne region of France to investigate subestrus. Cows which had not been observed in estrus since calving were allocated alternately to treatment groups between 60 and 90 d post partum as follows: Experiment 1-Group 1: GnRH (Day 0, 100 micrograms i.m.), PGF2 alpha (Day 7, 25 mg i.m.), GnRH (Day 9, 100 micrograms i.m.) and AI (Day 10); Group 2: PGF2 alpha (Day 0, 25 mg i.m.), AI at estrus, or, if estrus was not observed, a second PGF2 alpha injection on Day 13, and AI on Day 16 and Day 17. Treatments in Experiment 2 were as follows: Group 1: as Experiment 1-Group 1 but AI at the observed estrus after Day 0, or at Day 10 if estrus was not observed; Group 2: as Experiment 1--Group 2, however, if a second PGF2 alpha injection was given on Day 13, AI at the observed estrus. Progesterone was measured in serum at Day 0 and in milk at AI. Pregnancy diagnosis was performed by measuring bovine pregnancy-specific protein B (bPSPB; Day 50 +/- 3) and confirmed by ultrasonography when the result was doubtful. In Experiment 1, farmers observed 47/101 (46.9%) Group 1 cows in estrus, 33/91 cows on Day 10 and 10 cows before Day 10. The progesterone concentrations were compatible with estrus in 69/86 (80%) cows on Day 10. In Group 2, 36/83 (43.4%) cows were inseminated after the first PGF2 alpha injection. After the second PGF2 alpha injection, only 29/43 (67%) cows had a low progesterone concentration at AI. Pregnancy rates were 36.1 and 32.5% for Groups 1 and 2, respectively. In Experiment 2, estrus was observed in 31/93 (33.7%) Group 1 cows. In Group 2, 51/75 (66%) cows were inseminated after the first injection of PGF2 alpha, 13/75 (17.3%) cows after the second injection, while 11/75 (14.7%) were not observed in estrus. Pregnancy rates were 53.7 and 53.3% in Groups 1 and 2, respectively. In conclusion, it is recommended that subestrus be treated with PGF2 alpha followed by AI at the observed estrus when estrus detection is good, while the use of GnRH + PGF2 alpha + GnRH is recommended when estrus detection is poor.     

Effect of sequential treatment with prostaglandin F2 alpha and/or oxytocin on estrus and pregnancy rate of lactating dairy cows

A total of 335 lactating dairy cows was used to determine the effect of oxytocin or PGF2a given 8 h after treatment with a luteolytic dosage of PGF2a on the percentage of cows exhibiting estrus within 7 d after treatment, and the pregnancy rate to a single insemination at this time. On the initial day of treatment (Day 0), cows with a palpable corpus luteum on the ovary were treated with 25 mg, im of PGF2a. At 8 h later, the cows were divided into 3 groups. Cows in Group 1 (n = 112) were treated with oxytocin (0.33 IU/kg bwt im); cows in Group 2 (n = 112) were treated with 25 mg, im of PGF2a; and cows in Group 3 (n = 111) served as the untreated controls. Cows in all 3 groups were continuously observed for estrus visually or by way of an activated heatmount detector within 7 d after treatment, and were inseminated within 12 h of the observed estrus.Plasma progesterone (P4) concentration was determined using radioimmunoassay on Day 0 and Day 2. Of the cows with P4 greater than 1 ng/ml on Day 0, the percentage of cows observed in estrus within 7 d after treatment was 75, 89 and 72% for cows in Group 1, Group 2 and Group 3, respectively. When all cows were evaluated, the percentage of cows observed in estrus within 7 d after treatment was 60, 70 and 55% for cows in Group 1, Group 2 and Group 3, respectively. In both instances, the value for cows in Group 2 was significantly higher than that for either cows in Group 1 or Group 3. The pregnancy rate for cows inseminated within 7 d was similar for cows in all 3 groups. The results of this study demonstrated that treatment of dairy cows with 2 luteolytic dosages of PGF2a at an 8-h interval resulted in more cows being observed in estrus within 7 d than with 1 treatment with PGF2a, or with oxytocin given at an 8-h interval after a luteolytic dosage of PGF2a.     

