Folliculogenesis in buffalo (Bubalus bubalis): a review

The urgent need for improving the reproductive performance of buffalo necessitates a better understanding of the mechanisms controlling ovarian follicular growth and development. Attention needs to be focused on improving superovulation responses and conception rates, and reducing the variability in ovulation rate and embryo loss. Application of ultrasonic imaging has revealed that follicular turnover during an unstimulated oestrous cycle occurs in waves, with each wave involving synchronous development of a group of follicles, one dominant and several subordinate follicles. There is a predominance of two waves with the first wave beginning around Day 0 (day of ovulation) and the second wave around Day 9 or 10. Primary reasons for a lower superovulation response in buffalo compared with that in cattle is a lower number of primordial and antral follicles, a slower shift from small to large follicles during superovulation, a higher incidence of deep atresia and inability of several large follicles to ovulate, especially when superovulation is induced by equine chorionic gonadotrophin treatment. There is near complete lack of information in Bubalus bubalis on the factors controlling the selection of the dominant follicle, the period of functional dominance and the effects of environmental factors, such as climate and nutrition, on follicular dynamics.

Collection of oocytes through transvaginal ultrasound-guided aspiration of follicles in an Indian breed of cattle

The present study was undertaken in Karan Fries, an Indian breed of cattle to (1) determine the number of follicles available for puncture and (2) explore the potential of this breed as a donor of developmentally competent oocytes. Ovum pick-up (OPU) was performed using an ultrasound machine with a transvaginal convex transducer (5 MHz) with a needle guide, single lumen 19-gauge 60 cm long needle and a vacuum pressure of 90 mmHg. The number and size of follicles in each ovary was determined before puncture. The follicles were characterized on the basis of their diameter as small (3-5 mm), medium (6-9 mm) and large (>/=10 mm). The oocytes recovered were classified by quality. They were matured in vitro, irrespective of their grade, in 50 microl droplets of the in vitro maturation (IVM) medium (TCM-199+10% fetal bovine serum(FBS)+5 microg/ml follicle stimulating hormone (folltropin)+1 microg/ml estradiol-17beta+0.2 mM sodium pyruvate), covered with paraffin oil, in 35 mm petridish for 24 h in a CO(2) incubator (5% CO(2) in air) at 38.5 degrees C. The cleavage rate was recorded at day 2 post-insemination after subjecting the oocytes to in vitro fertilization (IVF). The differences in follicular populations of all size categories among individual donors were not significant. A total of 92 oocytes were recovered by aspiration of 157 follicles, with an overall recovery rate of 59% (range 35-79%). Of these, 32% were of grades A and B and the rest of grades C and D. The mean numbers of total follicles and the oocytes recovered per session did not differ significantly among individual donors. Out of the 73 oocytes subjected to IVM and IVF, 24 reached 2-4 cell stage at day 2 post-fertilization, with a cleavage rate of 33%. The total number of oocytes recovered was correlated with the number of small (R=0.54, P<0.01) but not with the number of medium and large follicles. This study demonstrates the use of OPU as a means of obtaining developmentally competent oocytes from an Indian breed of cattle for obtaining cattle oocytes in India where cow slaughter is not allowed for religious reasons.

Post-vitrification survival and in vitro maturation rate of buffalo (Bubalus bubalis) oocytes: effect of ethylene glycol concentration and exposure time

