Short Estrous Cycles Research Articles

Effect of termination of pregnancy or long-term progestogen exposure on subsequent estrous cycle length and concentration of progesterone in plasma of heifers.

An experiment was conducted to determine whether short estrous cycles following abortion of heifers between 70 and 75 d of gestation are due to factors associated with the previous presence of a conceptus or long-term exposure of the uterus and(or) ovaries to a progestogen. Fifty crossbred heifers were randomly allotted at estrus (d 0) to five groups: control (n = 10), pregnant (Preg.; n = 14), progestogen (norgestomet) implant (Norg.; n = 9), progesterone-releasing intravaginal device (PRID; n = 9), or hysterectomy (Hyst.; n = 8). Control heifers were injected during the mid-luteal phase of an estrous cycle with 25 mg prostaglandin F2 alpha (PGF2 alpha) and length of the subsequent estrous cycle was determined. Beginning 6 to 8 d after estrus, heifers in the Norg. or PRID groups were given norgestomet ear implants or intravaginal coils, respectively, every 10 d for 70 d. Heifers were hysterectomized 5 to 8 d after estrus. Seventy to 75 d after conception, progestogen treatment or hysterectomy, heifers were injected (i.m.) with 25 mg PGF2 alpha and the last norgestomet ear implants or PRIDs were removed. Interval from PGF2 alpha injection to first estrus (means +/- SE) ranged from 2.5 +/- .2 to 4.4 +/- .7 d (P greater than .05). Length of the first estrous cycle means +/- SE) following PGF2 alpha-induced luteolysis or progestogen withdrawal was shorter (P less than .01) for the Preg. group (8.2 +/- .4 d) than for the control, Norg. and PRID groups (21.5 +/- .6 d; 19.3 +/- 1.4 d; and 18.2 +/- 1.3 d, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Depression of ovarian function and plasma progesterone and estradiol-17 beta in female goats chronically infected with Trypanosoma congolense.

Adult normocyclic female goats experimentally infected with Trypanosoma congolense developed irregular and shorter estrous cycles before complete cessation at the fourth cycle post-infection. This was followed within a month by a decline in the mean plasma progesterone and estradiol-17 beta levels. The peak luteal progesterone as well as pre-ovulatory estradiol-17 beta level declined progressively from the second to the fourth cycle post-infection. The ovaries became atretic with reduced numbers of primordial and primary follicles. The larger follicles became atretic at the tertiary stage with subsequent lack of corpora lutea formation. The rapidity of ovarian dysfunction appeared to be related to the degree of susceptibility of the individual infected goats.

Short estrous cycles and associated progesterone in serum of beef heifers aborted at various stages of gestation

Estrous cycles were observed and concentrations of progesterone were measured after abortion in crossbred Angus heifers that were injected with a prostaglandin F 2 alpha analogue about day 50 (15 heifers), 75 (14 heifers), 100 (13 heifers) or 125 (49 heifers) of gestation. The average interval from injection to first estrus was 3.6, 4.2, 3.7 and 6.4 d for heifers injected at an average of 50, 75, 100 or 125 d of gestation, respectively. Cycles of fewer than 13 d were classified as short, those of 13 to 16 d as intermediate, those of 16 to 24 d as normal, and those of more than 24 d as long. Heifers aborted at 50 d of gestation had seven short and eight normal first cycles; heifers aborted at 75 d had 11 short cycles, two normal cycles, and one long cycle; heifers aborted at 100 d had 12 short cycles and one normal cycle; whereas heifers aborted at 125 d had 25 short cycles, 13 normal cycles, two long cycles, six intermediate cycles. Three heifers failed to exhibit a second estrus by 50 d after abortion. Of those heifers having short first cycles, short second cycles occurred in one of seven heifers aborted at Day 50, three of 11 at Day 75, seven of 12 at Day 100 and 18 of 25 at Day 125. Serum progesterone was measured at 0, 1 and 2 d after injection and at 5 and 10 d after the first estrus. Concentration of progesterone in serum declined before estrus, then increased by 5 d after estrus in all cases. Progesterone concentration increased between 5 and 10 d after estrus in heifers exhibiting normal estrous cycles but docreased in heifers having short cycles. Data indicate that the percentage of heifers having single or repeated short cycles after abortion increases as the duration of gestation increases to 100 d.

