Uterine influences on the formation of subnormal corpora lutea in seasonally anestrous ewes

The hypothesis that subnormal luteal function after induced ovulation in anestrous ewes was the result of uterine influences exerted during the periovulatory period was tested. Crossbred ewes (n = 27) in seasonal anestrus were induced to ovulate by administration of 12 doses of 250 ng of LHRH at 2-h intervals, followed immediately by a bolus injection of LHRH (250 micrograms; d 0). Ewes were unilaterally hysterectomized on either d -3 (PRELHRH) or 2 (POSTLHRH). Daily blood samples were collected and assayed for progesterone (P4) and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM). All ewes were slaughtered on d 10, and corpora lutea (CL) were collected, weighed, and assayed for concentration of P4. All ewes that ovulated exclusively in the ovary ipsilateral to the remaining uterine horn had a transient increase in plasma P4 of 2 to 3 d (short luteal phase). In ewes with at least one CL in the isolated ovary, elevated plasma P4 was maintained after hysterectomy but was consistently lower (P less than .05) in POSTLHRH ewes than in PRELHRH ewes. Concentrations of PGFM did not differ between treatments. The CL ipsilateral to the remaining uterine horn weighted less (P less than .01) and contained less P4 (P less than .01) than contralateral CL. These data confirm the hypothesis that premature regression of subnormal CL is uterine-dependent in a local fashion. Presence of the uterus during the follicular and(or) early luteal phase inhibited subsequent luteal function in seasonally anestrous ewes.     

The reproductive performance of Finn × German Mutton Merino and purebred German Mutton Merino Ewes

The sexual season, i.e. the sexual cycle activity, of Finn × German Mutton Merino (Finn × GMM) ewes was found to extend from August to March. In a group of purebred German Mutton Merino (GMM) ewes the sexual season extended from June to January.After July–August and October–November lambings, 90–95% of the Finn × GMM crosses renewed postpartum sexual activity within 90 and 75 days, respectively. Only 40% of the November lambing purebred GMM ewes started new cycles within 105 days postpartum.The responsiveness of the Finn × GMM ewes to hormonal treatment was high (90–100%) during different months of the year. The fertility at the synchronized or induced oestrus was 60–75% throughout the year, with a mean litter size of 2.0 lambs per lambing.     

Influencing factors on the level of the ovulation rate in sheep during the main breeding season--an ultrasonographic study

The main breeding season for sheep in Germany is from the beginning of September until the end of November. The aim of this study was to determine the factors which influenced the level of the ovulation rate (o. r.) during this period. The examination was conducted over three years and included Booroola.Mutton Merino crosses [heterozygous- (F+) carriers and non-carriers of the Booroola- (FecB) fecundity gene], German Mutton Merino (GMM) and German Blackheaded (GB). In total 1326 examinations were carried out. Between the 8th to 12th day after estrous detection an ovary diagnosis was performed by transrectal scanning with a 7.5 MHz linear probe. The number of the corpora lutea per ewe (o. r.) was documented. The weight and the body condition of the ewes was also determined. During the breeding season the breed of the ewe had the main effect on the level of the o. r. (p < 0.05). This is the reason that the statistical model can only be applied for each breed. The effects of age, year of examination and day of the main breeding season were tested. The age of the ewes and the date of the examination during the breeding season had the main effect on the o. r. In GMM and GB the age influenced the o.r. with an effect of 8.3% and 4.2%. The effect of the season was vice versa (Gmm 3.2%; GB 8.2%). Non-carriers of the Booroola- (FecB) fecundity gene behaved similar like the GMM. However, only the high fecundity carriers of the FecB-gene were strongly influenced by the season. For each breed there exists a typical threshold value for the body weight above which further weight has no effect on the o. r. (GMM 65-70 kg, GB 75-80 kg, non-carriers of the Booroola-FecB gene 55-60 kg and carriers of the FecB-gene 60-65 kg). This value lies at about 80% of the highest measured weight of each breed. The results demonstrated that a balanced age structure in combination with a optimum weight influenced the level of o. r. In addition the date of the season is especially important.     

