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PubMed1997

Circadian variation in basal plasma corticosterone and adrenocorticotropin in the rat: sexual dimorphism and changes across the estrous cycle.

Sexual dimorphism in the rat hypothalamic-pituitary-adrenal axis was investigated by determination of plasma corticosterone and immunoreactive (I-) ACTH in males and in females at each stage of the estrous cycle. A serial blood-sampling technique enabled assessment of covariation of the two hormones across the full circadian range of their concentrations within individual animals. Distinct diurnal rhythms in plasma corticosterone were evident in all rats, and the degree and timing of this rhythmicity, determined by cosinor analyses, did not vary with gender or cycle stage. There were, however, marked differences in absolute levels of corticosterone across the estrous cycle, with the average daily concentration (mesor) increasing progressively from a minimum at estrus (129 +/- 11 ng/ml) to a maximum 3 days later at proestrus (246 +/- 14 ng/ml). The mesor corticosterone value in male rats (102 +/- 21 ng/ml) was not different from that in estrous females, but was lower than that in females at all other stages of the cycle. In contrast, no gender- or cycle-related differences were detected in absolute levels of I-ACTH, although distinct diurnal rhythms, synchronous with those for corticosterone, were evident in all groups. Accordingly, a strong and positive within-rat relationship between plasma corticosterone and I-ACTH was observed in all groups, but there was a clear shift in the nature of this relationship across the estrous cycle, such that the slope (i.e. concentration of plasma corticosterone per unit concentration of I-ACTH) was minimal in males and estrous females and maximal in proestrous females. In conclusion, this study shows that the extent of sexual dimorphism in resting plasma corticosterone levels is dependent on estrous cycle stage, being absent at estrus and maximal at proestrus. Moreover, this variation in plasma corticosterone was not accompanied by corresponding changes in plasma I-ACTH, suggestive of cycle-related changes in responsiveness of the adrenal cortex to trophic stimulation.

Adrenocorticotropic Hormone↗
PubMed2002

Repeat breeding in dairy heifers: follicular dynamics and estrous cycle characteristics in relation to sexual hormone patterns.

Repeat breeding occurs at an incidence of 10% in the Swedish dairy cow population. Evidence is available for a hormonal asynchrony around estrus in repeat-breeder heifers (RBH). This asynchrony seems to be the underlying cause for a series of dysfunctions such as prolonged standing estrus and delayed ovulation, leading to fertilization failure. For further determinations of repeat-breeder estrous cycle characteristics, seven strictly selected RBH and six virgin heifers (VH) were studied during 3-7 consecutive cycles, with particular attention paid to the estrous period. Follicular dynamics were studied by ultrasonography and related to estrous behavior and pattern of sexual hormones (progesterone, estradiol-17beta, and LH) in peripheral circulation. Mean group data were compared and a classification model was designed. The most prominent findings for RBH were prolonged duration of estrus, delayed LH peak, prolonged lifespan of the preovulatory follicle, and a late postovulatory rise in plasma progesterone. There was also a strong tendency for peri-ovulatory suprabasal progesterone levels in RBH. It is suspected that these deviations cause changes in the microenvironment of the preovulatory follicle, negatively affecting the final maturation of the oocyte. The heterogeneity of the RBH group underlines the multifactorial cause of the repeat-breeder syndrome. The VH formed a homogenous group with data varying within physiological limits. A classification model based on three characteristic variables managed to identify 81% of the VH and 79% of the RBH correctly. Results from this study propose that some heifers have general, consistent problems in synchronizing estrous events, displayed as varying symptoms in the course of consecutive estrous cycles. These subfertile animals could be classified as repeat-breeders.

Animals↗
PubMed2000

Induction of superovulation and recovery of fertilized oocytes in prepubertal miniature pigs after treatment with PG600.