The present study was undertaken to investigate the effects of ethylene glycol concentration and time of exposure to equilibration solution on the post-thaw morphological appearance and the in vitro maturation rate of buffalo oocytes. Vitrification solution-I (VS-I) consisted of 4.5M ethylene glycol (EG), 3.4M dimethyl sulphoxide, 5. 56mM glucose, 0.33mM sodium pyruvate and 0.4% w/v bovine serum albumin in Dulbecco's phosphate buffered saline (DPBS), whereas vitrification solution-II (VS-II) contained 3.5M EG, with other constituents at same concentrations as in VS-I. The equilibration solutions-I and II were prepared by 50% dilution (v/v) of VS-I and VS-II, respectively, in DPBS. Prior to vitrification, the cumulus-oocyte complexes (COCs) were exposed to equilibration solution-I or II for 1 or 3min at room temperature (25-30 degrees C). Groups of four to five oocytes were then placed in 15microl of respective vitrification solution, and immediately loaded into 0. 25ml French straws, each containing 150microl of 0.5M sucrose in DPBS. The straws were placed in liquid nitrogen (LN(2)) vapour for 2min, plunged and stored in LN(2) for at least 7 days. The straws were thawed by keeping in warm water at 28 degrees C for 20s, and the oocytes were equilibrated for 5min in 0.5M sucrose for one-step dilution. The percentage of oocytes found to be morphologically normal varied from 89 to 96% for the two equilibration solutions and the two exposure times. Among the damaged oocytes, cracking of zona pellucida was the abnormality observed most frequently. The nuclear maturation rate of oocytes equilibrated in equilibration solutions-I and II for 1 (28 and 24%, respectively) or 3min (32 and 33%, respectively) did not differ significantly. These results show that it is possible to cryopreserve buffalo oocytes by vitrification using a combination of 3.5M EG and 3.4M DMSO with an exposure time of 3min.

Vitrification of buffalo (Bubalus bubalis) oocytes

The objective of the present study was to develop a method for the cryopreservation of buffalo oocytes by vitrification. Cumulus-oocyte complexes (COCs) were obtained from slaughterhouse ovaries. Prior to vitrification of COCs in the vitrification solution (VS) consisting of 4.5 M ethylene glycol, 3.4 M dimethyl sulfoxide, 5.56 mM glucose, 0.33 mM sodium pyruvate and 0.4% w/v bovine serum albumin in Dulbecco's phosphate buffered saline (DPBS), the COCs were exposed to the equilibration solution (50% VS v/v in DPBS) for 1 or 3 min at room temperature (25 to 30 degrees C). The COCs were then placed in 15-microL of VS and immediately loaded into 0.25-mL French straws, each containing 150 microL of 0.5 M sucrose in DPBS. The straws were placed in liquid nitrogen (LN2) vapor for 2 min, plunged and stored in LN2 for at least 7 d. The straws were thawed in warm water at 28 degrees C for 20 sec. For dilution, the COCs were equilibrated in 0.5 M sucrose in DPBS for 5 min and then washed 4 to 5 times in the washing medium (TCM-199+10% estrus buffalo serum). The proportion of oocytes recovered in a morphologically normal form was significantly higher (98 and 88%, respectively; P<0.05), and the proportion of oocytes recovered in a damaged form was significantly lower (2 and 12%, respectively; P<0.05) for the 3-min equilibration than for 1 min. For examining the in vitro developmental potential of vitrified-warmed oocytes, the oocytes were placed in 50-microL droplets (10 to 15 oocytes per droplet) of maturation medium (TCM-199+15% FBS+5 microg/mL FSH-P), covered with paraffin oil in a 35-mm Petri dish and cultured for 26 h in a CO2 incubator (5% CO2 in air) at 38.5 degrees C. Although the nuclear maturation rate did not differ between the 1- and 3-min equilibration periods (21.5+/-10.7 and 31.5+/-1.5%, respectively), the between-trial variation was very high for the 1-min period. This method of vitrification is simple and rapid, and can be useful for cryopreservation of buffalo oocytes.

Effect of naloxone on GnRH-induced LH and FSH release in buffalo, Bubalus bubalis

The effect of naloxone on GnRH-induced LH and FSH release was measured in buffaloes in luteal phase of estrous cycle. Animals were administered intravenously, naloxone/saline (50 mg/injection) every 15 min for 3 hr followed by GnRH (100 micrograms). Peripheral plasma LH and FSH concentrations were measured in blood samples collected at 15 min intervals from 1 hr prior to beginning of naloxone/saline treatment up to 3 hr post GnRH administration and every 30 min for the subsequent 3.5 hr. Between the animals of Group I administered naloxone and those of Group II given saline, GnRH-induced peak LH and FSH concentrations, the total LH and FSH released in response to GnRH, and the time to peak LH and FSH concentrations were not significantly different. The results of the present study suggest the absence of a direct effect of naloxone on pituitary responsiveness to GnRH.