Suppressive action of gonadotropin-releasing hormone and luteinizing hormone on function of the developing ovine corpus luteum

Experiments were conducted to examine the effects of exogenous GnRH and LH on serum concentrations of progesterone (P4) in the ewe. Ewes in Exp. 1 and 2 were laparotomized on d 2 of an estrous cycle and ewes with corpora lutea (CL) in both ovaries were unilaterally ovariectomized. Ewes with CL in one ovary only were not ovariectomized. While they were anesthetized, ewes (n = 5) were injected with 25 micrograms GnRH (Exp. 1) or 50 ng GnRH (Exp. 2) into the artery supplying the ovary bearing the CL. Control ewes (n = 5 in each experiment) were injected similarly with saline. In Exp. 3, six ewes were injected i.v. (jugular) on d 2 with 100 micrograms oLH (t = 0) and 50 micrograms oLH at 15, 30 and 45 min; six control ewes were injected similarly with saline. Jugular blood was collected from all ewes at frequent intervals after treatment for LH analysis and on alternate days of the cycle through d 10 or 11 for P4 analysis. Treatment with 25 micrograms GnRH increased serum concentrations of LH at 15, 30, 45 and 60 min postinjection (P less than .001) and reduced serum concentrations of P4 on d 7 through 11 (treatment x day interaction; P less than .05). Injection with 50 ng GnRH caused a slight increase in serum concentrations of LH at 15 min but had no effect on serum concentrations of P4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian activity,transuterine embryo migration and prenatal losses in Ethiopian highland ewes

A study was conducted on 1442 Ethiopian highland ewes to determine the seasonality of ovarian activity, intrauterine embryo migration and prenatal reproductive wastage. Assessment of ovarian follicular activity revealed that a higher (p < 0.01) proportion of ewes ovulated in the dry season than in the heavy and light rainy seasons. However, there was a tendency (p = 0.057) of decline in the mean number of ovulations per ewes during the light rains. The mean diameter of the largest follicle on the ipsilateral ovary was higher (p < 0.01) in both ewes with single and those with twin corpora lutea (CL) than on the contralateral ovary; and, compared to ewes with single CL, it was higher (p < 0.05) in those with twin CL. The right ovary was more active (p < 0.001) only in single-ovulating ewes. Similarly, a higher (p < 0.001) proportion of ewes were pregnant in the right horn. Embryos migrated to the opposite horn in single-, twin- and triple-ovulating ewes. There was a higher (p < 0.001) tendency for the left-to-right migration than the opposite. There was significant (p < 0.01) association between embryo loss and site and number of ovulations. Embryo loss was higher (p < 0.01) in ewes with twin ovulations on the right ovary. It is very likely that these results indicate a better chance of embryo survival in the right uterine horn.     

Characterization of ovine follicles destined to form subfunctional corpora lutea

A study was done to test whether ovulatory follicles destined to form subfunctional corpora lutea differed from normal ovulatory follicles in steroidogenic function. Twenty-five ewes were treated with prostaglandin F2 alpha on d 11 of the estrous cycle, then unilaterally ovariectomized before (n = 13) or after (n = 12) the surge of luteinizing hormone (LH) at the induced estrus to collect "control" follicles, which would have produced normal corpora lutea. In 15 ewes, the second ovary was removed 63 to 84 h later to collect "treated" follicles before (n = 7) or after (n = 8) the second expected surge of LH. Five ewes (control) were allowed to ovulate from the remaining ovary at first estrus and another five (treated) at the second estrus (3 to 4 d later). Treated ewes had lower serum progesterone than control ewes during the ensuing cycle (P less than .05). Treated follicles contained less estradiol in the theca (4.4 +/- .6 vs 10.0 +/- 2.5 ng; P less than .05), less androstenedione (.1 +/- .1 vs 1.0 +/- .2 ng) and estradiol (.5 +/- .1 vs 2.9 +/- 2.2 ng) in the granulosa (P less than .05) and less progesterone in the follicular fluid (.8 +/- .4 vs 3.3 +/- .8 ng; P less than .05) than control follicles, when removed before the surge of LH. Follicles removed after the surge of LH did not differ. In conclusion, ovulatory follicles with low steroidogenic function became corpora lutea that secreted lower-than-normal quantities of progesterone.     

Ram influence on ovarian and sexual activity in anestrous ewes: effects of isolation of ewes from rams before joining and date of ram introduction.