The purpose of this study was to examine whether superovulation can be induced by hormonal treatment with PG600 (400 IU eCG and 200 IU hCG) at the prepubertal stage in miniature pigs. In Experiment 1, 14 prepubertal miniature pigs received 1, 1/2 or 1/4 vial of PG600, im on Day 0 (the first day of treatment). Presentation of estrus was monitored thereafter. On Days 10 to 13 (i.e., 6 to 8 d after estrus), the number of corpora lutea (CL) and residual follicles was counted by an exploratory laparotomy. Injection of 1/2 vial of PG600 effectively induced estrus and ovulation in the pigs. In Experiment 2, 15 prepubertal miniature pigs that received 1/2 vial of PG600 were artificially inseminated into the uterus by an exploratory laparotomy at 100 to 104 h after PG600 injection. Oocytes were recovered from the oviducts at 121 to 145 h after PG600 administration. The oocyte recovery rate was 66% (15 oocytes/pig, average), and 84% of these were at the 1-cell stage. In Experiment 3, 5 prepubertal miniature pigs that received 1/2 vial of PG600, followed by 100 IU hCG 70 h later, were artificially inseminated into the uterus. Oocytes were recovered synchronously at 120 to 122 h after PG600 treatment. The recovery rate was 80% (17 oocytes/pig, average) and 90% of the oocytes recovered were at the 1-cell stage. These results suggest that superovulation of prepubertal miniature pigs can be induced by 1/2 vial of PG600 injection, and by the combined treatment with PG600 and hCG injection, the fertilized ova can be synchronously recovered at around 120 h after PG600 injection. This procedure may provide a useful system for biomedical research using the miniature pigs, especially for producing transgenic animals for use in human disease models.

Animals↗
PubMed1997

Behavioral dominance and corpus luteum function in red deer Cervus elaphus.

Times of the ovulatory LH surge and characteristics of the rise in circulating progesterone concentrations after ovulation in red deer hinds were investigated in relation to each animal's dominance status. Observations were made during the 1992 (experiment 1) and 1993 (experiment 2) breeding seasons, while the same 12 hinds were held in a pen in the absence of a stag. Ovulation was synchronized by administration of progesterone followed by luteolytic prostaglandin F2 alpha analogue. Social status was determined for each hind by noting dyadic agonistic interactions during the period of progesterone treatment. Hinds were weighed before and after the experiments. Time of onset of estrus (lordosis) was recorded while handling at 3-hr intervals (for 81 hr in experiment 1; 96 hr in experiment 2) after progesterone withdrawal, and blood samples were collected at these times to characterize the preovulatory LH surge. Subsequently, daily blood samples were collected for up to 11 days for measurement of progesterone concentrations. There was a tendency for weight change to be related to dominance status in experiment 1 and this was significant in experiment 2 (p < 0.01). The rate of increase in circulating progesterone concentration after ovulation was related to status (data of experiments 1 and 2 combined; p < 0.02), but was not correlated with the time of estrus or with the time or height of the LH surge. A third experiment (carried out in 1993), when the same hinds were kept with a stag after induced ovulation, showed that time of estrus (mating) was not related to dominance status. The data suggest that corpus luteum function is affected by social status. The results are discussed in the context of mechanisms by which dominance status influences the sex of a hind's calves.

Animals↗
PubMed1999

Bovine viral diarrhea virus: its effects on estradiol, progesterone and prostaglandin secretion in the cow.

Bovine viral diarrhea virus (BVDV) is a major cattle pathogen responsible for a spectrum of symptoms, including reproductive failure. This study was designed to establish the effects of BVDV infection on estradiol, progesterone and PGF2alpha secretion in the cow. Seven BVDV-free cows were challenged with non-cytopathogenic BVDV (strain Pe 515: 5x10(6) tissue culture infected dose50) so that peak viremia occurred during the initial phase of luteal development in a synchronized estrous cycle. Ovulation was also synchronized in 7 sham-infected animals. Within 2 wk of inoculation, viremia, leukopenia and serum neutralizing antibodies were recorded in all of the BVDV-infected cows but not the sham-infected animals. Between Day 4 and Day 9 post estrus the BVDV-infected cows had significantly (P<0.01) lower plasma estradiol levels than the sham-infected animals. However, the BVDV infection did not alter rectal temperatures, plasma progesterone concentrations or PGF2alpha secretion 17, 18 and 19 d post estrus. These data highlight a potential causal link between BVDV viremia, endocrine dysfunction and poor fertility in the cow.