Laboratory production of buffalo (Bubalus bubalis) embryos

There is an increasing interest in large-scale in vitro production (IVP) of buffalo embryos through in vitro maturation (IVM), fertilization (IVF) and culture (IVC) of oocytes for faster multiplication of superior germplasm. The recovery of total and usable quality oocytes from slaughterhouse ovaries is low in this species. The nuclear maturation rates of buffalo oocytes matured in the presence of follicular fluid or serum and hormones like luteinizing hormone, follicle-stimulating hormone and oestradiol vary from 70 to 80% and are comparable to those reported for cattle oocytes. However, with fertilization rates of 40-55%, and the yield of blastocysts at around 10-15%, the efficiency of IVP is much lower than that in cattle. The in vitro sperm preparation procedures and the systems employed for performing IVF and culture of zygotes up to blastocyst stage are suboptimal and need substantial improvements. The quality and viability of blastocysts produced need to be checked by cell count, and after transfer to synchronized recipients, for development of quality control standards.

Changes in follicular populations following treatment of buffaloes with PMSG (eCG) and Neutra-PMSG for superovulation

Some 19 buffaloes were synchronized by administration of a prostaglandin (PG) salt Lutalyse, with a single intramuscular (i.m.) injection of 25 mg at day -13. Luteolysis was induced by administration of 50 mg PG, in divided doses of 30 and 20 mg i.m. 12 h apart on day 0 of experiment. The 30 mg PG injection was designated as 0 h of experiment. Group I animals (n = 6) received saline and served as controls while animals in Groups II (n = 7) and III (n = 6) received 2500 I.U. PMSG (eCG) i.m. at day -2. Group III animals were administered 5 ml Neutra-eCG intravenously at 60 h. The number of follicles, classified on the basis of diameter as small (2-5 mm), medium (6-9 mm) and large (> or = 10 mm) was assessed by ultrasonography on days -2, -1, 0, 1, 2, 5 and 7 of experiment. The number of corpora lutea (CL) was recorded by palpation per rectum on day 8. The number of small follicles which did not differ among the three groups on days 0, 1 and 2 was significantly lower (P < 0.05) in Group II animals compared to those in Groups I and III on days 5 and 7. The number of medium follicles increased after eCG treatment and was significantly higher (P < 0.05) in animals of Groups II and III on days 0 and 1, compared to control animals of Group I. It was, however, not different among the three groups on subsequent days of experiment. The number of large follicles which did not differ among the three groups on days -2, 0, 1 and 2 was significantly higher in Groups II (P < 0.01) and III (P < 0.05) animals compared to those of Group I on day 5. On day 7, the number of large follicles was in the order (P < 0.05) Group II > Group III > Group I. The number of CL in Group II animals was significantly higher (P < 0.05) than that in Group I animals but was not different from that of Group III animals. These results suggest that treatment of buffaloes with eCG for superovulation reduces the number of small follicles and increases the number of large follicles 5-7 days after PG treatment. Administration of Neutra-eCG 60 h after PG treatment can partly reverse this trend but has no effect on ovulation rate. The possibility that part of the variability in ovulation rates in this study may have resulted from Neutra-eCG been given prior to or at the LH surge, or from the absence or presence of a dominant follicle at the time of eCG treatment cannot be ruled out.

