Follicular dynamics and concentrations of steroids and gonadotropins in lactating cows and nulliparous heifers

Differences in follicular development and circulating hormone concentrations, between lactating cows and nulliparous heifers, that may relate to differences in fertility between the groups, were examined. Multiparous, cyclic, lactating Holstein cows (n=19) and cyclic heifers (n=20) were examined in the winter, during one estrous cycle. The examinations included ultrasound monitoring and daily blood sampling. Distributions of two-wave and three-wave cycles were similar in the two groups: 79 and 21% in cows, 70 and 30% in heifers, respectively. Cycle lengths were shorter by 2.6 days in heifers than in cows, and in two-wave than in three-wave cycles. The ovulatory follicle was smaller in heifers than in cows (13.0+/-0.3 mm versus 16.5+/-0.05 mm). The greater numbers of large follicles in cows than in heifers corresponded well to the higher concentrations of FSH in cows. The duration of dominance of the ovulatory follicle tended to be longer in cows than in heifers. Estradiol concentrations around estrus and the preovulatory LH surge were higher in heifers than in cows (20 versus 9 ng/ml). Progesterone concentrations were higher in heifers than in cows from Day 3 to Day 16 of the cycle. Circulating progesterone did not differ between two-wave and three-wave cycles. The results revealed differences in ovarian follicular dynamics, and in plasma concentrations of steroids and gonadotropins; these may account for the differences in fertility between nulliparous heifers and multiparous lactating cows.     

Effects of progesterone administered to dairy heifers on sensitivity of corpora lutea to PGF(2)alpha and on plasma LH concentration

To determine whether progesterone facilitates PGF(2)alpha-induced luteolysis prior to day 5 of the estrous cycle, 48 Holstein-Friestian heifers were assigned at random to four treatments: 1) 4 ml corn oil/day + 5 ml Tris-HCl buffer (control); 2) 25 mg prostaglandin F(2)alpha (PGF(2)alpha); 3) 100 mg progesterone/day (progesterone); 4) 100 mg progesterone/day + 25 mg PGF(2)alpha (combined treatment). Progesterone was injected subcutaneously daily from estrus (day 0) through day 3. The PGF(2)alpha was injected intramuscularly on day 3. Estrous cycle lengths were decreased by progesterone: 20.2 +/- 0.56, 19.2 +/- 0.31 (control and PGF(2)alpha); 13.2 +/- 1.40, and 11.7 +/- 1.27 (progesterone and combined). The combination of progesterone and PGF(2)alpha did not shorten the cycle any more than did progesterone alone (interaction, P>0.05). PGF(2)alpha treatment reduced progesterone concentrations on day 6 (P<0.05) and both progesterone and PGF(2)alpha reduced plasma progesterone on day 8 (P<0.01 and P<0.05, respectively). LH was measured in blood samples collected at 10- min intervals for 4 hr on day 4 from three heifers selected at random from each of the four treatment groups. Mean LH concentration for control heifers ranged from 0.35 to 0.63 ng/ml (overall mean, 0.49 ng/ml) and for progesterone-treated heifers ranged from 0.12 to 0.30 ng/ml (overall mean, 0.23 ng/ml). LH concentrations were greater in control heifers (P<0.01). The mean LH pulse rate for control heifers was 2.7 pulses/heifers/4 hr, while that for the progesterone-treated heifers was 1.7 pulses/heifer/4 hr. The mean pulse amplitude for control and progesterone treatments was 0.47 ng/ml and 0.36 ng/ml, respectively. Neither pulse amplitude nor frequency were different between treatment groups.     

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).     

