Follicular populations during the estrous cycle in heifers. II. Influence of right and left sides and intraovarian effect of the corpus luteum

Ovarian follicles ≥2 mm were studied in 22 Holstein heifers by daily ultrasound examinations. Data were partitioned by right vs. left ovary and corpus luteum bearing ovary vs. the contralateral ovary. There were significantly more (P < 0.03) follicles 4–6 mm, > 13mm and total ≥2 mm in the right ovary, regardless of the presence of a corpus luteum. Significantly more (P < 0.05) follicles 2–3 mm, > 13 mm and total ≥2 mm were observed in the ovary bearing the corpus luteum. Interactions between day and corpus luteum appeared to be due to a greater number of follicles in the ovary bearing the corpus luteum during the first part of the interovulatory interval. There was also a day by right side vs. left side interaction for the number of follicles > 13 mm. Interpretation of the interactions was that the presence of a corpus luteum was conducive to the development of more anovulatory diestrous follicles > 12 mm. However, as regression of the corpus luteum progressed, there was an apparent proclivity for preovulatory follicular development in the right ovary. There was no apparent pattern of alternating sides of ovulation or of alternating sides of development of anovulatory diestrous follicles and preovulatory follicles in heifers observed for more than one interovulatory interval. There was not a significant difference in the maximum diameter attained by the anovulatory diestrous follicle or preovulatory follicle between ovaries ipsilateral or contralateral to the corpus luteum; however, the maximum diameter attained by the preovulatory follicle was greater (P < 0.05) than that attained by the anovulatory diestrous follicle.     

Ultrasonic anatomy of equine ovaries

A linear-array ultrasound scanner with a 5-MHz transducer was evaluated for studying follicular and luteal status in mares, and the ultrasonic properties of equine ovaries were characterized. Follicular diameters were estimated in vivo and after removing and slicing six ovaries. Correlation coefficients between the two kinds of determinations were 0.91 for number of follicles >/=2 mm in diameter and 0.95 for diameter of largest follicle. The ovaries of five mares were examined daily until all mares had been examined from three days before an ovulation to three days after the next ovulation. There was a significant difference among days for diameter of largest follicle and second largest follicle and for number of follicles 2-5 mm, 16-20 mm, and >20 mm. Differences seemed to be caused by the presence of many 2- to 5-mm follicles during early diestrus, initiation of growth of large follicles at mid-cycle, selective accelerated growth of an ovulatory follicle beginning five days before ovulation, and regression of large nonovulatory follicles a few days before ovulation. In one of the five mares, the corpus luteum was identified throughout the interovulatory interval, and the corresponding corpus albicans was identified for three days after the second ovulation. In the other four mares, the corpus luteum was last identified an average of 16 days after ovulation or five days before the next ovulation. In a blind study, the location of the corpus luteum (left or right ovary) as determined by ultrasonography agreed with a previous determination of side of ovulation by palpation in 88% of 40 mares on days 0-14. In the remaining 12% and in all of 12 estrous mares, the location was recorded as uncertain. The ultrasound instrument was judged effective for monitoring and evaluating follicles and corpora lutea.     

Ultrasonography of the bovine ovary

A linear-array ultrasound scanner with a 5-MHz transducer was evaluated for the study of follicular and luteal status in heifers. The ovaries of five heifers were monitored daily until all heifers were examined for a period from three days before an ovulation to three days after the next ovulation. There was a significant difference among days for diameter of the largest follicle and second largest follicle and for the number of follicles 4-6 mm and >10 mm. Differences seemed to be caused by the presence of several 4- to 6-mm follicles in early diestrus, growth to an ostensibly ovulatory size and subsequent regression of a follicle during mid-cycle, and selective accelerated growth of the ovulatory follicle four days before ovulation. The corpus luteum became visible approximately three days after ovulation and was identifiable throughout the rest of the interovulatory interval. In two of the five heifers, the corresponding corpus albicans was identified for three days after the second ovulation. Two heifers were induced to superovulate and follicular growth was monitored. The results indicated that the follicles which ovulated originated from the population present when the superovulation treatment was initiated. The ultrasound instrument was judged effective for monitoring and evaluating ovarian follicles and corpora lutea in normal and superovulated heifers.     

