Influence of flushing on LH secretion, follicular growth and the response to estrus synchronization treatment in suckled beef cows

The effects of energy supplementation (flushing) on LH and estradiol secretion, follicular growth and the response to estrus synchronization treatment (Norgestomet + PMSG initiated 41.9 +/- 3.4 d after calving) were investigated in 16 suckled beef cows fed either 70% (Group C, n = 8) of energy requirements from calving to 3 wk after AI or fed the same restricted diet until 11 d before synchronization and then were supplemented with 2 kg concentrate until 3 wk after AI (Group S, n = 8). Concentrations of LH and estradiol 17 beta were measured from 3 sampling periods: 25 and 39 d after calving and between 29 and 49 h after implant removal. Ovaries were examined by ultrasonography 11 d before treatment to implant withdrawal (IR). The effects of energy level, day (or hour) of observation and corresponding interactions were tested on repeated measurements by split-plot ANOVA. No positive effect of flushing was observed on characteristics of LH secretion on Day 39. However, the size of the largest follicle and the number of large follicles were higher in Group S than in Group C cows, respectively, 7 and 9 d after the beginning of flushing to 2 d after the start of treatment. After IR, the estradiol secretion tended to be higher in Group S than in Group C cows (9.8 +/- 0.4 pg/mL vs 7.2 +/- 0.2 pg/mL; P = 0.06), but no effect on LH secretion was observed. After implant removal 12 cows ovulated (Group S: 7/8 vs Group C: 5/8; P > 0.05), 7 were pregnant at 21 d after AI (Group S: 6/8 vs Group C: 1/8; P < 0.05) and 4 at 45 d after AI (Group S: 4/8 vs Group C 0/8; P > 0.05). To conclude, flushing had a positive effect on follicular growth, which does not seem to be mediated by LH. In cows fed a restricted diet, flushing enhanced follicular growth, increased the fertilization rate and/or reduced early embryonic death.     

Pattern of follicular growth and resumption of ovarian activity in post-partum beef suckler cows

The ovaries of 18 post-partum beef suckler cows were examined daily, using ultrasound, from Day 5 post partum until a normal oestrous cycle was completed. Periods of growth and regression of medium-sized (5-9 mm) follicles were identified before one medium follicle became dominant (single large follicle greater than or equal to 10 mm). The mean (+/- s.e.m.) number of days from parturition to detection of the first post-partum dominant follicle was 10.2 +/- 0.5. The first post-partum dominant follicle ovulated in 2/18 (11%) cows. The interval from calving to first ovulation (mean +/- s.e.m. = 35.9 +/- 3.3 days) was characterized by the growth and regression of a variable number (mean = 3.2 +/- 0.2; range 1-6) of dominant follicles. The maximum diameter of the dominant follicle increased as the cows approached first ovulation (P less than 0.05). Behavioural oestrus was not detected in 16/18 (89%) cows at first ovulation. Following first ovulation, the length of the subsequent cycle was short (mean = 9.7 +/- 0.5 days; range 8-15 days) in 14/18 (78%) cows and was characterized by the development and ovulation of a single dominant follicle. During oestrous cycles of normal length (mean = 20.6 +/- 0.5 days; range 18-23 days) one (N = 2), two (N = 7) or three (N = 8) dominant follicles were identified. The growth rate, maximum diameter or persistence of non-ovulatory dominant follicles before first ovulation or during oestrous cycles were not different (P greater than 0.05). These data show that, in beef suckler cows, follicular development and formation of a dominant follicle occur early after parturition and the incidence of ovulation of the first dominant follicle is low. The number of dominant follicles that develop before first ovulation is variable; first ovulation is rarely associated with oestrus and short cycles are common after first ovulation. It is concluded that prolonged anoestrus in post-partum beef suckler cows is due to lack of ovulation of a dominant follicle rather than delayed development of dominant follicles.     