A 2-yr experiment was conducted to determine whether isolation of ewes from rams is necessary to achieve a high response to the ram effect and whether ewes respond as well in May as in June. The experiment was conducted at two locations, with the same four treatments at each location. The four treatments differed with respect to ewe proximity to rams before mating (isolated vs adjacent) and date of joining with novel breeding rams (May 15 vs June 15). The proximity treatment at one location was changed in the 2nd yr; teaser rams were joined with the ewes instead of being adjacent to them. Overall, 86% of the eligible ewes were judged to have responded to the ram effect. A period of isolation before mating did not increase response compared with ewes that remained adjacent to, or in contact with, rams (86 vs 85%). Response was greater (P less than .05) in June and in the 2nd yr (P = .05). A physiological response, different from that generally described, was identified. Ewes ovulated approximately 8 d (8.0 +/- .19 d) after joining with breeding rams. The subsequent ovulation, accompanied by estrus, occurred approximately 15 d later (15.3 +/- .29 d). Eighty-five percent (87/102) of the ewes sampled responded in this manner. However, 82% (31/38) of a sample of these ewes had at least one morphologically normal corpus luteum when examined by laparoscopy 4 d after joining. It seems that these corpora lutea were not completely functional with respect to progesterone production. The ram effect can be achieved without prior isolation of ewes from rams.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in Ovarian Follistatin Levels During the Oestrous Cycle in Sheep may Serve as an Intraovarian Regulator

The expression and concentration of follistatin and activin change during oestrous cycle suggesting their involvement in the regulation of follicular development. The aim of this study was to determine the level, source and potential role of follistatin in the sheep ovary. Follistatin in ovarian venous blood, measured by radioimmunoassay, remained at its low level from follicular phase (day ?1 and 0) to mid‐luteal phase (days 11–13) phase but were significantly elevated during the late luteal phase (days 14 and 15) when corpora lutea underwent regression. Western blot analyses of follicular fluid at day 15 of the cycle showed two strong bands at 42 and 45 kDa and weakly stained bands at 39 and 31 kDa. At day 0, these bands became weaker and the 39 kDa band became undetectable. However, there were no differences in follistatin concentrations between ovaries with and without functional corpus luteum (CL) during the whole luteal phase. In addition, although the ovaries of Booroola ewes normally contain more corpora lutea than those of normal merino ewes, follistatin concentrations in both jugular and ovarian venous blood were similar in Booroola and normal merino ewes. It is concluded that the secretion of follistatin from the ovary is not related to the formation of CL or high ovulation rate of Booroola ewes. The elevation in follistatin concentration in follicular fluid and ovarian blood during late luteal phase may indicate a dual role of follistatin in the luteolysis of existing CL and development of new follicle cohort.     

Maintenance of the corpus luteum of early pregnancy in the ewe. III. Differences between pregnant and nonpregnant ewes in luteal responsiveness to prostaglandin F2 alpha

The effects of pregnancy and number of corpora lutea on luteal regression induced with prostaglandin F2 alpha (PGF2 alpha) were examined in 93 ewes. Bred and nonpregnant ewes were assigned randomly to receive a single im injection of PGF2 alpha: 0, 2, 4, 6, 8 or 10 mg/58 kg body weight. Injections were given on d 13 postestrus. The concentration of progesterone in serum 24 h after PGF2 alpha injection was affected by dose (P less than .001). The effect of pregnancy and the interaction of pregnancy with number of corpora lutea on levels of progesterone in serum were significant (P less than .05); therefore, data were partitioned according to pregnancy status and analyzed separately. There was an effect of number of corpora lutea on serum concentration of progesterone in pregnant (P less than .01) but not nonpregnant ewes (P greater than .10). Similar relationships among groups were observed for the concentration of progesterone in luteal tissue. In nonpregnant ewes the minimum dose of PGF2 alpha to produce a significant suppression of progesterone in serum (P less than .05) was 4 mg/58 kg body weight. In pregnant ewes with one or two corpora lutea, the minimum effective doses were 6 and 10 mg/58 kg body weight, respectively. The concentration of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) in serum was related to the dose of PGF2 alpha injected. There were no differences in the concentration of PGFM in serum between pregnant and nonpregnant ewes either before or after injection. Corpora lutea of early pregnancy appear to be resistant to the luteolytic effect of PGF2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)     

提高低产羊群产肉性能的技术研究

本试验对所有细度在60s以上的基础母羊全部采用"新吉"细毛羊配种改良;细度在60s以下的基础母羊,分别用德国肉用美利奴、白头萨福克、无角道赛特、夏洛莱和特克赛尔五个品种的肉用公羊杂交,试验结果表明,用肉羊品种与本地羊杂交能显著提高子代的产肉性能,其中以德国肉用美利奴的改良效果最好,德肉美公羊的细度达60～64s,对产毛性能较差的母羊有明显的改良作用。     