Relationships between insulin and glucose metabolism and pituitary-ovarian functions in fasted heifers

The effects of fasting between Days 8 and 16 of the estrous cycle on plasma concentrations of luteinizing hormone (LH), progesterone, cortisol, glucose and insulin were determined in 4 fasted and 4 control heifers during an estrous cycle of fasting and in the subsequent cycle after fasting. Cortisol levels were unaffected by fasting. Concentrations of insulin and glucose, however, were decreased (p less than 0.05) by 12 and 36 h, respectively, after fasting was begun and did not return to control values until 12 h (insulin) and 4 to 7 days (glucose) after fasting ended. Concentrations of progesterone were greater (p less than 0.05) in fasted than in control heifers from Day 10 to 15 of the estrous cycle during fasting, while LH levels were lower (p less than 0.01) in fasted than in control heifers during the last 24 h of fasting. Concentrations of LH increased (p less than 0.01) abruptly in fasted heifers in the first 4 h after they were refed on Day 16 of the fasted cycle. Concentrations (means +/- SEM) of LH also were greater (p less than 0.05) in fasted (11.2 +/- 2.6 ng/ml) than in control (4.7 +/- 1.2 ng/ml) heifers during estrus of the cycle after fasting; this elevated LH was preceded by a rebound response in insulin levels in the fasted-refed heifers, with insulin increasing from 176 +/- 35 pg/ml to 1302 +/- 280 pg/ml between refeeding and estrus of the cycle after fasting. Concentrations of LH, glucose and insulin were similar in both groups after Day 2 of the postfasting cycle. Concentrations of progesterone in two fasted heifers and controls were similar during the cycle after fasting, whereas concentrations in the other fasted heifers were less than 1 ng/ml until Day 10, indicating delayed ovulation and (or) reduced luteal function. Thus, aberrant pituitary and luteal functions in fasted heifers were associated with concurrent fasting-induced changes in insulin and glucose metabolism.     

Progesterone profile in buffaloes during various stages of oestrous cycle using radioimmunoassy technique

Investigation were carried out to study the norms of progesterone concentration in the blood serum of buffaloes during various phases of oestrous cycle. Twenty four animals (12 heifers and 12 cows) were used. The blood serum samples were stored at -20 degrees C until processed for progesterone assay. The progesterone concentrations were measured by the radioimmunoassay technique. The progesterone levels were 0.360 +/- 0.062 and 0.334 +/- 0.066 ng/ml on the day of oestrus in buffalo-heifers and buffalo-cows, respectively. The values were around 1 ng/ml till day 6, followed by a gradual increase to a peak average value of 4.888 +/- 0.399 and 5.119 +/- 0.415 ng/ml on day 15 of the cycle in heifers and cows, respectively. Thereafter, the progesterone concentration fell abruptly to a level similar to that at oestrus. The mean progesterone value a day before oestrus was 0.488 +/- 0.067 and 0.577 +/- 0.053 ng/ml in buffalo-heifers and buffalo-cows, respectively. The mean progesterone concentration of different days of the cycle (except day 16) did not differ significantly (P / -0.01) between heifers and cows.     

Prostaglandin F2 alpha-induced release of oxytocin from bovine corpora lutea in vitro

Two experiments were conducted to study the in vitro effects of prostaglandins F2 alpha (PGF2 alpha), E2 (PGE2), and luteinizing hormone (LH) on oxytocin (OT) release from bovine luteal tissue. Luteal concentration of OT at different stages of the estrous cycle was also determined. In Experiment 1, sixteen beef heifers were assigned randomly in equal numbers (N = 4) to be killed on Days 4, 8, 12, and 16 of the estrous cycle (Day 0 = day of estrus). Corpora lutea were collected, an aliquot of each was removed for determination of initial OT concentration, and the remainder was sliced and incubated with vehicle (control) or with PGF2 alpha (10 ng/ml), PGE2 (10 ng/ml), or LH (5 ng/ml). Luteal tissue from heifers on Day 4 was sufficient only for determination of initial OT levels. Luteal OT concentrations (ng/g) increased from 414 +/- 84 on Day 4 to 2019 +/- 330 on Day 8 and then declined to 589 +/- 101 on Day 12 and 81 +/- 5 on Day 16. Prostaglandin F2 alpha induced a significant in vitro release of luteal OT (ng.g-1.2h-1) on Day 8 (2257 +/- 167 vs. control 1702 +/- 126) but not on Days 12 or 16 of the cycle. Prostaglandin E2 and LH did not affect OT release at any stage of the cycle studied. In Experiment 2, six heifers were used to investigate the in vitro dose-response relationship of 10, 20, and 40 ng PGF2 alpha/ml of medium on OT release from Day 8 luteal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of steroid microspheres for control of estrus in cows and induction of puberty in heifers