Influence of lameness on follicular growth, ovulation, reproductive hormone concentrations and estrus behavior in dairy cows

The objective of this study was to examine the effect of a chronic stressor, lameness, on reproductive parameters. Seventy cows 30-80 days post-partum were scored for lameness and follicular phases synchronized with GnRH followed seven days later by prostaglandin (PG). Fifteen Lame animals did not respond to GnRH ovarian stimulation. Milk progesterone for 5 days prior to PG was lower in the remaining Lame cows than Healthy herdmates. Fewer Lame cows ovulated (26/37 versus 17/18; P = 0.04) and the interval from PG to ovulation was shorter in Lame cows. In Subset 1 (20 animals), the LH pulse frequency was similar in ovulating animals (Lame and Healthy) but lower in Lame non-ovulators. An LH surge always preceded ovulation but lameness did not affect the interval from PG to LH surge onset or LH surge concentrations. Before the LH surge, estradiol was lower in non-ovulating cows compared to those that ovulated and estradiol concentrations were positively correlated with LH pulse frequency. In Subset 2 (45 cows), Lame ovulating cows had a less intense estrus than Healthy cows, although Lame cows began estrus and stood-to-be-mounted earlier than Healthy cows. In conclusion, we have identified several parameters to explain poor fertility in some chronically stressed animals. From 30 to 80 days post-partum, there was a graded effect that ranged from 29% Lame cows with absence of ovarian activity, whereas another 21% Lame cows failed to express estrus or ovulate a low estrogenic follicle; in 50% cows, many reproductive parameters were unaffected by lameness.     

Seasonal effects on caprine response to synchronization of estrus and superovulatory treatment

Nubian doelings (n = 21, 7 of which were repeats) were synchronized and superovulated with Norgestomet ear implants and follicle stimulating hormone-pituitary (FSH-p) and were then mated during early and late periods of their breeding season in the southeastern United States. A 100% response rate to estrus synchronization treatment was found in doelings (n = 15, 2 of which were repeats) treated early in the breeding season, and the superovulation regimen resulted in the surgical collection of an average of 15.1 viable embryos per doeling. But only a 66.7% response rate to estrus synchronization treatment was observed in doelings (n = 6, 5 of which were repeats) treated late in the season; only 50% of these doelings (or 33.3% of the initial doelings treated) responded to superovulatory treatment, resulting in an average of 3.33 viable embryos collected surgically per doeling. Thus, a significantly higher number of viable embryos can be obtained from Nubian doelings when treated for estrus synchronization and superovulation early in the breeding season.     

Synchronization of estrus after treatment with Luprostiol in beef cows and in beef and dairy heifers

Four trials were conducted to study synchronous estrous response in beef cows and in beef and dairy heifers to Luprostiol (13, thia-PG-F(2)alpha analog) in comparison with other prostaglandin products. In Trial 1, 60 virgin beef heifers were observed for estrus for 5 d and artificially inseminated. Heifers not observed in estrus within 5 d were randomly assigned to receive 15 mg Luprostiol or 25 mg Lutalyse. In Trial 2, 75 multiparous, lactating beef cows were randomly assigned to receive either 15 mg Luprostiol, 25 mg Lutalyse or 500 mcg Estrumate. All cows received a second injection of the respective treatment 11 d later. In Trial 3, 96 multiparous, lactating beef cows were randomly assigned to receive 15 mg Luprostiol or 25 mg Lutalyse. All cows received a second injection of the respective treatment 11 d later. In Trial 4, virgin dairy heifers were palpated per rectum. Seventy-seven heifers with a palpable corpus luteum (CL) were randomly assigned to receive 15 mg Luprostiol or 500 mcg Estrumate. In all trials animals were artificially inseminated 12 h following observed estrus. Estrous response during the 5-d synchronized period was 44% for Luprostiol and 42% for Lutalyse treated heifers in Trial 1. It was 52, 56 and 60%, respectively, for Luprostiol, Lutalyse and Estrumate treated cows in Trial 2; 23% for Luprostiol and 19% for Lutalyse treated cows in Trial 3; and 68% for Luprostiol and 70% for Estrumate treated heifers in Trial 4. Treatment with Luprostiol results in a similar synchronous estrous response as with the other prostaglandin products used in these studies.     

The use of milk progesterone to monitor reproductive function in beef suckler cows

Milk progesterone analysis was used to monitor reproductive function in 134 autumn calving cross-bred suckler cows. Progesterone was measured in milk samples collected three times per week from around 4 week post-calving to around day 60 of pregnancy during 1st and 2nd lactation. The mean day of onset of luteal activity (OLA) was 40.7 +/- 1.1 with the distribution skewed towards a later return. Once cyclicity had been initiated the incidence of reproductive cycle problems (6.5%) was low, though animals with such problems (n = 14) exhibited a delayed interval to first service (P < 0.05), lower conception and calving rates (P < 0.001), increased services per pregnancy (P < 0.001) and a higher (P < 0.10) barren rate (14.3% versus 4.0%) compared to animals with normal cycles (n = 201). In conclusion, using milk progesterone analysis we found a relatively low incidence of reproductive cycle problems in beefxdairy suckler cows. However, while the incidence of cycle problems was low, those animals with problems showed significantly impaired reproductive function.     

