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.     

Follicular and hormonal dynamics during the first follicular wave in heifers

A few days after the first follicular wave emerges as 4-mm follicles, follicular deviation occurs wherein 1 follicle of the wave continues to grow (dominant follicle) while the others regress. The objectives of this study were to characterize follicle growth and associated changes in systemic concentrations of gonadotropins and estradiol at 8-h intervals encompassing the time of follicle deviation. Blood samples from heifers (n = 11) were collected and the ovaries scanned by ultrasound every 8 h from 48 h before to 112 h after the maximal value for the preovulatory LH surge. The follicular wave emerged at 5.8 +/- 5.5 h (mean +/- SEM) after the LH surge, and at this time the future dominant follicle (4.2 +/- 0.8 mm) was larger (P < 0.001) than the future largest subordinate follicle (3.6 +/- 0.1 mm). There was no difference in growth rates between the 2 follicles from emergence to the beginning of the deviation (0.5 mm/8 h for each follicle), indicating that, on average, the future dominant follicle maintained a size advantage over the future subordinate follicle. Deviation occurred when the 2 largest follicles were 8.3 +/- 0.2 and 7.8 +/- 0.2 mm in diameter, at 61.0 +/- 3.7 h after wave emergence. Diameter deviation was manifested between 2 adjacent examinations at 8-h intervals. Mean concentrations of FSH decreased, while mean concentrations of LH increased 24 and 32 h before deviation, respectively, and remained constant (no significant differences) for several 8-h intervals encompassing deviation. In addition to the increase and decrease in circulating estradiol concentrations associated with the preovulatory LH surge, an increase (P < 0.05) occurred between the beginning of deviation and 32 h after deviation. The results supported the hypotheses that deviation occurs rapidly (within 8 h), that elevated systemic LH concentrations are present during deviation, and that deviation is not preceded by an increase in systemic estradiol.     

Morphological characterization of follicle deviation in Nelore (Bos indicus) heifers and cows

Follicle diameter deviation is defined as the beginning of the differential change in growth rates between the largest and next largest follicles subsequent to wave emergence and is considered a key component of follicle selection. Follicle selection has been extensively studied in European breeds of cattle (Bos taurus) but has not been critically studied in Zebu breeds (Bos indicus). The objectives of the present study were to determine and compare the morphological characteristics of deviation associated with the first post-ovulatory wave (Wave 1) of the estrous cycle in Nelore heifers (n=8) and nonlactating cows (n=11). Beginning on the day of ovulation (day 0), the three largest follicles (F1-F3, respectively) were individually tracked every 12 h for 6d using transrectal ultrasonography. In individual animals, deviation was determined graphically using visual inspection of the diameter profiles of F1, F2 and sometimes F3 (observed deviation) and mathematically using segmented regression analysis of the diameter differences between F1 and F2 or sometimes F3 (calculated deviation). Mean day of emergence of Wave 1 when F1 reached >3 mm (approximately 1 d after ovulation) and growth rate of F1 during deviation (approximately 1.4 mm/d) were not significantly different between heifers and cows. The results of determining the beginning of deviation within heifers and cows using the observed and calculated methods were not significantly different. Averaged over both methods, diameter deviation occurred 2.8 d after ovulation when F1 reached 5.7 mm in heifers, and 2.4 d after ovulation when F1 reached 6.1 mm in cows. In conclusion, the emergence of Wave 1 and growth rates and diameters of the future dominant follicles at the beginning of deviation were similar in Nelore heifers and nonlactating cows, regardless of the methods used to determine deviation. Relative to Holstein cattle, emergence of Wave 1 appeared to occur about 1 d later and diameter of the future dominant follicle at the beginning of deviation was about 2 mm smaller in Nelore.     