Factors associated with shortened estrous cycles after abortion in beef heifers.

Forty-six crossbred Hereford heifers were allotted into five experimental groups. Fenprotalene, a prostaglandin analogue, was administered to induce abortion and (or) to regress the corpus luteum (CL) in four groups of heifers about 75 d after conception. The four groups were 1) pregnant heifers, 2) pregnant heifers with the ovary contralateral to the gravid uterine horn removed 24 h after fenprostalene injection, 3) same as Group 2 but with the ipsilateral, rather than the contralateral, ovary removed and 4) heifers with uterus removed (ovaries intact) about 35 d after conception. A fifth group of nonpregnant heifers received implants containing norgestomet from 10 to 76 d after estrus and were given fenprostalene 24 h before removal of the implant. Average length of the first estrous cycle after the fenprostalene injection was 11.2, 8.3, 9.7 and 19.1 for Groups 1, 2, 3 and 5, respectively. Estrous cycles were longer (P less than .05) in norgestomet-treated heifers. Hysterectomized heifers (Group 4) did not exhibit a second estrus by 50 d after fenprostalene treatment; otherwise, all first estrous cycles after the fenprostalene injection were either "short" (7 to 13 d) or "normal" (17 to 23 d). Twenty-two of 24 heifers that aborted had short estrous cycles and two had normal estrous cycles. Short estrous cycles occurred after abortion regardless of whether the ovary ipsilateral or contralateral to the previously gravid uterine horn ovulated. Early regression of the CL (short luteal phase) did not occur in nonpregnant heifers after long-term progestogen stimulation or after hysterectomy, but it did occur in heifers with a previously gravid uterus.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of intrauterine infection on the function of the corpora lutea formed after first postpartum ovulations in dairy cows

This study was carried out to determine the relationship between postpartum intrauterine infections, endocrine patterns and the function of corpora lutea formed following the first postpartum ovulations in dairy cows. Blood samples were collected daily starting from the day of parturition until 30 d after parturition or until the second postpartum estrus, whichever occurred first. Sera were assayed for progesterone (P 4), prostaglandin F 2α metabolite (PGFM), and luteinizing hormone (LH) concentrations. Palpations per rectum and real-time ultrasound scanning of the reproductive tracts were carried out in all cows once every 4 d for 1 mo, starting from Day 4 after parturition. In addition, endometrial swabs were collected aseptically from each cow once every 4 d during the first month postpartum. The swabs were cultured for aerobic and anaerobic bacteria. Twelve cows (60%) exhibited short estrous cycles (SC; 6 to 14 d long) following first postpartum ovulations. The mean preovulatory LH surges and LH patterns during the first postpartum cycles were similar in both groups, leading us to believe that lack of luteotrophic stimulation was not a factor in the occurrence of SC. Bacterial isolations were frequent in SC cows. The occurrence of moderate to heavy bacterial growth patterns and the repeated isolations of the similar organisms during postpartum suggests the persistence of uterine infections in SC cows. Increases in PGFM concentrations prior to luteolysis in SC cows were associated with moderate to heavy infection. Thus, postpartum uterine infections do not appear to affect ovulations, but prostaglandin (PGF 2α) released in response to uterine infection may contribute to early demise of the corpus luteum formed after the first postpartum ovulation.

