Prostaglandin responses in dairy herd breeding programmes

Ovarian follicular and luteal characteristics in Bos indicus-influenced beef cows using prostaglandin F2α with or without GnRH at the onset of the 5-day CO-Synch + controlled internal drug release (CIDR) protocol

A modification of the standard 5-day CO-Synch + CIDR procedure (5-day Bee Synch + CIDR; Bee Synch), developed for use in Bos indicus-influenced cows, utilizes the addition of prostaglandin F2α (PGF) on Day 0 of the protocol to eliminate mature corpora lutea (CL) and fixed-time AI (FTAI) at 66 h. Objectives were to test the hypothesis that elimination of GnRH on Day 0 (GnRH-1) does not impact significantly the synchronized development of a dominant follicle for presumptive FTAI. Seventy-one estrous cycling Brangus and Brahman x Hereford suckled cows were used in two replicates (35-36/replicate). Following stratification, cows were assigned randomly to a 2 × 3 factorial arrangement of treatments involving two truncated (no FTAI or GnRH-2) versions of Bee Synch (Bee Synch I_t and II_t), each begun 3, 7, and 10 days post-ovulation. Cows in Bee Synch I_t received 100 μg GnRH (GnRH-1), 25 mg PGF, and a CIDR on Day 0, whereas cows assigned to Bee Synch II_t received the same treatment but without GnRH-1. All cows received 50 mg PGF on Day 5 at CIDR removal. Synchronized new follicular wave emergence (NFWE; days 1-4) was observed in 68.6 and 38.9% of Bee Synch I_t and II_t, respectively (P =  0.01). This increased to 93.3% and 72.2%, respectively, if days 0-4 were considered. Inclusion of GnRH at CIDR insertion improved synchronized NFWE but size of the largest follicle at 66 h, the normal time of FTAI, did not differ due to treatment or day of the estrous cycle.

Controlled Breeding Systems for Dairy Cows

The economic consequence of low heat detection rates is the main reason cattle reproduction research programmes continue to focus on developing practical controlled breeding systems for dairy cows. Three approaches can be taken to control the oestrous cycle in cattle: (i) Use of the luteolytic agent prostaglandin F2α alone or one of its potent analogues, (ii) Cycle regulation using short-term progestagen treatments and (Hi) Prior follicle wave synchrony followed by induced luteolysis. Administration of prostaglandin F2α (PGF2α) to cows after about Day 5 of the oestrous cycle causes immediate regression of the CL with progesterone concentrations declining rapidly to basal concentrations within 24 hours. Because PGF2α is only effective in animals between Days 5 and 17 of the oestrous cycle up to 40% of any group of randomly cyclic animals will not respond to a single administration. A number of PGF2α administration regimens have been developed for dairy cows. A two-injection regimen, with an interval of 9-13 days between successive administrations, elicits a higher response, as all animals possess a susceptible CL the time of the second injection. In general, cyclic heifers respond with good precision of heat onset to two PGF2α injections 11 days apart. Fixed-time AI at 72 and 96 hours after the second injection can result in acceptable pregnancy rates. In post partum dairy cows the slower turnover of follicle waves, contribute to the greater variation in oestrus onset, resulting in more variable and generally lower pregnancy rates to fixed-time AI at 72 and 96 hours. Consequently, intensive oestrous detection and AI on the basis of observed oestrus is more appropriate for lactating cows following PGF2α administration. It is generally accepted that fertility of the cyclic heifer after PGF2α treatment is not impaired or may even be higher when compared with untreated control animals inseminated at a natural oestrus. However, in lactating cows, conception rate following PGF2α treatment have been frequently lower (about l0%) than in cows bred following a natural heat. Recently, aprotocol to synchronise follicular development using GnRH and to induce luteal regression using PGF2α was developed In this protocol (Ovsynch), GnRH is administered to cows at random stages of their cycle 7 days before luteolysis is induced with PGF2α; a second GnRH injection at 36-48 hours later induces ovulation. All cows are inseminated once at 16-20 hours after the second GnRH injection. Ovsynch system is not recommended for use in heifers. The development of progestogen delivery devices, such as the PRID, CIDR and Crestar has facilitated the use ofexogenous progestogens for oestrous cycle synchronisation in cattle. Oestradiol is administered at the start of treatment to (i) shorten the life span of the corpus luteum (CL) and (ii) to induce the emergence a new follicle wave. Generally, a high proportion (up to 85%) of the cows that exhibit oestrus after removal of the progestogen do so between 36 and 60hours ofremoval. This allows for either one (54-56 hours) or two fixed-time AIs (48 & 72 hours) after progestogen withdrawal. Alternatively, cows can be observed and inseminated once at a detected oestrus. While fixed-time AI of all treated cows gives 100% submission rate conception rates tend to be lower than when AI is on the basis of observed heat. However, the overall number of cows becoming pregnant (submission x conception rate) is frequently the same, reflecting submission and conception rate differences for the two AI options. Choice of AI option will depend the herdsman 's ability to accurately detect heat, semen costs and labour availability.