Exogenous progesterone enhances ova and embryo quality following superstimulation of the first follicular wave in Nelore (Bos indicus) donors

Three experiments were conducted to evaluate the effects of exogenous progesterone on superovulatory response and ova/embryo quality in Bos indicus donors superstimulated during the first follicular wave (FFW). We hypothesized that exogenous progesterone during gonadotropin treatments would improve ova and embryo quality. In Experiment 1, 18 Nelore cows were randomly allocated to three groups: (1) FFW; (2) FFW plus a progesterone-releasing device (FFW+P4); and (3) control (E2+P4). Cows in the FFW groups were superstimulated beginning at synchronized ovulation, whereas cows in the control group were superstimulated after synchronization of follicular wave emergence with estradiol plus progesterone (E2+P4). There were no differences in mean (± SD) numbers of transferable embryos between FFW+P4 (8.0 ± 4.5) and control (6.7 ± 4.8) groups, but both were higher (P = 0.006) than the FFW group (0.2 ± 0.4). In Experiment 2, FFW and FFW+P4 were compared in 20 Nelore donors; exogenous progesterone increased the number of transferable embryos (3.9 ± 3.4 vs. 1.3 ± 4.1, P = 0.003). In Experiment 3, FFW and FFW+P4 were compared in 10 Nelore donors except that cows were slaughtered 12 h after pLH (Lutropin-V^®, Bioniche Animal Health, Belleville, ON, Canada) treatment. More mature cumulus oocyte complex (COC) (expanded cumulus cell layers) were collected in the FFW+P4 group than in the FFW group (21.8 ± 13.1 vs. 10.8±14.7; P = 0.003). In summary, superovulatory response was satisfactory when FSH (Folltropin-V^®, Bioniche Animal Health) treatment was initiated at emergence of the first follicular wave in Nelore (Bos indicus) donors, and the hypothesis that administration of exogenous progesterone during the treatment will improve oocyte and embryo quality was supported.     

Plasma concentrations of progesterone, 17beta-estradiol and androstenedione and superovulatory response of Nelore cows (Bos indicus) treated with FSH

Progesterone (P(4)), 17beta- estradiol (E(2)) and androstenedione (A(4)) plasma concentrations were correlated with palpated corpora lutea (CL), recovered embryos and viable embryos in 13 Nelore cows induced to superovulate with FSH, starting on Day 10 of the estrous cycle. Administration of FSH increased the number of ovulations and recovered embryos. Plasma P(4), E(2) and A(4) levels on Day 0 and of P(4) on Days 10 and 11 of the cycle were not correlated with the superovulatory response. Determination of CL by palpation per rectum was used to estimate the number of recovered embryos. Plasma P(4) levels higher than 1 ng/ml on the induced estrus day (Day 14) had an adverse effect on the embryo viability rate. Plasma E(2) concentrations on Day 14 were positively correlated with the number of viable embryos collected, a correlation that has not been previously reported. The present data indicate that plasma P(4) and E(2) concentrations in FSH-PGF2alpha-treated Nelore cows are useful for the identification of 2 different populations of Nelore donors and are correlated with superovulatory response and, particularly, with the number of viable embryos.     

Plasma progesterone concentration in Bos taurus and Bos indicus heifers

Progesterone concentrations were determined by radioimmunoassay in the plasma of heifers of German Brown Swiss, Holstein-Friesian and White Fulani cattle during two consecutive estrous cycles in the dry and wet seasons in a tropical climate. Seasonal differences in the levels were not significant but peak levels were significantly higher in the $\text{Bos}$$\text{taurus}$ than in the $\text{Bos}$$\text{indicus}$ heifers. The low levels at estrus and the gradual rise five days after estrus were similar among the heifers. The levels on the 1st and 2nd days preceding estrus were significantly higher in the $\text{Bos}$$\text{taurus}$ than in the $\text{Bos}$$\text{indicus}$ heifers, and suggest a possible tendency for the former to be more susceptible to infertility arising from high progesterone levels 1 and 2 days preceding estrus and insemination. The genital tract and ovaries at the mature luteal phase were generally smaller in the $\text{Bos}$$\text{indicus}$ than in the $\text{Bos}$$\text{taurus}$ heifers.     