Influence of cumulus cells and sperm concentration on cleavage rate and subsequent embryonic development of buffalo (Bubalus bubalis) oocytes matured and fertilized in vitro

The objective of the present study was to investigate the effects of sperm concentration and presence or absence of cumulus cells on fertilization, cleavage rate and subsequent embryonic development upto the blastocyst stage in buffalo. Cumulus-oocyte-complexes (COCs) obtained from slaughterhouse ovaries were matured in vitro in TCM-199 + 10% FBS + 5 micrograms/mL FSH-P for 24 h. After maturation the COCs were either used as such (cumulus-intact) or freed from attached cumulus cells by repeated pipetting (cumulus-free). Frozen-thawed buffalo spermatozoa were treated with 10 micrograms/mL heparin and 2.5 mM caffeine for sperm capacitation. Oocytes were fertilized in vitro with 1 to 2, 4 to 5 or 9 to 10 million sperm/mL and the cleavage rate was recorded 42 to 44 h post insemination. The cleaved embryos were co-cultured with buffalo oviductal epithelial cells for 10 d post insemination, and the uncleaved oocytes were fixed and stained with aceto-orcein for determination of the penetration rate. The cleavage rate and the proportion of cleaved embryos that developed to morula and blastocyst stages were significantly higher (P < 0.05) whereas the proportion of degenerated oocytes and those that became arrested at the 2 to 16-cell stage were significantly lower (P < 0.05) with cumulus-intact than with cumulus-free oocytes at the 3 sperm concentrations. Increasing the sperm concentration increased the cleavage rate significantly (P < 0.05) from 1 to 2 million through 9 to 10 million sperm/mL but had no effect on the proportion of cleaved embryos that developed to morula and blastocyst stages. In conclusion, the results of the present study suggest that cumulus cells have a positive influence on fertilization, cleavage and subsequent embryonic development. Increase in sperm concentration increases cleavage rate without affecting subsequent embryonic development.

In vitro maturation and fertilization, and subsequent development of buffalo (Bubalus bubalis) embryos: effects of oocyte quality and type of serum

In Experiment 1, to determine the developmental potential of buffalo oocytes of different qualities, compact cumulus-oocyte complexes (COCs) with an unexpanded cumulus mass, and with homogeneous ooplasm were classified as Grade 1 (with > or =5 layers of cumulus cells) and Grade 2 less than 4 layers of cumulus cells). Grade-3 oocytes were either without cumulus cells or with expanded cumulus mass, and with irregular ooplasm. The oocytes were matured for 24 h at 38.5 degrees C, 5% CO2 in air in maturation medium (10% fetal bovine serum (FBS) in TCM-199 supplemented with 5 microg mL(-1) follicle stimulating hormone-P). The nuclear maturation and cleavage rates, and the proportion of cleaved embryos which developed to morula and blastocyst stage were in the order Grade 1>Grade 2>Grade 3 (P < 0.05). For Experiment 2, the maturation medium consisted of TCM-199 supplemented with one of the following sera at 10% concentration: (1) buffalo oestrus serum (BOS), (2) superovulated buffalo serum (SBS), (3) fetal bovine serum (FBS) and (4) steer serum (SS). After in vitro fertilization (IVF), the oocytes were co-cultured with buffalo oviductal epithelial cells in TCM-199 containing the respective sera at 10% concentration for the subsequent 9 days. The extent of cumulus expansion and nuclear maturation were not different among different groups. The cleavage rates were lower (P < 0.05) with FBS than with BOS, SBS and SS. The proportion of cleaved embryos which developed to blastocyst stage was higher (P < 0.05) with SBS than with BOS, FBS and SS.

Effect of presence of a dominant follicle on the superovulatory response in buffalo (Bubalus bubalis)