Ovarian follicular populations during early pregnancy in heifers

Ovarian follicles >/=2mm were studied in 14 pregnant and 14 nonpregnant Holstein heifers by daily ultrasound examinations. There were significant differences among days, from Day 0 (day of ovulation) to Day 21, in the diameter of the largest follicle and the diameter of the second largest follicle in pregnant and nonpregnant heifers. There was an interaction of day and reproductive status (P < 0.001) for the diameter of the largest follicle. Significant differences among days were also observed in the numbers of follicles 2 to 3 mm, 4 to 6 mm, 7 to 10 mm, 11 to 13 mm, and >13 mm, and the total number of follicles >/=2 mm. There was a significant main effect of reproductive status for the number of follicles 11 to 13 mm. An interaction of day and reproductive status was observed for the number of follicles >13 mm, but not for any of the other diameter categories. The effect of reproductive status for number of follicles 11 to 13 mm and the interactions for the number of follicles >13 mm and the diameter of the largest follicle seemed due to the selective growth and ovulation of the follicle destined to ovulate in nonpregnant heifers. The differences in ovarian follicular populations between pregnant and nonpregnant heifers were attributed solely to the presence of a physiological mechanism for the selection of an ovulatory follicle in nonpregnant heifers. There were no significant differences among days for any follicular endpoint during Days 22 to 60 in the pregnant heifers.     

Intraovarian relationships among dominant and subordinate follicles and the corpus luteum in heifers

Previous studies demonstrated that waves of follicular activity develop approximately every 9 d in cattle during the estrous cycle and early pregnancy. A dominant follicle develops from each wave and the remaining follicles (subordinates) begin to regress after a few days. In this study, intraovarian luteal and follicular interrelationships were examined during the follicular waves of the estrous cycle and pregnancy using data obtained by ultrasonography. During the estrous cycle, no intraovarian relationships were found between the ovary containing the corpus luteum and the ovary containing the dominant follicle (n = 165), or between the location of the corpus luteum and the characteristics of the dominant follicle. During pregnancy, however, the frequency distribution for the number of follicular waves with the dominant follicle and corpus luteum on the same or opposite ovaries differed (P<0.05) among Waves 1 to 10. The two structures (dominant follicle and corpus luteum) were more often in opposite ovaries during Waves 3 to 10 (combined frequency, 75%) than during Waves 1 and 2. During pregnancy, dominant follicles of consecutive waves differed (P<0.05) among Waves 1 to 8 in the frequency with which they appeared in the same versus the opposite ovary. The difference seemed primarily due to an increased frequency of consecutive follicles on the same ovary for Waves 4 to 8 (combined frequency, 80%). During both the estrous cycle and pregnancy, there was no significant intraovarian effect of the dominant follicle on the day of detection of the next dominant follicle, on the growth rate of the largest subordinate follicle, or on the length of the interval from wave origin to cessation of growth of the largest subordinate; these results indicate that previously postulated suppressive effects between follicles are exerted through systemic channels.     

Effects of lactational and reproductive status on ovarian follicular waves in llamas (Lama glama)

