Induced parturition in dairy cattle: A comparison of a corticoid (flumethasone) and a prostaglandin (PGF2α) in different age groups

Parturitions were induced in 66 dairy cows and heifers of the German Black Pied breed, 11 to 13 days before term, using either a highly potent corticosteroid (flumethasone: 2 × 5 mg, 10 to 14 hr apart), or prostaglandin F_2α (20 mg i.v.) and initiating treatments either in the morning (A.M.) or late afternoon (P.M.). At those dose levels parturition was induced in $\text{50}\text{50}$ animals treated with flumethasone, and in $\text{9}\text{9}$ heifers, but only in $\text{5}\text{7}$ cows treated with PGF_2α; placentas were retained in all cases in which parturition was induced. Intervals between initiation of treatments and parturition were shorter in flumethasone-treated animals (flumethasone: 42.5 hr; PGF_2α 57.2 hr); with both drugs, they were approximately 10 to 15 hr shorter in younger animals. The first flumethasone treatment at P.M. prolonged the intervals to parturition in cows (first treatment A.M.: 37.8 hr; P.M.: 52.9 hr), but not in normal age heifers (A.M.: 27.6 hr; P.M.: 25.9 hr); in early bred heifers, this trend was reversed (A.M. 41.6 hr; P.M.: 31.8 hr). No circadian differences in response to PGF were noted. Mean intervals to postpartum conceptions were 93 and 94 days for PGF_2α-treated cows and heifers, and 123.5 and 125 days for flumethasone-treated cows and heifers, respectively.     

Effect of transfer of one or two in vitro-produced embryos and post-transfer administration of gonadotropin releasing hormone on pregnancy rates of heat-stressed dairy cattle

Pregnancy rates following transfer of an in vitro-produced (IVP) embryo are often lower than those obtained following transfer of an embryo produced by superovulation. The purpose of the current pair of experiments was to examine two strategies for increasing pregnancy rates in heat stressed, dairy recipients receiving an IVP embryo. One method was to transfer two embryos into the uterine horn ipsilateral to the CL, whereas the other method involved injection of GnRH at Day 11 after the anticipated day of ovulation. In Experiment 1, 32 virgin crossbred heifers and 26 lactating crossbred cows were prepared for timed embryo transfer by being subjected to a timed ovulation protocol. Those having a palpable CL were randomly selected to receive one (n = 31 recipients) or two (n = 27 recipients) embryos on Day 7 after anticipated ovulation. At Day 64 of gestation, the pregnancy rate tended to be higher (P = 0.07) for cows than for heifers. Heifers that received one embryo tended to have a higher pregnancy rate than those that received two embryos (41% versus 20%, respectively) while there was no difference in pregnancy rate for cows that received one or two embryos (57% versus 50%, respectively). Pregnancy loss between Day 64 and 127 only occurred for cows that received two embryos (pregnancy rate at Day 127=17%). Between Day 127 and term, one animal (a cow with a single embryo) lost its pregnancy. There was no difference in pregnancy rates at Day 127 or calving rates between cows and heifers, but females that received two embryos had lower Day-127 pregnancy rates and calving rates than females that received one embryo (P < 0.03). Of the females receiving two embryos that calved, 2 of 5 gave birth to twins. For Experiment 2, 87 multiparous, late lactation, nonpregnant Holstein cows were synchronized for timed embryo transfer as in Experiment 1. Cows received a single embryo in the uterine horn ipsilateral to the ovary containing the CL and received either 100 microg GnRH or vehicle at Day 11 after anticipated ovulation (i.e. 4 days after embryo transfer). There was no difference in pregnancy rate for cows that received the GnRH or vehicle treatment (18% versus 17%, respectively). In conclusion, neither unilateral transfer of two embryos nor administration of GnRH at Day 11 after anticipated ovulation improved pregnancy rates of dairy cattle exposed to heat stress.     