The effect of estrus synchronization scheme, injection protocol and large ovarian follicle on response to superovulation in beef heifers

Two trials were conducted to examine the effects of estrus synchronization scheme, gonadotropin injection protocol and presence of a large ovarian follicle on response to superstimulation of follicular development and the ensuing superovulation. Estrus was synchronized with either a progestin compound (MGA) or by the use of a luteolytic agent (PGF). Superstimulation was induced with 280 mg equivalents of pFSH administered either by a single subcutaneous injection or by a series of 8 intramuscular injections over 4 d. Follicular development was followed for 5 d with real-time ultrasound, and the heifers were retrospectively classified as to the presence or absence of a large follicle (> or = 8 mm; morphologically dominant follicle) at the start of superstimulation. The 2 trials differed by season of the year and genetic origin of the heifers. In Trial I (20 heifers), the ovulation rate was influenced by the 3-way interaction of the synchronization scheme, injection protocol and morphologically dominant follicle (P = 0.05). The number of large follicles on Day 5 (Day 0 = day of start of superstimulation) and ovarian score (scale 1 to 5 based on extent of follicular development; 1 = least, 5 = most) on Day 5 were significantly correlated (P < 0.05) with ovulation rate. In Trial II (20 heifers), the ovulation rate, number of embryos recovered, number of transferable embryos and ovarian weights were all greater (P < 0.05 to P < 0.01) with the 8-injection protocol than the 1-injection protocol. The number of medium follicles (5 to 7 mm) on Days 2 and 3, number of large follicles (> or = 8 mm) on Days 3, 4 and 5 and ovarian scores on Days 4 and 5 were all significantly correlated (P < 0.05) with ovulation rate. In both trials, differences in follicle populations were not seen until Day 3 of the superstimulation procedure. Collectively, these trials do not provide strong support for a single injection of FSH, as used here, nor does it indicate a clear advantage for either MGA or PGF as a means of enhancing the ovulation rate or embryo quality.     

Control of FSH, follicular development and estrus synchronization in the mare with steroid-free follicular fluid

Twenty-two pony mares were used in a project designed to determine the effectiveness of different treatments in controlling FSH, follicular development and synchronization of estrus and ovulation. Mares in Group 1 (n=8) received daily oral altrenogest (0.044 mg/kg); those in Group 2 (n=7) received daily altrenogest (0.044 g/kg) and, during the last 4 days of treatment they received steroid-free follicular fluid, (15 cc) intravenously (I.V.) two times a day; Mares in Group 3 (n=7) received daily intramuscular (I.M.) injections of progesterone (80 mg) and estradiol valerate (7 mg). All treatments lasted for 10 days, at the end of which prostaglandin (PgF(2)alpha, 10 mg) was administered. Sexual behavior, follicular development and FSH concentrations were monitor daily. Concentrations of FSH in Group 2 mares, were not significantly different (P>0.05) from those of Group 1 until the mares in Group 2 were treated with follicular fluid (P<0.05). Concentrations of FSH in Group 3 mares, were significantly lower than those of Groups 1 and 2 (P<0.05) until the mares in Group 2 were treated with steroid-free follicular fluid. At this point there was no significant difference between groups 2 and 3 (P>0.05). Steroid-free follicular fluid appears to induce atresia in larger follicles (>11 mm), and the initiation of new follicular wave. The combination of progesterone and estradiol valerate appears to delay follicular growth and not to induce atresia, since larger follicles (>11 mm) continued to grow after treatment. Both treatments (groups 2 and 3) resulted in ovulations within 5 days period. The treatment in Group 1 did not have any effect on FSH or follicular development and ovulations were dispersed through a 9-day period. We concluded that steroid-free follicular fluid offers a new possibility to synchronize ovulation in the mare by controlling FSH and follicular development.     