The effects of lactational status and reproductive status on patterns of follicle growth and regression were studied in 41 llamas. Animals were examined daily by transrectal ultrasonography for at least 30 days. The presence or absence of a corpus luteum and the diameter of the largest and second largest follicle in each ovary were recorded. Llamas were categorized as lactating (N = 16) or non-lactating (N = 25) and randomly allotted to the following groups (reproductive status): (1) unmated (anovulatory group, N = 14), (2) mated by a vasectomized male (ovulatory non-pregnant group, N = 12), (3) mated by an intact male and confirmed pregnant (pregnant group, N = 15). Ovulation occurred on the 2nd day after mating with a vasectomized or intact male in 26/27 (96%) ovulating llamas. Interval from mating to ovulation (2.0 +/- 0.1 days) and growth rate of the preovulatory follicle (0.8 +/- 0.2 mm/day) were not affected by lactational status or the type of mating (vasectomized vs intact male). Waves of follicular activity were indicated by periodic increases in the number of follicles detected and an associated emergence of a dominant follicle that grew to greater than or equal to 7 mm. There was an inverse relationship (r = -0.2; P = 0.002) between the number of follicles detected and the diameter of the largest follicle. Successive dominant follicles emerged at intervals of 19.8 +/- 0.7 days in unmated and vasectomy-mated llamas and 14.8 +/- 0.6 days in pregnant llamas (P = 0.001). Lactation was associated with an interwave interval that was shortened by 2.5 +/- 0.05 days averaged over all groups (P = 0.03). Maximum diameter of anovulatory dominant follicles ranged from 9 to 16 mm and was greater (P less than 0.05) for non-pregnant llamas (anovulatory group, 12.1 +/- 0.4 mm; ovulatory group, 11.5 +/- 0.2 mm) than for pregnant llamas (9.7 +/- 0.2 mm). In addition, lactation was associated with smaller (P less than 0.05) maximum diameter of dominant follicles averaged over all reproductive statuses (10.4 +/- 0.2 vs 11.7 +/- 0.3 mm). The corpus luteum was maintained for a mean of 10 days after ovulation in non-pregnant llamas and to the end of the observational period in pregnant llamas. The presence (ovulatory non-pregnant group) and persistence (pregnant group) of a corpus luteum was associated with a depression in the number of follicles detected and reduced prominence of dominant follicles (anovulatory group greater than ovulatory non-pregnant group greater than pregnant group).(ABSTRACT TRUNCATED AT 400 WORDS)     

Follicular dynamics prior to and during superovulation in heifers

The present ultrasonographic study examined the relationship between certain follicular parameters and the superovulatory response in gonadotropin-stimulated heifers. Thirty heifers received a total of 35 mg FSH twice daily for 4 d and 0.75 mg cloprostenol were given to induce luteolysis and estrus at 72 h after the initial FSH injection. Transrectal ultrasonography was performed once daily from 1 or 2 d before the initial FSH injection and until the day of estrus. The number of small (2 to 4 mm), medium (5 to 9 mm), and large (>/=10 mm) size follicles as well as the diameter of the large follicles were recorded. Embryos were recovered non-surgically 6 or 7 d after estrus, and the number of corpora lutea was determined by palpation per rectum. Heifers with >2 or 0.05). The number of large follicles and the sum of medium and large follicles were positively correlated (r=0.43 and r=0.54, respectively; P<0.05) with the number of corpora lutea palpated on the day of embryo recovery (6 to 7 d after estrus). In conclusion, there was an effect of the day relative to initiation of FSH treatment on all follicular categories in heifers responding positively to superovulation, and there was no effect of side (left or right ovary) or of corpus luteum diameter (ipsilateral or contralateral).     

The influence of ovarian activity and uterine involution determined by ultrasonography on subsequent reproductive performance of dairy cows

The objective of this study was to test the hypothesis that a follicle >8 mm diameter in the ovary ipsilateral to the previously gravid uterine horn (PGUH), between 14 and 28 days postpartum, improves subsequent reproductive performance. Lactating Holstein-Friesian cows (n=284) in 3 commercial herds were examined using transrectal ultrasonography once between 14 and 28 days postpartum to determine associations between uterine and ovarian measurements and subsequent fertility. There were fewer cows with a corpus luteum in the ovary ipsilateral to the PGUH compared with the contralateral ovary (16.9% vs. 37.0%; P<0.001). In addition, in the ovary ipsilateral to the PGUH there were fewer follicles >5 mm diameter (mean +/- SEM; 0.69 +/- 0.06 vs. 1.02 +/- 0.06; P<0.001) and fewer animals with a follicle >8 mm diameter (26.1% vs. 49.6%; P<0.001). These differences between the ovaries ipsilateral or contralateral to the PGUH declined with increasing time between 14 and 28 days postpartum. The presence of a purulent vaginal discharge decreased the number of animals with a corpus luteum in the ovary contralateral to the PGUH (45/143 vs. 60/141; P<0.05), but not in the ovary ipsilateral to the PGUH. The presence of a follicle >8 mm diameter in the ovary ipsilateral to the PGUH was associated with a shorter calving to conception interval compared with animals without such a follicle (99.0 +/- 5.6 days, n=74, vs. 112.8 +/- 4.4 days, n=210; P<0.05). These observations raise an intriguing issue: how does this follicle affect subsequent fertility--does the follicle exert a local influence on the uterus, or vice versa?     