Modifying the double-Ovsynch protocol to include human chorionic gonadotropin to synchronize ovulation in dairy cattle

The objectives were to determine whether rates of conception, ovulation, presynchronization, or follicle and CL characteristics were altered after modifying the Double-Ovsynch (DO) protocol to include hCG compared with the DO protocol. Primiparous and multiparous lactating dairy cows (N = 183), and nulliparous dairy heifers (N = 51) were used. Cows were blocked by parity and heifers were stratified by age and breed before being randomly assigned to one of two treatments. All females received either 100 μg GnRH or 2000 IU hCG im, at initiation of the Pre-Ovsynch (PO) portion of the DO protocol (PO: GnRH/hCG, 7 days PGF_2α and 3 days GnRH). After 7 days, females started the Breeding-Ovsynch portion of the DO protocol (Breeding-Ovsynch: GnRH, 7 days, PGF_2α, 48 or 56 h and GnRH 16 hours timed artificial insemination with sex-sorted semen). Transrectal ultrasonography and blood samples were used to assess ovarian structures, ovulation, pregnancy diagnosis, and concentration of progesterone in plasma. Conception rates were similar in females treated with GnRH or hCG in cows (32.2 and 25.0%) and in heifers (30.8 and 36.0%). Ovulation rates in cows at the onset of PO were increased with hCG compared to GnRH (77.2 vs. 62.2%, P < 0.05). Concentrations of progesterone 7 days post-hCG or GnRH were greater in cows treated with hCG compared with GnRH (least significant mean ± SEM; 4.3 ± 0.3 and 3.0 ± 0.3 ng/mL, P < 0.01), but did not differ in heifers (4.5 ± 0.9 and 2.9 ± 0.9 ng/mL). More cows ovulated within 7 days post-hCG and a greater proportion of these cows tended to have failed luteal regression by Day 3 post-PGF_2α compared with cows that had ovulated to GnRH (29.6 vs. 16.1%, P ≤ 0.10). The overall percentage of females which were synchronized to PO did not differ between GnRH- or hCG-treated cows (61.5% and 52.2%) and heifers (42.3% and 40.0%). In conclusion, no overall improvement in fertility was achieved by replacing the first injection of GnRH in the DO protocol with hCG.     

The influence of ovulation number and ovarian dimensions on embryo production in superovulated cattle

Twenty-one cycling Angus heifers and five Holstein cows received a subcutaneous (SC) injection of 50 mg of progesterone (P) in oil for 14 consecutive days. On day 6 of (P) treatment, animals were injected intramuscularly (IM) with 6 mg of estradiol valerate, and on day 13, received an IM injection of 2,000 IU of Pregnant Mare Serum Gonadotropin. Three additional Angus heifers were used as non-hormone treated controls. Seventeen of 21 heifers and 4 of 5 cows (81%) exhibited estrus within 48 to 132 hr following P treatment. Two of the five animals in which estrus was not observed were palpated as pregnant and discarded from the study. Treatment animals showing estrus were randomly assigned either to Group I, animals bred by natural service, or Group II, animals artificially inseminated with two straws of frozen semen at 12-hr intervals for a total of four breedings. Twenty-one animals were slaughtered 2 to 6 days after the onset of estrus, and those animals in which estrus was not detected were slaughtered 10 days after the last P injection. Two of the 24 treated animals had no ovulations. A total of 397 ovulation points ($\text{397}\text{22}$) were counted for a mean ovulation rate of 18 ovulations per animal. One hundred and fifty-six ova were recovered ($\text{156}\text{397}$) for a collection rate of 39%. Group I animals had 44 of 66 (67%) of their ova fertilized while 23 of 71 (32%) of the ova in Group II were fertilized. Nineteen unfertilized eggs were collected from the three animals not observed in estrus. No differences in fertilization rates between the Group I and Group II animals were found. Mean ovarian width, length and weight in the treated animals was measured and found to be 3.5 ± 1.1 cm, 4.8 ± 1.4 cm, and 21.7 ± 21.2 gm, respectively. Ovarian width, length and weight were all positively correlated with the number of ovulations per ovary r=.74, r=.74, and r=.55, respectively. No significant correlation existed between ovarian width (r=.16), lenght (r=.21), or weight (r=.13) when compared to ova recovery rate. This result suggests that ovarian size or weight may not be the limiting factor involved in embryo recovery.     

