Steroid priming shortens prostaglandin-based estrus synchronization program from 14 to 7 days in cattle

ELSEVIER

STEROID PRIMING SHORTENS PROSTAGLANDIN-BASED ESTRUS SYNCHRONIZATION PROGRAM FROM 14 TO 7 DAYS IN CATTLE A. Niasari-Naslaji,‘,‘”

SM. Hosseini,’ F. Sarhaddi: M. Bolourchi’ and M.R. Birjandi3

‘Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran; *Animal Science Research Institute, Karaj, Iran; 3Natural Resources and Animal Affairs, Ministry of Agricultural Jahad, Zahedan, Iran Received for publication: July 5, 2000 Accepted: March 5, 2001 ABSTRACT Single injection of estrogen and progesterone before prostaglandin (steroid priming) was used to shorten the prostaglandin-based estrus synchronization program. Sixty-five cyclic Sistani cattle, with parity ranging from 1 to 4 and postpartum period of >80 days were selected at unknown stages of the estrous cycle and assigned to 2 groups according to their age, weight and parity. Females in the control group (n=33; 58.4 + 4.3 months; 277 + 8 kg LW) received two consecutive injections of prostaglandin Fzcc analogue (500 pg; Cloprostenol, PG) 14 days apart (Day 0 = First PG injection). On Day 7, treated females (n=32; 60 + 4.8 months; 292 + 9 kg LW) were given an intramuscular injection of 100 mg progesterone and 2 mg estradiol benzoate followed by prostaglandin 7 days later, concurrent with the second PG injection of the control group. Estrus detection was carried out every 6 hours for 7 days, commencing from 24 hours after the last PG injection. Females that allowed to be mounted were identified (standing estrus) and inseminated with frozen semen 12 hours later. Pregnancy was diagnosed on Day 50 after AI through palpation per rectum. Data were analyzed using Chi-squared and t-test. The tightness of estrus synchrony (%), the interval from the end of treatment to estrus (h) and conception rates (%) were similar (P > 0.05) between control (69.6%, 77.7 + 5.96 h and 56.5%) and treatment (68.2%, 82.6 f 7.64 h and 54.5%) groups. In conclusion, steroid priming is an efficient way to shorten the prostaglandin-based estrns synchronization program from 14 to 7 days without compromising estrous response and fertility. 8 2001 by Elssv~er Science Inc. Keywords: estrus synchronization; estradiol; progesterone; prostaglandin )--Bos indicus Acknowledgements Research was supported by a grant from Animal Science Research Institute, Education & Research Deputy of the Ministry of Agricultural Jahad (Project No: 78-021010-02) and the Research Deputy of the University of Tehran (Project No: 219.1.305). The authors thank the director and station stuff of Sistani Cattle Research Farm at Zahak-Zabol for providing facilities and kind assistance throughout the experiment. a Correspondence and reprint requests: Dr Amir Niasari-Naslaji, P.O.Box: 14155-6453 Tehran, I.R.Iran. Tel: +9821 923510; Fax: +9821 933 222; E-mail: [email protected] Theriogenology 56:736-743,ZOOl Q 2001 Elsevier Science Inc.