Control of estrus and ovulation in dairy cows

The efficiency of a synthetic prostaglandin analog (ICI 80996) for the control of the estrus cycle in dairy cows has been tested with and without simultaneous use of progestagen implants (SC 21009, Searle). Synchronization of estrus is closer after combined progestagen-prostaglandin treatments than after prostaglandins alone (78.7 % in estrus in 48h vs 60.2 % ; P<0.001).The percentage of cows not observed in estrus during the first 96h after the end of treatment was also lower after combined treatments (20.7 % vs 31.8 % ; P<0.05). The best estrus synchronization was obtained by injecting prostaglandin analog two days before implant removal (86 % in estrus in 48h and 14.0 % not observed in estrus within 96h).Fertility was studied in a field trial after one or two inseminations at a predetermined time for each treatment. A higher pregnancy rate was obtained with two inseminations after combined progestagen-prostaglandin treatment (49.1 %). This pregnancy rate differed significantly (P<0.05) from those obtained with one A.I. after the same treatment or two A.I. after the prostaglandin treatment but did not differ from the pregnancy rate obtained with one A.I. 80h after the second prostaglandin injection. The most important problem in dairy cows is the fall in pregnancy rate between 21 days and 6 months (19.7 to 35.1 % depending on treatment ; P<0.05).     

Synchronization of estrus in beef heifers with a norgestomet implant and prostaglandin F2alpha

In a 5-year study (1973-1977), 281 cycling beef heifers were treated with a 7-day norgestomet (SC21009) ear implant and an intramuscular injection of prostaglandin F(2alpha) (PGF(2alpha)) at the time of implant removal or 24 hr before implant removal. Percentages of heifers in estrus by 36, 48, 60, 72, and 120 hr after implant removal were 32.4, 52.7, 71.6, 80.1, and 93.2, respectively. Onset of estrus occurred an average of 49.8 +/- 4.7 hr after treatment. Percentages of heifers in estrus 36 hr after treatment were 5.7 and 51.7 for those with a corpus luteum and those without a corpus luteum (or determined regressing by palpation) at implant removal, respectively. When PGF(2alpha) was injected 24 hr before implant removal, 55% of the heifers were in estrus by 36 hr after implant removal compared to 30% when PGF(2alpha) was injected at the time of implant removal; however, by 60 hr after implant removal the difference was 76% vs. 71%. First-service conception rates for synchronized and nonsynchronized heifers were 62.2% and 59.6%, respectively. During 1976 and 1977 heifers were checked for estrus every 4 hr and inseminated 2, 6, 10, 14, 18, 22, 26, or 30 hr after first detected to be in standing estrus. Conception rate was not significantly affected by time of insemination but tended to be higher for heifers bred 26 and 30 hr after first being detected in standing estrus (78.9% and 70.0% vs. average 59.2%). Treatment with a 7-day norgestomet implant plus a single injection of PGF(2alpha) 24 hr before or at implant removal appears to be a practical technique for synchronizing estrus in cycling heifers without affecting conception.     

Conception rates in repeat-breeders and dairy cattle with unobserved estrus after prostaglandin F(2) alpha and gonadotropin-releasing hormone