Breed and environmental influences on weaner lamb production in Zimbabwe

Performance of the Dorper and Mutton Merino breeds and their crosses was assessed from 1,305 ewe and 1,453 lamb records from six lambing seasons. Dorper and Mutton Merino were mated in all combinations under an accelerated lambing system and crossbred females were mated to Suffolk rams. The Dorper and Mutton Merino breeds were not significantly different for fertility, pre-weaning lamb growth and survival. Suffolk sired lambs from crossbred ewes grew rapidly and were heaviest at birth and at weaning. They also survived better than lambs from the other breeding groups and this contributed to the higher weaning rate (P less than 0.05) in crossbred ewes. Weight of weaned lambs per ewe exposed to the ram per season was 12% higher (P less than 0.05) in the Dorper than the Mutton Merino ewes. However lifetime production was 28% higher (P less than 0.01) in Mutton Merino ewes due to significantly superior longevity. Crossbred ewes were highly productive. Individual heterosis was not significant but estimates were positive for most traits. Growth rate and survival of lambs increased as age of dam increased to 48 and 40 months respectively. Lambs born to previously non-lactating ewes were heavier and survived better than lambs born to ewes lactating in the previous season. Lambs born and reared as singles were 25% heavier at birth (P less than 0.001) and 52% heavier at weaning (P less than 0.001) than those born and reared as twins. Male lambs grew faster and were 7% heavier at weaning than females (P less than 0.001).     

An antegrade surgical uterine flush technique for ova collection in the ewe

A surgical uterine flush technique was evaluated for percentage of ova/corpora lutea (CL) collected and development of reproductive adhesions in 79 superovulated ewes. The median collection rate for ova/CL was 70%, and 47 of 79 ewes had greater than or equal to 67% ova/CL. At 50 to 80 days after uterine flushing, celiotomies were performed on 50 of the 79 ewes to evaluate the reproductive tract for adhesions. Adhesions of the reproductive tract were not found. Thirty ewes were given prostaglandin F2 alpha, were mated, and became pregnant. The ova collection rates were comparable with rates reported in ewes in which oviductal flush methods were used; however, adhesions did not develop and reproductive function was maintained after surgery.     

In vitro effect of leptin on growth hormone (GH)- and insulin-like growth factor-I (IGF-I)-stimulated progesterone secretion and apoptosis in developing and mature corpora lutea of pig ovaries

This study was designed to determine whether leptin modulates growth hormone (GH)- and insulin like growth factor-I (IGF-I)-stimulated progesterone (P4) production by corpora lutea (CL). Luteal cells were recovered from early developing (ELP) and mature (MLP) corpora lutea and cultured in defined medium with various combinations of GH, IGF-I, and leptin (0-200 ng/ml). P4 concentrations in the media were determined after 48 h of culture. During the early luteal phase, leptin at all used doses had no effect on basal P4 secretion, but it did suppress caspase-3 activity. When added in combination with GH, it had no effect on either GH-stimulated P4 secretion or apoptosis. Concomitant treatment with IGF-I and leptin decreased P4 secretion and parallelly increased the apoptosis rate. In mature corpora lutea of full secreting capacity, leptin at all doses had no effect on basal and GH-stimulated P4 secretion and caspase-3 activity. Only at the highest dose (200 ng/ml) when leptin was added with IGF-I did P4 secretion decrease with no effect on the caspase-3 activity. We conclude that the role of leptin is to restrict the stage of CL formation. During this luteal phase, leptin acts as an antiapoptotic factor and, at the same time, reverses antiapoptotic action of IGF-I, thereby protecting cells from excessive apoptosis and supporting retention of appropriate cell numbers, which is necessary for maintenance of homeostasis in developing CL.     

Duration of pregnancy and diurnal distribution of lambing in sheep with different genotypes

Based on 1103 lambings the duration of pregnancy was determined for the breeds German Mutton Merino, German Blackhead Mutton and their Booroola crosses. Furthermore the influence of age and body mass of the ewes as well as number, sex and body mass of the born lambs were considered. German Blackhead Mutton have with 145/146 days on average a 4-5 days shorter duration of pregnancy than German Mutton Merino with 150 days. The examined effects influenced the pregnancy duration only insignificantly or not at all. An influence of the breed, however, was determined. In the pen with limited light during the night all genotypes lambed mostly between 9.00 a.m. and 3.00 p.m. During the day time 12-26% more ewes lambed than during the remaining 12 hours of the day.     

