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

Evolution over the last 40 years of the assisted reproduction technologies in cattle - the Brazilian perspective I - timed artificial insemination

The reproductive efficiency of the herd is correlated with higher productivity in livestock. Reproduction biotechniques, such as ovulation synchronization protocols, are important to optimize production and accelerate genetic profit in beef and dairy herds. The objective of this review is to describe the evolution over the last 40 years of the artificial insemination (AI) and the timed-AI (TAI) protocols in cattle from a Brazilian perspective. TAI protocols are based on synchronizing emergence of the wave of follicular growth, controlling circulating progesterone (P4) concentrations, stimulating the final growth of the follicle and inducing a synchronized ovulation. Hormonal alternatives that optimize the response at the end of the protocol and strategies to induce final follicle growth and ovulation in categories of females with low expression of estrus are described. Furthermore, the potential positive effect of previous exposure to injectable P4 on fertility of Bos indicus and Bos taurus cows is also discussed.

Prevalence and risk factors related to anovular phenotypes in dairy cows

The objective of the current study was to evaluate the relationship of body condition score (BCS) at 35 d in milk (DIM), milk production, diseases, and duration of the dry period with prevalence of anovulation at 49 DIM and then, specifically, with the prevalence of each anovular phenotype. We hypothesized that anovular follicular phenotypes, classified based on maximal size of the anovular follicle, have different etiologies. A total of 942 lactating Holstein cows (357 primiparous and 585 multiparous) from 1 herd had ovaries evaluated by ultrasonography at 35 ± 3 and 49 ± 3 DIM to detect the absence of a corpus luteum (CL), and to measure the diameter of the largest follicle. Cows were classified as cyclic at 49 DIM if a CL was observed in at least 1 of the 2 examinations, or anovular if no CL was observed at either examination. Cows considered anovular were divided into 3 groups based on the largest diameter of the largest follicle as follows: ranging from 8 to 13 mm, 14 to 17 mm, or ≥18 mm. Cows were evaluated for the following diseases: retained placenta, metritis, hyperketonemia, mastitis, lameness, respiratory problem, and digestive problem. At 35 DIM, BCS was determined, and milk yield for individual cows was recorded. A total of 28.5% (268/942) of cows were classified as anovular. Anovular cows had longer dry periods (90 vs. 71 d) and smaller BCS than cyclic cows (2.83 vs. 2.99). Cows with a single disease or multiple diseases had 2 and 3-fold increase in odds of being anovular, respectively. Anovular cows had follicles that ranged from 4 to 50 mm. The prevalence of anovular phenotype, among anovular cows, that had the diameter of the largest follicle ranging from 8 to 13 mm, 14 to 17 mm, and ≥18 mm was 29.9 (79/264), 37.5 (99/264), and 32.6% (86/264), respectively. Anovular cows with follicles of 8 to 13 mm had longer dry periods than those with follicles ≥18 mm (104 vs. 74 d), whereas anovular cows with medium size follicles had intermediate days dry (99 d). Cows with small and medium anovular follicles had smaller BCS and greater prevalence of multiple diseases than cyclic cows. For almost all risk factors, the cows with large anovular follicles (≥18 mm) were similar to cyclic cows and different from cows with smaller anovular follicles (8-13 mm). Thus, longer dry periods, less BCS at 35 DIM, and diseases were risk factors for anovulation. Moreover, the risk factors for the 3 distinct anovular follicle phenotypes differed.