Effects of intrauterine infusion of gentamicin sulfate on bovine fertility

Gentamicin sulfate was administered by intrauterine infusion 10 minutes following first-service insemination at the rate of 200 mgs to dairy cows allotted at random to treatment and control groups to evaluate the effect on fertility. Pregnancy was determined by palpation of fetal membranes $\text{per rectum}$ 45–75 days after breeding.The first-service pregnancy rate was 43.8% in 233 treated cows and 51.7% in 232 control cows (P>0.1). The second-service pregnancy rate was 54.7% in 106 treated cows and 47.4% in 95 control cows (P>0.1). The pregnancy rate for both first and second services was 68.7% for 233 treated cows and 71.1% for 232 controls (P>0.1). Fertility was not enhanced by this treatment.     

Conception, embryonic development and corpus luteum function in beef cattle open for two consecutive breeding seasons

High-fertility (control cows) and low-fertility (cows and heifers not pregnant after two consecutive breeding seasons — twice-open) cyclic bovine females were treated with a single injection of 1000 IU of human chrionic gonadotropin (HCG) or 100 μg of gonadotropin releasing hormone (GnRH) to enhance and/or hasten corpus luteum formation and progesterone secretion, and improve conception rate in the low-fertility females. Hormone treatments were administered to 38 parous control cows, 34 twice-open parous cows, and 27 twice-open nonparous heifers immediately after natural mating by a fertile bull. Blood samples were collected on Days 3, 6, 9, 12, and 18 after mating for determination of systemic progesterone concentrations. Pregnancy rate at necrospy approximately 33 days after mating (range 31–37) was higher in control cows (73.0%) than in twice-open cows (48.4%; P<0.05) or twice-open heifers (34.6%; P<0.01). Pregnancy rate was not affected by the HCG or GnRH treatment. The HCG treatment increased plasma progesterone concentrations in twice-open heifers but not in control or twice-open cows. Progesterone was unaffected by the GnRH treatment. Systemic progesterone concentrations were higher in control than in twice-open females but did not differ between pregnant and nonpregnant females of Days 3, 6, 9 and 12 after mating. Enhanced gonadotropin stimulation at estrus by injection of either HCG or GnRH did not increase pregnancy rate or systemic progesterone concentrations (except in HCG-treated twice-open heifers) in low- or high-fertility females. Lower pregnancy rates in twice-open females were not associated directly with the lower systemic progesterone concentrations.     

Plasma progesterone concentration in Bos taurus and Bos indicus heifers

Progesterone concentrations were determined by radioimmunoassay in the plasma of heifers of German Brown Swiss, Holstein-Friesian and White Fulani cattle during two consecutive estrous cycles in the dry and wet seasons in a tropical climate. Seasonal differences in the levels were not significant but peak levels were significantly higher in the $\text{Bos}$$\text{taurus}$ than in the $\text{Bos}$$\text{indicus}$ heifers. The low levels at estrus and the gradual rise five days after estrus were similar among the heifers. The levels on the 1st and 2nd days preceding estrus were significantly higher in the $\text{Bos}$$\text{taurus}$ than in the $\text{Bos}$$\text{indicus}$ heifers, and suggest a possible tendency for the former to be more susceptible to infertility arising from high progesterone levels 1 and 2 days preceding estrus and insemination. The genital tract and ovaries at the mature luteal phase were generally smaller in the $\text{Bos}$$\text{indicus}$ than in the $\text{Bos}$$\text{taurus}$ heifers.     