Two trials were designed to test whether a single treatment with a microsphere formulation of progesterone (P) could simulate the luteal phase of the estrous cycle and lead to estrus and subsequent luteal development. The first experiment was to characterize the pattern of serum P concentrations and estrus in cows treated with a microsphere formulation (P + E) that contained 625 mg P and 50 mg estradiol (E). Four cows with palpable corpora lutea were treated with 25 mg prostaglandin F2 m. Each cow was given P + E (i.m.) 12 h later. Tail vein blood samples were taken on Days 1 and 2 following P + E treatment and then three times weekly for 24 days. Serum P increased from 0.8 +/- 0.1 ng/ml at P + E treatment to 4.7 +/- 0.6 ng/ml on Day 1, declined gradually to 4.1 +/- 0.3 ng/ml on Day 7 and then declined more rapidly to 0.6 +/- 0.1 ng/ml on Day 13. Treated cows showed estrus 16.25 +/- 0.7 days after P + E treatment. Thereafter, serum P increased beginning on Day 20 after P + E treatment, as expected following estrus. In Experiment 2, Angus and Simmental heifers (10.5-11.5 months of age) were administered i.m. either the vehicle (controls), E (50 mg), P (625 mg) or P + E (n = 13 per group). While treatment with E resulted in behavioral estrus (1-2 days after treatment) in each treated heifer, it did not (P > 0.5) initiate estrous cycles as indicated by subsequent increased serum P. In contrast, the P and P + E treatments increased (P < 0.05) the proportion (11/13) of heifers that showed estrus by 21 days after treatment followed by elevated serum P. We conclude that the microsphere formulation of P simulated the pattern of serum P concentrations during the luteal phase of the estrous cycle and initiated estrous cycles in peripubertal heifers with or without E.     

Decreased pulsatile LH secretion in heifers superovulated with eCG or FSH

This study was designed to test the hypothesis that treatment with super-ovulatory drugs suppresses endogenous pulsatile LH secretion. Heifers (n=5/group) were superovulated with eCG (2500 IU) or FSH (equivalent to 400 mg NIH-FSH-P1), starting on Day 10 of the estrous cycle, and were injected with prostaglandin F(2alpha) on Day 12 to induce luteolysis. Control cows were injected only with prostaglandin. Frequent blood samples were taken during luteolysis (6 to 14 h after PG administration) for assay of plasma LH, estradiol, progesterone, testosterone and androstenedione. The LH pulse frequency in eCG-treated cows was significantly lower than that in control cows (2.4 +/- 0.4 & 6.4 +/- 0.4 pulses/8 h, respectively; P<0.05), and plasma progesterone (3.4 +/- 0.4 vs 1.8 +/- 0.1 ng/ml, for treated and control heifers, respectively; P<0.05) and estradiol concentrations (25.9 +/- 4.3 & 4.3 +/- 0.4 pg/ml, for treated and control heifers, respectively; P<0.05) were higher compared with those of the controls. No LH pulses were detected in FSH-treated cows, and mean LH concentrations were significantly lower than those in the controls (0.3 +/- 0.1 & 0.8 +/- 0.1, respectively; P<0.05). This suppression of LH was associated with an increase in estradiol (9.5 +/- 1.4 pg/ml; P<0.05 compared with controls) but not in progesterone concentrations (2.1 +/- 0.2 ng/ml; P>0.05 compared to controls). Both superovulatory protocols increased the ovulation rate (21.6 +/- 3.9 and 23.0 +/- 4.2, for eCG and FSH groups, respectively; P>0.05). These data demonstrate that super-ovulatory treatments decrease LH pulse frequency during the follicular phase of the treatment cycle. This could be explained by increased steroid secretion in the eCG-trated heifers but not in FSH-treated animals.     

