Studies on Ovarian Follicular Dynamics and Steroid Profiles in Sahiwal Cattle

2021 ◽  
Author(s):  
Vinny Dodiyar ◽  
Parkash Singh Brar ◽  
Narinder Singh ◽  
Mrigank Honparkhe
Keyword(s):  
Corpus Luteum ◽  
Estrous Cycle ◽  
Maximum Diameter ◽  
Endocrine Regulation ◽  
Dominant Follicle ◽  
Estrous Cycles ◽  
Significant Difference ◽  
Sahiwal Cattle ◽  
Sahiwal Cows ◽  
Follicular Dynamics

Background: Understanding of ovarian follicular dynamics and endocrine regulation is essential to design and use interventions to optimize reproductive efficiency. Bos indicus and Bos taurus cows have some differences in their follicular dynamics and ovarian steroidal hormones. The present study was planned to understand follicular dynamics vis-a-vis ovarian steroids profiles in Sahiwal cattle. Methods: The study was conducted in normal cyclic, pluriparous, non-lactating Sahiwal cows (n=7). Trans-rectal ultrasonography was performed to record the location, size, number of follicles and size of corpus luteum (CL) from the beginning, till the end of experiment. The dataset was used to characterize the follicular wave emergence, growth, regression, time of selection and ovulation of the dominant follicle in each cow. Result: Three Sahiwal cows showed two wave and four cows showed three wave estrous cycles with mean interovulatory length of 20.33±0.33 and 22.50±0.28 days, respectively. No significant difference was recorded in the maximum diameter of corpus luteum, P4 and E2 plasma levels between 2-wave and 3-wave estrous cycles. The peak progesterone values of 6.00±0.91 and 6.2±1.2 ng/ml and peak estradiol values of 15.83±0.60 and 14.31±0.44 ng/ml were recorded in 2-wave and 3-wave estrous cycle, respectively. The results showed that Sahiwal cows had 2-wave and 3-wave estrous cycle and the 3-wave estrous cycle had comparatively longer inter-ovulatory period and smaller maximum diameter of second wave dominant follicle than 2-wave estrous cycle.

scholarly journals Ovarian Follicular Dynamics during the Estrous Cycle in Jennies in Upper Egypt

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
R. I. Derar ◽  
H. A. Hussein
Keyword(s):  
Growth Rate ◽  
Estrous Cycle ◽  
Slow Rate ◽  
Ovarian Follicles ◽  
Maximum Diameter ◽  
Dominant Follicle ◽  
Upper Egypt ◽  
Follicular Wave ◽  
Preovulatory Follicles ◽  
Follicular Dynamics

The objective of the current study was to describe follicular dynamics in Egyptian Jennies throughout the estrous cycle. In this experiment, 8 estrus cycles in 8 cyclic Jennies were studied from February to June using ultrasonography. The result revealed that one follicular wave per cycle was recorded throughout the studied period. Dominant follicle (DF) was firstly detected at day in Jennies. The growth rate of DF was  mm/day. Left ovulations were nonsignificantly () more than right ovulations (55.6% versus 44.6%). The CL was firstly detected at D , developed in a rate of  mm/day, reached a maximum diameter of  mm at D , and started to regress on D with a mean regression rate of  mm d-1. Results of the present study indicated that Jennies had one follicular wave per cycle. The Day of the cycle has a significant effect on the number of different classes of the ovarian follicles, but not large ones. Ultrasonographic characteristics of the preovulatory follicles could be useful to predict ovulation. CL developed and regressed in a slow rate.

scholarly journals 228DOMINANT FOLLICLE DEVIATION IN GUZERA BREED (BOS INDICUS) COWS

2004 ◽  
Vol 16 (2) ◽  
pp. 235
Author(s):  
J.H.M. Viana ◽  
G.T.R.M. Coutinho ◽  
M.P. Palhao ◽  
L.S.A. Camargo ◽  
W.F. Sa ◽  
...  
Keyword(s):  
Bos Indicus ◽  
Maximum Diameter ◽  
Zebu Cattle ◽  
Dominant Follicle ◽  
Estrous Cycles ◽  
Portable Ultrasound ◽  
Follicular Wave ◽  
Lower Maximum ◽  
Ovulatory Follicles ◽  
Follicular Dynamics