Follicle deviation and ovulatory capacity in Bos indicus heifers

The objectives of Experiment 1 were to determine the interval from ovulation to deviation, and diameter of the dominant follicle (DF) and largest subordinate follicle (SF) at deviation in Nelore (Bos indicus) heifers by two methods (observed and calculated). Heifers (n = 12) were examined ultrasonographically every 12 h from ovulation (Day 0) to Day 5. The time of deviation and diameter of the DF and largest SF at deviation did not differ (P>0.05) between observed and calculated methods. Overall, deviation occurred 2.5+/-0.2 d (mean +/- S.E.M.) after ovulation, and diameters for DF and largest SF at deviation were 6.2+/-0.2 and 5.9 +/- 0.2 mm, respectively. Experiment 2 was designed to determine the size at which the DF acquires ovulatory capacity in B. indicus heifers. Twenty-nine heifers were monitored every 24 h by ultrasonography, from ovulation until the DF reached diameters of 7.0-8.4 mm (n=9), 8.5-10.0 mm (n=10), or >10.0 mm (n=10). At that time, heifers were treated with 25 mg of pLH and monitored by ultrasonography every 12 h for 48 h. Ovulation occurred in 3 of 9, 8 of 10, and 9 of 10 heifers, respectively (P<0.05). In summary, there was no significant difference between observed and calculated methods of determining the beginning of follicle deviation. Deviation occurred 2.5 d after ovulation when the DF reached 6.2 mm, and ovulatory capacity was acquired by DF as small as 7.0 mm.     

Proteome analysis of Nelore bull (Bos taurus indicus) seminal plasma

The Nelore bull (Bos taurus indicus) seminal plasma proteome was analyzed by MALDI-TOF MS and two-dimensional gel electrophoresis. A total of 260 spots were visualized in the 2-DE gel (pI range 3-10) and 13 spots could be identified by peptide mass fingerprinting corresponding to 11 different polypeptides. The results allowed the creation of the first proteomic map of Bos taurus indicus seminal plasma. The roles of the identified proteins in the bull seminal plasma are discussed.     

Follicular dynamics during postpartum anestrus and the first estrous cycle in suckled or non-suckled Brahman (Bos indicus) cows

Brahman (Bos indicus) cows, were selected at 28+/-10 days after calving and analyzed by real time rectal ultrasonography three times a week, in order to evaluate and compare follicular and corpus luteum development during postpartum (PP) anestrus and the first PP estrous cycle under sylvopastoril conditions. Suckling (S, n=11) or non-suckling (NS, n=5) cows were evaluated in a zone of tropical dry forest (450m of altitude, mean temperature=27 degrees C, annual rainfall=1000mm). Estrous detection was performed twice daily by direct observation. Progesterone was quantified using RIA. From 28+/-10 days postcalving to resumption of estrous cycles, there were no differences (P>0.05) between NS and S cows for diameter of the dominant or first subordinate follicle, follicular growth rate, or interdominance interval. Silent ovulation, corpus luteum formation and subsequent progesterone concentrations ranging from 0.3 to 9. 7ng/ml, were found in both groups. The first calving to ovulation and calving to standing estrus intervals were shorter (P<0.01) in NS (34.8+/-5.81 and 41.2+/-9.03 days) than in S (65+/-4.82 and 81+/-6. 21 days) cows. Follicular development and progesterone concentrations during the first PP estrous cycle did not differ (P>0. 05) between NS and S cows. These results suggest that Brahman cows could have an early PP resumption of follicular recruitment if fed under sylvopastoril system conditions. However, non-suckled cows did have an earlier standing estrus and ovulation than did suckled cows.     

Peripheral plasma progesterone concentration in zebu (Bos indicus) cows during pregnancy

Plasma progesterone concentrations were determined weekly during gestation averaging 283 +/- 2 d in Ethiopian zebu (Bos indicus) cows. Mean progesterone levels increased from 0.2 +/- 0.1 ng/ml at oestrus (service) to 3.1 +/- 1.6 ng/ml on d 7 and 8.1 +/- 2.1 ng/ml on d 21. Progesterone levels remained elevated throughout pregnancy. Hormone concentration differed significantly between cows (P less than 0.001) and with the wk of pregnancy (P less than 0.05); it tended to be higher during the last trimester of pregnancy. Mean levels dropped sharply to below 1 ng/ml during the last wk of pregnancy with considerable variation (C.V. = 39 to 63%) among cows. These data indicate that pregnancy in Ethiopian zebu cows can be reliably diagnosed by determining circulatory plasma progesterone levels.     