Plasma gonadotrophin responses in beef cows two progesterone plus prostaglandin treatment

Progesterone Releasing Intravaginal Devices (Prids) were inserted into six post-partum beef cows for nine days and 0.5 mg cloprostenol was injected i m on day eight. Blood samples were taken via jugular venous catheters at frequent intervals for seven days after Prid removal and assayed for LH, FSH and progesterone. The induced pre-ovulatory type LH and FSH surges occurred between 35 and 123h after Prid withdrawal in five of the cows. In four cows which underwent surges during the time of most intensive sampling, LH levels were significantly higher during the 30h period prior to the LH surge than during the 30h period after the surge. FSH values were low for the 30h period preceding and the 14h period following the time of maximum FSH/LH concentrations. 16 - 30h after the FSH and LH surges, FSH values were again significantly raised compared with the period immediately after the surge. Despite the success of this Prid/PG regime in inducing ovulation, the variability in time between progestagen withdrawal and the LH surge and ovulation is such that the use of fixed time artificial insemination may give poor results.     

Induction of ovulation and pregnancy in captive cottontail rabbits by exogenous gonadotrophin treatment and artificial insemination.

Attempts were made to induce ovulation in confined cottontail rabbits, $\text{Sylvilagus floridanus}$, by treatment with FSH and LH. FSH given twice daily for 3 days with LH on the 4th day induced ovulation. LH at 50 mg/kg bodyweight was significantly (P<0.05) more effective than at 25 mg/kg bodyweight in inducing ovulation. Daily doses of FSH in the amount of 0.05 mg to 0.20 mg induced follicular development which resulted in normal ovulation rates for the cottontail rabbit. Insemination of artifically ovulated rabbits with epididymal spermatozoa resulted in pregnancy in three of nine rabbits and in ovum fertilization in one of three rabbits.     

Pregnancy rates in cows and heifers inseminated at predetermined times using progesterone-releasing intravaginal devices

The time of estrus and ovulation were controlled using a proges-terone-releasing intravaginal device constructed from silicone rubber. Pregnancy rates were determined in beef cows and heifers inseminated with frozen semen at predetermined times after removal of the device. Two experiments were conducted using two types of devices. In experiment I, a sleeve-covered device was inserted into the vagina and left for 21 days. Thirty-six hours after the devices were removed each animal received 100 μg of synthetic GnRH intramuscularly and was inseminatec 48 hours after coil removal. Five percent of the heifers lost coils during the 21-day treatment period compared to 25% of mature cows. First service pregnancy rate was 26%. In experiment II, a PRID^® was used for a 14-day treatment period. Animals were not treated with GnRH as in experiment I and were inseminated from 56 to 68 hours after PRID removal. Only 3.5% of the coils were lost during the 14 days. Pregnancy rates ranged from 13 to 60%.     

Pregnancy rate of Nelore females inseminated with male-sexed semen

Pregnancy rates of Nelore females inseminated with male-sexed semen and conventional semen from the same bulls were evaluated. The females included 433 heifers (2 years old) and 230 non-suckling cows, totaling 663 animals. Average body condition score was 3.5 (1-5 scale). Estrus was induced with prostaglandin F2α. The total pregnancy rate of females inseminated with male-sexed semen of bulls A, B and C was 38.8% (131/338) less (P<0.0001) than the total pregnancy rate observed for females inseminated with conventional semen from the same bulls (57.9% [188/325]). Pregnancy rates of non-suckling cows inseminated with male-sexed semen was 43.3% (49/113), which was similar (P≥0.05) to the values found for heifers inseminated with male-sexed semen from the same bulls (36.4% [82/225]). The pregnancy rate of females inseminated with male-sexed semen was less compared with females inseminated with conventional semen. In addition, there was no significant difference in the pregnancy rate of heifers versus non-suckling cows.     