Injectable progesterone in timed artificial insemination programs in beef cows

The aims of this study were I) to compare the follicular diameter, corpus luteum diameter and serum progesterone (P4) concentrations in cows treated with conventional protocol vs. injectable P4 protocol; II) to determine the serum P4 profile in ovariectomized heifers; and III) to compare pregnancy rate between protocols. In experiment I, multiparous cows received a protocol for ovulation synchronization with an intravaginal P4 device (n = 38; device + EB day 0; device removal + PGF2α + eCG + EC day 8) or injectable P4 (n = 38; injection + EB day 0; PGF2α + eCG + EC day 8). In experiment II, ovariectomized heifers (n = 8) were treated with injectable P4 and blood samples were collected to determine the serum P4 profile. In experiment III, multiparous cows were timed AI with two different P4 approaches, intravaginal P4 device (n = 48) or injectable P4 (n = 47). In the first experiment, cows treated with P4 device had higher (P < 0.05) diameter of dominant follicle after ovulation induction (11.6 ± 1.8 vs.10.3 ± 1.8 mm) and ovulation rate (97%, 37/38 vs. 47.3%, 18/38) than cows treated with injectable P4. But, the follicular growth daily was higher (P < 0.05) in cows treated with injectable P4 than intravaginal device (1.3 ± 0.4 vs. 1.0 ± 0.3 mm/day, respectively). In experiment II, the P4 concentration peak occurred within 48 hours (6.54 ng/mL) and decreased after 96 hours (P < 0.05) after P4 injection. In experiment III, cows with P4 device had higher (P < 0.05) pregnancy rate than the injectable P4 group (60.4 vs. 34.0%, respectively). These results demonstrate that although the intravaginal P4 devices showed a higher pregnancy rate, a protocol with injectable P4 represents an easier method and a promising alternative for TAI in cattle.

Plasma PGFM and progesterone concentrations, luteolysis moment and estrous cycle length in Nelore cows submitted to uterine biopsies

ABSTRACTIn this study, endometrial samples were collected in 14 Nelore cows on days zero (ovulation), five, nine, thirteen and nineteen of the estrous cycle (biopsy group), and in 15 females these collections weren't performed (control group). Biopsies were done on the uterine horn endometrium contralateral to the ovary with corpus luteum. Blood samples were taken at -24, -16, -8, 0 +8, +16 and +24 hours in relation to progesterone drop (<1ng/mL, zero moment) and evaluated for 13, 14-dihydro-15-keto prostaglandin F2-alpha (PGFM) by radioimmunoassay (RIA). Plasma progesterone concentration was determined by RIA every 24 hours. Data were analyzed by ANOVA using the PROC GLM and MIXED of the SAS. The mean value for PGFM during the entire period evaluated was greater in the biopsy group. The mean concentration of PGFM at moment zero was not different between the groups; the mean concentration of PGFM was higher in the biopsy group before and after the drop in progesterone level. The maximum mean concentration observed was not different between the groups; however, the mean minimum concentration was different with high values in the biopsy group. Although the PGFM concentrations were higher in the biopsy group, the biopsy and control groups had similar length of estrous cycle showing that repeated endometrial biopsy on the side contralateral to the ovary with corpus luteum does not affect luteolysis and the length of the estrous cycle.

Relationship between growth of the preovulatory follicle and its steroidogenic activity on the onset and expression of estrus behavior in CIDR-treated Bos indicus cows: an observational study

Estrus synchronization induces cows to gather in sexually active groups (SAGs) composed of females displaying mounting activity. Although this technique promotes the enhancement of sexual behavior, there are cows in estrus (CE) that delay estrus expression and also cows not displaying estrus (CNDE) even in the presence of a preovulatory follicle (PF). To elucidate the physiological mechanisms of the delay in the onset of estrus or absence of estrus behavior, an observational study was undertaken in 17 Bos indicus cows treated with exogenous progesterone (CIDR) to synchronize estrus and to monitor follicular growth and its steroidogenic activity. After SAGs formation, cows were ovariectomized at 24, 48, and 72 h post-CIDR. Among ovariectomized groups there were only 9 CE which: 1) showed differences in the onset of estrus; 2) displayed distinctive follicular growth patterns; and 3) at 72 h produced the highest intrafollicular estradiol concentration, and showed a linear trend to increase expression of P450scc and P450arom. Comparison of CE vs. CNDE showed that: 1) both groups had progesterone levels indicative of cyclic activity, and a PF which grew at a similar rate and size; 2) CE showed a stronger association between time and growth; and 3) CE produced more intrafollicular estradiol and progesterone, together with the expression of higher levels of P450arom. Results suggest that pending on the pattern of growth of the PF and its steroidogenic potential to produce estradiol, the onset and expression of estrus behavior may be delayed probably until the establishment of the appropriate conditions to ensure ovulation.