Effect of follicular wave stage on potential fertility predictors and their repeatability coefficient in prepubertal Bos indicus (Nellore) and Bos taurus (Caracu) heifers

In an attempt to develop accessible methods for the precocious individual selection based on phenotypic attributes related to reproductive superiority, this study evaluated the effects of follicular wave stages (emergence and dominance) and the repeatability coefficients of potential fertility predictors (vulvar morphometry, uterine biometry, echogenicity and echotexture, ovarian biometry, and antral follicle count – AFC) in two breeds of purebred prepubertal heifers. Nellore (n = 30) and Caracu (n = 28) heifers were submitted to a sequence of 11 evaluations conducted every 48 h (D0 – random day of the antral follicular wave until D20) to study potential fertility indicators under natural conditions. The data obtained were compared according to breed and follicular wave stage. Statistical analysis included the fixed effects of breed, evaluation day, and their statistical interaction and was performed using MIXED, GENMOD, GLM, and CORR procedures of the SAS program. Breed was found to influence rima height, ovarian area, and AFC, which were greater in Nellore heifers (P < 0.02). The follicular wave stage also influenced most of the potential predictors, highlighting AFC which was higher in the presence of a dominant follicle in both breeds (P < 0.0001). The repeatability coefficients for vulvar width (0.76 and 0.66), ovarian area (0.70 and 0.62), and AFC (0.76 and 0.74) were considered to be high in Nellore and Caracu heifers, respectively. Only ovarian biometry was able to predict AFC (Pearson correlation coefficient ≥ 0.66; P < 0.0001) in prepubertal heifers. The results indicate that most of the phenotypic reproductive parameters analyzed can be characterized throughout prepuberty using a single measure since they are intrinsic attributes of the individual.     

Alterations in follicular IGFBP mRNA expression and follicular fluid IGFBP concentrations during the first follicle wave in beef heifers

The objective was to determine the pattern of IGFBP-2, -3 and -4 gene expression and follicular fluid concentrations of IGFBP-2, -3, -4 and -5 during emergence, selection and dominance of the first follicle wave of the estrous cycle in cattle and during exogenous steroid treatment. Heifers (n = 35) were ovariectomized at 36 (n = 7), 66 (n = 8), 84 (n = 12) and 108 (n = 8) h after the onset of estrus. Heifers in the 84 h ovariectomy group were sub-divided to receive either no treatment (n = 6) or were treated with a progesterone-releasing intravaginal device (n = 6, PRID) and 0.75 mg estradiol benzoate i.m. at the approximate time of ovulation, 30 h post estrus until ovariectomy. Within heifers the four largest follicles recovered following ovariectomy were ranked on size (F1, F2, F3 and F4). At 36 h IGFBP gene expression and follicular fluid IGFBP concentrations were similar in all follicles (F1-F4). Mean diameter of the F1 follicle increased (P < 0.05) between 36 and 84 h with no difference between 84 and 108 h. The F1 follicle had the highest (P < 0.05) concentration of estradiol compared with the F2, F3 and F4 at 84 and 108 h. There was no granulosa cell IGFBP-2 mRNA in F1 follicles at 84 or 108 h. Intrafolliclar IGFBP-2 concentrations were lower (P < 0.05) in the F1 compared with F3 and F4 follicles at 108 h. There was no difference in theca cell IGFBP-4 mRNA expression at 108h, but amounts of follicular fluid IGFBP-4 were lower (P < 0.05) in F1 follicles compared with F3 and F4 follicles at 108 h. IGFBP-3 mRNA was localized in the theca layer of all follicles examined with no difference in expression or follicular fluid concentrations during emergence, selection and dominance of the first follicle wave. IGFBP-5 concentrations were higher (P < 0.05) in follicular fluid of F3 follicles at 108 h compared with the F3 at 36 h. In conclusion follicular dominance was associated with low or decreased follicular fluid concentrations of IGFBP-4 and -5, increased estradiol and differential regulation of IGFBP production.     