Comparison of PUFA Profiles in the Blood and in Follicular Fluid and its Association with Follicular Dynamics after PGF2α Induced Luteolysis in Dairy Cows

The objectives of the present study were to examine the fatty acid (FA) profiles in serum and in the follicular fluid (FF) and the association between polyunsaturated fatty acid level (PUFA) and follicular growth dynamics following induced luteolysis in dairy cows. A total of 29 dairy cows (CL>25mm, follicle≈15mm) at d0 (start of the experiment) were submitted to ultrasound guided transvaginal follicular aspiration for FF collection from the largest follicle and were injected with 500 μg of cloprostenol. The cows were subdivided into Group A1 (n=11) and Group A2 (n=8) resuming follicular growth either from a secondary follicle less than or larger than 8.5mm, respectively, present at the moment of aspiration and Group A0 (n=10) not resuming follicular growth. Follicular development was monitored daily by ultrasonography until the next dominant follicle reached ≈15mm and was subsequently punctured in Group A1 and A2 (d1). Serum and FF samples for FA determination were taken at d0 from all cows and at d1 in Group A1 and A2. No differences were observed between the FA profile in serum nor in FF between sampling days. Regarding the PUFA levels, the serum linoleic acid (C18:2n6) levels at d0 and d1 were significantly higher than in FF, while alpha linolenic acid (C18:3n3) was lower in the serum than in FF, both at d0 and d1. At d0, a tendency for negative correlation between serum and the FF C18:2n6 with subsequent daily follicular growth rate was observed, while, at d1 there was a strong negative correlation between the serum C18:2n6 and daily growth rate (r=−0.71; p=0.0006). The present study revealed similarities of the FA profiles in the serum and in the FF and association between serum and FF PUFA content with the follicular dynamics after induced luteolysis.

Luteal function, largest follicle, and fertility in postpartum dairy cows treated with 14dCIDR-PGF2α versus 2xPGF2α-Ovsynch for timed AI