Comparison of ovulation, fertilization and embryonic survival in low-fertility beef cows compared to fertile females

The objective was to determine physiological causes of low fertility in beef cows. Fertility was compared between low-fertility cows (34 British cows and 64 Brahman crossbred cows; cows that did not get pregnant when mated to fertile bulls in one or two previous breeding seasons); fertile cows (16 Brahman crossbreds; cows having a calf in several of the preceding breeding seasons), and virgin heifers (45 Brahman crossbreds, 2 yr of age). Females were mated to fertile bulls and killed 3 or 34 d after breeding to obtain reproductive tracts. There were no significant differences among groups in rates of ovulation or fertilization. Overall, 14% of females failed to ovulate and 24% that ovulated failed to undergo fertilization. The proportion of cows that were not detected in estrus before Day 34 of pregnancy was lower (P < 0.01) for low-fertility British cows (5 of 16 cows, 31%) than for other groups, including low-fertility Brahman crossbred cows (23/32, 72%), fertile cows (8/9, 89%), and heifers (21/24, 88%). All cows that did not return to estrus by Day 34 had an identifiable conceptus. The proportion of conceptuses recovered at Day 34 that were classified as normal (weight and length) was lower (P < 0.05) for cows with low fertility (British: 2/5, 40%; Brahman crossbred: 9/23, 39%) than for fertile cows (8/8, 100%) or heifers (18/21; 86%). Similarly, the proportion of cows in which a normal embryo was recovered (cows with normal embryos/number of cows mated) was lower (P < 0.001) for low-fertility British cows (2/16, 13%) and low-fertility Brahman crossbred cows (9/32, 28%) than for fertile cows (8/9, 89%) and heifers (18/24, 75%). In conclusion, cows that were infertile in previous breeding seasons did not experience reduced ovulation or fertilization rates, but had greater embryonic mortality. These data highlighted the importance of ovulation and fertilization failure and embryonic mortality as important determinants of pregnancy success. Moreover, increased embryonic loss after Day 34 contributed to infertility in low-fertility cows.     

Uterine infections in the postpartum cow: II. Possible synergistic effect of Fusobacteriumnecrophorum and Corynebacteriumpyogenes

Clinical conditions, which were observed in primiparous Angus and Hereford heifers with postpartum uterine infections are reported. Forty-three of sixty-four cows (67%) had uterine infections. $\text{Corynebacterium}$$\text{pyogenes}$ and $\text{Fusobacterium}$$\text{necrophorum}$ were the most frequently isolated aerobe and anaerobe, respectively. Twelve of the sixty-four cows (18.8%) had infections that involved these species. Three of these twelve cows were infected only with $\text{C.}$$\text{pyogenes}$, two were infected only with $\text{F.}$$\text{necrophorum}$, and seven were infected with both organisms. All five of the cows which were infected with either $\text{C.}$$\text{pyogenes}$ or $\text{F.}$$\text{necrophorum}$ showed signs of estrus and four of the five cows conceived by 110 days postpartum. The single cow that did not conceive was infected with $\text{C.}$$\text{pyogenes}$. Three of the seven cows which were infected with both organisms showed signs of estrus and none of the seven cows conceived by 110 days postpartum. In addition, when only $\text{C.}$$\text{pyogenes}$ or $\text{F.}$$\text{necrophorum}$ was isolated from the uterus, cows had either mild or no clinical signs of infection. In contrast, the seven cows which were infected with both organisms had severe clinical signs of infection that included excessive vulvar discharge, uterine abscesses and pelvic adhesions. These observations suggested that a pathogenic synergism between $\text{C.}$$\text{pyogenes}$ and $\text{F.}$$\text{necrophorum}$ might have caused the increased severity of postpartum uterine infections, and the subsequent detrimental effect on return to estrus and conception.     