Differences between Brahman and Holstein cows in response to estrus synchronization,superovulation and resistance of embryos to heat shock

Embryos from Bos indicus are more resistant to elevated culture temperature (i.e. heat shock) than embryos from some Bos taurus breeds. The present experiment was designed to determine if Brahman embryos have greater resistance to heat shock than Holstein embryos at a stage in development before the embryonic genome was fully activated. A second objective was to test breed effects on estrus synchronization and superovulation responses. A total of 29 Brahman and 24 Holstein cows were subjected to estrus synchronization using gonadotropin releasing hormone (GnRH) and prostaglandin F2alpha (PGF2alpha) superovulation. Embryos were collected at 48 h and day 5 after insemination. There was a tendency for a lower proportion of Brahmans to be detected in standing estrus than Holsteins. There were no differences between breeds in the proportion of cows detected in estrus using both tailpaint and standing estrus as criteria or in interval from PGF2alpha to estrus. The degree of synchrony in estrus was greater for Brahmans. Superovulation response was generally similar between breeds. At 48 h after insemination, there was a tendency for a greater proportion of Brahman oocytes to have undergone cleavage. Uncleaved oocytes were cultured for an additional 24 h-at this time, cleavage rate was similar between breeds. When embryos reached the 2-4-cell stage, they were heat-shocked for 4.5 h at 41 degrees C. This heat shock reduced the proportion of embryos that developed to the blastocyst stage but there was no breedxtreatment interaction. At day 5 after insemination, the number of embryos recovered was too low to allow comparison of breed effects. In conclusion, genetic effects on cellular thermotolerance that make Brahman embryos more resistant to heat shock are not expressed at the 2-4-cell stage. There were few differences between Brahman and Holstein in response to estrus synchronization and superovulation. The fact that cleavage tended to occur earlier in Brahman than Holstein embryos suggests breed differences in timing of ovulation, fertilization or events leading to cleavage.     

Effects of cloprostenol, human chorionic gonadotropin and estradiol benzoate treatment on estrus synchronization in dairy cows

Two consecutive experiments were conducted. In Experiment 1, 24 Friesian lactating cows were randomly assigned to two groups. Cows in Group I received intramuscularly (i.m.) 500 mcg of cloprostenol, 1250 IU of human chorionic gonadotropin (hCG) and 5 mg of estradiol benzoate 12 h after cloprostenol treatment. Cows in Group II received 750 IU i.m. of hCG and 3 mg of estradiol benzoate 12 h after cloprostenol treatment. Treatment was given on Day 16 after estrus in both groups. All animals showed estrus within 24 to 48 h after cloprostenol treatment. The average interval from cloprostenol injection to the onset of estrus was not influenced by treatments. Four cows in Group I failed to ovulate and became cystic. In Experiment 2, 71 Friesian lactating cows were randomly assigned to two groups. Cows in Group I received 500 mcg i.m. of cloprostenol after corpus luteum detection by palpation per rectum. Cows in Group II received 500 mcg of cloprostenol plus 750 IU of hCG and 3 mg of estradiol benzoate 12 h after. When estrus ready for service was confirmed by rectal examination, cows were inseminated. The percentage of cows ready for service tended to be lower (P < 0.06) between cows in Group I (88%) and those in Group II (100%). The average interval from cloprostenol treatment to service was longest (P < 0.001) in Group I (78.7 h +/- 14.9, X +/- SD) vs Group II (48 h +/- 2.9). The degree of readiness for service synchrony was lowest (P < 0.001) in Group I (59.3%) vs Group II (94.2%). The pregnancy rates of cows synchronized or treated were not altered by hCG-estradiol benzoate treatment (P > 0.25). These results suggest that in dairy cows treated with cloprostenol following palpation per rectum of a corpus luteum and then with 750 IU of hCG and 3 mg of estradiol benzoate 12 h later, a single fixed-time insemination at 48 h after cloprostenol treatment should be performed.     

Environmental,genetic and social factors affecting the expression of estrus in beef cows