Follicular dynamics of Zebu Cattle are characterized by lower maximum diameter and persistence of dominant follicles, when compared to European breeds. However, the main effects of follicular dominance on subordinated follicle population, and consequently on oocyte recovery and embryo production, have been shown to be similar among breeds. The aim of this study was to evaluate the dominant follicle establishment period, indicated by follicle divergence, in Zebu cows. Pluriparous, non-lactating Guzera breed (Bos indicus) cows (n=5), presenting a mean body weight of 518.0±48.5kg and similar body score condition (ranging from 3.5 to 4, in a 1 to 5 scale), were used. In a first trial, follicular dynamics were evaluated daily during 1 (n=2) or 2 (n=3) estrous cycles, using a portable ultrasound device equipped with a linear rectal 5MHz transducer (Aloka SSD500, Aloka Co., Tokyo, Japan). In a second trial, estrous cycles were synchronized using progesterone intravaginal-releasing devices (CIDR, Pharmacia, Sao Paulo, Brazil), and follicular dynamics were evaluated every 6h after ovulation, during the first follicular wave, until the largest follicle achieved a diameter of 10mm. During each evaluation ovaries were mapped, and evolution of follicles followed individually. Data are normalized for the moment of follicular divergence, and analyzed by ANOVA. Results are presented as mean±SD. Data from the first evaluations confirmed the occurrence of cycles with three (4/8) and four (1/8) follicular waves, despite a mean cycle length of 19.1±1.9 days, with a maximum diameter of 11.6±2.4mm for non-ovulatory follicles, and 14.4±0.5mm for ovulatory follicles. Follicular deviation during the first follicular wave occurred 49.2±5.0h after ovulation, when the largest follicle presented a diameter of 7.3±0.6mm, and the second largest follicle 6.8±0.7mm. Growth rates of the dominant and the largest subordinated follicles were similar before (0.35mm/6h vs. 0.33mm/6h, respectively;; P>0.05), but significantly different after deviation (0.52mm 6h v. −0.04mm 6h; P<0.05). These results shows that the lower maximum diameter and persistence of dominant follicles, in Zebu cattle, is partially compensated by an earlier dominant follicle deviation.

Follicular dynamics, corpus luteum growth and regression in lactating dairy cattle

1991 ◽  
Vol 71 (1) ◽  
pp. 61-68 ◽  
Author(s):  
C. Taylor ◽  
R. Rajamahendran
Keyword(s):  
Dairy Cows ◽  
Corpus Luteum ◽  
Estrous Cycle ◽  
Follicular Growth ◽  
Dominant Follicle ◽  
Lactating Dairy Cows ◽  
Ovulatory Follicle ◽  
Second Wave ◽  
Lactating Dairy Cattle ◽  
Follicular Dynamics

Ultrasound imaging and progesterone (P4) profiles were used to characterize follicular and corpus luteum (CL) growth and regression in 10 cycling dairy cows. Thirteen of sixteen cycles were characterized by two waves of follicular growth, the second wave giving rise to the ovulatory follicle. The remaining three cycles had three waves. There was no difference between two- and three-wave cycles with regard to the day of emergence of the first or second dominant follicle (day 2.5 ± 0.9 vs. day 2.4 ± 1.2 and day 12.4 ± 1.6 vs. day 12.0 ± 2.0, respectively) or the onset of regression of the first dominant follicle (day 12.5 ± 1.5 vs. day 12.3 ± 1.5). In two wave cycles, estrous cycle length was shorter (20.8 ± 1.7 d vs. 29.7 ± 4.9 d), the first day of decline in P4 (day 16.2 ± 1.5 vs. day 23.7 ± 5.5) and the onset of CL regression (day 17.1 ± 1.3 vs. day 24.3 ± 5.5) was earlier. It is concluded that two waves of follicular growth in an estrous cycle is the norm in lactating dairy cows. The presence of an additional wave is due to a prolonged luteal phase. Key words: Follicle, corpus luteum, estrous cycle, dairy cow