Plasma progesterone levels during the estrous cycle of Holstein and Brahman cows, Carora type and cross-bred heifers

Daily plasma progesterone (P(4)) was determined during one estrous cycle of 19 cows and 18 heifers of four different breeds: Holstein (H), Brahman (B), Carora-type (C) and crossbred (CB) females. Estrus detection was made by visual observation and using a teaser bull with a chin-ball marker. The P(4) profiles showed no differences among groups. In Group 1 (H), P(4) levels ranged from 0.5 ng/ml plasma on the day of estrus (Day 0) to 5.1 ng/ml at the luteal phase peak (Day 13). In Group 2 (B), P(4) levels ranged from 0.5 ng/ml on Day 0 to 9.2 ng/ml on Day 13. In Groups 3 (C) and 4 (CB), P(4) levels ranged from 0.5 ng/ml, on Day 0, to 13.7 ng/ml on Day 12 and 8.8 ng/ml on Day 13. These last two groups were moved to the same location and then compared. It was found that P(4) concentrations were significantly higher (P < 0.025) in Group 3 between Days 7 and 14 of the estrous cycle. In all groups, P(4) levels were lower than 1 ng/ml one day before the next estrus, and levels of 0.4, 0.5, 0.4 and 0.4 ng/ml were obtained the day of estrus in Groups 1 to 4, respectively. Results indicated that the pattern of P(4) for each one of the groups was similar to those reported by other investigators.     

Effect of calf removal on serum luteinizing hormone and cortisol concentrations in postpartum beef cows

Serum luteinizing hormone (LH) and cortisol concentrations were measured in ten fall calving, Angus cows averaging 38 +/- 8 days postpartum. Calves from five cows were weaned at the beginning of the study. Blood samples were collected at 20 min. intervals for 48 h after weaning and for 8 h on day 4 and day 6 postweaning. Mean serum LH concentrations increased (P<0.01) in weaned cows (W) from 0.55 +/- 0.01 ng/ml at time of calf removal to 1.3 +/- 0.04 ng/ml 48 h afterwards. Comparable LH concentrations for suckled cows (S) were 0.65 +/- 0.08 ng/ml and 0.62 +/- 0.03 ng/ml respectively. Average serum LH concentrations at 48 h after weaning were greater (P<0.01) for W cows than S cows and a treatment by time interaction occurred (P<0.01) with serum LH concentrations increasing (P<0.01) from time of calf removal to 48 h after calf removal in W cows. Frequency of LH peaks increased (P<0.01) in W cows and by 48 h after weaning was greater (P<0.01) in W cows than in S cows. Magnitude of LH peaks did not differ between the two groups. Serum cortisol concentrations were not different between W and S cows except for a transient elevation (P<0.01) in W cows from 7.6 +/- 0.9 ng/ml to 11.9 +/- 1.0 ng/ml 9 to 12 h after calf removal. Since serum LH concentrations were increased in W cows but not in S cows at 48 h and serum cortisol concentrations increased transiently in W cows we suggest that circulating cortisol levels may not be a physiological inhibitor of LH secretion in the suckled postpartum beef cow.     