Genetic, social and environmental factors affecting behavioral estrus were evaluated in Angus (n = 10), Brahman (n = 10) and Senepol (n = 10) cows during a PGF2alpha synchronized estrus and subsequent spontaneous estrus. Cows were equally stratified by breed to two groups of 15. Both groups were pre-synchronized with a modified two-injection PGF2alpha protocol. At the start of the experiment, cows were treated with 25 mg PGF2alpha followed by a second and third administration of 12.5 mg PGF2alpha, 11 and 12 days later to induce synchronized estrus. The subsequent estrus was designated as spontaneous estrus. Behavioral estrus data including the onset and end of estrus, estrous duration and the total number of mounts received for the synchronized and spontaneous estruses were collected using HeatWatch". Interval from the third PGF2alpha, treatment to the onset of a HeatWatch" estrus occurred earlier (P < 0.05) in Angus (31 +/- 5 h) than Brahman (53 +/- 7 h) or Senepol (53 +/- 4 h) cows, with dominant Senepol and Brahman cows taking longer to exhibit estrus after PGF2alpha than subordinate cows. The duration of the synchronized estrus tended to be shorter (P < 0.06) in Senepol (12 +/- 3 h) than in Angus (19 +/- 2 h) or Brahman (17 +/- 2 h) cows. Behavioral estrus data between the two periods were confounded by greater temperature-humidity index (THI) values during spontaneous estrus. The THI during spontaneous estrus appeared (P = 0.09) to affect the duration of estrus (9 +/- 1 h versus 16 +/- 1 h) and did affect (P < 0.0001) the total number of mounts received (8 +/- 4 mounts versus 34 +/- 4 mounts) during spontaneous estrus compared to synchronized estrus. Breed had no effect (P > 0.10) on the duration and total number of mounts received during synchronized and spontaneous estruses. In conclusion, type of estrus (synchronized or spontaneous), THI, social dominance and breed exerted significant effects on characteristics associated with behavioral estrus in beef cattle in subtropical environments.     

Synchronization of estrus and fertility in zebu beef heifers treated with three estrus synchronization protocols

The effects on estrus and fertility of 3 estrus synchronization protocols were studied in Brahman beef heifers. In Treatment 1 (PGF protocol; n=234), heifers received 7.5 mg, i.m. prostianol on Day 0 and were inseminated after observed estrus until Day 5. Treatment 2 (10-d NOR protocol; n = 220) consisted of norgestomet (NOR; 3 mg, s.c. implant and 3 mg, i.m.) and estradiol valerate (5 mg, i.m.) treatment on Day -10, NOR implant removal and 400 IU, i.m. PMSG on Day 0, and AI after observed estrus through to Day 5. Treatment 3 (14-d NOR+PGF protocol; n = 168) constituted a NOR implant (3 mg, sc) on Day -14, NOR implant removal on Day 0, PGF on Day 16, and AI after observed estrus through to Day 21. All heifers were examined for return to estrus at the next cycle and inseminated after observed estrus. The heifers were then exposed to bulls for at least 21 d. During the period of estrus observation (5 d) after treatment, those heifers treated with the PGF protocol had a lower (P<0.01) rate of estrual response (58%) than heifers treated with the 10-d NOR (87%) or 14-d NOR+PGF (88%) protocol. Heifers treated with the 10-d NOR protocol displayed estrus earlier and had a closer synchrony of estrus than heifers treated with either the PGF or the 14-d NOR+PGF protocol. Heifers treated with the 14-d NOR+PGF protocol had higher (P<0.05) conception and calving rates (51 and 46%) to AI at the induced estrus than heifers treated with the PGF (45 and 27%) or the 10-d NOR (38 and 33%) protocol. Calving rate to 2 rounds of AI was greater (P<0.05) for heifers treated with the 14-d NOR-PGF (50%) protocol than heifers treated with the 10-d NOR (38%) but not the PGF (43%) protocol. Breeding season calving rates were similar among the 3 protocols. The results show that the 14-d NOR+PGF estrus synchronization protocol induced a high incidence of estrus with comparatively high fertility in Brahman heifers.     

Breed differences in growth hormone and insulin secretion between lactating Japanese Black cows (beef type) and Holstein cows (dairy type)

This study was performed to clarify the levels of growth hormone (GH) and insulin (INS) secretions and the glucose response to INS during lactation in a representative beef breed in Japan, Japanese Black cows, and to compare them with their counterparts in a dairy breed, Holstein cows. Six Japanese Black and seven Holstein primiparous cows received a single intravenous injection of GH-releasing factor (GRF; 0.25 microg/kg), glucose (112.5 mg/kg), or INS (0.2 U/kg) from late pregnancy (2 weeks antepartum) to mid-lactation (6 months postpartum). Japanese Black cows had one-tenth of the total milk yield of Holstein cows during lactation, and significantly lower GRF-induced GH and higher glucose-induced INS secretions than Holstein cows at all stages. In Japanese Black cows, even with lactation, these secretions remained essentially unchanged, whilst Holstein cows showed higher GH and lower INS secretions after the onset of lactation as compared with cows in late pregnancy. Both breeds had similar glucose response to INS at the respective stages. These results suggest that, during lactation, Japanese Black cows may minimize the catabolic effects of GH and sustain the anabolic effects of INS, in contrast with Holstein cows, but have similar ability to inhibit INS-mediated glucose utilization in peripheral tissues to Holstein cows.     