Comparison of different methods to induce luteal regression with prosolvin during superovulatory treatment in heifers and cows

The objective of the present study was to determine whether parity is a factor that influences the estrous and ovulatory responses of female goats when they are stimulated by males that show increased sexual activity. To stimulate sexual activity, four adult male goats were subjected to photoperiodic treatment for 2.5 months comprising long days, with the treatment commencing on 1 November. On 14 April at 1900 h, a group of multiparous females (n = 21) and a group of 16 months-old nulliparous females (n = 19) were exposed to four bucks (two per group) for 15 days. Throughout the study period, the estrous behavior of these female goats was detected twice on a daily basis. Ovulations of the female goats were determined by ecography on days 7 and 18 after exposure to males. The sexual behavior of males was recorded twice every day from 0800 to 0900 h and from 1730 to 1830 h during the first 4 days after introduction in the pen of females. The total cumulative proportion of multiparous females that had ovulations (100%) and displayed estrous behavior (100%) during the 15 days of exposure to males did not differ (P > 0.05) from that of nulliparous females (100% and 95%, respectively). The interval between introduction of males and onset of estrous behavior did not differ (P > 0.05) between multiparous (1.9 ± 0.1 days) and nulliparous (1.7 ± 0.2 days) females. The proportion of females displaying a short estrous cycle was greater (P < 0.05) in multiparous (13/21, 62%) than in nulliparous (5/19, 26%) females. Duration of these shorter than typical estrous cycles did not differ (P > 0.05) between groups (multiparous: 5.2 ± 0.3 days, nulliparous: 4.5 ± 0.1 days). The number of anogenital sniffings was greater (P < 0.001) in males exposed to nulliparous than in those exposed to multiparous females. In contrast, the number of mounting attempts was greater (P < 0.01) in males that were introduced to multiparous than in those that were introduced to nulliparous does. The number of flehmen, nudging, self-marking with urine, and mounts was not different (P > 0.05) between males that were in contact with multiparous and nulliparous females. These results indicate that regardless of parity, female goats respond to male introduction if they are stimulated by males that were previously exposed to artificial long days to increase their sexual behavior.

Reproductive Senescence in Female C57BL/6J Mice: Ovarian Impairments and Neuroendocrine Impairments that Are Partially Reversible and Delayable by Ovariectomy*

Ovarian and neuroendocrine impairments were examined before and after the age-correlated loss of estrous cycles in C57BL/6J female mice. The role of ovarian secretions in inducing neuroendocrine impairments before and after the loss of estrous cycles was also examined by determining neuroendocrine impairments after prolonged ovariectomy. Young (6-month-old) cycling, middle-aged (12-, 14-, and 16-month-old) cycling or acyclic, and old (18-month-old) acyclic mice were used. Ovarian impairments were assessed by grafting old ovaries into young hosts. Neuroendocrine impairments were assessed by grafting young ovaries into middle-aged and old hosts, ovariectomized either at grafting or 2 months before, and by inducing a LH surge in mice that had been ovariectomized for 4 days, 1 month, or 2 months. One group of 16-month-old and one group of 18-month-old mice were also ovariectomized at 6 months of age; these groups were used to examine the steroid-induced LH surge. The LH surge was induced by inserting sc a single priming estradiol (E2) implant, followed by two more (surge-inducing) implants 6 days later; 33 h after the second implantation, mice were decapitated (1800 h). The number of estrous cycles supported by middle-aged and old ovaries grafted into young hosts was reduced by more than 90% compared with that in young ovaries. The number of estrous cycles supported by middle-aged and old hosts given young ovarian grafts was reduced by 60% and 90%, respectively, compared with that in young hosts. Middle-aged and old hosts also had progressively longer estrous cycles than young hosts. Levels of the E2-induced LH surge in middle-aged and old mice were also reduced by 60% and 90%, respectively, compared with levels in young mice. In old acyclic mice, ovariectomy for 2 months partially reversed impairments in the LH surge and partially restored the ability to support cycles with young grafts; these functions, normally 90% impaired in old mice, were only 60% impaired after prolonged ovariectomy. Moreover, ovariectomy 2 months before grafting in old hosts resulted in shorter estrous cycles and 60% fewer pituitary adenomas. In middle-aged cycling mice, ovariectomy for 2 months did not affect impairments in the LH surge or in the ability to support estrous cycles with young grafts; these functions remained 60% impaired in middle-aged mice ovariectomized for 2 months. If mice were ovariectomized when young, the age-correlated impairments of the E2-induced LH surge at 16 months were largely prevented.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of Low and High Fill Diets on Dry Matter Intake, Milk Production, and Reproductive Performance During Early Lactation