scholarly journals Follicular dynamics in zebu cattle

2000 ◽  
Vol 35 (12) ◽  
pp. 2501-2509 ◽  
Author(s):  
JOÃO HENRIQUE MOREIRA VIANA ◽  
ADEMIR DE MORAES FERREIRA ◽  
WANDERLEI FERREIRA DE SÁ ◽  
LUIZ SÉRGIO DE ALMEIDA CAMARGO
Keyword(s):  
Estrous Cycle ◽  
Bos Indicus ◽  
Maximum Diameter ◽  
Zebu Cattle ◽  
Dominant Follicle ◽  
Serum Progesterone ◽  
Portable Ultrasound ◽  
Follicular Waves ◽  
Ovulatory Follicle ◽  
Follicular Dynamics

The aim of this study was to investigate the follicular dynamics during estrous cycle in Gir breed (Bos indicus) cows. Follicular growth and atresia during estrous cycle were evaluated using a portable ultrasound device. Luteal activity was evaluated by serum progesterone levels. Cycles with two (6.67%), three (60.00%), four (26.67%) and five (6.67%) follicular waves were observed. There was no difference (P>0.05) in dominant or subordinate follicles growth or atresia rates among follicular waves. The maximum diameter of the ovulatory follicle was higher than the diameter of the other dominant follicles in cycles with four waves, and higher than the diameter of the second dominant follicle in cycles with three waves (P<0.05). There was no difference (P>0.05) in estrous cycle length (21.11±1.76 and 22.25±1.71 days) or progesterone levels during diestrous (4.48±1.45 and 5.08±1.40 ng/mL) between cycles with three or four waves. Follicular dynamics in Gir cattle is characterized by a higher incidence of cycles with three or four waves, associated with a low persistence of the dominant follicle.

Comparison of bovine uterine horns for progesterone and oxytocin levels with bilateral corpus luteum

1996 ◽  
Vol 76 (3) ◽  
pp. 463-464 ◽  
Author(s):  
W. A. Cerbito ◽  
M. P. B. Wijayagunawardane ◽  
M. Takagi ◽  
K. Sato ◽  
A. Miyamoto ◽  
...  
Keyword(s):  
Key Words ◽  
Corpus Luteum ◽  
Estrous Cycle ◽  
Luteal Phase ◽  
Uterine Horn ◽  
Corpora Lutea ◽  
Uterine Tissue ◽  
Tissue Samples ◽  
Significant Difference ◽  
The Right

Bovine uterine horns with both ovaries containing a corpus luteum (CL) were compared for progesterone (P4) and oxytocin (OT) concentrations during the luteal phase of the estrous cycle. Uterine tissue samples from five Holstein cows with bilateral CL obtained from the slaughterhouse were used for this study. No significant difference was observed in P4 and OT levels in the right and left horns with corpora lutea in both ovaries. The data clearly indicate that both sides of the uterine horn having a functional CL are exposed to similar levels of P4 and OT, supporting the hypothesis that luteal products are delivered locally to the uterus. Key words: Progesterone, oxytocin, uterine horn, bilateral, corpus luteum, cow

295 SUPEROVULATORY RESPONSE IN COWS FOLLOWING SYNCHRONIZATION OF FOLLICLE WAVE EMERGENCE WITH ESTRADIOL AT DIFFERENT STAGES OF THE ESTROUS CYCLE

2008 ◽  
Vol 20 (1) ◽  
pp. 227
Author(s):  
A. Garcia Guerra ◽  
G. A. Bó ◽  
J. Villarreal ◽  
G. M. Brogliatti
Keyword(s):  
Estrous Cycle ◽  
Buenos Aires ◽  
Animal Health ◽  
Ovarian Response ◽  
Buenos Aires Province ◽  
Transfer Program ◽  
Dominant Follicle ◽  
Follicular Wave ◽  
Significant Difference ◽  
Group 2