Estrogen and progesterone concentrations in bovine milk during the estrous cycle

Estrogen and progesterone concentrations in milk during the estrous cycle were estimated in 18 normally cycling Holstein dairy cows. The estrogen and progesterone concentrations in milk during the estrous cycle followed the pattern described for them in blood in the corresponding period. During most of the estrous cycle, estrogen concentration remained at approximately 200 pg/ml and reached a proestrous peak of 360 +/- 127 pg/ml on day 19. The progesterone concentration in milk during the estrous cycle increased to a peak on day 13 (45.5 +/- 6.6 ng/ml) and thereafter declined towards estrus. Estrus detection/prediction based on milk progesterone concentrations appears feasible in view of the significant differences in milk progesterone concentrations between the early luteal (post-ovulatory), luteal and rapid follicular growth periods of the estrous cycle.     

Induction of cyclicity in postpartum anestrous beef cows using progesterone, GnRH and estradiol cypionate (ECP)

The objective of the present study was to determine whether treatment of postpartum multiparous and primiparous anestrous beef cows with an intravaginal progesterone-releasing insert (CIDR) and PGF(2alpha), with and without the addition of GnRH or estradiol cypionate (ECP) at the time of CIDR insertion, is effective in stimulating onset of estrous cycles. Postpartum lactating Angus primiparous (n=47, 2 years of age, 495+/-6 kg) and multiparous (n=76, >or=3 years of age, 553+/-9 kg) cows were assigned by calving date to four blocks spaced 21-day apart. Cows were assigned sequentially by calving date to four treatment groups: (1) PGF(2alpha) (n=30), (2) CIDR-PGF(2alpha) (n=30), (3) GnRH-CIDR-PGF(2alpha) (n=33), and (4) ECP-CIDR-PGF(2alpha) (n=27). Intravaginal CIDR inserts were in place from days -7 to 0. A single 100 microg injection of GnRH or 2 mg ECP were administered on day -7, and 25mg PGF(2alpha) was administered on day 0. Day 0 averaged 38+/-1 day postpartum. Blood samples were collected on days -19, -9, 0, 5, 9, 12, 16, 19, 23, 26, and 30 for determination of plasma progesterone concentrations. Pre-treatment luteal activity (progesterone>or=1 ng/ml) was detected in 19% of primiparous and 8% of multiparous cows. Progesterone concentrations on day 0 were greater (P<0.001) in primiparous (3.2+/-0.3 ng/ml) than multiparous (2.0+/-0.2 ng/ml) cows. Following CIDR withdrawal, progesterone concentrations from days 5 to 30 were used to categorize response profiles as either: (1) treatment-induced onset of estrous cycles, (2) continued anestrus, or (3) spontaneous ovulation and subsequent formation of a CL. Incidence of treatment-induced onset of estrous cycles, which was defined as progesterone concentrations >or=1 ng/ml in three or more consecutive samples from days 9 to 19, was influenced by treatment and parity. Percentages of cows initiating estrous cycles were greater (P<0.001) in the three CIDR-treated groups than in the PGF(2alpha) group (55 and 8%, respectively). Percentages of cows initiating estrous cycles in the CIDR-PGF(2alpha), GnRH-CIDR-PGF(2alpha), and ECP-CIDR-PGF(2alpha) groups were 55, 58, and 52%, respectively. Incidence of treatment-induced estrous cycles in the three CIDR-treated groups of cows was greater (P=0.008) in primiparous (76%) than multiparous (43%) cows. Treatment of postpartum anestrous primiparous and multiparous beef cows with CIDR-PGF(2alpha) approximately 40-day postpartum provides an approach to increase the percentage of cows that have reinitiated estrous cycles by the start of the breeding season.     