Follicular populations during the estrous cycle in heifers. I. Influence of day

Ovarian follicles ⩾ 2 mm were studied in 22 Holstein heifers by daily ultrasound examinations. There were significant differences (P < 0.0001) among days of the estrous cycle for diameter of the largest and second largest follicles and in the numbers of follicles 2–3 mm, 4–6 mm, 7–10 mm, 11–13 mm, > 13 mm, and total number of follicles ⩾2 mm. Patterns of the mean profiles for all follicular endpoints except the number of follicles 4–6 mm and total number of follicles ⩾ 2 mm were bimodal. The days encompassed by the first and second portions, respectively, of the bimodal profiles were approximately: diameter of largest follicle, Days 0–14 and 15–21 (ovulation); diameter of second largest follicle, Days 0–7 and 8–20; number of follicles 2–3 mm, Days 1–11 and 12–20; number of follicles 7–10 mm, Days 0–6 and 7–18; number of follicles 11–13 mm, Days 0–8 and 9–20; and number of follicles > 13 mm, Days 2–14 and 16–21. Data for the various categories were recombined to demonstrate relationships between the numbers of follicles 2–3 mm and ⩾ 4 mm during the interovulatory interval. There were significant differences (P < 0.0001) among days in both 2–3 mm and ⩾ 4 mm follicular categories. Differences appeared due to periods of higher mean numbers of follicles 2–3 mm which began between Days 2 or 3 and Days 15 or 16 and reached maximum levels on Day 7 and Day 19, respectively. There was an inverse relationship between the number of follicles 2–3 mm vs ⩾ 4 mm and between the diameters of largest and second largest follicles. The process of selection of the follicle destined to ovulate appeared to become manifest as selective growth of the preovulatory follicle with concurrent decrease in diameter of the second largest follicle and regression of the other follicles in the various follicular categories. A similar process apparently occurred early in the interovulatory interval. There was apparently selective growth of a follicle to preovulatory size by Day 6, coincident decrease in diameter of the second largest follicle, and apparent regression of other follicles in the ultrasonically detectable pool. The only apparent difference was that the follicle which attained preovulatory diameter early in the interovulatory interval remained in the ovary for 5 or 6 days, then regressed, while the follicle which attained preovulatory diameter at approximately Day 18–20 ovulated.     

Morphometry of ovarian structures by transrectal ultrasonography in Serrana goats