Feedstuffs analyzed for rate and extent of ruminal neutral detergent fiber disappearance were used to formulate two diets that differed for predicted time required for ruminal clearance of neutral detergent fiber. Diets with slow and fast estimated disappearance rate of neutral detergent fiber were termed and high and low fill, respectively. For both diets, crude protein, acid detergent fiber, neutral detergent fiber, net energy of lactation, and soluble protein were similar. Twenty-eight lactating cows were limit fed the rations 2 wk prior to calving, then fed for ad libitum consumption until 8 wk after calving.Cows fed low fill produced more milk (30.3 vs. 26.3kg) and milk protein (.97 vs. .78kg) and had higher incidence of short estrous cycles and fewer acyclic cows by 8 wk postpartum than cows offered high fill. Dry matter intake, fat-corrected milk yield, daily fat production, and solids-not-fat did not differ between diets. Rumen fermentation measurements for pH and ammonia-nitrogen concentrations were also not different between diets. Cows fed low fill tended to have higher rates of solids and liquid turnover and lower total dry matter in the rumen compared with cows fed high fill. Low ruminal pH on both diets as well as other physiological mechanisms may have been responsible for failure of rates of nuetral detergent fiber disappearance to affect intake of dry matter.

Cell Proliferation in the Principal Target Organs of the Dog (Beagle) Ovary during Various Periods of the Estrous Cycle

Cell proliferation in the principal target organs of the ovary was studied in 7 beagle dogs during proestrus, early estrus, secretory and regressive metestrus. Pulse labelling with (3H)-thymidine and autoradiography were applied and labelling indices were determined. Organs with squamous and with glandular epithelium except the mammary gland showed a proliferation peak during early proestrus, the incidence of labelling being higher in organs with squamous epithelium. During early proestrus the intensity of labelling decreased in organs with squamous epithelium in the following order: vulva, vagina, portio vaginalis, and portio supravaginalis. At this time cell replication was higher in the superficial glands of the cervix and corpus uteri as well as the circular layer of the myometrium compared with values from the basal glands or the longitudinal layer. The steepest decline of the proliferative activity occurred between the proestrous period. While some labelled cells were observed during secretory metestrus, labelling was almost absent during regressive metestrus. By contrast, the mammary gland began to develop at the periovulatory period and was at the height of its proliferative activity during secretory metestrus. It is concluded for species with a long estrous cycle that: (1) the rate of cell replication in the vulva, vagina, uterus and oviduct is at its peak at the beginning of the estrous cycle and declines during proestrus; (2) as compared to observations in species with short estrous cycles, cell proliferation is very low during metestrus.

Ovarian activity during normal and abnormal length estrous cycles in the goat.