Endocrinology of the postpartum period in the Pelibuey ewe

The postpartum (PP) period in the Pelibuey ewe was studied. Laparotomies were performed on 14 ewes in the first year at d 10, 20 and 30 PP, and at d 10 and 20 PP in the second year on 17 ewes. Progesterone concentrations were determined in serum taken daily, from 4 to 7 d after parturition until estrus. Temporal fluctuation of luteinizing hormone (LH) was determined in samples taken at 30-min intervals for 4 h weekly. The mean interval from lambing to first ovulation was longer (P less than .001) in 1980 (59 +/- 4.9 d) than 1979 (26 +/- 3.1 d), the mean interval from lambing to first estrus was also longer (P less than .001) in 1980 (91 +/- 5.6 d) than 1979 (51 +/- 5.5 d). Follicles were present on the ovaries of the majority of the ewes at d 10. The mean diameter of the largest follicles on each ovary was reduced (P less than .025) in ewes in 1980 (6 mm) compared with 1979 (7.7 mm). Corpora lutea (CL) occurred in 67 and 75% of the ewes by d 20 and 30, respectively in 1979; no CL were found by d 20 in 1980. Progesterone profiles suggested that the PP period was composed of a period of anestrus, and a period of cyclic ovarian activity with one, two or three ovulations without behavioral estrus. In some ewes, the first cycle was of shorter duration, and its CL secreted less progesterone (P less than .05) relative to CL of silent and regular estrous cycles. Luteinizing hormone peaks were recorded as early as 6 d PP. When progesterone concentrations were elevated to luteal phase levels, the frequency, but not magnitude, of LH peaks per 4-h bleeding period was reduced (P less than .05) relative to anestrus. It is concluded that there are periods of anestrus and of silent cycles, which precede the first postpartum estrus in Pelibuey ewes.     

Ovulation rate and litter size of Barbados, Targhee and crossbred ewes

Ovulation rate was measured in Barbados Blackbelly (United States strain; B), Targhee (T), Barbados X Targhee (B X T) and Barbados X Dorset-Targhee (B X DT) ewes at first and second estrus following synchronization of cycles early in the breeding season. Body weight at sponge removal differed (P less than .001) between B (30.9 kg) and T ewes (54.9 kg) and was intermediate for B X T (44.9 kg) and B X DT (43.5 kg) ewes. Ovulation rate was higher (P less than .01) at first and second estrus for B (1.86, 2.04), B X T (1.93, 2.04) and B X DT (1.72, 1.80) than for T (1.29, 1.40) ewes. Regressions of ovulation rate on body weight within the breed groups did not differ significantly from each other and the average was significant (b = .049 +/- .014 CL/kg at first estrus and b = .046 +/- .011 CL/kg at second estrus, where CL = number of corpora lutea), but differences between the groups in body weight did not explain the differences in ovulation rate. Litter size for B, B X T, B X DT and T groups was 1.71, 1.84, 1.84 and 1.28, respectively. The B X T ewes were superior to the average of the B and T ewes for ovulation rate (P less than .05) and litter size (P less than .01); there was no direct estimate of embryo survival, but the results indirectly indicate superiority of the crossbreds for this component also.(ABSTRACT TRUNCATED AT 250 WORDS)     

Breed differences in uterine and ovarian measurements in gestating swine

Ovulation rate, ovary weight, corpora lutea weight and uterine length were measured at 10 or 35 d of gestation in Duroc (199) and Yorkshire gilts (114). Embryos were counted at d 35. Yorkshires had significantly more corpora lutea than Durocs (13.6 vs 12.3 at d 10; 13.9 vs 12.4 at d 35). At d 10 breeds did not differ in uterine length, but by d 35 Duroc uteri were longer (P less than .01) than Yorkshire uteri (411 vs 375 cm) despite having fewer (P greater than .05) embryos (9.9 vs 10.5). Ovary weight did not differ between breeds at 10 or 35 d. Homogeneity analyses showed that the correlation matrices were significantly different between breeds at d 35 but not at d 10. In Durocs, high positive correlations existed between total embryo number and corpora lutea number (.57), ovary weight (.53) and corpora lutea weight (.25), whereas corresponding correlations were small in Yorkshires (.21, -.02 and -.03, respectively). In Yorkshires, strong negative correlations existed between total embryo survival and corpora lutea number (-.55), ovary weight (-.30) and corpora lutea weight (-.55), but in Durocs corresponding correlations were small (-.12, .14 and -.10, respectively). These results suggest that animal scientists should consider breed differences in levels of performance and its relationships among traits when designing or interpreting experiments.     