The accuracy of transrectal real-time ultrasonography (RTU) scanning technique to detect ovarian structures (follicles and corpus luteum) of Serrana goats was compared to the data obtained by observation of ovarian sequential slices. This slicing technique (SLI) was considered as reference method. The laparoscopy and laparotomy techniques were also used for corpora lutea identification. For this purpose the ovaries of 14 females were observed, 7-8 days after ovulation, by transrectal ultrasonography followed by laparoscopic examination. Then ovaries were removed and studied by slicing. In the sliced sections of each ovary (n=28), follicles and corpus luteum (CL) were identified and counted. CL and follicular diameters were measured using a millimetre scale. The total number of follicles, counted by RTU, was significantly lower than that observed by SLI (P <0.01). This difference was mainly due to the under estimation of <2 mm follicles category. The correlation coefficient between category data obtained by RTU and SLI methods for the number of follicles > or =3 mm was high (r2=0.95, P <0.001), which highlights the use of UTR as a potential methodology to study the follicular dynamic of goats. There were no significant differences (P >0.05) between the average number (mean +/- S.D.) of corpus luteum identified per ovary by RTU (0.71 +/- 0.75), laparoscopy (0.58 +/- 0.71), laparotomy (0.67 +/- 0.76) or SLI (0.83 +/- 0.76) methods. The accuracy for the identification of ovulation, validated by CL detection on D7-D8 by SLI (100%), was 91.7%, 87.5% and 83.3% by RTU, laparotomy and laparoscopy, respectively. The negative predictive value of RTU, laparotomy and laparoscopy to verify the absence of a CL in the ovary was 81.8%, 75.0% and 69.2%, respectively. The specificity of all three methods for the CL identification was 100%. No significant differences (P >0.05) were found in the probability to detect the exact number of CL (0, 1 or 2) counted in each ovary between the RTU (87.5%), laparotomy (83.3%) and laparoscopy (75.0%) methods when compared with the reference method. The diameter of spherical CL could be estimated with reliability (r2=0.86; P <0.001). The real-time ultrasonographic scanning proved to be a highly accurate method for detection and measurement of several categories of follicles and CL size in Serrana goats. The results of the present study show that laparoscopy and RTU are similarly reliable techniques for CL detection. However, the RTU represents a non-traumatic technique with advantages to animal welfare both in experimental and reproductive evaluation of the size of ovarian structures.     

Evolution of the diameters of the largest healthy and atretic follicles during the human menstrual cycle

Analysis of ovaries from 31 women with normal ovarian function permitted study of the diameter of the largest healthy and atretic follicles during the menstrual cycle. The follicle destined to ovulate is selected during the early follicular phase (Days 1-5). Throughout the cycle the diameter of the largest healthy follicles, with the exception of the dominant follicle, did not exceed, on average, 6 mm during the follicular phase and 4 mm during the luteal phase. Consequently, excluding the dominant follicle during the second half of the follicular phase, the largest follicles present in the human ovary are atretic. From these data, it was concluded that a new ovulation could not occur very soon after a spontaneous or experimentally induced premature disappearance of the dominant follicle or the corpus luteum of the cycle.     

Growth and regression of ovarian follicles during the follicular phase of the oestrous cycle in heifers undergoing spontaneous and PGF-2 alpha-induced luteolysis

Ultrasonography was used to monitor the growth, ovulation and regression of individual ovarian follicles greater than or equal to 5 mm during the late luteal and follicular phases of the oestrous cycle in heifers treated with injections of PGF-2 alpha to induce luteolysis and in heifers undergoing spontaneous luteolysis. Six heifers were given a single injection of PGF-2 alpha between Day 12 and 15 of the oestrous cycle and their ovaries were examined daily by transrectal ultrasonography until ovulation occurred. Another group of 5 heifers was examined daily by ultrasound from Day 14 or 15 of the cycle through spontaneous luteolysis and ovulation. Blood samples were taken twice daily from this group and analysed for progesterone to determine when luteolysis occurred. All heifers were checked for oestrous behaviour twice daily. Mean diameters of ovulatory follicles on each of the 3 days before oestrus were not different between PGF-2 alpha-treated and untreated heifers. In both groups there was large variation among heifers in the sizes and growth rates of the ovulatory follicles. At 3 days before oestrus the diameters of ovulatory follicles were between 7.5 and 11 mm in PGF-2 alpha-treated heifers and between 6 and 11.5 mm in untreated heifers. Non-ovulatory follicles decreased in size during the 3 days before oestrus and the number of non-ovulatory follicles within the size ranges of ovulatory follicles decreased. The ovulatory follicle was not consistently the largest follicle on the ovaries until the day of oestrus but was always one of the 2 largest follicles during the 3 days before oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Noninvasive monitoring of follicle development,ovulation, and corpus luteum formation in the marmoset monkey (Callithrix jacchus) by ultrasonography