In Experiment 1, cows with a history of at least two previous unsuccessful inseminations were allocated to four groups. At the repeated estrus (third or greater service), some of the cows were inseminated according to the a.m.-p.m. rule (Controls, n = 83), or received i.m. 100 mug gonadotropin-releasing hormone (GnRH, n = 32) within 30 sec after insemination. Ovaries of the remaining cows to be treated were palpated during the anticipated ensuing luteal phase to determine the presence of a corpus luteum. Cows found to have luteal tissue received i.m. 25 mg prostaglandin F(2)-alpha (PGF(2)-alpha) and were inseminated after detected estrus or at 72 and 96 h after PGF(2)-alpha in the absence of estrus. Cows given PGF(2)-alpha either received no further treatment (PGF(2)-alpha, n = 40) or were given i.m. 100 mug GnRH (PGF(2)-alpha + GnRH, n = 29) after insemination or at 72 h after PGF(2)-alpha in the absence of estrus. Conception rate of control cows (39%) was similar to that of cows given PGF(2)-alpha (40%) or PGF(2)-alpha + GnRH (43%), but it tended to be lower (P = 0.13) than that of cows given only GnRH at insemination (54%). In Experiment 2, cows with unobserved estrus and diagnosed not pregnant (palpation) were palpated to detect a corpus luteum. Cows with luteal tissue received i.m. PGF(2)-alpha (n = 52) or PGF(2)-alpha + GnRH (n = 45) and were inseminated as described above. Conception rates were similar (39% vs 33%, respectively). In Experiment 3, cows in a large commercial dairy with (n = 93) or without (n = 420) previous reproductive problems were given i.m. 100 mug GnRH after insemination (n = 169) or were left untreated (n = 344) at repeat services (third and fourth services). Treatment with GnRH improved (P < 0.05) conception in normal (47% vs 36%) and abnormal (25% vs 12%) repeat-breeding cows. Treatment with PGF(2)-alpha alone or in conjunction with GnRH failed to further improve conception rates and only delayed intervals to rebreeding when administered during the luteal phase after the repeated estrus. The use of GnRH failed to reduce intervals from treatment to insemination or improve conception in cows with unobserved estrus compared to treatment with PGF(2)-alpha alone.     

Synchronization of estrus with PGF2 alpha administered 18 days after a progesterone treatment in lactating dairy cows

In a previous study we showed that estrus synchronization with 2 treatments of PGF2 alpha 13 d apart reduced conception rate at the synchronized estrus and that this reduction occurred mainly in cows in the early luteal phase at the second PGF2 alpha treatment. The objective of the present study was to determine the efficacy of a synchronization regimen in which PGF2 alpha was administered during the mid- to late-luteal phase to cows that had previously been synchronized with progesterone. Spring-calving cows from 6 dairy herds were used in this study. On Day -32 (Day 1 = the start of the breeding season), cows that had calved 2 or more weeks ago were randomly assigned to a synchronization (S, n = 732) or control (C, n = 731) group. Cows in Group S were treated with an intravaginal progesterone device (CIDR) for 12 d from Day -32 to Day -20, while those in Group C were left untreated. Similar percentages of cows in Group S (80.6%) and C (82.9%) had cycled by Day -7. The CIDR treatment synchronized the onset of estrus, resulting in 92.9% of cows in estrus being detected within 7 d after CIDR removal. Cows in Group S that had cycled by Day -7 were treated with PGF2 alpha (25 mg, i.m., Lutalyse) on Day -2. Cows in both groups that were anestrous on Day -7 were treated with a combination of progesterone and estradiol benzoate (EB) to induce estrus and ovulation (CIDR and a 10 mg EB capsule on Day -7, CIDR removal on Day -2, and injection of 1 mg EB 48 h after CIDR removal). The PGF2 alpha treatment synchronized the onset of estrus in 87.5% of the cows. Group S and C cows had similar conception rates to first (61.0 vs 58.3%) and second (58.4 vs 60.9%) AI; similar pregnancy rates over the AI period (82.8 vs 79.2%) and over the whole breeding season (91.9 vs 90.6%); and required a similar number of services per pregnancy to AI (1.7 vs 1.8). The interval from the start of the breeding season to conception for cows conceiving to AI or to combined AI and natural mating was shorter (P < 0.001) by 5.7 and 6.2 d, respectively, for the Group S cows. It is concluded that the treatment regimen tested in the present study achieved satisfactory estrus synchronization, had no detrimental effect on fertility at the synchronized estrus, and shortened the interval from start of the breeding season to conception.     