Abortion, Veterinary↗
PubMed1999

Fertility in zebu cattle (Bos indicus) after prostaglandin administration and artificial insemination.

A total of 137 cycling zebu cows, each receiving a single dose of prostaglandin PGF(2alpha)were used in an oestrus synchronization programme on three different farms. Of the cows on the three farms, 60.6 and 90.5% showed overt oestrus and luteolysis, respectively. Pregnancy rate to fixed time inseminations following single injection of PGF(2alpha)was 61.4% for farm 1, significantly higher than the values of 45.7 and 46.9% for farms 2 and 3, respectively. The pregnancy rates to second service of rebred cows were 53.3, 50.0 and 50.0% for the three farms, respectively, with no significant differences between each. Fertility classification of the cows based on progesterone (P(4)) concentration showed that 6.6% of cows on the three farms were incorrectly diagnosed as having corpora lutea; 2.9% of them had incomplete luteolysis and 5.1% may have lost their embryos between days 21 and 45 post-insemination. The pregnancy rate was 10% higher in the rainy season than in the dry season. Cows with body condition scores of 3 and 4 had a higher overall pregnancy rates than those with a body condition score of 2. The findings of this study further confirm the luteolytic efficacy of prostaglandin in inducing oestrus in zebu cattle and indicate that the nutritional status of the cows must be satisfactory before embarking on oestrus synchronization programmes.

Animal Feed↗
PubMed1980

Effect of stage of diestrus and number of cloprostenol (ICI 80, 996) injections on intervals to estrus, LH peak and ovulation in heifers.

Intervals to the onset of estrus, luteinizing hormone (LH) peak and ovulation were compared in diestrous heifers after each of two cloprostenol treatments. Diestrous heifers were grouped at the first treatment (T1) according to day of the cycle, with heifers on days 5 through 8 designated as early diestrus and heifers on days 9 through 17 designated as late diestrus. Cloprostenol treatment was repeated (T2) 11 days after T1, at which time heifers in both groups were at similar stages of the estrous cycle. Visual observation, identification of the preovulatory LH peak, and rectal palpation were utilized to estimate data parameters. Split-plot analysis of variance showed a significant treatment x group interaction (P < .05). Time from prostaglandin treatment to the onset of estrus was similar for the early diestrous group after T1 (x = 53.1 hours ) and the early and late diestrous groups after T2 (x = 49.4 hours and 45.4 hours respectively). This interval was longer (P < .05) for the late diestrous group after T1 (x = 60.8 hours ) than for either group after T2, but not different from that for the early diestrous group after T1. Serum progesterone concentrations were higher (P < .05) at the time of T1 in the late diestrous group (x = 5.8 ng/ml ) than in the early diestrous group (x = 3.0 ng/ml ) or in either group at the time of T2 (x = 2.8 and 3.2 ng/ml respectively). Over all heifers, the synchrony of the onset of estrus was more precise (P < .05) after T2 than T1. Intervals from the onset of estrus to ovulation were not affected by group or treatment (overall mean = 24.4 +/- 1.0 hours, n = 42). We conclude that different recommendations for appointment artificial insemination (AI) may be indicated depending on the number of prostaglandin injections which are used in a prostaglandin synchronization program prior to insemination.

Journal Article↗
PubMed1990

Early pregnancy associated thrombocytopenia as an initial response to pregnancy in cattle.