Ovarian and behavioral cyclicity were studied during 3-5 estrous cycles in a group of 10 multiparous, Nubian does. Changes in ovarian morphology throughout the estrous cycle were identified and photographed laparoscopically. Forty-eight estrous cycles were observed during the study and of these, 21 were abnormally short in duration (mean +/- SEM, 6.5 +/- 0.5 days). Mean duration of the estrous cycle for the 27 normal length cycles was 21.5 +/- 0.8 days. Eighteen/21 (86%) of the short cycles and 6/27 (22%) of the normal cycles were initiated during early breeding season (between September 1st and October 15th). There were no differences (P greater than 0.05) in the duration of estrus for the short (mean, 2.9 +/- 0.3 days) and normal (mean, 2.8 +/- 0.8 days) cycle groups. A total of 6/11 (55%) of the short duration cycles examined laparoscopically appeared to be anovulatory, but ovulation was observed in all normal cycles examined. The number of corpora lutea (CL) observed during normal length and short estrous cycles was 3.1 +/- 0.2 and 2.2 +/- 0.2, respectively (P less than 0.01). The cumulative percentage of does that showed morphological evidence of ovulation by the first, second and fifth day after the onset of estrus was 30%, 60% and 100%, respectively. Based on distinct differences in morphology and development, 2 types of CL were identified. The maximum visible diameter of Type I and Type II CL was 9.4 +/- 0.6 mm and 5.1 +/- 0.5 mm, respectively. These data document ovarian morphology throughout the normal and abnormal duration estrous cycle of the goat and indicate that 1) short estrous cycles observed early in the breeding season are associated with prematurely regressing CL or anovulation and 2) the ovary produces 2 morphologically distinct types of CL which differ not only in size and appearance, but also potentially in postovulatory function and longevity.

Short estrous cycles in postpartum cows as influenced by level of milk production, suckling, diet, season of calving and interval to first estrus

The frequency of short cycles after the first postpartum estrus was determined from data collected in three experiments. Short estrous cycles (SEC) were defined as those less than 17 days long. Cows that were bred at the first estrus postpartum and conceived were included in the non-short cycle count. In Exp. 1, designed to determine the influence of genetic ability for milk production on postpartum traits, 16 of 118 Holstein cows (13.6%) had short estrous cycles. The incidence of SEC was greater in the low milk production group, but the differences were not significant (P>.25). This group had a shorter mean postpartum interval to first estrus (PPI) when compared to the high milk production cows (P<.025). Exp. 2 was designed to test the influence of suckling versus nonsuckling on postpartum traits, and seven of 54 Angus cows (13.0%) had SEC. The incidence of SEC in suckled and nonsuckled cows was 2 26 and 5 28 , respectively (P<.25). The nonsuckled cows had a shorter (P<.005) PPI than suckled cows. When these cows were grouped according to winter or summer calving, the incidence of SEC was 1 20 vs 6 34 (P<.25). In Exp. 3, designed to determine breed of sire x nutrition interactions on postpartum traits, there were 14 SEC out of 174 (8.0%) first estrous cycles in three parities of 58 crossbred cows. There was a tendency (P<.15) for more SEC to occur in the high nutrition group, but this may have been due in part to two cows in the high nutrition group that exhibited SEC in more than one parity. The high nutrition group also tended (P<.10) to have a shorter mean PPI than the low nutrition group. In all experiments, there were more SEC among cows displaying first estrus before 20 days postpartum.

Evidence for ovulation and fertilization in beef cows with short estrous cycles

Calves were weaned from 15 Polled hereford anestrous cows 25 to 42 days after calving. In eight cows the uterus was flushed on day 6 or 8 after the first postweaning estrus (day 0), and in seven cows the oviduct ipsilateral to the ovary containing an ovulation papilla was removed and flushed on day 3. One ovum (morula) was recovered from the eight uterine flushings, while six ova were recovered from six of the seven oviductal flushings. Of the six, three were fertilized (4 to 8 cells), two unfertilized and only the broken zona pellucida of one was recovered. An ovulation papilla was observed in all cows at the time of oviduct removal. Six of the 15 cows had cycles less than 12 days, and from four of those six fertilized ova were recovered. The data indicate that previously anestrous cows ovulate at their first postweaning estrus and the ova released are capable of being fertilized. Failure to maintain pregnancy appears to be due to early corpus luteum regression.