Induction of estrus in cattle by intraovarian injection of prostaglandin F2alpha

An effective, reduced dosage (1 10 to 1 20 the systemic dose) method for administering prostaglandin F(2alpha) in heifers to induce estrus is presented in this study. The PGF(2alpha) was injected intraovarially in five heifers at a dose of 2 mg and in another five heifers at a dose of 1 mg. Five additional heifers were injected intraovarially with 0.5 ml of distilled water and served as the controls. Regression of the corpus luteum (CL) occurred in all PGF(2alpha)-treated heifers resulting in marked decline of the peripheral levels of progesterone 24 h after treatment. Estrus was expressed 1 to 3 d later. Regression of the CL, estrus, and decline in the peripheral levels of progesterone were not observed in the control heifers. Conception rates in the heifers given either 2 mg and 1 mg PGF(2alpha) were 60 and 100%, respectively. Seven calves were born at the end of the normal gestation period while one calf was aborted.     

Synchronisation of oestrus in dairy cows using prostaglandin F2alpha,gonadotrophin-releasing hormone,and oestradiol cypionate

An oestrous synchronisation protocol was developed for use in lactating dairy cows using PGF(2alpha), GnRH, and oestradiol cypionate (ECP). In experiment 1, lactating dairy cows received two injections of PGF(2alpha) (on days 0 and 11) (PP; n=10) or two injections of PGF(2alpha) (days 0 and 11) and 100 microg of GnRH on day 3 (PGP; n=10). In experiment 2, cows were treated with PGP (n=7), or PGP and 1 mg of ECP at the same time (PGPE(0); n=7) or 1 day after the second PGF(2alpha) injection (PGPE(1); n=7). In experiment 3, 101 lactating dairy cows in a commercial herd were assigned to one of three treatments; PP, PGP, or PGPE(1). Follicular growth was measured by ultrasound in experiments 1 and 2. Every cow (experiments 1, 2, and 3) was blood sampled at selected intervals for progesterone and oestradiol assays and inseminated at oestrus. In experiment 1, a higher percentage of GnRH-treated cows ovulated after the first PGF(2alpha) injection (90% versus 50%; P<0.05). The GnRH-treated cows tended to have a larger dominant follicle present at the time of the second PGF(2alpha) injection (16.5+/-0.5 mm versus 15.0+/-0.7 mm; P<0.10). The percentage of cows that ovulated after the second PGF(2alpha) injection was similar (60%). In experiment 2, cows treated with ECP had higher peak preovulatory concentrations of oestradiol in plasma (6.99+/-0.63 versus 3.63+/-0.63; P<0.01) following the second PGF(2alpha) injection and a higher percentage ovulated (86% versus 43%; P<0.05). A higher percentage of PGPE(1)-treated cows in experiment 3 were observed in standing oestrus and ovulated after the second PGF(2alpha) injection (standing oestrus, 26.4, 34.3, and 62.6%, P<0.01; ovulated, 56, 63, and 78%, P<0.05; PP, PGP, and PGPE(1), respectively). In conclusion, the PGP protocol increased the number of cows that ovulated after the first PGF(2alpha) injection and produced a more mature dominant follicle at the time of the second PGF(2alpha) injection. Adding ECP to PGP (PGPE(1)) enhanced the expression of oestrus and increased ovulation percentage. The combination of PGP and ECP is potentially a new method to routinely synchronise oestrus and ovulation in dairy cows.     

Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2alpha and progesterone

The objective of this study was to evaluate the reproductive performance of lactating cows in seasonal dairy herds after estrus synchronization with PGF2alpha (PG) with or without supplementation with progesterone (P4). In Trial 1, synchronized cows (S1; n = 521) were compared with untreated control cows (C; n = 518) in 5 herds. Estrus of cows in the S1 group was synchronized with 2 treatments of PG (Lutalyse) 13 d apart. The breeding season started 2 d after the second PG. Cows were first bred by AI for 7 wk and then herd sires were used. Compared with C cows, estrus synchronization in the treated cows reduced the conception rate to first AI (61.1 vs 70.5%; P < 0.01) and the intervals from start of the breeding season to conception for cows conceiving to AI (11.0 vs 14.6 d; P < 0.05) or to both AI and natural mating (16.5 vs 18.4 d; P < 0.05). There was no effect on conception rate to second AI (68.8%), on pregnancy rate by Day 24 (72.3%) or Day 49 (86.3%) of the breeding season, or on the percentage of cows not pregnant at end of the breeding season (5.0%). In Trial 2, effects of P4 supplementation before the second PG on reproductive performance were evaluated in 4 herds. Estrus of each cyclic cow was synchronized with PG as in Trial 1. Half of the cows in each herd were treated with an intravaginal P4 device (CIDR) for 5 d before the second PG (S2+P4, n = 608), whereas the remaining half received no CIDR treatment (S2, n = 593). Compared with S2 cows, P4 treatment increased the estrous response rate to the second PG (89.6 vs 82.9%; P < 0.01), the conception rate to first AI (65.1 vs 59.7%; P = 0.07), the pregnancy rate by Day 6 of the breeding season (59.3 vs 49.0%; P < 0.001), and reduced the intervals from start of the breeding season to conception for cows conceiving to AI (8.6 vs 10.4 d; P < 0.10) or to both AI and natural mating (12.7 vs 16.4 d; P < 0.01). Treatment with a used CIDR from Days 16 to 21 after start of breeding to re-synchronize returns to service had no effect on conception rate to first or second AI but may decrease the conception rate to second AI in cows previously treated with CIDR. In conclusion, estrus synchronization with the double PG system can reduce fertility, while P4 supplementation for 5 d before the second PG can improve estrous response and overall reproductive performance. Stage of the estrous cycle at the time of the second PG can affect fertility following synchronization.     

Alterations in embryo development in progestogen-supplemented cows administered prostaglandin F2alpha

The objective was to examine effects of elevated prostaglandin F2alpha (PGF) on embryo development in cows supplemented with exogenous progestogen. Cows were artificially inseminated at estrus (Day 0) and a synthetic progestogen supplemented in the feed from Days 3 to 8. Cows were allotted randomly to receive either 15 mg PGF (TRT) or saline (CON) at 06:00, 14:00 and 22:00 h from Days 5 to 8. Blood samples were collected at 06:00 and 22:00 h from Days 5 to 8 for determination of progesterone and 13,14-dihydro-15-keto-PGF2alpha (PGFM). Single embryos were recovered on Day 8, assigned a quality score, and stage of development recorded. Progesterone was lower from Days 5 to 8 in TRT versus CON cows (P = 0.0001). Concentrations of PGFM from Days 5 to 8 were elevated in TRT compared to CON cows (P = 0.0001). Embryo quality was reduced in TRT cows compared to CON cows (P = 0.059). Percentage of embryos considered transferable was decreased by administration of PGF (P = 0.003). Sixty-four percent of TRT embryos were retarded in development at Day 8, whereas 80% of CON embryos had developed to expanded blastocysts (P = 0.003). In conclusion, treatment of progestogen-supplemented cows with PGF reduced quality and retarded development of embryos. Decreased fertility in conditions causing elevated concentrations of PGF may result from altered embryo development and quality.     

Conception rates in dairy cows after timed-insemination and simultaneous treatment with gonadotrophin releasing hormone and/or prostaglandin F2 alpha

This study was designed to determine conception rates in dairy cows after timed-insemination and simultaneous treatment with gonadotrophin releasing hormone (GnRH) and/or prostaglandin F2 alpha (PGF2alpha). A total of 2352 cows was randomly assigned to six groups. Cows in Groups 1 to 5 were palpated per rectum to determine the presence of a corpus luteum (CL) on the ovary, and blood samples were obtained for the determination of plasma progesterone (P4) concentrations. Cows with a CL and P4 concentrations >1 ng/ml were treated (Day 0) with PGF2alpha (25 mg, i.m.) and were observed for estrus. Cows in estrus prior to 72 hours after treatment (Group 5, n = 106) were bred, but were not treated. Cows not observed in estrus by 72 hours were divided into four remaining groups, were bred between 72 and 80 hours and were assigned as follows: Cows in Group 1 (n = 203) were not treated; Cows in Group 2 (n = 200) were treated with GnRH (100 ug, i.m.); Cows in Group 3 (n = 201) were treated with PGF2alpha (25 mg, i.m.); and cows in Group 4 (n = 202) were treated with both GnRH and PGF2alpha. Cows in Group 6 (n = 1440) were not treated with PGF2alpha on Day 0 and were estrual cows that were bred on days when cows in Groups 1 to 5 were time-inseminated. The percentage of cows in all groups pregnant at 45 to 50 days after one insemination was compared using analysis of variance (P<0.05). The conception rate of cows in Group 2 was significantly higher than that of cows in Groups 1 to 4. There was a significant group-by-season interaction. Cows treated with GnRH during the spring had a higher conception rate than at other times of the year. Conception rates of cows in Groups 1 to 4 that were inseminated during the summer were low and not significantly different from each other. Conception rates of cows in Groups 5 and 6 inseminated during the summer were not significantly different from each other, but were significantly higher than that of cows in Groups 1 to 4 that were inseminated during the summer.     