This study was conducted to determine if early pregnancy-associated thrombocytopenia exists in cattle as has been demonstrated in mice and in humans. Three experiments were designed to compare peripheral platelet counts in pregnant versus nonpregnant animals. In Experiment 1 heifers (n = 25) were artificially inseminated 12 h after the onset of estrus. Peripheral platelet counts in 19 pregnant versus 6 nonpregnant heifers did not reveal any significant differences between groups after insemination. In Experiment 2 embryos were collected nonsurgically from superovulated cows (n =18) on Days 6 to 7 after estrus. Platelet counts were monitored every 12 h after the first insemination until 60 h after the second insemination. Platelet counts and the number of embryos collected nonsurgically from these superovulated donors did not show any significant correlations (P>0.05). Ten recipient heifers synchronized to donor animals received either an unfertilized ovum or a good quality embryo via nonsurgical transfer into the uterus. There were no significant reductions in platelet counts after transfer. In Experiment 3 platelet counts were monitored daily in four pregnant and five nonpregnant recipient heifers between Day 0 and Day 30 after embryo transfer on Day 8 of the cycle. The platelet counts did not reveal any significant differences between the pregnant and nonpregnant groups throughout Days 0 to 30. These results indicate that early pregnancy-associated thrombocytopenia cannot be demonstrated in cattle. Peripheral platelet counts cannot be used as an indicator of early pregnancy in cattle.

Journal Article↗
PubMedDate not supplied

Synchronous assessment of sperm motility and fertilizing ability in the hamster following treatment with alpha-chlorohydrin.

To investigate the relationship between sperm motion parameters and fertilizing ability, a model was developed to assess both of these endpoints synchronously using a toxicant that inhibits sperm motion. alpha-Chlorohydrin (ACH) was administered daily for 4 days to male hamsters at 0, 33, 49, 66, and 83 mg/kg body weight. These males were then allowed a 45-minute breeding period with untreated estrus females on the morning of day 5. One hour after breeding, sperm samples were surgically recovered from the uteri of the females for motility analysis. Six hours later, eggs were flushed from the oviducts and evaluated for fertilization. Cauda epididymal sperm were also collected from the males shortly after breeding. Proportions of motile and progressively motile sperm were manually quantified, and overall sperm velocity and the velocity of representative vigorously swimming sperm in both the uterine and epididymal samples were measured by computer-aided sperm analysis. Significant decreases in in vivo fertilization rates and epididymal sperm motion parameters were observed at 66 and 83 mg/kg ACH, whereas uterine sperm motion was adversely affected at all ACH dosages used. All sperm motion parameters except the percentage of motile sperm in the epididymis were significantly correlated with fertilization rates by both linear and logistic regression. Overall, uterine and epididymal sperm endpoints predicted fertilizing ability comparably well. Stepwise multiple linear regression gave a model containing epididymal sperm velocity (EVCL) and uterine sperm percent motility (UMOT) with an R2 value of 0.649. Stepwise multiple logistic regression gave models containing EVCL alone and EVCL and UMOT in binary (fertile/infertile) and quantal models, respectively.

Acetylcholine↗
PubMed1980

Circadian pacemaker times gonadotropin release in free-running female hamsters.

Female golden hamsters (Mesocricetus auratus) were housed individually on a photoperiod of LD 6:18 (lights 1000-1600 h). Estrous cyclicity was interrupted for an average of 16 wk after which cycles resumed spontaneously. Such animals are photorefractory, remaining cyclic on normally nonstimulatory photoperiods. Photorefractory females were exposed to continuous darkness in which estrous cyclicity in the population rapidly became asynchronous as each hamster's "day" assumed the endogenous periodicity (tau) of her circadian clock. Tau usually approximated but rarely equaled 24 h. Successive estrous cycles in each animal possessed a periodicity of 4 tau. Preovulatory luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release occurred at a specific time of the animal's circadian day, bearing a discrete phase relationship of 2 to 3 h to the circadian rhythm of locomotor activity. Thus, although seemingly asynchronous with respect to laboratory time, peak preovulatory gonadotropin release on proestrus in free-running hamsters was synchronized with respsect to circadian time. We conclude that a circadian pacemaker times preovulatory gonadotropin release in hamsters.