Influence of naloxone and yohimbine administration on pulsatile LH secretion in luteal phase beef cows

This study examined the effects of two specific neurotransmitter receptor antagonists, naloxone (NAL; mu-opioid) and yohimbine (YOH; alpha(2)-adrenergic), on pulsatile luteinizing hormone (LH) release during the luteal phase (Day 10; Day 0 = estrus) of beef cows. Treatments were saline i.m. (C; n = 4); 1mg/kg NAL i.m. followed 3 h later by two 0.5 mg/kg injections spaced 2.5 h apart (N; n = 4); 0.2 mg/kg YOH i.v. (Y; n = 3); or combined N and Y regimens, with Y preceding N by 30 min (NY; n = 4). Blood samples were collected for 8 h before (Period I) and after (Period II) initiation of treatment. Respiration rates of Y cows were similar to C cows during Period II. However, respiration rates of N and NY animals increased 70% within 30 min of the first NAL injection. Acute LH release was not observed in response to either NAL or YOH. Pulsatile LH secretion was unchanged in N, Y and NY cows during Period II when compared with Period I. In contrast, basal and pulsatile LH secretion was inhibited in C cows during Period II. The inhibition of LH secretion in C animals following NAL indicate that the cows were under stress during Period II. Thus, these data suggest that the inhibition of LH release in stressed animals can be overcome by pharmacologic attenuation of inhibitory (N) or accentuation of stimulatory (Y) signals to LHRH-containing neurons.     

Effects of estradiol and progestins on follicular regression before, during, and after follicular deviation in postpartum beef cows

The objective was to evaluate the effect of estradiol benzoate (EB), in association with three progestin protocols, on ovarian follicular regression of suckled beef cows treated at three stages of follicular development (pre-deviation, deviation, or post-deviation). Thirty-six suckled beef cows (60-90 d postpartum, given 125 μg cloprostenol on two occassions, 12 h apart). Forty-eight hours after the first cloprostenol treatment, all follicles >5 mm were ablated and transrectal ultrasound scanning (8 MHz) was performed every 24 h until Day 7 (Day 0 = treatment). When the largest follicle reached a designated diameter of 5-7, 8-10 or >10 mm, cows were randomly allocated to receive 2 mg of EB im in association with an intravaginal device containing 250 mg of medroxyprogesterone acetate (MPA) with or without 100 mg of progesterone (P₄) given im, or an intravaginal device containing P₄ (3 × 3 factorial design). Treatments induced follicular regression in all cows, independent of follicular stage or treatment. There was no interaction between progestin treatment and follicular stage, nor was there any difference in the time of follicular regression or new wave emergence among follicular stages. Treatment with MPA plus P₄ delayed follicular regression. In conclusion, EB in association with various progestins induced regression of growing follicles and emergence of a new follicular wave in postpartum beef cows, regardless of the stage of follicular development.     

Comparison of two estrus synchronization and resynchronization treatments in lactating dairy cows

Reproductive performance in cows following synchronization of estrus with intravaginal progesterone releasing devices (IVD) has varied with the length of treatment, cyclic status and prolonged return to estrus intervals in some cows following first AI. The objective of this study was to compare two methods of synchronizing and resynchronizing estrus on the reproductive performance of lactating dairy cows. Cows were treated with an IVD (Day 0) for 7 days (n = 350) or 8 days (n = 350), cloprostenol (0.5 mg i.m.) at the time of device removal and estradiol benzoate (EB) at the time of device insertion (1.5mg i.m.), and again 9 days later (1.0 mg i.m.). Cows were also resynchronized starting on Days 23 and 46 by reinsertion of IVDs for either 7 or 8 days and treatment with EB (1mg i.m.) at the time of device insertion and again 9 days later. Cows were inseminated on detection of estrus for 4 days after removal of devices at each of the synchronized estrous cycles. No significant differences in reproductive performance were detected between each treatment throughout the study period. Synchrony of estrus was more precise at the first and second estrus after treatment with an IVD for 8 days compared to 7 days. Cows classified as anestrous had lower reproductive performance than cows classified as cycling and had longer intervals to estrus at the second (P < 0.001) and third estrus (P < 0.06), but not at the first estrus (P = 0.09). Mean time to onset of estrus after IVD removal was less in cows treated with an IVD for 8 days compared to 7 days at each synchronized estrus (P < 0.01). More Holstein-Friesian cows were classified as non-pregnant and not detected in estrus than crossbreed cows (15.7%, 54/343 versus 9.0%, 24/266; [P < 0.05). The results of the study suggested that the main effects of the treatments that were used to synchronize and resynchronize estrus were to alter the timing and synchrony of estrus without affecting fertility.     