A method for timed artificial insemination (AI) that is used for beef cows, beef heifers, and dairy heifers employs progesterone-releasing inserts, such as the controlled internal drug release (CIDR; Zoetis, New York, NY, USA) that are left in place for 14 days. The 14-day CIDR treatment is a method of presynchronization that ensures that cattle are in the late luteal phase of the estrous cycle when PGF2α is administered before timed AI. The objective of this study was to test the effectiveness of the 14dCIDR-PGF2α program in postpartum dairy cows by comparing it with the traditional "Presynch-Ovsynch" (2xPGF2α-Ovsynch) program. The 14dCIDR-PGF2α cows (n = 132) were treated with a CIDR insert on Day 0 for 14 days. At 19 days after CIDR removal (Day 33), the cows were treated with a luteolytic dose of PGF2α, 56 hours later were treated with an ovulatory dose of GnRH (Day 35), and 16 hours later were inseminated. The 2xPGF2α-Ovsynch cows were treated with a luteolytic dose of PGF2α on Day 0 and again on Day 14. At 12 days after the second PGF2α treatment (Day 26), the cows were treated with GnRH. At 7 days after GnRH, the cows were treated with PGF2α (Day 33), then 56 hours later treated with GnRH (Day 35), and then 16 hours later were inseminated. There was no effect of treatment or treatment by parity interaction on pregnancies per AI (P/AI) when pregnancy diagnosis was performed on Day 32 (115/263; 43.7%) or Days 60 to 90 (99/263; 37.6%) after insemination. There was an effect of parity (P < 0.05) on P/AI because primiparous cows had lesser P/AI (35/98; 35.7%) than multiparous cows (80/165; 48.5%) on Day 32. Cows observed in estrus after the presynchronization step (within 5 days after CIDR removal or within 5 days after the second PGF2α treatment) had greater P/AI than those not observed in estrus (55/103; 53.4% vs. 60/160; 37.5%; observed vs. not observed; P < 0.01; d 32 pregnancy diagnosis). When progesterone data were examined in a subset of cows (n = 208), 55.3% of cows had a "prototypical" response to treatment (i.e., the cow had an estrous cycle that was synchronized by the presynchronization treatment and then the cow responded appropriately to the subsequent PGF2α and GnRH treatments before timed AI). Collectively, cows with a prototypical response to either treatment had 52.2% P/AI that was greater (P < 0.001) than the P/AI for cows that had a nonprototypical response (19%) (P/AI determined at 60-90 days of pregnancy). In conclusion, we did not detect a difference in P/AI when postpartum dairy cows were treated with 14dCIDR-PGF2α or 2xPGF2α-Ovsynch before timed AI. The primary limitation to the success of either program was the failure of the cow to respond appropriately to the sequence of treatments.

Effect of oestradiol benzoate given after prostaglandin at two stages of follicle wave development on oestrus synchronisation, the LH surge and ovulation in heifers

Oestrus synchronization following prostaglandin-induced luteolysis is variable and dependent on follicle wave status in cattle. Oestradiol benzoate (ODB) has been used following prostaglandin to reduce the interval to oestrus and ovulation, but the effect of follicle wave status at the time of ODB administration is not clear. The aim of this study was to characterize the endocrine and follicular responses following ODB after luteolysis at different stages of the follicle wave. Prostaglandin was administered at either emergence or dominance of the second follicle wave. Twenty-four hours later animals received either 0.5mg ODB in oil or a control oil injection. Follicular development was monitored daily by ultrasonography, oestrous behavior was determined and blood samples were collected. In animals treated with ODB at emergence, there was a reduction (P<0.05) in the maximum diameter of the ovulatory follicle (11.7+/-1.2 mm versus 13.1+/-0.1 mm) and in the interval from prostaglandin to oestrus (52.0+/-2.3 h versus 88.0+/-9.6h), to the LH surge (53.3+/-3.5 h versus 89.1+/-6.5 h) and to ovulation (96+/-0.0 h versus 129.6+/-9.6h), compared with controls. In animals treated with ODB at dominance, there was a reduction (P<0.05) in the interval from prostaglandin to the LH surge (54.0+/-3.1 h versus 70.9+/-4.8 h), but not in the interval from prostaglandin to oestrus (53.3+/-2.7 h versus 65.7+/-4.5 h; P=0.11), to ovulation (96.0+/-0.0 h versus 110.4+/-4.8 h; P=0.12) or the maximum diameter of the ovulatory follicle (12.7+/-0.3 mm versus 13.6+/-0.4 mm; P=0.12), compared with controls. Treatment did not affect (P>0.05) the length of the subsequent oestrous cycle or corpus luteum size. In conclusion, the use of ODB advanced, but did not alter the temporal relationships among oestrus, the LH surge and ovulation, regardless of stage of follicle development at treatment.