Animals↗
PubMed1985

Pregnancy rates relative to recipient plasma progesterone levels on the day of nonsurgical transfer of frozen/thawed bovine embryos.

A total of 71 synchronized dairy heifers (Holstein Friesian x German Black Pied) were used as recipients of seven-day old frozen/thawed bovine embryos. Plasma progesterone concentrations and corpus luteum quality on the day of nonsurgical transfer (= day 7) were determined and related to pregnancy rates or estrus intervals in nonpregnant recipients. A total of 32 recipients (45.1 %) maintained pregnancy; 39 recipients (54.9 %) did not. No significant differences could be detected between progesterone levels in recipients that remained pregnant (3.14 +/- 0.24 ng/ml; x +/- SEM ) and those that did not maintain pregnancy (3.23 +/- 0.28 ng/ml). Optimal progesterone levels were between 2 and 5 ng/ml coinciding with a pregnancy rate of 51.1 % (24 47 ). Pregnancy rates apparently were decreased when progesterone levels were below 2 ng/ml (35.3 %; 6 17 ) or above 5 ng/ml (28.6 %; 2 7 ). Hence, optimal progesterone levels were identical to those for freshly collected embryos reported previously by Remsen et al. (1). Bovine corpus luteum quality graded by rectal palpation was related to some extent to progesterone levels but not to pregnancy rates. Out of 39 nonpregnant recipients seven animals (17.9 %) with a mean plasma progesterone level of 3.76 +/- 0.72 ng/ml showed an extended estrus interval of more than 55 days, probably indicating early embryonic mortality. Progesterone levels did not significantly differ between nonpregnant recipients with estrus intervals of various length. Plasma progesterone levels at the time of transfer are of limited diagnostic value for screening recipients prior to transfer of frozen/thawed embryos.

Journal Article↗
PubMed1981

The differential effect of progesterone on concentrations of luteinizing hormone and follicle-stimulating hormone in heifers.

The effects of progesterone on LH and FSH concentrations in cattle are not clearly understood. The objective of this experiment was to determine the effect of various concentrations of progesterone on serum concentrations of LH and FSH in heifers. After estrous synchrony, animals were assigned to four different treatment groups (n = 10/group). Heifers received vaginal coils containing either 2% or 6.75% progesterone between days 8-10 (luteal phase) or days 17-18 (follicular phase) after estrus. Coils remained in place for 7 days. One day before removal of coils, all animals received an injection of prostaglandin-F2 alpha to cause regression of existing corpora lutea. Both the stage of the cycle and the percentage of progesterone in the coil affected serum concentrations of progesterone while the coils were in the vagina. Concentrations of FSH during progesterone treatment were not different for animals on different treatments. While coils were in the vagina, there was a significant increase in serum LH concentrations in heifers in the follicular phase given 2% progesterone coils, but no increase in LH was observed in the other three treatment groups. After removal of the progesterone coils, but before the preovulatory gonadotropin surges, LH increased but not FSH. The LH and FSH surges occurred synchronously. After the surges, FSH concentrations increased at a faster rate than LH. These data suggest that differential feedback mechanisms exist for LH and FSH in heifers. (Endocrinology 108: 568, 1981)

Animals↗
PubMed2003

Invited review: Treatment of cows with an extended postpartum anestrous interval.