Reducing the incidence of short estrous cycles in beef cows with norgestomet

Twenty-nine anestrous cows suckling calves 27 to 67 days old were allotted to 3 treatment groups according to calving date. Calves were weaned from all cows; 9 cows received no further treatment, while 10 were implanted with 6 mg of norgestomet 9 days before calves were weaned and 10 were implanted when calves were weaned. All implants were removed after 9 days. Twenty-two cows exhibited estrus within 10 days after treatment, and all exhibited estrus within 25 days. In the cows exhibiting estrus in 10 days, norgestomet reduced the incidence of 8 to 12-day cycles from 83.3 percent in the control group to 30 percent when implanted before weaning and to zero when implanted at weaning. Conception rates at first service were increased from zero for cows which were not implanted to 33.3 and 80 percent for those implanted before and at weaning, respectively. These data demonstrate that the presence of a progestogen before the first postpartum estrus increases conception rates and reduces the percentage of previously anestrous cows exhibiting short estrous cycles after their calves are weaned.

Short estrous cycles and associated serum progesterone levels in beef cows

Short estrous cycles in beef cows were investigated in two experiments. In trial 1, breeding dates from 2,854 fall-calving Angus cows were used to determine the incidence of short estrous cycles. Of 198 cycles of less than 17 days, 170 were between the first and second detected estrus. Estrous cycles of 7 to 10 days occurred more frequently (P<.005) than other short estrous cycles. Eight-day estrous cycles were most frequent. In the second experiment, calves were weaned from 25 of 33 anestrous spring-calving, crossbred Simmental cows. Compared to herdmates still nursing calves, an increased percentage of cows which had calves weaned were observed in estrus within 10 and 25 days after the date of weaning (P<.005) and a higher percentage had 7- to 10-day estrous cycles. Cows that were observed in estrus within 10 days after weaning were inseminated with Angus semen at their first estrus and with Simmental semen at their second estrus. No cows conceived on the first estrus of 7- to 10-day estrous cycles; 61.5% conceived on the second estrus. Serum progesterone was higher (P<.01) before the second estrus than the first.

Reinstatement of Estrous Cycles in Middle-Aged Spontaneously Persistent Estrous Rats: Importance of Circulating Prolactin and the Resulting Facilitative Action of Progesterone*

Spontaneous persistent estrus (SPE), although a common feature of senility, may occur in middle-aged rats. Thus, in Charles River CD rats it often appears in virgin females 6-12 months old. Whereas in aged SPE rats a single injection of LH is commonly followed either by pseudopregnancies (PSPs) in repetition or by PSP succeeded by a number of short estrous cycles, the usual result in middle-aged CD SPE rats is the immediate occurrence of I or more short cycles, after which SPE returns. Among 46 such animals, only 10 (22%) presented PSP, while 30 (65%) merely presented short cycles. The other 6 rats returned promptly to SPE after a brief diestrus. From these results it is postulated that events after a luteinizing dose of LH or the introduction of a set of corpora lutea by any other means are determined by the amount of basal PRL secretion in the days after treatment. If PRL is minimal, SPE returns promptly; if moderately elevated, short cycles appear because of low grade progesterone secretion from the co...

Effect of infusion of uterine purulent exudate into the bovine uterus

Purulent exudate from the uteri of two nonlactating Holstein cows with chronic pyometra was aspirated into a 50 cc syringe via an artificial insemination pipette. The two fractions were mixed, cultured, divided into 14 equal parts and infused into the uteri of 14 other nonlactating cows. All recipient cows had had at least one estrous cycle of normal length and were in the early luteal phase (day 4–8). On days 3, 7, 14 and 21 following infusion, the reproductive tract was examined per rectum, content of the uterus was cultured for bacteria, and endometrial condition was assessed by biopsy and histopathology. The lengths of the estrous cycles of the recipient cows were shortened P < 0.01) from 21 ± .5 days to 13.3 ± 1.4 days. Estrus was determined by palpation per rectum and/or observation. Over the experimental period, Pasteurella sp., Corynebacterium pyogenes and other diphtheroids were isolated from 64, 57 and 86% of the cows, respectively. An inflamed endometrium was associated (P<0.10) with the presence of Pasteurella sp. on day 7 following infusion. No other associations were found when the presence of bacteria, vaginal discharge, or short estrous cycles were compared. The infusion of purulent exudate apparently irritated the endometrium causing an early return to estrus rather than causing pyometra. It is probable that postpartum and lactational stress are involved in the development of pyometra.