This is the first paper to describe ovarian changes associated with follicular growth, ovulation, and corpus luteum (CL) formation as monitored by ultrasonography in a multiovular primate, the marmoset monkey (Callithrix jacchus). Examinations were carried out transabdominally on unsedated females using a 10 MHz probe. Cycles were monitored by plasma progesterone and controlled by administration of prostaglandin F2α (PGF). The reliability of ultrasound was validated by comparing findings with direct observation of the ovaries at laparotomy. In eight females, 25 follicles were counted, of which 92% were depicted correctly by ultrasound. Of 14 CLs in five females, number and position were confirmed at laparotomy for 78%. Ultrasound examinations of ovaries throughout the follicular and luteal phase were performed in eight cycles and related to plasma profiles of luteinizing hormone (LH) and progesterone. One of these cycles was anovulatory. In the remaining seven cycles, 19 follicles were considered ovulatory follicles since they were seen on consecutive days and found again as CLs. Growth of individual follicles was monitored by measurements of follicle diameter from day 7 onward. Disappearance of follicles or changes in echogenicity were noted between days 9 and 11, preventing further measurements. Mean follicle size increased from 2.1 mm (range 1.6 mm–2.7 mm) on day 7 to 3.2 mm (range 2.7 mm–4.0 mm) on the day last seen. With one exception, the day follicles were last seen by ultrasound was consistent with the day of the preovulatory LH surge (day 9–11). The postovulatory rise in progesterone occurred 1–2 days later (day 11–13). These findings suggest that the day of ovulation as observed by ultrasound was characterized by either disappearance of follicles or increased follicular echogenicity. In conclusion, ultrasonography provides a reliable, noninvasive method for examinations of the ovarian cycle in the marmoset monkey. © 1996 Wiley-Liss, Inc.     

Effects of unilateral ovariectomy on follicular development and ovulation in cattle

In a study of 4 cyclic dry cows (Trial I) and 6 cyclic puberal heifers (Trial II), unilateral ovariectomy increased the number of ovulatory follicles, did not alter the hormone profile, cycle length or the number of follicular waves. Ovarian follicular development in all 4 cows was monitored daily using transrectal ultrasonography until the day of ovulation, during which period daily blood samples were also taken from the tail vein for determination of plasma FSH, LH and P4 concentrations. Unilateral ovariectomy was performed on the day after ovulation and ovarian activity was again monitored daily (ultrasonography and blood sampling for FSH, LH and P4) for 2 consecutive cycles (8 cycles in all). Estrus in all 6 heifers was synchronized using 2 injections of PGF2 alpha given 12 d apart. Similarly, ovarian activity in the 6 puberal heifers was monitored daily using ultrasonography and blood sampling for 1 complete control cycle. Following estrus and ovulation the left ovary was removed in all the animals, and thereafter 1 complete cycle was followed. Mean cycle length, FSH, LH and P4 concentrations before and after unilateral ovariectomy were compared using paired sample t-test. The results show that unilateral ovariectomy neither altered the cycle length nor the number of follicular waves in the cows, but it increased the number of ovulatory follicles (2 follicles developed and ovulated in 6 of the 8 cycles). The mean diameter of the largest follicle was 16.1 +/- 0.9 mm and the second largest 12.5 +/- 0.9 mm. No significant (P > 0.05) differences were observed in FSH (0.72 +/- 0.09 vs 0.71 +/- 0.07), LH (0.42 +/- 0.1 vs 0.37 +/- 0.07) and P4 (2.8 +/- 0.6 vs 2.6 +/- 0.4) levels before and after unilateral ovariectomy. Of the 6 heifers, 5 had 2 waves and 1 heifer had 3 waves of follicular growth during the control cycle, and this pattern did not change after the procedure. Mean cycle length (20.7 +/- 0.9 vs 21 +/- 0.9) did not differ before and after unilateral ovariectomy, and 4 of the 6 heifers ovulated twin follicles following ovariectomy. The mean diameter of the largest follicle was 14.5 +/- 0.7 mm and second largest measured 12.1 +/- 0.8 mm. No significant (P > 0.05) differences were observed in FSH (0.16 +/- 0.09 vs 0.21 +/- 0.07), LH (0.11 +/- 0.1 vs 0.15 +/- 0.07) and P4 levels (3.6 +/- 0.26 vs 3.8 +/- 0.29) before and after unilateral ovariectomy. Based on these results, we conclude that unilateral ovariectomy is an ideal method for obtaining twin ovulations in cows and heifers.     