0093-691WOl/$-see front matter PII: SOO93-691X(01)00603-3

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INTRODUCTION Successful estrus synchronization programs must be able to control both luteolysis and follicular wave emergence in order to provide low variation in estrus response without compromising fertility. To be practical, the program must be simple, short and cost-effective with minimal stress to the animal from excessive handling. Commercial estrus synchronization programs in cattle are based on two main approaches: (a) shortening the luteal phase (prostaglandin approach), and (b) prolonging the luteal phase (progestogen approach; 40) Prostaglandin Fzcl as a luteolytic agent is more efficient if it is used between Days 7 and 15 of the estrous cycle when females carry an active corpus luteurn (CL; 53). Theoretically, only 55% of the cyclic females have a CL responsive to prostaglandin on any given day (26). Therefore, two doses of PG 11 to 14 days apart, are recommended to cover most of the herd mates in a synchronization program (17,45). In order to enhance estrus response in Bos indicus heifers, a 1Cday interval is recommended between the two PG injections (14). Although the prostaglandin approach is simple, variable results in fertility have been reported, depending on the stage of the estrous cycle at the time of PG injection (53, 60, 63). Variation in estrous response after PG administration occurs due to the lack of control on follicular development (23, 24). In order to obtain a precise onset of estrus in progestogen-based estrus synchronization programs, long-term progestogen treatment (more than 14 days) was used. However, fertility was reduced after such treatment (19, 44) due to the formation of a persistent dominant follicle with ovulation of a subfertile oocyte (32, 33, 43, 48). Therefore, short-term progestogen treatment was recommended to compensate for lower pregnancy rates. However, in such programs, luteolytic agents are required as the life span of the CL may continue after progestogen removal, which in turn, delays the onset of estrus (25, 27, 28, 29, 44, 56, 61). The main compounds used to synchronize follicular wave emergence, within the progestogen approach of estrus synchronization, are estrogen and progestogen (5). An acute treatment of progestogen alone (1, 8, 34) or in conjunction with estrogen (5, 7, 13, 42) was used. To the best of our knowledge, acute treatment with these steroids has not been used in the absence of long-term progestogen treatment. Our preliminary reports indicated that a single injection of estradiol benzoate (2 mg) and progesterone (100 mg) 6 days before PG injection is able to synchronize follicular wave emergence and estrus (20, 38). The objective of the present study was to compare estrous response and fertility after two estrus synchronization programs in Bos indicus cattle: (a) estradiol and progesterone injection followed by PG, seven days apart; and (b) conventional two consecutive injections of PG, 14 days apart. MATERIALS AND METHODS Experimental Location The experiment was performed at the research farm of the Research Centre for Natural Resources and Animal Affairs of Sistan and Balouchestan Province (Latitude: 30’54” N; Longitude 61’41” E; Altitude 483 m) of Iran during spring months (March to April).

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Experimental Animals Sixty-five cyclic Sistani cattle (an Iranian native Bos indicus breed) including 20 heifers and 45 cows with parity ranging from 1 to 4 and a postpartum period of >80 days, were selected at unknown stages of the estrous cycle and randomly assigned to 2 groups according to their age, weight and parity. Females received ration consisting of 10% crude protein and 2.1 Meal/kg DM energy according to NRC recommendations (39) for beef cattle, including wheat straw (39%), Lucerne hay (28%), and concentrate (33%). The cyclicity was confirmed by the presence of CL at either one of the examinations obtained 10 days apart, using an ultrasound scanner (Pie medical 480, Netherlands) equipped with a 5:MHz rectal probe. Experimental Design Females in the control group (n=33; 58.4 f 4.3 months; 277 f 8 kg LW) received two consecutive intramuscular injections of prostaglandin Fza analogue (500 pg; Cloprostenol, Nasr Pharmaceutical Co., Iran) 14 days apart (Day 0 = First PG injection). On Day 7, treated females (n=32; 60 + 4.8 months; 292 f 9 kg LW) were given an intramuscular injection of estradiol benzoate (2 mg, Aburaihan, Iran) and progesterone (100 mg, Aburaihan, Iran) dissolved in sesame oil followed by PG injection 7 days later, concurrent with the second PG injection of females in control group. The estrous behavior was detected every 6 hours for 7 days starting 24 hours after the last PG injection. Artificial insemination was performed with the frozen semen collected from a single ejaculate of the fertile Sistani bull 12 hours after observing standing estrus. Pregnancy was detected on Day 50 after artificial insemination (by palpation per rectum). Measurements and Statistical Analyses Tightness of estrus synchrony (the greatest percentage of females that express standing estrus within 48 hours), the interval from the end of treatment to estrus (hour) and conception rates (the percentage of females conceived out of total females inseminated) were calculated and analyzed using the Chi-squared procedure (50) in the CATMOD procedures of SAS/STAT (47). The fixed effects of treatment, number of days postpartum, parity and the interactions of each with treatment were included. The student t-test of SAS/STAT was used to compare two means of continuous variables after testing the assumption for conformity of residual variance. Data were presented as mean + SEM. RESULTS Figure 1 shows the distribution of the onset of estrus. Figure 2 shows the cumulative percentage of heifers detected in estrus after cessation of treatment. There were no significant differences (P > 0.05) between the control (two consecutive injections of prostaglandin 14 days apart) and treatment (estradiol benzoate and progesterone injection, 7 days before prostaglandin injection) groups in estrus response (23/33; 69.7% versus 22/32; 68.7%), tightness of estrus synchrony (16123, 69.6% versus 15122, 68.2%) and conception rates (13/23, 56.5 % versus 12122, 54.5%).