Incidence of short estrous cycles after weaning in beef cows (1979)

Incidence of short estrous cycles after weaning in beef cows (1979)

Short Estrous Cycles in New Zealand Dairy Cattle

Over 18% of cows returning to service within 49 days of first insemination were remated within the first 17 days. A distinct peak representing 31.4% of all short return intervals occurred from 8 to 10 days after first insemination. Because nonreturn rates to second insemination following these service intervals were equal to nonreturn rates for first inseminations, it is probable that some cows were experiencing short estrous cycles of about 9 days duration. The incidence of these cycles increased with increasing herd size and was most common among second calving 3 year-old cows. As this same phenomenon was also apparent where entire or vasectomised bulls ran with cows in large herds, these 8 to 10 day return intervals were not the consequence of behavioral sub-estrus. However, since cows were not examined, occurrence of ovulation at each estrus could only be presumed.

Use of Progestational Compounds Alone or in Combination with Estrogen for Synchronization of Estrus

Three trials using injections of progesterone alone or in combination with an estrogen were conducted. In trial I two hundred twenty cycling, virgin heifers were synchronized with daily injections for 24 days of 20 mg. of progesterone alone or in combination with 10, 20 or 40 mcg. of estradiol or 40 mg. of progesterone alone or in combination with 20, 40, or 80 mcg. of estradiol. Two other groups received the progesterone plus three injections of estradiol on the 23rd, 24th and 25th days. Synchronization varied from 70 to 100% of the heifers showing estrus in a 4-day period. Fertility was lowered at the synchronized estrus in all treated groups except in the group receiving 40 mg. of progesterone and 80 meg. of estradiol. In trial II one hundred four cycling, virgin heifers were injected with either 20 or 40 mg. of progesterone and either 80 or 160 meg. of estradiol. Ninety-five to 100% of the heifers showed estrus in a 4-day period; however, fertility was lower than that in the controls. In trial IIIninety cycling, virgin heifers received a single injection of 62.5, 125 or 250 mg. of an acetophenone derivative of 16a, 17a dihydroxyprogesterone (AD) either alone or in combination with estradiol enanthate (ENT) in a ratio of either 250 or 500 parts AD to one part of ENT. Another group of 120 heifers received either 75, 100 or 125 mg. of AD in a ratio of six AD to one ENT. Poor synchronization was experienced in all groups of heifers receiving a single injection. Inclusion of ENT in the injection at the higher level caused many short estrous cycles.

Factors Associated with Estimated Fertilization and Service Efficiency of Cows1,2

Summary Embryonic mortality was estimated by using the difference between percentage of estrous cycles recurring between 18 and 25 days for the cows which were bred at the previous estrus compared with those which were not bred. The study included 6,719 calvings carried to term, 668 abortions, and 1,915 estimated embryos lost, for a total of 9,302 fertilizations. The estimated embryonic loss for all cows was 20.6% and abortion loss was 7.2%. Clinically normal cows averaged 11.4% and clinically normal cows and heifers averaged 16.6% embryonic loss. Though fertilizing capacity was equal, normal heifers had a significantly higher embryo loss than cows in their second and third reproductive periods. Fourth and fifth reproductive period cows had the highest efficiency as determined from the percentage of services carried to term. Fertilizations per service and embryo loss declined markedly with increasing age. Reproductive efficiency was very low for cows with infections of the genital tract and estimated embryo loss exceeded 40%. Losses were equally high for cows with cystic ovaries. Cows having only short estrous cycles averaged 28.8% embryo loss and 24.2% services carried to term. Cows with an abnormal calving from the preceding gestation averaged 14.4% embryo loss and 39.2% services carried to term. Monthly differences in reproductive efficiency were relatively unimportant as compared with yearly differences.