Ovarian asynchrony and variability in response to superstimulation remain the most limiting factors in any embryo transfer program (Armstrong D 1993 Theriogenology 39, 7–24). Ovarian response can be increased and less variable if superstimulatory treatment is started at the time of follicular wave emergence (Bö GA et al. 1995 Theriogenology 43, 31–40). A combination of progesterone (P4) and estradiol have been used to synchronize follicular wave for superstimulation. A retrospective analysis was done to compare the ovarian response, superovulatory response and embryo production of cows in Argentina that received progesterone and estradol prior to superstimulation at different stages of the estrous cycle. This research was carried out using different breed of donors (n = 584, 88% Angus) during the last 4 years in Buenos Aires province, Argentina. Heat detection was performed twice a day. At random stages of the estrous cycle, donors received an intravaginal progesterone device (DIB; Syntex, Buenos Aires, Argentina), 2 mg of estradiol benzoate and 50 mg of progesterone (Syntex, Buenos Aires, Argentina) IM on the same day. On day 4 after DIB insertion, superestimulatory treatment was initiated on a decreasing dose regimen of FSH (Pluset; Callier, Spain, or Folltropin, Bioniche Animal Health Inc., Belleville, Ontario, Canada) as IM injections every 12 h over 4 d. On day 6, DIBs were removed, and cows received two doses of 2 mL of cloprostenol 12 h apart. At heat detection, all donors received a dose of 2 mL of GnRH (Dalmarelin; Fatro Von Franken, Buenos Aires, Argentina) by IM injection and were inseminated 12 and 24 h later. Seven days later, embryo collection was performed and ovarian response was evaluated as number of CL + unovulated follicles by transrectal ultrasound using a 7.5-MHz transducer (Pie Medical, Maastricht, the Netherlands). Ova/embryos were evaluated and classified according to the IETS manual. Donors were assigned to receive DIB and estradiol during the following stages of the cycle: group 1: between days 4 and 7 post-estrus (dominant follicle period), group 2: between days 8 and 12 post-estrus (emergence of the second follicular wave), and group 3: between days 13 and 21 post-estrus (dominant follicle of the second wave). Kruskal-Wallis test was used to compare variables among groups, and results are shown in Table 1. Ovarian response as CL + unovulated follicles and number of ovulations were significantly different among groups (P < 0.05). However, there was no significant difference in the number of fertilized ova or transferable embryos. Nevertheless, numeric differences that show that group 2 (started between days 8 and 12 post-estrus) was always superior for all variables. In conclusion, data suggest that estradiol may be more effective in synchronizing follicle wave emergence for superstimulation during the mid-part of the estrous cycle. Table 1. Superovulatory response in cows in which follicle wave emergence was synchronized with estradiol at different stages of the estrous cycle (mean ± SD) Research supported by Centro Genetico Bovino Eolia S.A.

208 OVARIAN FOLLICULAR DYNAMICS IN SOUTH AMERICAN CAMELIDS: EFFECT OF PLANE OF NUTRITION AND SPECIES

2010 ◽  
Vol 22 (1) ◽  
pp. 262
Author(s):  
M. P. Cervantes ◽  
T. Orban ◽  
G. P. Adams
Keyword(s):  
Body Condition ◽  
Suppressive Effect ◽  
Maximum Diameter ◽  
Dominant Follicle ◽  
Observational Period ◽  
Engineering Research ◽  
South American Camelids ◽  
Nutritional Conditions ◽  
Main Effects ◽  
Follicular Dynamics