Ten buffalo were superovulated by administration of 8 doses of FSH in a descending schedule spread over 4 d (5.5/5.5, 4.5/4.5, 3.5/3.5 and 2.5/2.5 mL, i.m.; total dose of 64 AU in 32 mL) beginning on Day 10 of an unstimulated estrous cycle, and 30 and 20 mg Lutalyse was given alongwith the 5th and 6th injections of FSH, respectively, to induce luteolysis. The number of corpora lutea (CL) was determined on 6 d post estrus. The ovaries were examined daily by ultrasonography from Day -5 to Day 5 (Day 0 = day of start of superovulation). The animals were retrospectively classified into 2 groups depending upon the presence (n = 4) or absence of a dominant follicle (n = 6). The mean diameter of the largest follicle (F1) increased from 8.25 +/- 0.48 mm on Day -5 to 10.75 +/- 0.25 mm on Day 0 in the dominant group, whereas in the nondominant group the F1 follicle exhibited a progressive decrease from 9.00 +/- 0.45 mm to 7.00 +/- 0.65 mm during the same period, the difference in profiles between the 2 groups was significant (P = 0.042). The profile of the diameter of the second largest follicle (F2) and the difference in diameters between largest and second largest follicles (F1-F2) were not significantly different between the 2 groups. The profile of mean number of large (> or = 10 mm diameter), but not small (2 to 5 mm diameter) or medium (6 to 9 mm diameter) follicles differed significantly (P = 0.001) between the 2 groups from Day -5 to Day 5 (P = 0.030). The number of CL was not significantly different between nondominant (4.00 +/- 0.97) and dominant groups (3.25 +/- 1.31). The number of CL was positively correlated (P < 0.01) with the number of medium follicles and the total number of follicles on the day of initiation of superovulation, but not with follicles of any size category or total number of follicles on any previous day. The results of this study indicate that following the use of morphological criteria based on the size of the largest follicle alone, the superovulation response is not affected by the presence of a dominant follicle at the initiation of superovulation in buffalo.

Follicular fluid immunoreactive-inhibin concentrations in relation to follicular diameter and estradiol-17 beta, progesterone and testosterone concentrations in individual ovarian follicles in buffalo, Bubalus bubalis

The objective of this study was to measure the concentrations of immunoreactive inhibin (ir-inhibin) in follicular fluid from individual ovarian follicles and relate them to follicular diameter and follicular fluid concentrations of estradiol-17 beta, progesterone and testosterone in buffalo. Follicular size was measured with an ultrasound machine and follicles were categorized as small (4 to 5 mm diam.), medium (6 to 9 mm diam.) and large (10 mm and above in diam.). Ir-inhibin concentrations varied markedly between and within follicles of same size category. Follicular fluid ir-inhibin concentrations (microgram/ml) were positively related to follicular diameter (R = 0.32, n = 262, P < 0.001) and were significantly higher (P < 0.05) in large (8.32 +/- 0.56) in comparison to medium (7.02 +/- 0.31) follicles which, in turn had inhibin concentrations significantly higher (P < 0.001) than those in small follicles (5.13 +/- 0.48). Ir-inhibin and estradiol-17 beta concentrations were positively related in medium (R = 0.38, n = 128, P < 0.001) and large (R = 0.64, n = 35, P < 0.001) but not in small follicles. There was a negative relationship between ir-inhibin and progesterone concentrations in large follicles (R = 0.46, n = 33, P < 0.01), with no relationship between the two hormones in small and medium follicles. Ir-inhibin was positively related to molar ratios of estradiol-17 beta to progesterone in medium (R = 0.30, n = 124, P < 0.01) and large (R = 0.49, n = 24, P < 0.01) but not in small follicles. There was no relationship between ir-inhibin and testosterone concentrations in follicles of all size categories. The results of the present study suggest that follicular inhibin production is related to follicular size as well as intrafollicular estradiol-17 beta and progesterone concentrations.

Replacement of serum and hormone additives with follicular fluid in the IVM medium: Effects on maturation, fertilization and subsequent development of buffalo oocytes in vitro