Temporal changes in serum prostaglandin F2alpha and oxytocin in dairy cows with short luteal phases after the first postpartum ovulation

Luteolysis in the cow depends upon an interaction between prostaglandin F(2alpha) (PGF(2alpha)) and oxytocin. The objectives of our study were 1) to determine oxytocin concentrations in postpartum dairy cows and 2) to identify the temporal relationship between oxytocin and PGF(2alpha) release patterns during luteolysis in normal and abbreviated estrous cycles in the postpartum period. Serum oxytocin and PGF(2alpha) metabolite (PGFM) concentrations from nine cows which had short estrous cycles (< 17 d) were compared with those of six cows which had normal estrous cycles. Serum basal oxytocin concentrations in short estrous cycle cows (23.7 to 31.1 pg/ml) were higher (P<0.05) than those of normal estrous cycle cows (14.6 to 19.8 pg/ml). Oxytocin concentrations increased to peak values in both short and normal cycle cows, during luteolysis. Basal PGFM concentrations (112.2 to 137.4 pg/ml) were higher in cows with short cycle (P<0.05) than in cows with normal cycles (62.9 to 87.5 pg/ml). The increase in PGFM concentrations during luteolysis was significant in both normal cycle and short cycle cows (P<0.05). Increases in serum PGFM concentrations were always associated with increases in serum oxytocin concentrations in normal cycle and short cycle cows and the levels decreased simultaneously before the subsequent estrus. Results support the idea of a positive relationship between PGF(2alpha) and oxytocin concentration during the estrous cycle as well as a possible synergistic action of these hormones in the induction of luteolysis in dairy cattle.     

Sequential administration of cronolone and prostaglandin F2alpha for estrus synchronization in goats.

Fifteen does received intravaginal pessaries impregnated with 20 mg fluorogestone acetate (Cronolone) at various times after the end of estrus for a period of fourteen days. The does were then treated on days 2, 4, 5, 12, or 16 after onset of estrus following the progestin treatment, with 15 mg of prostaglandin F2_α (Lutalyse) injected intramuscularly. Seventy three percent of the does showed estrus within 2 days after withdrawal of progestin treatment. Ten out of 11 does treated with prostaglandins 4 to 16 days after the end of estrus exhibited estrus within 44 to 72 hours after treatment. Breeding following the use of prostaglandin in these does resulted in a high pregnancy rate. It is concluded that a sequential use of progestin and prostaglandin may be a useful method for achieving estrus synchronization associated with high fertility in does.     

Doses of prostaglandin F(2)alpha effective for induction of estrus in goats

A total of 11 cycling does weighing between 24 and 50 kg were injected with varying dosages of prostaglandin F(2)alpha (PGF(2)alpha) between 7 and 10 days into each estrous cycle. Five injections each of 1.25, 2.5, 5.0, or 7.5 mg PGF(2)alpha were alternated with five injections of 1.0 ml saline. Saline treated does served as controls. All does were teased twice daily with a buck and observed for signs of estrus for 5 days post-injection. Daily systemic concentrations of progesterone (P(4)) were determined by radioimmunoassay. The mean (+/- S.E.) hours from injection to estrus was 47 +/- 3.3, 42 +/- 4.3, 44 +/- 8.5, and 43 +/- 5.5 for does receiving 1.25, 2.5, 5.0, and 7.5 mg PGF(2)alpha, respectively. None of the does receiving saline exhibited estrus in the 5-day post-injection observation period. Mean (+/- S.E.) concentrations of systemic P(4) in all does on the day of injection was 4.22 +/- 0.45 ng/ml. Concentrations 24 hours post-injection were 0.21 +/- 0.02, 0.15 +/- 0.05, 0.17 +/- 0.04, 0.16 +/- 0.04, and 4.5 +/- 1.36 ng/ml for does receiving 1.25, 2.5, 5.0, and 7.5 mg PGF(2)alpha, and 1.0 ml saline, respectively. The results suggested that 1.25 mg PGF(2)alpha was effective for induction of estrus in the cycling goat.     