Oocyte retrieval and histological studies of follicular population in buffalo ovaries

Ovaries (N = 250) from slaughtered buffaloes were collected to study follicular population and compare methods of oocyte retrieval. The number and size of surface follicles were recorded and grouped into different categories. Different sized follicles in relation to oocyte diameter were studied histologically. Yield of oocytes per ovary were less (P < 0.05) from ovaries bearing a corpus luteum (CL). Techniques used for oocyte recovery included slicing, follicle puncture and aspiration. The oocyte recovery rate was greatest (P < 0.05) using slicing. The average number of visible surface follicles was 5.20 ± 0.97 with mean numbers of 2.5, 1.2, 0.82 and 0.62 per ovary for follicles sized 4, 8, 12 and 12 mm respectively. Histological studies revealed large numbers of primordial follicles in prepubertal and atretic follicles in senile buffaloes. They also established a biphasic relationship of growth between oocyte diameter and follicular size.     

Pattern of growth of dominant follicles during the oestrous cycle of heifers

Ovarian follicular development was studied in 13 heifers by daily ultrasound examination during 2 complete and consecutive natural oestrous cycles. In 21 cycles (81%) 3 dominant follicles were identified, in 4 cycles (15%) 2 and in the remaining cycle 1 (4%). Consistently, the first dominant follicle was detected on average on Day 4, reached a maximum size on Day 6, went through a period of relative stability between Days 6 and 10, then began to decrease in size and was undetectable by Day 15. The second dominant follicle was detected by Day 12, reached maximum size on Day 16 (or 19 in the 4 cycles in which the 2nd dominant follicle was the ovulatory follicle) and was undetectable by Day 19. The 3rd (ovulatory) follicle was identified on average by Day 16 (range Days 10 to 19) and maximum size was reached on Day 21. The ovulatory follicles were larger (P less than 0.05) than the previous ones and the stage of the cycle at which maximum size was reached was significantly different for each dominant follicle (P less than 0.05). The analysis of the rates of growth and atresia suggest that the rate of growth is slowest during mid-cycle. The number of dominant follicles that developed in the ovary ipsilateral to the corpus luteum was greater (P less than 0.05) than in the contralateral ovary.     

Ovarian response of prepubertal Murrah heifers to exogenous GnRH

The aim of the current study was to evaluate the ovarian follicular response to GnRH at two dose levels in prepubertal Murrah buffalo heifers during hot-humid months. Heifers received 10μg (Group A, n=7) or 20μg (Group B, n=6) of GnRH during the growing phase of the dominant follicle (DF>6mm), as identified by pretreatment regular ultrasound scanning. A similar dose was repeated approximately 30 days later, again coinciding with another growing DF. Post-treatment ovarian activity was studied by alternate day transrectal ultrasonography until 25 days post-second GnRH. In both groups, three types of response were recorded: formation of a corpus luteum (CL), luteinization of the follicle wall, i.e. luteinized follicle (LF) or no response (NR). Pooled data at GnRH injections revealed that the DF diameter in relation to the type of response in Group A heifers was, NR: 6.83±0.17 (n=3), LF: 8.10±0.67 (n=6) and CL: 8.88±0.96mm (n=5), while respective values in Group B heifers were 8.68±0.44mm (n=4), 9.37±0.46 (n=6) and 8.95±0.55mm (n=2). The pattern of response was more evident in Group A but unpredictable in Group B. Corpora lutea developed in response to both the GnRH injections were short-lived. Mean maximum diameter of LFs in Groups A and B were 16.07±0.99 and 16.58±1.20mm respectively and wave duration of these follicles in both groups was 23.33±1.67 and 25.33±1.12 days, respectively. None of the heifers commenced cyclicity following regression of the CL or LF.     