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0 Control H Treatment

36

42

48

54

60

66

72

78

84

90

96

102

Time after the last prostaglandin (hr) Figure I. Distribution

100

g

aI .E

onset ofestrus

after cessation

of treatment.

1 q Control

80 1

n Treatment

36

42

48

54

60

66

72

78

Time after the last prostaglandin Figure

2.

Cumulative

onset of estrus

after

cessation

84

90

96

102

(hr)

of treatment.

The time interval from the end of treatment to estrus was similar (P > 0.05) in control (77.7 f 5.96 h; 42 to 168 h) and treatment (82.6 f 7.64 h; 48 to192 h) groups. In both groups, the tightness of estrus synchrony was between 54 and 102 hours after the last treatment. A small number of females in the control (n=7) and treatment (n=8) groups exhibited standing estrus during the nighttime (19pm to 4am). In contrast, the majority of females in the control (n=16) and treatment (n=14) groups showed estrous behavior in the daytime (5am to 18pm). Totally

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66.7% (30145) and 33.3% (15145) of females in both groups exhibited estrus during day and nighttime, respectively. Total estrous response of (45/65, 69.2%) and conception rates of (25/45, 55.5%) were achieved in this study.

DISCUSSION The results of the present study demonstrate that priming with estradiol benzoate and progesterone can be used as an effective method to shorten the conventional estrus synchronization program. Estrous response (Total: 69.2%; Control: 69.7%; Treatment 68.7%) in this study was comparable with the results in Bos indicus cattle using two PG injections 14 days apart (58%; 13) and 11 days apart (70%; 59). The mean and median interval from cessation of treatment to estrus in this study (control: 77.7 f 5.96, 70 h; treatment: 82.6 f 7.64, 69 h) were comparable to the results reported previously in Bos indicus cattle (9, 59) but did not support the report on the Nelore breed (41). In this study, 66.7% of females displayed estrus during the daytime, which contradicts other reports in which most estrus, in Bos indicus cattle, occurred after sunset and before sunrise (3, 10, 11, 41). In the present study, an ambient temperature and increasing day-length might be considered as enhancing factors for estrus expression during daytime explained previously in Bos indicus cattle (16). In most estrus synchronization programs in cattle, estrogen and progesterone were used to synchronize follicular wave emergence in order to enhance the tightness of estrus synchrony (1, 4, 8, 34, 37). Estrogen plays an important role in several reproductive event that occur around the time of estrus such as triggering LH surge and ovulation (12), luteolysis (55) estrous behavior (22) and mucus discharge (22). However estrogen can produce adverse effects such as ovarian cysts (35, 62) and false estrous behavior (27, 31, 36) if it is given in the absence of progesterone. Therefore association of progesterone with estrogen is necessary to avoid such adverse effects. The combination of estrogen and progesterone suppresses the growth of ovarian follicles by suppressing the frequency and amplitude of LH pulses (2, 42, 46, 52). The direct regressing effect of estrogen on the growing ovarian follicles without any alteration in serum LH and FSH concentrations was shown in monkeys (15,21); existence of such effects was debated in cattle (6). The atretogenic effect of estrogen and progesterone on ovarian follicles was used to synchronize follicular wave emergence in long-term progesterone-treated cattle (5, 37). Although acute treatment of progestogen alone or in conjunction with estrogen was used for synchronizing follicular wave emergence (1, 8, 34), Murray et al. (34) found better results with the combination of estradiol 17p (2 mg) and progesterone (100 mg) in Brahman heifers. Recently Caccia and Bo (7), in a dose-response study, suggested the minimum effective dose of estradiol benzoate (2.5 mg) in conjunction with progesterone (50 mg) for consistent emergence of a new follicular wave in CIDR treated beef cattle. In all studies in which estradiol and progesterone were used to synchronize follicular wave emergence, the supplementation of progesterone for 7 to 14 days was used and the new follicular wave emerged 3 to 5 days after estrogen and progestogen injection (5, 7, 8). In the present study we used a single injection of estradiol benzoate (2 mg) and progestogen (100 mg), without progesterone supplementation. The amount of estradiol benzoate used in this study did not produce false estrus, mucus discharge or ovarian cysts (20). After regression of the growing follicles, a new follicular wave occurred between 3 and 6 days (3.7 + 0.33 days; 38) after steroid injection. Based on our resources, the cost of steroid injections at doses recommended in the present study is about