Influence of management factors on pregnancy attrition in dairy cattle

The present study was conducted to determine the influence of management factors on pregnancy attrition in dairy cattle. Data from 3162 diagnosed pregnancies in parous cows and 1050 in heifers at 9 commercial dairy herds in northeastern Spain were used. Pregnancy diagnosis by palpation per rectum was performed from 30 to 70 d post insemination. Pregnancy attrition was registered when pregnancy diagnosis resulted negative in a second palpation carried out between 120 and 150 d following insemination. Overall proportion of pregnancy losses was 7.9% (9.6% in parous cows and 2.8% in heifers). Data analysis was performed by multiple logistic regression methods. For all animals, effect of time of pregnancy diagnosis was shown (Odds ratio = 0.97 for 1 d increase; P = 0.0042). Conceptus loss in heifers was lower than in parous cows (Odds ratio = 0.28; P = 0.0001), and a higher proportion of pregnancy attritions was detected in animals inseminated in spring, summer and winter, compared to those inseminated in autumn (P < 0.04). Herd effect on pregnancy attrition was also significant. Similar results were observed in the subanalysis for parous cows and, furthermore, no effect of lactation number and of interval from previous calving to pregnancy was shown in this group. In heifers, no effect of time of pregnancy diagnosis and of insemination season on pregnancy attrition was shown, and only a herd effect was observed. Our data suggest that the influence of parity status (heifer vs cow) could affect the proportion of pregnancy attrition rather than early diagnosis, and, in pregnant cows, adaptation to seasonal changes associated with temperature decreases seem more efficient.     

Postpartum fertility in beef cattle producing twins

Postpartum fertility was measured in 42 plur iparous Hereford cows and first calf Hereford heifers that calved after embryo transfer to induce twins. Dams were exposed to a Hereford bull from 4: 00 P.M. to 8:00 A.M. each day from 60 days postpartum until pregnancy was confirmed or calves were weaned at 180 days of age. Days open ($\text{X}\text{± SE}$) for dams that produced single and twin calves were 84.1 ± 4.6 (n = 12) and 94.9 ± 6.2 (n = 30), respectively. Corresponding values for dams that nursed one calf, including six females that lost one calf of a twin set at birth, and dams that nursed twins were 89.3 ± 6.4 (n = 18) and 93.4 ± 8.5 (n = 24). No significant differences were observed due to calving or suckling twin calves. Heifers that calved twins had a shorter mean interval to conception than cows that calved twins. These results are interpreted to mean that with proper management during the prepartum and postpartum periods, reduced fertility in beef cattle that produce twins need not occur.     

Transfer of cultured bovine embryos

A total of 126 bovine embryos were surgically collected from 16 superovulated donor heifers 5 days after estrus and randomly selected for either immediate transfer to synchronized recipients or $\text{in}$$\text{vitro}$ culture at 37°C for 24 hours and subsequent transfer. Twenty-four of 56 (42.8%) embryos maintained for 24 hours in Ham's F10 medium supplemented with 10% heat treated fetal calf serum (HTFCS) and transferred to 32 recipients produced live calves. Survival of 70 noncultured embryos transferred to 35 recipients was 55.7% (39 calves). The percentages of recipients that were diagnosed pregnant at 42 days with cultured and control embryos were 59.4% ($\text{19}\text{32}$) and 74.3% ($\text{26}\text{35}$), respectively. No statistical difference was observed between the $\text{in}$$\text{vitro}$ cultured and control embryos for viability following transfer to recipient females.In a second study, Day 7 embryos maintained in Ham's F10 medium supplemented with 10% HTFC serum for various culture periods were tested for viability following nonsurgical transfer to recipient females. A total of $\text{1}\text{5}$, $\text{1}\text{3}$ and $\text{0}\text{4}$ embryos cultured for 24, 48 and 72 hours, respectively, resulted in pregnant recipients following transfer.     