Follicular dynamics around the recruitment of the first follicular wave in the cow

The present study aimed to test the generally accepted view that a follicular wave starts with follicles newly recruited from the population smaller than 3 mm, which later compete for dominance. According to this view, subordinate follicles are expected to be too atretic to join the next follicular wave. Ten cows were ovariectomized shortly prior to the LH surge, thus around the start of the first follicular wave of the cycle. Per cow, on average, 14.4 follicles of >/=3 mm were dissected. Follicular health was determined on the basis of four parameters: 1) judgment of the degree of atresia by stereomicroscope, 2) incidence of apoptotic nuclei among the granulosa cells, 3) estradiol and progesterone concentrations, and 4) insulin-like growth factor-I (IGF-I) binding proteins (IGFBPs)-2, -4, and -5 concentrations in the follicular fluid. In addition to the preovulatory follicle, 3.1 other follicles, mainly sized 3-4.5 mm, were found to be healthy based on the proportion of apoptotic nuclei, and concentrations of estradiol/progesterone, and IGFBPs. The ability of these follicles to respond with growth on the preovulatory and periovulatory FSH surges was supported by a comparison to the follicular population of four cows 31-68 h after the LH surge. The present results point to an alteration of the view on the follicular wave. The larger follicles during the first days of the follicular wave are, in general, derived from follicles that also joined the previous wave. A portion of these growing follicles are estradiol active and compete for dominance. Other growing follicles lack estradiol production and are probably derived from rather atretic follicles. The first newly recruited follicles do not reach the size of 3 mm before 31 h after the preovulatory FSH surge. At that time, the larger follicles are already competing for dominance.     

Fertility on synchronized estrus in crossbred (Bos taurus x Bos indicus) heifers

This study was performed in Western Maharastra (India). The 272 crossbred heifers were randomly allocated within herds to one of the four following groups: 1) silastic coils, 10 days treatment (n = 65); 2) Norgestomet implants, 10 days treatment (n = 71); 3) prostaglandin F(2alpha) two injections 11 days apart (n = 70); and 4) control (n = 66). Almost all heifers in the treated groups were detected in heat during the four days following treatment (88-100%) vs 26% in the control group in the first 21 days. Mean conception rates at first AIs were respectively 62,48 and 60% in groups 1,2 and 4 (p > 0.05) and only 29% in group 3. By 90 days after treatment, 66, 59, 46 and 33 per cent of the females were pregnant for groups 1 to 4, respectively (p < 0.001). In conclusion, progestogen treatments seemed to be highly satisfactory both in terms of conception rates and intervals from treatment to pregnancy.     

Plasma concentration of progesterone during normal estrous cycles and following prostaglandin F(2alpha) treatment of Bos indicus and tropic-adapted Bos taurus heifers

The introduction of the use of prostaglandin F(2alpha) (PGF(2alpha)) to synchronize estrus in cattle adapted to the tropics suggests a need to investigate the endocrine response to this treatment. Progesterone (P) concentrations in blood plasma of Bos indicus and tropic-adapted Bos taurus heifers during normal estrous cycles and following estrus synchronization were compared. After PGF(2alpha) administration, the heifers were divided into two groups on the basis of response to treatment. Mean P levels in heifers showing estrus after the first injection ranged from 1.0-3.0 ng/ml, decreasing to 0.2-0.4 ng/ml 24 to 48 hr after treatment. The second group exhibited estrus only after the second PGF(2alpha) injection and had low P (0.2-0.9 ng/ml) in plasma before the first injection. Mean peak P levels in both groups 8 to 12 d after the first injection in the periestrous period were not different from values in the same heifers at similar periods of the preceding control estrous cycle. Neither the tropical location nor breed affected the luteolytic effect of PGF(2alpha).     

Ovarian function in Nelore (Bos taurus indicus) cows after post-ovulation hormonal treatments

Maternal recognition of pregnancy in the cow requires successful signaling by the conceptus to block luteolysis. Conceptus growth and function depend on an optimal uterine environment, regulated by luteal progesterone. The objective of this study was to test strategies to optimize luteal function, as well as prevent a dominant follicle from initiating luteolysis. Nelore (Bos taurus indicus) beef cows (n=40) were submitted to a GnRH/PGF(2alpha)/GnRH protocol. Cows that ovulated from a dominant ovarian follicle (ovulation=Day 0) were allocated to receive: no additional treatment (G(C); n=7); 3000IU of hCG on Day 5 (G(hCG); n=5); 5mg of estradiol-17beta on Day 12 (G(E2); n=6); or 3000IU of hCG on Day 5 and 5mg of estradiol-17beta on Day 12 (G(hCG/E2); n=5). Ultrasonographic imaging of the ovaries, assessment of plasma progesterone concentration, and detection of estrus were done daily from Day 5 to the day of subsequent ovulation. Treatment with hCG induced an accessory CL, increased CL volume, and plasma progesterone concentration throughout the luteal phase (P<0.01). Estradiol-17beta induced atresia and recruitment of a new wave of follicular growth; it eliminated a potentially estrogen-active, growing ovarian follicle within the critical period for maternal recognition of pregnancy, but it also hastened luteolysis (Days 16 or 17 vs. Days 18 or 19 in non-treated cows). In conclusion, the approaches tested enhanced luteal function (hCG) and altered ovarian follicular dynamics (estradiol-17beta), but were unable to extend the life-span of the CL in Nelore cows.     