The effects of ovarian function on estrus synchronization with PGF in dairy cows

Milk progesterone concentration (P4), milk yield, milk composition, ovarian structures and pregnancy status were studied in 108 cows treated with two doses of PGF 14 days apart and inseminated at fixed time (TAI) 80-82 h later. The synchronization protocol was started at 70+/-1.4 days after parturition. Milk P4 profiles revealed that anestrus, failure of luteolysis following treatment with PGF and failure to ovulate following luteolysis were the main reasons for low pregnancy rate with TAI. Anestrous cows had a higher percentage of milk fat (P<0.05) and higher fat to protein ratio (P<0.01), and cows that did not undergo luteolysis had higher milk yield (P<0.05) and lower percentage of milk protein (P<0.05) than cows that responded to PGF treatment. Cows that did not undergo luteolysis and cows that did not ovulate following luteolysis had lower milk P4 during the luteal phase preceding the second PGF injection (P<0.01 and P<0.05, respectively). Pregnancy rates 24 and 47 days after TAI in cows that responded as expected to the synchronization treatment were 62% and 54%, respectively. Pregnancy was precluded in non-responsive cows. The largest follicle at the time of TAI in cows experiencing late embryonic mortality was smaller (P=0.02) than in cows that successfully maintained pregnancy. Results suggest that a primary reason for low pregnancy rate in dairy cows after administration of PGF and TAI is inappropriate ovarian function prior to, or following treatment.     

Follicular growth, estrus and pregnancy after fixed-time insemination in beef cows treated with intravaginal progesterone inserts and estradiol benzoate

An experiment was performed to compare the effects of 3 short-term treatments with progesterone and estradiol benzoate (EB) on follicular growth, synchrony of estrus and pregnancy rate after fixed-time insemination in lactating postpartum beef cows. In Treatment 1 (n = 46), each cow received a progesterone-containing intravaginal insert for 7 d with injection of EB (2 mg, i.m.) at the time of device insertion. In Treatment 2 (n = 46), the insert was used for only 5 d with injection of EB (2 mg, i.m.) at the time of insertion. Cows in Treatment 3 (n = 47) received an insert for 5 d with no EB at the time of insertion. Each cow in the 3 groups received PGF2 alpha (25 mg, i.m.) at the time of insert removal, followed by EB (1 mg, i.m.) 30 h later. The cows were then inseminated 28 to 30 h after treatment with EB (58 to 60 h after insert removal). Treatment with 2 mg EB terminated the growth of the largest ovarian follicle (> 5 mm in diameter) at device insertion in 16/16 and 14/15 cows in Treatments 1 and 2, respectively. Estrus was detected within an 8-h target period (48 to 56 h after insert removal) in 93, 87 and 81% of cows in Treatments 1, 2 and 3, respectively (P > 0.05). Pregnancy rates at 39 d post insemination were 60, 50 and 51% for Treatments 1, 2 and 3, respectively (P > 0.05). The pregnancy rates did not differ between cows that were anovulatory or those that had ovulated before the initiation of treatments (54%), or among cows that were 28 to 40, 41 to 60 or > 60 days post partum at insemination (43, 59 and 54%, respectively). Treatment with progesterone inserts for 5 or 7 d, PGF2 alpha at the time of insert removal and 1 mg EB 30 h later induced the high degree of synchrony of estrus and ovulation necessary for fixed-time insemination.     