Buffalo follicular fluid was used in the IVM medium in place of serum and hormone additives for stimulating nuclear and cytoplasmic maturation of buffalo oocytes in vitro. Follicular fluid (buFF) was aspirated from visible surface follicles from buffalo ovaries. Cumulus oocyte complexes (COCs) were matured for 24 to 26 h at 38.5 degrees C, 5% CO(2) in air in the maturation medium (TCM-199). When used, the concentration of fetal bovine serum (FBS) was 10% and that of FSH-P was 5 mug/ml. In Experiment 1 TCM-199 was supplemented with 1) FBS, 2) FBS + FSH-P, 3) 20% buFF and 4) 40% buFF. The matured oocytes were denuded and stained with Giemsa stain to study nuclear maturation. The proportion of oocytes which completed nuclear maturation was similar in medium containing FSH (74%) and 20 or 40% buFF (67%), which was higher (P < 0.05) than in medium with FBS but without FSH or buFF (47%). In Experiment 2, which was aimed at examining the effects of buFF on cumulus expansion and rates of fertilization and subsequent development to the blastocyst stage after IVF, the maturation medium was supplemented with 1) FBS + FSH-P, 2) 20% buFF and 3) 40% buFF. The COCs matured in medium containing 20 or 40% buFF had significantly higher (P < 0.01) cumulus expansion than those matured in medium with FBS + FSH-P. Of the COCs matured in medium with FBS + FSH-P and 20 or 40% buFF, the fertilization rates indicated by the incidence of cleavage (56, 51 and 52%, respectively) and the proportion of cleaved COCs developing to morula (58, 54 and 57%, respectively) and blastocyst stage (30, 31 and 35%, respectively) were not significantly different. In Experiment 3, supplementation of the maturation medium with 1) FBS + FSH-P and 2) FBS + FSH-P + 20% buFF resulted in similar rates of morulae (41 and 38%, respectively) and blastocysts (31 and 25%, respectively), indicating that simultaneous presence of FBS, FSH-P and buFF did not have an additive effect on embryo yield. The results show that the gonadotropin and serum source in the IVM medium can be replaced by buFF at the 20% level to achieve comparable morula and blastocyst yields.

Changes in peripheral inhibin levels and follicular development following treatment of buffalo with PMSG and Neutra-PMSG for superovulation

Fourteen buffalo were synchronized by administration of a prostaglandin (PG) salt Lutalyse in a double injection schedule, with a single intramuscular (im) injection of 25 mg at Day -13, followed by 30 mg and 20 mg im 12 h apart on Day 0 of the experiment. The 30-mg PG injection was designated as 0 h of the experiment. Group I animals (n = 4) received saline and served as the controls, while animals in Groups II and III (n = 5 each) received PMSG (2500 IU im at -48 h. Group III animals were administered 5 ml Neutra-PMSG intravenously at 60 h. Blood samples were collected every 48 h from Day -12 to Day -4, every 24 h from Day -4 to Day 0, every 3 h from Day 1 to Day 4 and every 24 h from Day 5 to Day 10 of experiment for the measurement of peripheral plasma inhibin concentrations by RIA. The number of large follicles (> 10 mm diameter) in animals of Groups II and III was assessed by ultrasonography on Days -2, -1, 0, 1, 2, 5 and 7 of the experiment. Treatment with PMSG of Group II animals resulted in a significant increase (P < 0.05) in plasma inhibin concentrations over that of control animals of Group I at 24 to 99 h, with a peak inhibin concentration of 1.01 +/- 0.31 ng/ml at 48 h. Treatment with Neutra-PMSG in Group III animals caused a significant reduction (P < 0.05) in the peripheral inhibin concentrations at 84 to 120 h and in the number of large unovulated follicles at 168 h compared with that in Group II animals. Peripheral inhibin levels in Group III animals came down to those of Group I after 21 h of Neutra-PMSG treatment. These results suggest that treatment of buffalo with PMSG for superovulation causes a marked rise in peripheral inhibin concentrations. Administration of Neutra-PMSG after PG treatment reduces the peripheral inhibin concentrations and the number of large unovulated follicles.

Peripheral inhibin levels in relation to climatic variations and stage of estrous cycle in buffalo ()