Follicular turnover and hormonal association in postpartum goats during early and late lactation

To clarify the effect of lactation period on ovarian follicular activity and associated hormonal levels in goats, six goats were monitored daily by ultrasonographic examination with blood sampling during early (Days 5 to 25; Day 0 was the day of kidding) and late (Days 40 to 60) lactation. While the presence of a corpus luteum of pregnancy retarded follicular growth in the ipsilateral ovary until Days 11-13 postpartum, the total follicular number (TFN) and area (TFA) increased during late lactation due to the significant increase in the number of medium- and large-sized follicles and decrease in the number of small follicles. Four goats showed a similar pattern of follicular development during the period studied characterized by the emergence of five and six waves during the early and late lactation, respectively. The largest follicle diameter of the first three waves monitored during early lactation was significantly smaller as compared with the diameter of those existing during late lactation. TFN showed a positive correlation with FSH but showed a negative correlation with immunoreactive (ir-) inhibin and estradiol during the postpartum period. TFA was positively correlated with ir-inhibin, estradiol and PRL and negatively correlated with FSH during the monitored periods. The plasma levels of ir-inhibin and progesterone were significantly higher during late lactation compared with the levels recorded during early lactation. Ir-inhibin levels showed a significant positive correlation with LH and estradiol during early and late lactation but showed a negative correlation with FSH during the whole lactation period. LH was positively correlated with estradiol and PRL during early and late lactation, respectively. These results suggest that the lactation period has a detrimental effect on ovarian activity during the early postpartum period in goats.

Postpartum follicular development in Brahman cows under two stocking rates

The aim was to study postpartum follicular population dynamics in Brahman cows in the Mexican humid tropics and under different stocking rates. Lactating adult cows (n = 104) grazed native grammas (Paspalum spp., Axonopus spp.) under two stocking rates: 2.8 (high) or 1.7 (low) cows/ha. Follicle numbers and their size (millimetres) were measured by ovarian ultrasound scanning. Animals detected in oestrus and inseminated were taken out of the study. Both stocking rates produced similar (P < 0.05) body condition scores (BCS) and follicular dynamics. The percent of follicles, averaged over stocking rates, of <4 mm diminished and those of 5-8 mm increased with time, whilst those of >9 mm remained constant; respective values for the previously mentioned sizes were 60 days postpartum (n = 101), 49%, 56% and 5%; 120 days (n = 70), 28%, 66% and 6%; and 180 days (n = 15), 9%, 79% and 12%. There was a positive correlation between BCS and follicle number for size <4 mm (r = 0.73, P < 0.01), whilst for size 5-8 mm, this was negative (r = -0.51, P < 0.05), for follicles >9 mm, no difference was found (r = -0.08, P > 0.05). It was concluded that stocking rate did not affect follicular population dynamics of Brahman cows, but BCS dictated the number and categories of follicles present regardless of the stocking rate utilised.

The use of hormonal treatments to improve reproductive performance of anestrous beef cattle in tropical climates

Most of the world's bovine herd is found in tropical regions. Bos indicus predominates, due to their adaptation to the climate and management conditions. Anestrous is the main factor that negatively affects reproductive performance of animals bred in these regions of the globe. Several factors affect postpartum anestrous, including suckling and maternal-offspring bond, and pre- and postpartum nutritional status. The short duration of estrus and the tendency to show estrus during the night, greatly affect the efficiency of artificial insemination (AI) programs in B. indicus cattle managed in tropical areas. Several restricted suckling or weaning procedures (temporary or permanent), and hormonal treatments have been used to induce ovulation and cyclicity in postpartum cows. Most hormonal treatments are based on progesterone/progestogen (P4) releasing devices associated with estradiol benzoate (EB), or a combination of GnRH/PGF(2alpha)/GnRH (Ovsynch). Treatments with GnRH/PGF(2alpha)/GnRH has presented inconsistent results, probably due to the variable number of cows in anestrous. Treatments using P4 devices and EB have resulted in apparently more consistent results than Ovsynch programs in B. indicus cattle; however, pregnancy rates are low in herds presenting high anestrous rates and moderate to low body condition. The addition of an eCG treatment at the time of device removal, which increased plasma progesterone concentrations and pregnancy rates in anestrous postpartum suckled B. indicus cows, may be useful to improve reproductive performance of beef cattle in tropical climates.