Cows with an extended interval from calving to first ovulation (PPI) have increased intervals from calving to conception and are more likely to be culled compared with cows with a short PPI. In year-round calving dairy herds, between 11 and 38% of cows are reported as anestrus by 50 or 60 d after calving. In seasonally calving dairy herds, between 13 and 48% of cows are diagnosed as anovulatory anestrus at the start of the breeding period. Ovulation and estrus after calving are delayed when the positive feedback effects of estradiol on release of LH from the pituitary, and circulating concentrations of metabolic hormones such as insulin and insulin-like growth factor-I, are reduced by a variety of environmental factors. The main factors are limited energy intake, lower body reserves, increased partitioning of energy to milk production, suckling, and peripartum disease. Treatment options for cows with an extended PPI include hormonal and management strategies. Hormonal treatments that include a period of progesterone supplementation result in the majority of treated animals displaying estrus with a subsequent luteal phase of normal duration and improved pregnancy rates compared with untreated controls. Hormonal interventions also tend to have more predictable outcomes compared with management changes, such as manipulating body condition or dietary intakes after calving, and usually have some estrous synchronization effect, thus facilitating the use of artificial insemination. However, responses to any treatment are variable and are related to those factors that influence duration of the PPI, such as body condition and parity.

Anestrus↗
PubMed1988

Thermal, productive, and reproductive responses of high yielding cows exposed to short-term cooling in summer.

Effect of cooling on body temperature, milk production, estrous behavior, and reproductive performance was examined in 66 estrous-synchronized, Israeli-Holstein dairy cows. Cooling was by an automated system, which actuated sprinkling (30 s) followed by forced ventilation (4.5 min) for 30-min periods. Cows were cooled 9 times/d between 0500 and 2100 h over 10 d, starting 1 d before expected estrus until d 8 post estrus. Cooling reduced typical diurnal rise of body temperature in summer heat-stressed cows by .5 to .9 degrees C, and body temperature was maintained close to normothermic temperature (38.6 degrees C). Milk production of cooled cows was 2.6 kg/d (+8%) above control at end of the cooling period. More cooled cows than noncooled exhibited standing estrous behavior; in noncooled cows, silent ovulations or anestrus were more frequent. Conception rate of cooled cows did not differ from control, suggesting need for a longer than a 10-d cooling period for improvement of fertility. The cooling system has potential to alleviate heat stress in dairy cows and to improve their thermal balance, productive, and reproductive performances.

Animals↗
PubMed1986

Phasic changes in immunocytochemical stainability of pituitary luteinizing hormone cells associated with their ultrastructural changes during estrous cycle in the rat.

Changes in the immunoreactivity of pituitary luteinizing hormone (LH) cells and in their fine structure were studied in 4-day-cyclic female rats along with the radioimmunoassay of pituitary and serum LH. Pituitary LH increased during diestrus (DE) and in early proestrus (PE) to a maximal level at noon of PE, followed by a marked decrease by 2100 h PE. Serum LH stayed at low levels in estrus (E) and in DE, while they displayed a significant increase at PE. Light microscopic immunocytochemistry distinguished intensely and weakly stained cells using rat LH beta antiserum. The populations of intensely stained cells were 80% at PE, 30% at E and 75% at DE. This suggests that all of the LH cells do not secrete LH synchronously on the afternoon of PE. Immunoreactivity of LH cells was related to the amount of secretory granules stored in the cells as determined by the superimposition technique. Analysis of the LH storage site by the protein A-gold method confirmed that the small secretory granules, which accumulated in LH cells at DE or PE, certainly contain LH. At least two LH cell types were distinguished: one is the oval or polygonal cell with flattened rER numerous mitochondria, abundant small secretory granules (about 200 nm), a well developed Golgi complex, and a round nucleus. The other has similar structural characteristics along with large secretory granules which are more than 300 nm in diameter. At noon of PE almost all of the LH cells were the first type while the second ones were mainly found at DE or E. The relationship of these LH cell types of the male gonadotrophs is discussed.

Animals↗
PubMed2005

Fish meal supplementation alters uterine prostaglandin F2alpha synthesis in beef heifers with low luteal-phase progesterone.