The present study investigated the peripheral plasma inhibin levels in relation to 1) the stage of estrous cycle and the effect of climatic variations. Blood samples were collected from cyclic buffalo (n=5) once daily for 32 consecutive days during the tropical hot humid (summer) and cold (winter) seasons. Estrus was recorded by parading a vasectomized bull as well as by plasma progesterone determination. In the winter season, peripheral inhibin concentrations which were lowest (0.35 +/- 0.02 ng/ml) during the mid-luteal phase of estrous cycle (Day 6 to Day 14, Day 0 = day of estrus) increased significantly (P < 0.02) to 0.47 +/- 0.04 ng/ml during the late luteal phase (Day -4 to Day -2) and then further to 0.52 +/- 0.03 ng/ml (P< 0.02) during the periestrus phase (Day -1 to Day 1). Inhibin concentrations then decreased significantly (P < 0.02) to 0.40 +/- 0.03 ng/ml during the early luteal phase (Day 2 to Day 5). In the summer season the differences in peripheral inhibin concentrations among different phases of estrous cycle were found to be nonsignificant. A comparison of the circulating inhibin concentrations between the two seasons indicated that inhibin concentrations were significantly higher in the late luteal phase (P < 0.01) and periestrus phase (P < 0.05) during the winter season compared with corresponding periods during the summer season. The present study suggests that peripheral inhibin concentrations change in the estrous cycle during cooler breeding season and that environmental heat stress can cause a reduction in peripheral inhibin concentrations.

Effect of gestation on GnRH-induced LH and FSH release in buffalo ()

This study examined the effect of gestation on the hypophyseal responsiveness of buffalo to GnRH-induced LH and FSH release. Peripheral plasma LH and FSH concentrations were measured at 1 h before and upto 6 h after administration of GnRH (1 ug/kg body weight) or saline at Days 60, 150 and 240 of gestation in 2 groups of buffalo (n = 4 each). Basal LH concentrations did not vary at the 3 stages of gestation, while basal FSH concentrations exhibited a significant reduction (P < 0.05) from Day 60 to Day 150 of gestation. There was a significant reduction in the total LH (P < 0.05) and FSH (P < 0.01) released in response to GnRH from Day 60 to Day 240 of gestation. The duration of LH and FSH peaks and the time to attain peak concentration was not affected by the stage of gestation. The results of the present study point to a progressive decline in LH and FSH release responses to GnRH during the advancement of gestation in the buffalo.

Inhibin in individual buffalo ovarian follicles in relation to size

A sensitive and specific radioimmunoassay was validated and applied for measurement of inhibin in follicular fluid (bFF) obtained from individual buffalo ovarian follicles. Follicular size was measured with an ultrasound machine and follicles were categorized as small, medium and large. Presence of inhibin was detected in all the antral follicles above 3 mm diameter. Inhibin concentration showed a positive relationship (R = 0.27, P < 0.01) with follicular diameter and was significantly higher (P < 0.05) in bFF from medium and large follicles (8.44 +/- 0.54 and 7.70 +/- 0.45 micrograms/ml, respectively) in comparison to that from small follicles (5.74 +/- 0.80 micrograms/ml). Total inhibin content was highly correlated (R = 0.92, P < 0.001) with follicular diameter and the inhibin content was higher (P < 0.001) in large > medium > small follicles.

Peripheral inhibin levels during estrous cycle in buffalo ()

A sensitive, specific RIA was validated and used for measurement of peripheral plasma immunoreactive inhibin (irinhibin) levels during the estrous cycle in Murrah buffalo. The RIA employed an 125-I iodinated inhibin as tracer and an antiserum against dimeric inhibin. The procedure had a sensitivity of 16 pg/tube, and the nonspecific effects of buffalo plasma were compensated for by including 200 ul bullock plasma in the standards. Separation of free and bound inhibin was affected by the use of a second antibody and precipitation with polyethylene glycol. Blood samples were collected once daily for 30 d from Murrah buffalo (n = 6) during the hot month of July. Cyclic activity and estrus were confirmed by plasma progesterone determination. Peripheral plasma concentrations of ir-inhibin fluctuated between 0.40 +/- 0.07 and 0.67 +/- 0.13 ng/ml during the estrous cycle in buffalo. During the same period, plasma progesterone levels increased from 0.21 +/- 0.01 ng/ml at Day 0 to a peak of 3.30 +/- 0.72 ng/ml on Day 13, declining sharply by Day -5. Ir-inhibin levels exhibited an increase during the follicular phase, with the maximum concentration of 0.65 +/- 0.01 ng/ml occuring on the day of estrus, a decline thereafter, and no pattern during the luteal phase. The differences, however, were not statistically significant throughout the estrous cycle.