Controversy exists regarding characteristics of follicular waves in llamas and alpacas. Lactational status has been shown to influence follicular dynamics, but the effects of species and nutrition have not been critically examined. A 2 × 2 experimental design was used to determine the effects of species (llama v. alpaca) and nutritional status (high-plane v. low-plane) on ovarian follicular wave dynamics. Adult female llamas (n = 16) and alpacas (n = 19), ≥ 3 years old, were assigned randomly to either a high or low plane of nutrition. Nutritional planes were defined by the grazing condition of the native pasture. The respective nutritional conditions were imposed 2 weeks before the start of the observational period. Body condition was estimated at the start of the observational period using a subjective scoring system (1 = very thin, 10 = very fat) and ovarian dynamics were monitored daily by transrectal ultrasonography for 38 days. Data were analyzed by two-way ANOVA and are expressed as mean ± SEM. Body condition scores were not different among groups (6.9 ± 0.35 and 6.6 ± 0.19 for llamas on high and low planes of nutrition, respectively, and 7.2 ± 0.25 and 6.8 ± 0.18 for alpacas on high and low planes of nutrition, respectively). The growing phase of the dominant follicle tended (P = 0.1) to be longer in llamas than in alpacas (9.8 ± 0.47 v. 8.8 ± 0.45 days) and in animals on a high plane of nutrition than in animals on a low plane (9.6 ± 0.50 v. 8.6 ± 0.42 days). Accordingly, the maximum diameter of the dominant follicle tended to be larger in llamas than in alpacas (10.1 ± 0.37 v. 9.1 ± 0.30 mm; P = 0.06) and in animals on a high plane of nutrition than in animals on a low plane (9.9 ± 0.39 v. 9.1 ± 0.27 mm; P = 0.14). The interwave interval was similar between llamas and alpacas (16.5 ± 0.66 v. 15.6 ± 0.42 days; P = 0.29), but was longer (P < 0.01) in animals on a high plane of nutrition than in animals on a low plane (16.9 ± 0.54 v. 15.0 ± 0.44 days); there was no interaction between main effects (P = 0.31). The total lifespan (duration of detection) of the dominant follicle was similar in both llamas and alpacas (22.9 ± 0.75 v. 21.9 ± 0.73 days; P = 0.38) and in animals on a high plane of nutrition than in animals on a low plane (22.7 ± 0.78 v. 22.0 ± 0.70 days; P = 0.53). There was no interaction between main effects (P = 0.21). All females (n = 35/35, 100%) had a follicle ≥ 7 mm (ovulatory size) from Days 7 to 12 after wave emergence. In conclusion, a low plane of nutrition had a suppressive effect on dominant follicle growth, resulting in a shortened interwave interval in llamas and alpacas. The interwave interval was not significantly longer in llamas than in alpacas despite a tendency for a longer growing phase and a larger dominant follicle. Research supported by Mitchell Group’s Mallkini Alpaca Breeding and Genetic Centre and the Natural Sciences and Engineering Research Council of Canada.

Effect of mid-luteal phase progesterone levels on the first wave dominant follicle in cattle

1994 ◽  
Vol 74 (2) ◽  
pp. 281-285 ◽  
Author(s):  
C. Taylor ◽  
R. Rajamahendran
Keyword(s):  
Key Words ◽  
Estrous Cycle ◽  
Luteal Phase ◽  
Follicular Growth ◽  
Dominant Follicle ◽  
Prostaglandin F ◽  
Follicular Dynamics

A wave-like-pattern of follicular growth and regression during the luteal phase has been described in the bovine. The factors responsible for inducing the onset of regression of nonovulatory dominant follicles are unknown. The present study was designed to examine the effect of progesterone (P4) administration early in the estrous cycle on the first wave dominant follicle. Nine heifers were administered P4 on day 3 (200 mg), day 4 (100 mg) and day 5 (50 mg) of the estrous cycle (Day 0 = day of estrus) and seven heifers received vehicle to serve as controls. All heifers received a luteolytic dose of prostaglandin F2α (PGF2α) on day 7. Follicular dynamics were monitored by daily ultrasonography. All seven control heifers ovulated the first wave dominant follicle. In four P4 treated heifers, the first wave dominant follicle regressed prior to PGF2α administration and a dominant follicle from the second pool of follicles ovulated. The remaining five P4 treated heifers ovulated the first wave dominant follicle. However, in these heifers the growth of the first wave dominant follicle was slower (0.65 ± 0.13 mm day−1 between days 3 to 7 for treated vs 1.46 ± 0.23 mm day−1 for control; P < 0.05) and estrus and ovulation were delayed compared to controls (3.8 ± 0.3 vs 2.4 ± 0.2 and 5.2 ± 0.4 vs 3.9 ± 0.2 days after PGF2α, respectively; P < 0.05). The results indicate that P4 administered early in the estrous cycle to mimic the mid luteal phase levels alters follicular dynamics and is capable of inducing premature regression of the first wave dominant follicle. Key words: Progesterone, dominant follicle, cattle, atresia, ovulation