Synchronization of estrus in yearling beef heifers with melengestrol acetate and prostaglandin F(2alpha)

This study was designed to test the efficacy of melengestrol acetate (MGA) in combination with prostaglandin F(2alpha) (PGF(2alpha)) in synchronizing estrus in cyclic and noncyclic heifers. One hundred thirty-one cyclic and prepubertal crossbred heifers were randomly assigned to three treatment groups: Controls (n = 43); MGA (0.5 mg/d for 7 d) and PGF(2alpha) (25 mg i.m. on Day 7; n = 44); and PGF(2alpha) (25 mg i.m. on Day 7; n = 44). Observations for estrus were made at 6-n intervals throughout the 7-d treatment period followed by a 34-d artificial insemination breeding season. A greater percentage (P < 0.05) of MGA-PGF(2alpha) noncyclic heifers showed behavioral estrus (91%) than did Control (67%) or PGF(2alpha) heifers (61%) during the 34-d artificial insemination period. There was no difference (P > 0.05) between synchronization rates of the MGA-PGF(2alpha) heifers and PGF(2alpha) heifers 7 d after PGF(2alpha) administration. The percentage of control animals in estrus during the first 25 d of the breeding season did non differ from the synchronized rates of MGA-PGF(2alpha) and PGF(2alpha) heifers (P > 0.05). Conception rates (heifers pregnant/heifers inseminated) did not differ (P > 0.05) for cyclic or prepubertal heifers among Control, MGA-PGF(2alpha) or PGF(2alpha) heifers. Though conception rates did not differ, there was a trend toward lowered conception rates in MGA-PGF(2alpha) heifers.     

Estrus response of indigenous Nigerian Zebu cows after prostaglandin F2 alpha analogue treatment under continuous observations for two seasons

The study was undertaken to determine the estrus response pattern of Zebu cows indigenous to Nigeria following treatment with prostaglandin F(2alpha) analogue and to determine the effect of season on the estrus parameters. Eighty cyclic Zebu cows were used in both the dry and wet seasons. Two single intramuscular injections of 25 mg of PGF(2alpha) analogue were given per cow 11 days apart regardless of the stage of the estrous cycle. The cows were then observed continuously for 168 h following each injection. The proportion of treated cows responding to PGF(2alpha) treatment in the wet season (90%) was significantly higher (P<0.005) than in the dry season (70.0%). The mean post-injection interval to onset of non-standing estrus (mucus discharge) was 30.6 h and 28.5 h in the dry and wet seasons, respectively. Similarly, the intervals to standing estrus were 69.7 h and 63.9 h in the two seasons, respectively. Seasonal effects were not significant. The duration of non-standing estrus was similar for the two seasons (164.2 h and 162.0 h) while the duration of standing estrus was significantly (P<0.01) longer in the wet season (19.2 h) than in the dry season (12.6 h). Also there was seasonal influence on the body condition score of cows, the palpability of corpora lutea (CL) and the intensity of estrus as determined by the number of mounts (17.9+/-2.0 and 51.2+/-3.4 mounts per cow per estrus period in the dry and wet seasons, respectively).     