Exogenous hormonal manipulation of ovarian activity in cattle

To achieve precise control of the oestrous cycle in cattle it is necessary to control both the life span of the corpus luteum and the follicle wave status at the end of the treatment. Antral follicle growth in cattle occurs in distinct wavelike patterns during the ovarian cycle and the postpartum anoestrous period. The emergence of each new wave is stimulated by a transient increase in FSH. Each follicle wave has an inherent life span of 7-10 days as it progresses through the different stages of development, viz., emergence, selection, dominance and atresia or ovulation. The dominant follicle (DF) is distinguishable from other subordinate follicles by its enhanced capacity to produce oestradiol, maintenance of low intrafollicular concentrations of insulin-like growth factor binding proteins-2, -4 and -5 and follistatin and an increase in free intrafollicular concentrations of IGF-I as well as an increase in size. Three approaches can be taken to control ovarian activity and regulate the oestrous cycle in cattle: (i) use of the luteolytic agent prostaglandin F2alpha (PGF2alpha) alone or one of its potent analogues, (ii) administration of exogenous progesterone-progestagen treatments combined with the use of exogenous oestradiol or gonadotrophin releasing hormone (GnRH) to control new follicle wave emergence and shorten the life span of the corpus luteum, and (iii) prior follicle wave synchrony followed by induced luteolysis. A number of different oestrous synchronisation regimens, viz., PGF2alpha-based only, short-term progesterone with prior follicle wave synchrony using oestradiol or GnRH have been developed but the problem of obtaining good follicle wave synchrony and CL regression limit their widespread application. GnRH-prostaglandin-GnRH regimens have recently been developed for beef and dairy cows. However, their success is variable. A better understanding of the hormonal control of follicle growth is a prerequisite in order to obtain more precise control the oestrous cycle allowing one AI at a predetermined time giving high pregnancy rates without recourse to detection of oestrus.

Advances in bovine theriogenology in New Zealand. 2. Breeding management and technologies for improved reproduction

The importance of submission rates (SR) on conception patterns in dairy herds during a short artificial breeding (AB) programme was first reported in 1973. Subsequent research has focussed on achieving 3-week SRs of 90% through improved detection of oestrus utilising tailpainting and vasectomised bulls fitted with chin-ball harnesses. Despite nutritional limitations of spring pasture as a sole diet, conception rates to first insemination of 65% have been recorded in cycling cows in many trials. Anovulatory anoestrus (AA) has become a major factor compromising SRs as well as reducing average conception rates and herd in-calf rates by 4-7 weeks after the planned start of mating (PSM). Whole herd synchronisation programmes have been developed but not widely used on dairy cows and have had only limited use on dairy heifers, despite a focus on concentrated conception patterns. The related technologies have become most commonly used to increase the SR of AA cows. Extreme variation in the weekly demand for processed semen in seasonally-intensive AB programmes has been accommodated by the development of a unique semen diluent, Caprogen. Its use has allowed sperm to be temporarily stored without freezing and used at dose rates of 1 million sperm/insemination. Sire variation with this form of semen processing is lower than with deep frozen semen. The greater use of production genes derived from Holstein-Friesian sires of North American origin in most AB programmes has left progeny with reduced reproductive performance. This effect has been greater than that associated with the increased productivity of dairy cows achieved through continued use of semen from intensively selected groups of progeny tested sires.

Recent advances in bovine reproductive endocrinology and physiology and their impact on drug delivery system design for the control of the estrous cycle in cattle

When methods of drug intervention are being developed to control estrous cycles, a thorough understanding of the endocrine and functional changes together with the reproductive behavior of the animals are essential. This review presents our current knowledge on reproductive endocrinology, physiology and behavior, and the methods of drug intervention to control estrous cycles. It also describes current efforts to develop advanced drug delivery systems that meet the animal scientist's demands to control the estrous cycle in cattle.

Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2α 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.

A retrospective analysis of the effect of prostaglandin F2a on conception rates in commercial dairy herds

The objective of this retrospective analysis was to determine the effect of prostaglandin F2a (PGF2a) on conception rates in commercial dairy herds. During routine herd visits, cows were selected for palpation if they had been milking for at least 60 days and had not been observed in estrus, or if they had been inseminated at least 30 days prior to the study selection. Nonpregnant cows with a palpable corpus luteum of sufficient size were injected with PGF2a. The herdsmen were instructed to inseminate animals within 6 to 12 hours after the observed estrus. The insemination rate within 6 days of treatment was 77.6%. The conception rate for the treated animals (47.9%) was statistically the same as that for the nontreated controls (47.2%).