scholarly journals Ovarian follicular dynamics in Boran and Crossbred heifers in Ethiopia: Implications for assisted reproductive techniques

2020 ◽  
Vol 24 (2) ◽  
pp. 54-72
Author(s):  
Jeilu Jemal ◽  
Tamrat Degefa ◽  
Tefera Yilma ◽  
Sayid Ali ◽  
Lemma Alemayehu
Keyword(s):  
Recovery Rate ◽  
Ovarian Follicle ◽  
Reproductive Potential ◽  
Progesterone Level ◽  
Maximum Diameter ◽  
Serum Progesterone ◽  
Estrous Cycles ◽  
Follicular Waves ◽  
Follicular Dynamics

The study was conducted to characterize the follicular dynamics of purebred Boran (Bos indicus) and Boran * Holstein Friesian crossbred heifers  during estrous cycles; for use in ovum pick up and in-vitro embryo production. Insight of reproductive physiology of cattle would help to understand and exploit the reproductive potential of elite animals for breed improvement. Follicular development, growth and atresia during estrous cycles were evaluated using a trans-rectal real-time B-mode ultrasound system for three consecutive estrus cycles. Luteal activity was evaluated by serum progesterone level. Follicular aspirations were done to investigate the potential of Boran cattle and their crosses for transvaginal oocyte production; using a vacuum pressure pump and Aloka SSD Prosound-2 ultrasound device. Boran heifers (n=15) manifested two (n = 6, 40%), three (n = 5, 33%), four (n= 3, 20%) and five (n=1, 6.7%) follicular waves. Crossbred heifers (n=14) showed one (n= 2, 14%), two (n= 6, 43%) and three (n= 6, 43%) follicular waves. Interovulatory interval was 21.1 ± 3.4 and 21.4 ± 2.7 days for Boran (n=45) and crossbred (n=42) heifers, respectively. The progesterone level in Boran and Crossbred heifers during diestrus was 9.5 ± 11.0 and 4.6 ± 8.8 ng/ml, respectively. The maximum diameter of the ovulatory follicle for crossbred heifers was higher (15.4 ± 1.6 mm) than the diameter of the Boran (14.0 ± 1.9 mm) heifers (p<0.005). Differences (p<0.005) were observed in the size of both right (26.6 ± 5.14 and 28.6 ± 5.1 mm) and left (21.7 ± 4.85 and 24.1 ± 5.07 mm) ovaries of Boran and Crossbred heifers, respectively. Difference (p<0.005) was also observed in follicular count of the  right ovaries of Boran (4.84 ± 1.96) and Crossbred  (5.13 ± 2.05) heifers. Oocyte recovery rate in once weekly collection scheme for Boran and their crossbred heifers was (n=19, 42.08%) and (n=17, 42.55%), respectively. The recovery rate for twice weekly collection scheme was (n=24, 34.53%) and (n=23, 40.44%) for Boran and crossbred heifers, respectively. Follicular dynamics in Boran heifers is characterized by a higher incidence of cycles with two, three and four waves, associated with a low persistence of the dominant follicles; and smaller size of ovulatory follicles and less intense heat signs from their crossbred counterpart. Boran heifers proved to have potential for comparable number of follicular population and ease of aspiration procedures that can be tapped for advancedreproductive techniques. Keywords: Estrus cycle; follicular wave; ovarian follicle; ovum pickup; ultrasound.