The synchrony of prostaglandin-induced estrus in cows was reduced by pretreatment with hCG

The induction of optimal synchrony of estrus in cows requires synchronization of luteolysis and of the waves of follicular growth (follicular waves). The aim of this study was to determine whether hormonal treatments aimed at synchronizing follicular waves improved the synchrony of prostaglandin (PG)-induced estrus. In Experiment 1, cows were treated on Day 5 of the estrous cycle with saline in Group 1 (n = 25; 16 ml, i.v., 12 h apart), with hCG in Group 2 (n = 27; 3000 IU, i.v.), or with hCG and bovine follicular fluid (bFF) in Group 3 (n = 21; 16 ml, i.v., 12 h apart). On Day 12, all cows were treated with prostaglandin (PG; 500 micrograms cloprostenol, i.m.). In Experiment 2, cows were treated on Day 5 of the estrous cycle with saline (3 ml, i.m.) in Group 1 (n = 22) or with hCG (3000 IU, i.v.) in Group 2 (n = 20) and Group 3 (n = 22). On Day 12, the cows were treated with PG (500 micrograms in Groups 1 and 2; 1000 micrograms in Group 3). Blood samples for progesterone (P4) determination were collected on Day 12 (Experiment 1) or on Days 12 and 14 (Experiment 2). Cows were fitted with heat mount detectors and observed twice a day for signs of estrus. Four cows in Experiment 1 (1 cow each from Groups 1 and 2; 2 cows from Group 3) had plasma P4 concentrations below 1 ng/ml on Day 12 and were excluded from the analyses. In Experiment 1, cows treated with hCG or hCG + bFF had a more variable (P = 0.0007, P = 0.0005) day of occurrence of and a longer interval to estrus (5.9 +/- 0.7 d, P = 0.003 and 6.2 +/- 0.8 d, P = 0.005) than saline-treated cows (3.4 +/- 0.4 d). The plasma P4 concentrations on Day 12 were higher (P < 0.0001) in hCG- and in hCG + bFF-treated cows than in saline-treated cows (9.4 +/- 0.75 and 8.5 +/- 0.75 vs 4.1 +/- 0.27 ng/ml), but there was no correlation (P > 0.05) between plasma P4 concentrations and the interval to estrus. In Experiment 2, cows treated with hCG/500PG and hCG/1000PG had a more variable (P = 0.0007, P = 0.002) day of occurrence of and a longer interval to estrus (4.2 +/- 0.4 d, P = 0.04; 4.1 +/- 0.4 d, P = 0.03) than saline/500PG-treated cows (3.2 +/- 0.1 d). The concentrations of plasma P4 on Days 12 and 14 of both hCG/500PG- and hCG/1000PG-treated cows were higher (P < 0.05) than in saline/500PG-treated cows (7.3 +/- 0.64, 0.7 +/- 0.08 and 7.7 +/- 0.49, 0.7 +/- 0.06 vs 5.3 +/- 0.37, 0.5 +/- 0.03 ng/ml). The concentrations of plasma P4 on Days 12 or 14 and the interval to estrus were not correlated (P > 0.05) in any treatment group. The concentrations of plasma P4 on Days 12 and 14 of hCG/500PG- or hCG/1000PG-treated cows were correlated (r = 0.65, P < 0.05; r = 0.50, P < 0.05). This study indicated that treatment of cows with hCG on Day 5 of the estrous cycle reduced the synchrony of PG-induced estrus and that this reduction was not due to the failure of luteal regression.     

Detection of estrus in cattle housed in stanchions by constant human observation of behavioral traits

Five heifers and five lactating dairy cows were locked in adjacent stanchions and monitored continuously by human observation for 18 consecutive nights from 7:00 p.m. to 4:00 a.m. Total standing and lying time, number of position changes, and prevalence of bellowing was recorded. The animals were housed in stanchions for 20 hours each day and in outside lots for four hours each day. Estrus was synchronized by giving prostaglandins on Days 1 and 11. There were 16 documented estrous periods, and an increase (P < 0.05) in standing time occurred in two of 16. Similarly, an increase (P < 0.05) in number of position changes occurred in two of 16 estrous periods. Mean +/- SE standing time (during the nine-hour nightly observation period) for heifers and cows was 148 +/- 6.8 and 278 +/- 9.6 (P < 0.01) minutes, respectively. The prevalence of bellowing was very low and not always associated with estrus. These results indicate that standing time, number of position changes, and bellowing are rather weak indicators of estrus.     