Relationship among the status of the human oocyte, the 17 beta-estradiol concentration in the antral fluid and the follicular size

We studied the relationship among the status of the human oocytes, the E2 concentration in the antral fluid and the follicular size in the different phases of the menstrual cycle, in order to determine the microenvironment of the follicles with healthy or degenerative oocytes in the human ovary. In the follicular phase of the menstrual cycle, follicles which contained a healthy but not degenerative oocyte had a significantly higher level of 17 beta-estradiol (E2). In the late follicular phase, the larger follicles (greater than or equal to 13 mm, in diameter) had only health oocytes. It seems that the follicle containing a degenerative oocyte does not develop physiologically until maturation of the preovulatory follicle. In the luteal phase, there were no relationships among the status of the oocyte, E2 concentration in the antral fluid and the follicular size. However, the E2 levels of the antral follicles with healthy oocytes in an ovary with corpus luteum were significantly lower than those in the contralateral ovary. The results suggest that the corpus luteum may exert an influence on the adjacent follicles.     

Relationship between more follicles in right than left ovary in recently born calves and right ovary propensity for ovulation in cattle

The mechanism for more frequent ovulation from right ovary (RO) than left ovary (LO) was considered by determining if RO of recently born calves had a propensity for more follicles. Rationale was from reports that RO in heifers has more 6-mm follicles before selection of the future ovulatory follicle as well as greater frequency of RO ovulation. Dimensions, weight, and number of follicles per ovary were compared between LO and RO in 10 Holstein calves (age, 1 to 7 days). Weight of an ovary was greater (P < 0.05) for RO (0.393 ± 0.04 g) than LO (0.355 ± 0.05 g). Follicles were delineated by translucency of follicular fluid from transmitted light. Follicles from 0.3 mm diameter (smallest identified) to 4.8 mm (largest present) were counted. Mean number of translucent antral follicles (8.1 ± 1.8 vs 5.3 ± 1.2 follicles) and means for follicle diameter, fluid volume, and surface area were each greater (P < 0.01) for RO than LO. Combined for all diameters (0.3–4.8 mm), the hypothesis was supported that more follicles are present in RO than LO in calves 1 to 7 days of age. Although follicle activity in the fetus has not been compared between LO and RO, more follicles in RO than LO in recently born calves is consistent with the concept that the propensity for RO ovulation is congenital.     

Ovarian follicular dynamics in Nelore breed (Bos indicus) cattle

The most common beef cattle raised in Brazil is the Nelore breed (Bos indicus). Information obtained by ultrasonography on follicular growth in Bos taurus cattle has been accumulating rapidly. However, there are few publications to date on follicular development in Bos indicus breeds. The follicular dynamics in Nelore heifers and cows during natural or prostaglandin (PG)-induced estrous cycle were studied. From the detection of estrus onward, all animals were examined daily by ultrasonography for one (n = 35) or two (n = 10) consecutive estrous cycles. The follicular dynamic in Nelore cattle was characterized by the predominance of 2 follicular waves in the cows (83.3%, n = 18, P < 0.05) and 3 waves in the heifers (64.7%, n = 16, P < 0.05). Most of the cattle observed over 2 consecutive estrous cycles presented the same pattern of follicular waves in the first and second cycle, and only 30% showed variation in the number of waves from one cycle to the other. Most of the follicular parameters analyzed were not affected by PG treatment or age but were altered by follicular waves. Consequently, data on cows and heifers were combined according to the number of follicular waves. The ovulatory follicle was larger than the other dominant follicles (P < 0.05), and the ovulatory wave was shorter than the preceding waves (P < 0.05). The interovulatory interval was longer in animals showing 3 waves than those exhibiting 2 waves (P < 0.05). Maximum diameter of the dominant follicle (around 11 mm) and of the corpus luteum (CL, approximately 17 mm) were smaller than those reported for European breeds. In conclusion, the results demonstrate that although the dominant follicle and corpus luteum are smaller than in European breeds, the follicular dynamics in Nelore cattle were similar to those observed in European breeds and were characterized by 2 or 3 follicular waves for cows and heifers, respectively, during the natural or prostaglandin-induced estrous cycle.