Pattern and manipulation of follicular development in Bos indicus cattle

Bos indicus cattle are widespread in tropical regions due to their adaptation to these environments. Although data on reproductive performance have indicated both inferior and superior results for B. indicus cattle, there is little doubt that B. indicus cattle are superior than Bos taurus cattle when they are both kept in tropical or subtropical environments, where stressors like hot temperatures, humidity, ectoparasites and low quality forages are greater. Reproductive endocrinology and oestrus behaviour of the B. indicus cattle have been studied for over 30 years; however, the application of technologies such as real time ultrasonography and Heat-Watch systems has expanded our knowledge on the ovarian follicular-wave dynamics during the oestrous cycle and the time of ovulation. Ovarian follicular dynamics in B. indicus cattle is characterised by the occurrence of two, three or sometimes four waves of follicular development. While dominance is similar to that in B. taurus cattle, maximum diameters of the dominant follicle and CL are smaller than those reported in B. taurus and are probably due to a lower capacity for LH secretion than in B. taurus. Duration of oestrus is approximately 10 h and the interval from oestrus to ovulation is about 27 h. However, the variability in response to prostaglandin F2alpha (PGF) treatments and the difficulty for oestrus detection in B. indicus cattle have limited the widespread application of artificial insemination (AI) and emphasizes the need for treatments that control follicular development and ovulation. Follicular-wave development in B. indicus cattle can be controlled mechanically by ultrasound-guided follicle ablation, or hormonally by treatments with GnRH or oestradiol and progestogen/progesterone in combination. Treatments with GnRH plus PGF and a second GnRH (synchronization protocol known as Ovsynch) or oestradiol benzoate (known as GPE) have resulted in acceptable pregnancy rates after fixed-time AI (FTAI) in cycling cows, but results were lower in heifers and cows in postpartum anoestrus. Alternatively, treatments with oestradiol and progestogen/progesterone releasing devices resulted in synchronous emergence of a new follicular wave, and a second oestradiol or GnRH treatment after device removal resulted in synchronous ovulation and acceptable pregnancy rates to FTAI. Furthermore, oestradiol and progesterone treatments combined with eCG (given at the time of device removal) increased pregnancy rates in suckled B. indicus cows and may be useful for the treatment of cows in postpartum anoestrus. In summary, exogenous control of luteal and follicular development facilitates the application of assisted reproductive technologies in B. indicus cattle by offering the possibility of planning AI programs without the necessity of oestrus detection and without sacrificing the overall results.

Physiological classification of anovulatory conditions in cattle

Evaluation of follicular growth patterns by ultrasound combined with measurement of circulating reproductive hormones has allowed designation of three functionally critical follicular sizes during the final stages of follicular growth: emergence (-4 mm), deviation (-9 mm), and ovulation (variable from 10 to 20 mm). Classification of anovulatory conditions on the basis of these three critical points is logical and provides for rational diagnosis and treatment of the underlying physiological condition. In extreme undernutrition, there is growth of follicles to emergence but not to deviation; however, the underlying pathophysiology is not defined because of relatively few scientific investigations of this condition. Anovulatory conditions with growth of follicles to deviation but not to ovulatory size have been extensively studied. Undernutrition and/or suckling can cause this anovulatory condition. It is characterized by a greater negative feedback effect of estradiol on GnRH/LH pulses than found in normally cycling cows. Another anovulatory condition that is common in high producing lactaing dairy cows is characterized by growth of follicles to larger than ovulatory size, such as is observed in cows with follicular cysts. This condition is characterized by an insensitivity of the hypothalamus to the positive feedback effects of estradiol. Thus, these last two common anovulatory conditions appear to be primarily due to changes in the responsiveness of the hypothalamus to estradiol. Treatments that increase circulating progesterone concentrations can help in the treatment of these two conditions by potentially altering GnRH/LH pulses and allowing the final stages of follicular growth or resetting the hypothalamic responsiveness to the positive feedback effects of estradiol.

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.