Hormonal interelationships and physiological responses of lactating dairy cows to a shade management system in a subtropical environment

Lactating cows (n = 64) were assigned randomly to shade or no shade treatments for a continuous trial (20 wk) during summer of 1976. Respirations/min and rectal temperatures were higher for no shade cows. Dry matter forage intake was 9.7% higher for shade cows, whereas water intake was 19% greater for no shade cows. Milk yield and conception rates were higher for shade managed cows. Mean plasma corticoid concentrations were high throughout the entire estrous cycle in no shade compared to shade cows (13.04 > 8.72 ng/ml). No shade cows had higher progesterone and LH concentrations, and a lower estradiol to progesterone ratio during the cycle. Results indicated that endocrine changes were indicative of recurring estrous cycles in thermal stressed lactating dairy cows. However, alterations in water intake and thermoregulation of stressed cows were associated with decreased fertility and milk production, and changes in steroid concentrations that may reduce uterine blood flow.     

The effect of exogenous acth and pen-confinement on estrous cycle length, plasma steroid levels and ovarian function of beef heifers

Each of 24 pasture-reared crossbred beef heifers were herded from a large pasture on day 14 of the estrous cycle and assigned randomly to one of four treatment groups as follows: Field Control (FC), Field ACTH (FA), Pen Control (PC) and Pen ACTH (PA). Field groups were maintained in a small field, and pen groups were confined in a pen in a pole barn. ACTH groups received 200 IU of ACTH IM daily for days 17 through 21 of the cycle and control groups received only the gelatin carrier IM on the same cycle days. Average cycle lengths for FA and PA heifers were 25 and 24.3 days with an average period from plasma progesterone decline below 1 ng/ml to estrus of 5.5 days. During the ACTH injection period, follicular growth was suppressed and the proestrus plasma estrogen rise was delayed. Average cycle lengths for FC and PC heifers were 20.8 and 22.8 days respectively. All control group heifers exhibited estrus within 2 days of the plasma progesterone decline below 1 ng/ml. In addition, pen confinement heifers showed a trend for extended luteal function and consequent extended estrous cycle length.     

Reproductive characteristics of cloned heifers derived from adult somatic cells.

This study examined the onset of puberty, follicular dynamics, reproductive hormone profiles, and ability to maintain pregnancy in cloned heifers produced by somatic cell nuclear transfer. Four adult somatic cell-cloned heifers, derived from a 13-yr-old Holstein cow, were compared to 4 individual age- and weight-matched heifers produced by artificial insemination (AI). From 7 to 9 mo of age, jugular venous blood samples were collected twice weekly, and from 10 to 11 or 12 mo of age, blood sampling was carried out every other day. After the heifers reached puberty (defined as the first of 3 consecutive blood samples with peripheral plasma progesterone concentrations of >1 ng/ml), ultrasound examination of ovaries and jugular plasma sample collection were carried out daily for 1 estrous cycle. Cloned heifers reached puberty later than controls (mean +/- SEM, 314.7 +/- 9.6 vs. 272 +/- 4.4 days and 336.7 +/- 13 vs. 302.8 +/- 4.5 kg for clones and controls, respectively; P < 0.05). However, cloned and control heifers were not different in estrous cycle length, ovulatory follicle diameter, number of follicular waves, or profiles of hormonal changes (LH, FSH, estradiol, and progesterone). Three of the 4 clones and all 4 control heifers became pregnant after AI. These results demonstrate that clones from an aged adult have normal reproductive development.     