Effect of dexcloprostenol on endogenous prostaglandin F2alpha release in dairy heifers

Cloprostenol was previously believed to be unable to release endogenous prostaglandin F2alpha (PGF2alpha) when administered during early bovine diestrus. A prostaglandin release is, however, seen in late diestrus. The aim of this study is to find out whether dexcloprostoenol (containing the only biologically active isomer, d-isomer, of cloprostenol) induces endogenous PGF2alpha release during early and late diestrus. Twelve heifers of the Finnish Ayrshire breed were allocated into two equal groups. Their estrous cycles were synchronized with dexcloprostenol. A further luteolysis was induced with 0.15 mg of dexcloprostenol either on Day 7 (group D7 or early diestrus) or on Day 14 (group D14 or late diestrus) after ovulation. Blood for progesterone and the PGF2alpha metabolite 15-ketodihydro-PGF2alpha determinations was collected immediately before dexcloprostenol treatment and thereafter every second hour for 48 h. Five of the six heifers in both groups showed significantly increased blood levels of 15-ketodihydro-PGF2alpha at some time during the 48-h experimental period. The intervals from treatment to the first significant increases of the PGF2alpha metabolite were 32.8+/-2.3 h (min. 30 h, max. 36 h) and 20.0+/-4.2 h (min. 14 h, max. 24 h) in groups D7 and D14, respectively (P < 0.01). We have concluded that dexcloprostenol induced endogenous PGF2alpha release in most cases, regardless the time of its administration (early or late diestrus). This release, however, differs from that observed during spontaneous luteolysis.     

Reproductive performance of lactating dairy cows treated with gonadotrophin-releasing hormone (GnRH) and/or prostaglandin F2a (PGF2a) for synchronization of estrus and ovulation

The objective of this study was to determine the reproductive performance of lactating dairy cows treated with GnRH and/or PGF2a for synchronization of estrus and ovulation. Between Days 43 and 57 post partum, a total of 374 dairy cows was divided into 4 groups. Cows in Group 1 (n = 62) were treated with 25 mg, i.m. PGF2a on Days 43 and 57; cows in Group 2 (n = 65) were not treated at this time; cows in Group 3 (n = 118) were treated with 100 ug, i.m. GnRH on Day 50, 25 mg, i.m. PGF2a on Day 57, 100 ug, i.m. GnRH on Day 59, and time-inseminated 16 h later; cows in Group 4 (n = 129) were treated with 25 mg, i.m. PGF2a once on Day 57. Cows in Groups 1 and 4 were inseminated at an induced estrus within 7 d after the last PGF2a treatment, and cows in Group 2 were inseminated at a noninduced estrus within a corresponding period of time. Conception rate, estrus detection rate and pregnancy rate were analyzed using logistic regression, and controlled for lactation number, body condition score and time of year. Days from calving to conception were analyzed using the GLM procedures of SAS, and the model included group, body condition score, lactation number, time of year, and their interactions. Cows in Group 3 had a significantly higher pregnancy rate than cows in Groups 1, 2 and 4. Orthogonal contrasts of mean days from calving to conception showed that cows in Group 3 had significantly (P < 0.01) less days from calving to conception than cows in Group 1 and Group 4. There was a significant effect of time of year on pregnancy rate and days from calving to conception, but there was no interaction between time of year and these reproductive characteristics. There was no effect of body condition score and lactation number on the reproductive characteristics evaluated. From the results of this study, it was concluded that better reproductive performance was observed in cows inseminated at a synchronized ovulation than in those inseminated at a synchronized estrous period.     

Synchronization of estrus in early diestral dairy heifers with Prostaglandin F(2)alpha and estradiol benzoate

Following observation of estrus, 134 Holstein heifers were given injections of Prostaglandin F(2)alpha (PGF(2)alpha) between Days 5 and 10 of their cycle (estrus = Day 0). They were then randomly assigned to either a group receiving 400 mug of estradiol benzoate (E(2)B) 40 h or maintained as controls. Heifers observed in estrus within 120 h of PGF(2)alpha administration were inseminated (approximately 12 h after initial observation of estrus). Blood samples for progesterone determination were drawn from the coccygeal vein on Days 15 and 21 after insemination. Pregnancy was confirmed by palpation per rectum between Days 5.0 and 60 post insemination. When control and treated heifers were compared it was found that a higher percentage of heifers treated with E(2)B exhibited estrus after PGF(2)alpha, but there had been no effect on subsequent progesterone concentrations or pregnancy rates.