Effects of biostimulation and nutritional supplementation on pubertal age and pregnancy rates of Nelore heifers (Bos indicus) in a tropical environment

To determine effects of biostimulation (BIO) and dietary supplementation (BIO+S) on pubertal age and pregnancy rates, Nelore heifers (n=392) were randomly assigned to one of four treatment groups (n=98/group). All animals were in tropical environmental conditions, in the middle-west region of Brazil, grazing in pastures of Brachiaria brizantha, cv. Marandu; Panicum Maximum, cv. Tanzania and Brachiaria humidícula. The heifers of the BIO group were kept in the presence of bulls while being maintained on pasture; the animals in the BIO+S group were kept in the presence of bulls while being managed on pasture and were fed a diet with greater energy and protein content to produce 0.49 kg of BW gain/day; the animals in control group (the NBIO) were kept away from bulls and under pasture conditions; and the animals in the NBIO+S group were kept away from bulls, were maintained on pasture, and were fed the same diet as the BIO+S group. Heifers were bred at 22-23 months of age, and pregnancy diagnosis was made 45 days after the end of the breeding season. There were differences (P<0.05) between groups regarding pubertal heifers up to 19 months (NPH), final body weight (FBW) and pregnancy rates (P<0.01), with an advantage for the animals in the BIO and BIO+S groups. Although the effect of a diet with greater protein and energy content was not clear in this experiment, the exposure of heifers to a male during the prepubertal period decreased age at the first breeding season, resulting in a significant reduction in age of first pregnancy in Nelore heifers kept under extensive management systems in a tropical environment.     

Ovarian follicular dynamics in suckled zebu (Bos indicus) cows monitored by real time ultrasonography

The pattern of follicular growth was studied in 17 suckled zebu cows with average body condition and under extensive management in a tropical environment (23 degrees C, 78% humidity; 2200 mm annual rainfall; 1000 m altitude). The study covered the period from parturition to weaning at 12 months postpartum (PP). Data were collected by transrectal ultrasonography (7.5 MHz) at 48 h intervals, and progesterone (P4) measurements were performed by RIA. The sequential development of ovarian follicles greater than 4 mm was followed until regression or ovulation. Ovarian activity as characterized by growth and regression of follicles of 4 to 6 mm, with sporadic dominance, and a long interdominance interval was observed in every cow and from as early as 26 +/- 2 days PP. This follicular pattern was highly variable during the first 6 months: cows presented 2 to 20 follicular waves (FW) in which a dominant follicle (DF) grew to 8 +/- 1 mm with daily growth rates of 1.1 +/- 0.5 mm/day. The duration of dominance varied from 2 to 8 days and the interdominance time interval was 0 (overlapped waves) to 60 days. Neither behavioural oestrus nor ovulation was observed during this period. From 6 to 12 months PP, cows presented 7 to 20 FW, some with ovulation and/or corpora lutea (CL) formation. The ovulation was preceded by oestrus in some cases (43%). The mean (+/- sem) diameter of DF was 9 +/- 2.7 mm, their mean growth rate 1.4 +/- 0.2 mm/day, their duration of dominance was 2 to 8 days and the interdominance interval was 0 to 14 days. Progesterone concentrations (P4) from 1.0 to 13 ng/ml were found when a CL was present. Once cyclicity re-commenced at 217 to 278 days PP, the cows presented either normal (21 +/- 3 days), short (10 +/- 2 days), or long (50 +/- 4 days) cycles. The resumption of cyclicity was characterized by an increased frequency of emerging follicular waves. Under the conditions of this study, the suckled Bos indicus cows re-commenced ovarian follicular activity as early as described in B. taurus breeds, but the establishment of cyclicity was substantially later. These data add further to the panorama of postpartum reproductive physiology in tropical cattle.     