Effect of early postpartum treatment with prostaglandin F2alpha on subsequent fertility in the dairy cow

Eighty Holstein dairy cows were treated with 25 mg of prostaglandin F2alpha (PGF2alpha) on Days 14 to 16 post calving. Eighty-four herd mates served as saline controls in the double blind study. The reproductive parameters used to measure fertility were mean days to first service on all cows and mean days open, first service conception rates and services per pregnancy on cows that became pregnant. Mean days to first service was similar in both groups (71.8 +/- 27, treated; 68.5 +/- 28.6, controls; P = 0.5352). The mean days open was 98.6 +/- 52.0 d for treated cows compared to 118.8 +/- 71.2 d for controls (P = 0.0680). First service pregnancy rates (treated, 41.3%; control, 35.7%) were not significantly different (P = 0.0630); however, the mean services per pregnancy (treated, 1.64; control, 2.33) were significantly (P = 0.0021) improved in the treated group. Ten cows in the treated group and twelve cows in the control group were diagnosed as having retained fetal membranes and/or metritis. For treated and control cows mean days to first service were 82.2 +/- 34.8 d and 82.8 +/- 58.7 d (P = 0.5652). Days open were 97.0 +/- 32.5 d and 133.4 +/-58.4 d (P = 0.3636); services per conception were 1.83 and 2.50 (P = 0.3178), respectively. In all treated cows reproductive parameters were similar whether cows had high serum progesterone ( > 1 ng/ml) or low serum progesterone ( < 1 ng/ml) on the treatment day. This study suggests that early postpartum treatment of lactating dairy cows with prostaglandin produces an improvement in fertility.     

Body condition influences maintenance of a persistent first wave dominant follicle in dairy cattle

The objective of this study was to determine whether plasma concentrations of progesterone (P4) from a controlled internal drug releasing (CIDR) device (approximately 2 ng/ml) were adequate to sustain a persistent first wave dominant follicle (FWDF) in low body condition (LBC, body condition score [BCS] 1 = lean, 5 = fat [2.3 +/- 0.72, n = 4]) compared with high body condition (HBC, BCS = 4.4 +/- 0.12, n = 4) nonlactating dairy cows. On Day 7 of the estrous cycle (Day 0 = estrus), cows were treated with PGF2 alpha (25 mg i.m. Lutalyse, P.M., and Day 8 A.M.) and a used CIDR device containing P4 (1.2 g) was inserted into the vagina until ovulation or Day 16. Plasma was collected for P4 and estradiol (E2) analyses from Day 5 to Day 18 (or ovulation), and ovarian follicles were monitored daily by ultrasonography. Mean concentrations of plasma P4 were greater in HBC than LBC cows between Days 5 and 7 (4.6 > 3.4 +/- 0.37 ng/ml; P < 0.04). All LBC cows maintained the first wave dominant follicle and ovulated after removal of the CIDR device (18.3 +/- 0.3 d, n = 3; Cow 4 lost the CIDR device on Day 11 and ovulated on Day 15), whereas in the HBC cows ovulation occurred during the period of CIDR exposure (11.3 +/- 0.3 d; n = 3; a fourth cow developed a luteinized first wave dominant follicle that did not ovulate during the experimental protocol on Day 19). Mean day of estrus was 17 +/- 0.4 for LBC (n = 3) and 10 +/- 0.4 for HBC (n = 3) cows. Sustained concentrations of plasma E2 (12.9 +/- 2.8 pg/ml; Days 8 to 17) in LBC cows reflected presence of an active persistent first wave dominant follicle. The differential effect of BCS on concentrations of plasma P4 (y = ng/ml) was reflected by the difference (P < 0.01) in regressions: yLBC = 19.9 - 3.49x + 0.166x2 vs yHBC = 37.3 - 7.04x + 0.340x2 (x = day of cycle, Days 7 to 12). Although P4 concentration was greater for HBC cows prior to Day 8, a greater clearance of plasma P4 released from the CIDR device in the absence of a CL altered follicular dynamics, leading to premature ovulation in the HBC cows. A greater basal concentration of P4 was sustained in LBC cows that permitted maintenance of a persistent first wave dominant follicle.     

Peripheral inhibin levels during estrous cycle in buffalo (Bubalus bubalis)

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.