scholarly journals 14OVARIAN FOLLICULAR DYNAMICS IN COWS TREATED WITH A CIDR, ESTRADIOL AND PROGESTERONE LATE IN THE ESTROUS CYCLE

2004 ◽  
Vol 16 (2) ◽  
pp. 129 ◽  
Author(s):  
J.P. Kastelic ◽  
M.G. Colazo ◽  
J.A. Small ◽  
D.R. Ward ◽  
R.J. Mapletoft
Keyword(s):  
Estrous Cycle ◽  
Ovarian Follicle ◽  
Animal Health ◽  
Beef Cows ◽  
Control Group ◽  
Dominant Follicle ◽  
Chi Square ◽  
Follicular Wave ◽  
Follicle Diameter ◽  
Follicular Dynamics

The objective was to characterize ovarian follicular dynamics in beef cows treated with a CIDR (Bioniche Animal Health; Belleville, Ontario, Canada) and an injection of estradiol-17β (E2), with or without progesterone (P4), late in the estrous cycle. Previously synchronized, non-lactating, crossbred beef cows (n=36) received a CIDR (Day 0) 16 to 18 days after ovulation and were randomly allocated to one of three treatment groups: no further treatment (Control, n=12), an injection of 5mg E2 (E2, n=12), or 5mg E2 plus 100mg P4 (E2P4, n=12; both from Sigma Chemical Co., St.Louis, MO, USA) i.m. in 2mL canola oil. On Day 7, CIDR were removed and cows received 500μg i.m. of cloprostenol (Estrumate, Schering Plough Animal Health, Pointe-Claire, Quebec, Canada). Ovaries were examined once daily by transrectal ultrasonography to detect ovarian follicle growth profiles, and determine the time of ovulation. Blood samples were taken daily for progesterone determination. Data were analyzed by ANOVA (LSD and Bartlett’s tests), Student’s t-test and chi-square procedures. Diameter of the CL and the dominant follicle, and progesterone concentration on Day 0 did not differ among groups (P=0.6; overall mean (±SD), 16.8±2.7mm, 14.1±2.0mm, and 1.5±1.9ngmL, respectively). Thirteen cows ovulated within 3 days of treatment (50% of E2- and E2P4-treated cows and 8.3% of Control cows; P=0.05); cows that ovulated had smaller CL diameters (15.2±1.7 v. 17.7±2.7mm; P&lt;0.004) and lower progesterone concentrations (0.4±0.2 v.2.1±2.2ngmL; P&lt;0.001) at the time of treatment. Follicular wave emergence occurred within 7 days in 4/12 Control cows, 10/12 E2-treated cows, and 10/12 E2P4-treated cows (P&lt;0.01). Although the interval from treatment to wave emergence did not differ among treatments (P=0.8; overall, 3.4±1.5 days), follicular wave emergence was more synchronous (P&lt;0.004) in the E2 group than in the Control or E2P4 groups. At CIDR removal, dominant follicle diameter was larger (P&lt;0.02) in the Control group (15.9±5.5mm) than in the E2 (11.9±1.8mm) or E2P4 (11.5±3.4mm)groups, but dominant follicle diameter was less variable (P&lt;0.003) in the E2 group than in the other two groups. Three cows did not ovulate after CIDR removal; two in the Control group and one in the E2P4 group. Interval to ovulation was shorter (P&lt;0.05) in the Control group (70.8±10.5h)than in the E2 (87.0±9.0h) or E2P4 (86.2±7.2h) groups, and the intervals to ovulation in cows that ovulated following treatment (91.0±8.0h) was longer (P&lt;0.001) than in those that did not (76.6±9.6h). In summary, treatment of cows with an estradiol-progesterone protocol late in the estrous cycle resulted in ovulation (50.0%), atresia (33.3%) or persistence (16.6%) of the dominant follicle present at that time. As length of follicular dominance and timing of ovulation were affected, fertility may be impaired following AI.

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