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one-third of a single luteolytic dose of PG, which in turn demonstrates a cost-benefit of steroidPG injections compared to PG-PG injections. The GnRH analogues were also used to modify the follicular growth pattern before PG injection (18, 54, 57, 58). The GnRH causes antral follicles to undergo atresia (30) or induces ovulation (49, 50) and subsequent formation of a new CL (58). The new follicular wave emerges within 3 days after GnRH administration (38, 49, 57). A 6 or 7 day interval between GnRH and PG resulted in a high degree of estrus synchronization with pregnancy rates comparable to those after treatment with 2 injections of PG 11 days apart (18, 55, 58). In conclusion, priming with steroids followed by PG injection can shorten conventional two consecutive PG injections from 14 to 7 days without compromising fertility and estrous response while maintaining the simplicity and cost-effectiveness of the program. This short estrus synchronization treatment would make artificial insemination more practical in extensive beef production. Research is underway to reduce the variation in estrous response after steroid-PG treatment, which in turn, may provide potential applications for fixed-time artificial insemination programs in beef cattle production systems. REFERENCES 1. Anderson LH, Day ML. Acute progesterone administration regresses persistent dominant follicles and improves fertility of cattle in which estrus was synchronized with melengesterol acetate. J Anim Sci 1994; 72:2955-2961. 2. Bergfeld EGM, Kojima FN, Cupp AS, Wehrman ME, Peters KE, Mariscal V, Sanchez T, Kinder JE. Changing doses of progesterone results in sudden changes in frequency of luteinizing hormone pulses and secretion of 17p estradiol in bovine females. Biol Reprod 1996; 54:546-553. 3. Bhattacharya S, Chowdhury TM. Observations on oestrous cycle in five breeds of indian dairy heifers. Indian Vet J 1965; 42:503. 4. Bo GA, Adams GP, Caccia M, Martinez M, Pierson RA, Mapletoft RJ. Ovarian follicular wave emergence after treatment with progestogen and estradiol in cattle. Anim Reprod Sci 1995; 39:193-204. 5. Bo GA, Adams GP, Pierson RA, Mapletoft RJ. Exogenous control of follicular wave emergence in cattle. Theriogenology 1995; 43:31-40. 6. Bo GA, Bergfelt DR, Brogliatti GM, Pierson RA, Adams GP, Mapletoft RJ. Local versus systemic effects of exogenous estradiol-170 on ovarian follicular dynamics in heifers with progestogen implants. Anim Reprod Sci 2000; 59:141-157. 7. Caccia M, Bo G A. Follicle wave emergence following treatment of CIDR-B implanted beef cows with estradiol benzoate and progesterone. Theriogenology 1998; 49:341. 8. Cavalieri J, Coleman C, Kinder JE, Fitzpatrick LA. Comparison of three methods of acute administration of progesterone on ovarian follicular development and the timing and synchrony of ovulation in Bos indicus heifers. Theriogenology 1998; 49: 133 1- 1343. 9. Cavalieri J, Rubio I, Kinder JE, Entwistle KW, Fitzpatrick LA. Synchronization of estrus and ovulation and associated endocrine changes in Bos indicus cows. Theriogenology 1997; 47:801-814. 10. Chenoweth PJ. Aspects of reproduction in female Bos indicus cattle: a review. Aust Vet J 1994; 711422-426.

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