Comparison of a prostaglandin-F2α-based reproductive program with an estrus detection-based reproductive program on a large commercial dairy herd

The purpose of this study was to describe biological outcomes of two reproductive management strategies in commercial dairy cows: estrus detection with and without the use of prostaglandin-F2alpha. At regular preinsemination examinations, cows were allocated randomly to two cohorts: 1) prostaglandin cohort -- cows with palpable corpora lutea were injected with 25 mg dinoprost tromethamine and were bred by appointment 72 and 96 hours later, followed one week later by standard estrus detection practices (twice daily observation and tail chalking, with breeding approximately 12 to 24 hours later); and 2) estrus detection cohort -- cows identified as exhibiting estrus (observed estrus) were bred through the above standard procedures, without exposure to prostaglandin therapy. Age, milk production, weight, milk progesterone levels and reproductive data were collected for all cows. Although certain between-cohort effects were statistically significant, no differences could be found between the cohorts regarding standard measures of reproductive performance (average days in milk at conception (P=0.79), services per conception (P=0.48), proportion of animals failing to conceive to artificial insemination (P=0.53), and survival analysis on time to conception (P=0.30). With evidence for biological equivalence between the two reproductive strategies, nonbiological standards such as economics or ease of execution would be appropriate in choosing between the two strategies.

Pharmacologic manipulation of fertility

The professional application of agents to the manipulation of fertility of cows requires basic and applied knowledge of the physiologic mechanisms that are affected and of the pharmacologic agents that are used. In all areas of the pharmacologic manipulation of fertility, the achievement is less than the ideal, and further research is required to improve the efficiency of treatments. The induction of estrus in acyclic animals can involve a reduction in the depth of anestrus, pretreatment with progestagen to ensure estrous behavior and the formation of a normal corpus luteum, and then treatment with exogenous gonadotropin. Responsiveness to treatment can be variable and reflects the depth of anestrus of the animals. Improved treatment regimens require a knowledge of the basic mechanisms involved with the depth of anestrus, a means of assessing the depth of anestrus, and an understanding of the hormonal requirements of ovarian follicles for development and maturation in animals at different depths of anestrus. The optimal precision in the synchronization of estrus (and ovulation) in cyclic animals requires the synchronization of both follicular waves and the end of progestational phase. The end of progestational phase can be synchronized effectively using prostaglandin F2a (or analogs), or by treatment with progestagens with or without luteolytic agents. Procedures to synchronize follicular waves need to be established. The induction of superovulation can be achieved readily using gonadotropins prior to estrus synchronization using prostaglandin F2a. The responses to standard treatments in terms of ovulation rates and yield of transferable embryos are highly variable. The development of procedures to reduce this variability requires an understanding of the intra-ovarian mechanisms involved in recruitment of follicles for a wave of follicular growth, in the selection of dominant follicles for further development, and in the mechanisms controlling follicular atresia. Cystic ovarian disease can be treated effectively using HCG or GnRH (follicular cysts) or prostaglandin F2a (luteal cysts). The basic mechanisms resulting in failure of estrogen positive feedback on LH secretion (that results in cystic follicles) remain to be determined. Small but significant increases in pregnancy rates can be achieved treating cows with prostaglandin during the post-partum period, with prostaglandin to induce estrus for insemination, with GnRH or HCG at estrus, and with GnRH or progestagen treatment during diestrus. Beneficial effects of treatment have been shown in some trials but not in others.(ABSTRACT TRUNCATED AT 400 WORDS)

Will the first dominant follicle of the estrous cycle of heifers ovulate following luteolysis on day 7?