Comparison of three methods of acute administration of progesterone on ovarian follicular development and the timing and synchrony of ovulation in Bos indicus heifers

The aim of this study was to induce the formation of a persistent dominant ovarian follicle and to compare the effects of 3 methods of acute administration of P4 on ovarian follicular development and on the timing and synchrony of ovulation. Stage of the estrous cycle was initially synchronized in Bos indicus heifers with a norgestomet implants (3 mg) for 10 d and with an analogue of PGF2 alpha (15 mg) on the first and last day of norgestomet treatment. Eight days after removal of the implants, heifers were randomly assigned to 4 groups. All heifers received a norgestomet implant (Day 0), which was removed 17 d later (Day 17); PGF2 alpha was administered on Days 0 and 4. Heifers in the control group (n = 5) received no other treatment. On Day 10 heifers in Group P4C (n = 5) were treated with a CIDR for 24 h; heifers in Group P4O (n = 5) were administered 100 mg i.m. of P4 in oil, while heifers in Group P4S (n = 5) were administered 100 mg i.m. of P4 in saline/alcohol. Data were analyzed using bootstrap estimates of location (mean) and spread (standard deviation; SD). Compared with the control heifers, day of emergence of the ovulatory follicle was delayed, and age and duration of dominance of the ovulatory follicle were reduced in the P4C and P4O heifers (P < 0.05) but not in the P4S heifers (P > 0.05). In all groups treated with P4 both the mean and variability (SD) in the timing of ovulation did not differ with that of the control group (P > 0.05) but there was less variability in the day of emergence, age, duration of dominance and diameter of the ovulatory follicle than in the control group (P < 0.05). Delayed timing and reduced synchrony (SD) of ovulation and greater age of the ovulatory follicle (P < 0.05) occurred in P4S heifers than in P4C heifers. We conclude that administration of 100 mg of P4 in oil is as effective as treatment with a CIDR for synchronizing emergence and ovulation of a newly recruited dominant follicle. However, reduced synchrony of ovulation, greater age of the ovulatory follicle and delayed timing of ovulation occurred following administration 100 mg of P4 in saline/alcohol compared with the CIDR device.     

LH and FSH concentration and follicular development in Nellore heifers submitted to fixed-time artificial insemination protocols with different progesterone concentrations

Nine heifers were pre-synchronized (PGF2α, 12 days) and assigned into three groups with 6 repetitions each: (1) CL (～8 days old, n=13); (2) DIB+CL (n=18); (3) DIB+EB (150 μg of PGF2α and 2mg estradiol benzoate, n=18). After progesterone (P4) device removal (8 days) and/or final PGF2α, heifers were injected with either GnRH or EB in a 3×2 factorial totalling 49 observations (5 were excluded). The blood sampling schedule: every 12 h during P4 period; for LH pulse frequency on Days 3-5, every 15 min for 6 h during P4 period; after P4 removal and EB treatment, samples were collected every 3 h for 24 h or after GnRH every 1 h for 10 h. Ovarian follicle number and diameter were evaluated by ultrasonography every 12 h until the last blood sample and then 24 h and 48 h later. After device insertion (12 h), the DIB+CL group had a lesser LH concentration than the DIB+EB group. After 36 h, all DIB+CL-treated heifers had less LH than CL-heifers, and after 60 h, the DIB+EB group had less LH than the CL-group. Considering all P4 groups combined, LH peak amplitude was greater after GnRH compared to EB treatment but total area of LH peak amplitude and time to first peak was less. The CL-group had fewer follicles and a greater largest follicle diameter than DIB+CL and DIB+EB groups. When treated with EB, the DIB+CL group had a lesser ovulation rate at 24 h than the CL- and DIB+EB-groups. Fixed time artificial insemination (FTAI) protocols promoted a pre-ovulatory LH peak, independent of previous exposure to the DIB coupled with a CL or not. The progesterone excess interfered with FSH and LH secretion, follicular development and ovulation within 24 h.