The objective of the current study was to evaluate the effect of omega-3 fatty acids in fish meal on mitigating uterine PGF2alpha synthesis in heifers with low luteal-phase concentrations of progesterone. Animals were individually fed a corn silage-based diet supplemented with fish meal (5% of DMI; n = 12) or corn gluten meal (6% of DMI; n = 13). Estrous cycles were synchronized using PGF2alpha beginning on d 25 of supplementation. Random heifers from each supplement group (n = 6 fish meal, and n = 7 corn gluten meal) were given three additional i.m. injections of PGF2alpha (25 mg) at 12-h intervals beginning at 0600 on d 3 after estrus to induce formation of corpora lutea that secrete lower concentrations of progesterone. Jugular blood samples were collected daily commencing on d 1 and continuing through d 16 of the estrous cycle to determine serum progesterone concentrations. Oxytocin was administered i.v. (100 IU) to heifers on d 16 after estrus to stimulate uterine PGF2alpha synthesis. Before statistical analyses, heifers were sorted to either normal or low luteal-phase progesterone as determined from serum progesterone on d 9 of the estrous cycle. After sorting, treatment groups consisted of 1) normal luteal progesterone + fish meal (n = 6); 2) low luteal progesterone + fish meal (n = 6); 3) normal luteal progesterone + corn gluten meal (n = 6); and 4) low luteal progesterone + corn gluten meal (n = 7). Serum concentrations of the PGF2alpha metabolite following oxytocin stimulation tended (P = 0.09) to be greater in heifers with low luteal-phase progesterone compared with heifers with normal luteal-phase progesterone. Fish meal supplementation mitigated this response in heifers with low luteal-phase progesterone (P < 0.05), but had no effect on heifers with normal luteal-phase progesterone. In conclusion, the omega-3 fatty acids in fish meal seem to decrease uterine PGF2alpha synthesis in heifers with low luteal-phase serum concentrations of progesterone.

Animal Feed↗
PubMed1998

Close synchrony of ovulation in superstimulated heifers that have a downregulated anterior pituitary gland and are induced to ovulate with exogenous LH.

The synchrony of ovulation was examined in superstimulated heifers that had a downregulated pituitary gland and which were induced to ovulate by injection of exogenous LH. The pituitary was downregulated and desensitized to GnRH by treatment with the GnRH agonist deslorelin. Nulliparous heifers (3.5 yr old) at random stages of the estrous cycle were assigned to 1 of 3 groups, and on Day -7 received the following treatments: Group 1 (control, n = 8), 1 norgestomet ear implant; Group 2 (GnRH agonist, n = 8); Group 3 (GnRH agonist-LH protocol, n = 8), 2 deslorelin ear implants. Ovarian follicle growth in all heifers was superstimulated with twice-daily intramuscular injections of FSH (Folltropin-V): Day O, 40 mg (80 mg total dose); Day 1, 30 mg; Day 2; 20 mg; Day 3, 10 mg. On Day 2, all heifers were given a luteolytic dose of PGF (7 A.M.), Norgestomet implants were removed from heifers in Group 1 (6 P.M.). Heifers in Group 3 were given an injection of 25 mg, i.m. porcine LH (Lutropin) on Day 4 (4 P.M.). Ovarian follicle status was monitored at 8-h intervals from Day 3 (8 A.M.) to Day 6 (4 P.M.) using an Aloka Echo Camera and 7.5 MHz transducer. Heifers in Groups 2 and 3 exhibited estrus earlier (P < 0.05) than heifers in Group 1. Heifers in Group 2 did not have a preovulatory LH surge and they did not ovulate. Individual control heifers in Group 1 ovulated between 12 A.M. on Day 5 and 8 A.M. on Day 6. Heifers with deslorelin implants and injected with LH in Group 3 ovulated between 4 P.M. on Day 5 and 8 A.M. on Day 6. It was confirmed that superstimulated heifers with GnRH agonist implants can be induced to ovulate with LH. It was also demonstrated that ovulation is closely synchronized after injection of LH. Thus, a single, fixed-time insemination schedule could be used in a GnRH agonist-LH superovulation protocol, with significant practical and economic advantages for superovulation and embryo transfer programs.

Animals↗