The pattern of turnover of dominant follicles involves the sequential growth and regression of two to three dominant follicles during the estrous cycle. The dominant follicle that ovulates is the one that develops concomitantly with the regression of the corpus luteum. The aim of this paper was to determine if the first dominant follicle would ovulate following induction of luteolysis with prostaglandin F2 alpha analogues (PGF) on Day 7 of the cycle. Heifers (n = 43) were checked for estrus (Day 0); their ovaries were scanned daily from Day 6 of the cycle for one week, and the fate of the first dominant follicle was determined. Luteolysis was induced on Day 7 with PGF analogues, and blood samples were taken daily for progesterone and estradiol measurement and at 3-h intervals for 33 h for luteinizing hormone (LH) measurement. Of the 43 heifers given PGF, complete luteolysis occurred in 40 animals. Of these, the first dominant follicle ovulated in 37 heifers; the dominant follicle was not the ovulatory follicle in 2 heifers and the dominant follicle became cystic in one heifer.

Effects of cloprostenol, human chorionic gonadotropin and estradiol benzoate treatment on estrus synchronization in dairy cows

Two consecutive experiments were conducted. In Experiment 1, 24 Friesian lactating cows were randomly assigned to two groups. Cows in Group I received intramuscularly (i.m.) 500 mcg of cloprostenol, 1250 IU of human chorionic gonadotropin (hCG) and 5 mg of estradiol benzoate 12 h after cloprostenol treatment. Cows in Group II received 750 IU i.m. of hCG and 3 mg of estradiol benzoate 12 h after cloprostenol treatment. Treatment was given on Day 16 after estrus in both groups. All animals showed estrus within 24 to 48 h after cloprostenol treatment. The average interval from cloprostenol injection to the onset of estrus was not influenced by treatments. Four cows in Group I failed to ovulate and became cystic. In Experiment 2, 71 Friesian lactating cows were randomly assigned to two groups. Cows in Group I received 500 mcg i.m. of cloprostenol after corpus luteum detection by palpation per rectum. Cows in Group II received 500 mcg of cloprostenol plus 750 IU of hCG and 3 mg of estradiol benzoate 12 h after. When estrus ready for service was confirmed by rectal examination, cows were inseminated. The percentage of cows ready for service tended to be lower (P<0.06) between cows in Group I (88%) and those in Group II (100%). The average interval from cloprostenol treatment to service was longest (P<0.001) in Group I (78.7 h+/-14.9, X+/-SD) vs Group II (48 h+/-2.9). The degree of readiness for service synchrony was lowest (P<0.001) in Group I (59.3%) vs Group II (94.2%). The pregnancy rates of cows synchronized or treated were not altered by hCG-estradiol benzoate treatment (P>0.25). These results suggest that in dairy cows treated with cloprostenol following palpation per rectum of a corpus luteum and then with 750 IU of hCG and 3 mg of estradiol benzoate 12 h later, a single fixed-time insemination at 48 h after cloprostenol treatment should be performed.

Conception rates in repeat-breeders and dairy cattle with unobserved estrus after prostaglandin F2 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.

Controlling first service and calving interval by prostaglandin F2 alpha, gonadotropin-releasing hormone, and timed insemination

Our objective was to determine if calving intervals could be shortened and made less variable by using prostaglandin F2 alpha to control the occurrence of first services. Holstein cows (n = 348) were assigned at calving to four treatment groups. Control cows (n = 88) were inseminated at their first observed estrus after 40 d postpartum. Estrous cycles of the remaining cows were synchronized with prostaglandin F2 alpha to allow insemination (first services) 80 h after the second injection (n = 86), insemination at 80 h preceded by gonadotropin-releasing hormone at 72 h (n = 86), or insemination at 72 and 96 h (n = 88) after the second injection (51 to 57 d postpartum). By design, interval to first service was reduced to 57 d for treated cows (63 d for controls) and was less variable (12% of that for controls). Conception rate at first service was lower after timed inseminations than that of controls. Intervals to conception and subsequent calving were similar in all treated cows and controls. Of cows sampled, 23 of 176 (13%) failed to respond with luteolysis when progesterone in serum exceeded 1 ng/ml, and 26 of 176 (15%) had low concentrations of progesterone in serum and could not respond to prostaglandin F2 alpha. Poor response to timed inseminations may have occurred because only 72% of 176 cows sampled responded with luteolysis. When only cows observed in estrus were considered, conception rate approached that of controls (51%).(ABSTRACT TRUNCATED AT 250 WORDS)