Serum testosterone concentration, efficiency of estrus detection and libido expression in androgenized beef cows

Twenty multiparous, cyclic, nonlactating beef cows were blocked by dominance rank and randomly and equally allotted to 1 of 4 treatment groups: an untreated control group, a synovex-treated group which received 8 Synovex-H implants with no additional hormones, a testosterone-treated group which received 500 mg, i.m. and 1500 mg, s.c. testosterone enanthate on Day 1 with additional 1000 mg, s.c. doses of testosterone enanthate every 14 d, and a synovex + testosterone-treated group which received 8 Synovex-H implants with 500 mg, i.m. and 1500 mg, s.c. testosterone enanthate on Day 1 only. Blood samples were collected via jugular venipuncture once a week beginning 3 wk prior to start of treatment. In addition, samples were collected just prior to treatment; once a day for 1 wk after initiation of treatment; and then twice a week until 225 d after treatment. Efficiency of estrus detection was assessed 22 d prior to start of treatment and every 14 d thereafter for 98 d, using estrus detection trials with synchronized females or modified libido tests. Scores for estrus detection trials included total mounts in 1 h and the percentage of estrous cows detected. Libido was scored on a scale of 0 through 6. All testosterone treatments raised plasma testosterone concentrations above control and pretreatment levels (testosterone and synovex + testosterone > synovex > control; all P < 0.05). Synovex-, testosterone- and synovex + testosterone-treated females performed more mounts in 1 h than the controls (18, 9, 6 and 1, respectively; all P < 0.05). All testosterone-treated cows mounted a higher number of estrous females than the controls (P < 0.05). Only synovex + testosterone- and testosterone-treated cows received libido scores above pretreatment and control values. However, libido of testosterone-treated cows decreased over time, while that of synovex + testosterone-treated females remained high until Day 98. Libido scores correlated positively with the number of mounts in 1 h and the percentage of estrous females detected (0.70 and 0.44, respectively), and the correlation coefficient for these two factors was 0.63. In conclusion, the synovex + testosterone treatment was most effective for producing estrus detector females and libido testing was useful for evaluating sexual activity in androgenized females.     

Induction of follicular wave emergence for estrus synchronization and artificial insemination in heifers

The objective was to synchronize follicular wave emergence among cattle for synchronization of estrus and ovulation, and to determine pregnancy rate after AI at observed estrus. At random stages of the estrous cycle, a controlled internal drug release device (CIDR-B) was inserted intravaginally (Day 0) in 67 cross-bred beef heifers, and they were randomly allocated to receive either no further treatment (Control; n = 18); 5 mg of estradiol-17beta and 100 mg of progesterone im (E/P; n = 16); 100 microg im of GnRH (GnRH; n = 16); or transvaginal ultrasound-guided follicular ablation of all follicles > or = 5 mm (FA; n = 17). All heifers received a luteolytic dose of PGF (repeated 12 h later), and CIDR-B were removed on Days 9, 8, 6 or 5, in Control, E/P, GnRH or FA groups, respectively, so the dominant follicle of the induced wave was exposed to exogenous progesterone for a similar period of time in each group. Mean (+/- SEM) intervals (and range, in days) from treatment to follicular wave emergence in these groups were 3.5 +/- 0.6 (-2 to 8), 3.4 +/- 0.1 (3 to 4), 1.5 +/- 0.3 (-1 to 4), and 1.0 +/- 0.1 (0 to 2), respectively. Although the interval was longest (P<0.01) in the E/P and Control groups, it was least variable (P<0.01) in the E/P and FA groups. Intervals (and range, in days) from CIDR-B removal (and first PGF treatment) to estrus were 2.3 +/- 0.2 (1.5 to 4.5), 2.2 +/- 0.2 (1.5 to 3.0), 2.1 +/- 0.1,(1.5 to 3.5), and 2.5 +/- 0.1 (2.0 to 3.5), and to ovulation were 3.5 +/- 0.2 (2.5 to 5.5), 3.4 +/- 0.1 (3.0 to 4.5), 3.5 +/- 0.1 (2.5 to 4.5), and 3.8 +/- 0.1 (3.0 to 4.5), for Control, E/P, GnRH and FA groups, respectively (ns). The proportion of heifers displaying estrus was higher in the Control than in the FA group (94% versus 65%, P<0.05) and intermediate in EP and GnRH groups (87% and 75%). Heifers were inseminated approximately 12 h prior to ovulation (based on estrous behavior and ultrasound examinations). Pregnancy rates were 78%, 80%, 69% and 65% for Control, E/P, GnRH and FA groups, respectively (P=0.73). Results support the hypothesis that synchronous follicular wave emergence results in synchronous follicle development and, following progesterone removal, synchronous estrus and ovulation with high pregnancy rates to AI. The synchrony of estrus and ovulation in the E/P, GnRH and FA groups suggest that these treatments, in combination with CIDR-B, could be adapted to fixed-time insemination programs.