Luteal toxicity evaluation in rats

The corpora lutea (CL) are endocrine glands that form in the ovary after ovulation and secrete the steroid hormone, progesterone (P4). P4 plays a critical role in estrous and menstrual cycles, implantation, and pregnancy. The incomplete rodent estrous cycle stably lasts 4–5 days and its morphological features can be distinguished during each estrous cycle stage. In rat ovaries, there are two main types of CL: newly formed ones due to the current ovulation (new CL), and CL remaining from prior estrous cycles (old CL). In the luteal regression process, CL were almost fully regressed after four estrous cycles in Sprague-Dawley rats. P4 secretion from CL in rodents is regulated by the balance between synthesis and catabolism. In general, luteal toxicity should be evaluated by considering antemortem and postmortem data. Daily vaginal smear observations provided useful information on luteal toxicity. In histopathological examinations, not only the ovaries and CL but also other related tissues and organs including the uterus, vagina, mammary gland, and adrenal glands, must be carefully examined for exploring luteal changes. In this review, histological and functional characteristics of CL in rats are summarized, and representative luteal toxicity changes are presented for improved luteal toxicity evaluation in preclinical toxicity research.     

Quantitative micromorphological study of the ovaries in sheep after estrus synchronization and superovulation in the autumn mating season

The quantitative micromorphological changes of tertiary follicles and corpora lutea (CL) were studied in ewes in the autumn mating season after oestrus synchronization, induced by administration of PGF2 alpha (Oestrophan Spofa) at a rate of 125 micrograms, and after superovulation, induced by administration of PMSG (Antex Leo, Denmark) at a rate of 1000 I. U., or PMSG at rates of 750 and 1000 I. U. together with 50,000 I. U. vitamin A (Axerophthol Spofa). The highest number of ovulations was obtained in ewes treated with 1000 I. U. together with vitamin A (3.4 +/- 3.0) and after administration of 1000 I. U. PMSG alone (2.6 +/- 2.74). The highest number of tertiary follicles was recorded in ewes after administration of PGF2 alpha. The proportion of tertiary atretic follicles was the highest in ewes after administration of PMSG (64.6%). The occurrence of the luteinizing form of atresia was recorded only in ewes treated with PMSG (4% of the total number of atretic follicles). Using the caryometric analysis of the luteal cells of corpora lutea, the ewes of the experimental groups had two-peak variation curves; this corresponds to the theory of the presence of two luteal types in the tissue of the corpus luteum in ewes. As determined morphometrically, the smallest proportion of connective tissue out of the total volume of ewes' ovaries was found after administration of 1000 I. U. PMSG together with vitamin A. Administration of vitamin A together with PMSG had a favourable influence on the over-all follicular response, on the average number of ovulations, and on the proportion of non-atretic follicles.     

Increased ovulation rate of adult ewes treated with anti-bovine LH antiserum during the normal breeding season

Adult Suffolk ewes (n = 14) were treated on d 10 of the estrous cycle with anti-bovine luteinizing hormone (LH) antiserum. Control ewes (n = 10) were treated with normal horse serum. Estrous behavior and the number of corpora lutea and ovarian follicles were examined at the subsequent estrous cycle. Daily plasma concentrations of progesterone (P4), follicle stimulating hormone (FSH) and estradiol were determined before and after treatment. Ewes treated with antiserum had a higher (P less than .05) ovulation rate (2.7 +/- .2) than did controls (2.1 +/- .1). No differences were found in the numbers of large (greater than 5 mm) or small (less than 5 mm) follicles between treatment groups. Estrus was delayed (P less than .025) approximately .6 d/in ewes treated with antisera. Immunoreactive FSH increased (P less than .05) within 1 d after treatment and remained higher than the controls for 5 d. Peak estradiol concentrations occurred on d 17 for treated ewes compared with peak concentrations on d 15 or 16 for control ewes. The P4 concentrations were generally less (P less than .025) in treated ewes throughout the luteal phase of the treatment cycle. These data demonstrate that ovulation rate is increased in ewes treated with LH antiserum. The marked increase in plasma FSH suggests a possible mechanism whereby ovulation rate is enhanced.