Synchronization of estrus in cyclic beef heifers with the prostaglandin analog alfaprostol

Seventy-eight Hereford-Angus crossbred heifers were injected intramuscularly twice with 6 mg of alfaprostol^b in 6 ml of propylene glycol. On each representative day of a 20-day estrous cycle (estrus = Day 0), either three or four heifers received their first injection. The second injection was given 12 days after the first, regardless of the response to the first injection. Thirty-nine heifers were not treated. The first alfaprostol injection reduced serum progesterone to less than 1 ng/ml in all heifers injected after Day 4. A total of 79.5% ($\text{62}\text{78}$) of the heifers exhibited estrus by five days after the first injection. Average interval from injection to estrus was 63 hours. The second injection occurred on Days 6 through 16 for all but one heifer, with 75.6% ($\text{59}\text{78}$) falling on Days 8 through 11 of the estrous cycle. Estrus was detected in 93.6% ($\text{73}\text{78}$) of the heifers within five days after the second injection, with an average interval to estrus of 66 hours.Day of cycle at second injection did not affect the interval to estrus. Conception occurred in 79.4% ($\text{58}\text{73}$) of the heifers inseminated in the five days after the second injection. Occurrence of estrus and conception was no different in treated heifers after five days of the insemination period than in nontreated heifers after 21 days of the insemination period, where 94.9% ($\text{37}\text{39}$) were observed in estrus and 83.8% ($\text{31}\text{37}$) conceived. Overall percent conception for a 55-day insemination period was 89.7 ($\text{70}\text{78}$) for treated and 87.2 ($\text{34}\text{39}$) for nontreated heifers. Day of cycle at first or second injection did not affect conception after the second injection. Some signs of estrus were observed in 11 of the 16 heifers injected before Day 5.A second trial to determine if alfaprostol induced luteolysis early in the cycle was conducted. Twenty purebred Angus, Hereford, or Simmental heifers received either one or two injections of alfaprostol on either Day 1, 2, 3, or 4. Only five heifers showed any signs of estrus, and the three that were inseminated did not conceive. Subsequent cycle length indicated that luteolysis occurred in only one heifer.Data suggest that alfaprostol is an effective luteolytic agent in cyclic beef heifers after Day 4 and that two injections 12 days apart will effectively synchronize estrus in heifers when distributed throughout the cycle at the first injection without affecting conception rate.     

Prostaglandin levels in preovulatory follicles from rabbit ovaries perfused invitro

Prostaglandin (PG) levels in follicular fluid from preovulatory follicles of rabbit ovaries perfused $\text{in}$$\text{vitro}$ were measured in order to compare PG changes in this model system with those that occur $\text{in}$$\text{vivo}$ and in isolated, LH-treated follicles $\text{in}$$\text{barvitro}$. One ovary from each rabbit was perfused without further treatment (control). The other ovary was exposed to LH (0.1 or 1 ug/ml) beginning 1 hour (h) after initiation of perfusion. Samples of perfusion medium were taken at frequent intervals for measurement of PGE, PGF, progesterone and estradiol 17β. The perfusions were terminated when the first ovulation occurred or appeared imminent as judged by changes in the size and shape of the follicles. Follicular fluid was then rapidly aspirated from all large follicles on both ovaries for PGE and PGF measurement.Ovulations occurred only in the LH-treated ovaries. Progesterone and estradiol levels were significantly elevated in the perfusion medium within 1 h of LH treatment in comparison to controls. PG levels in perfusion medium from the control and LH-treated ovaries were not different throughout perfusion and increased in both groups. In contrast, PG levels measured in follicular fluid from LH-treated ovaries were 4- to 5-fold greater than in fluid from control ovaries. It is concluded that ovulation induced by LH in this experimental model is accompanied by an increase in follicular PG levels similar to that seen in other $\text{in}$$\text{vivo}$ and $\text{in}$$\text{vitro}$ models. This difference in follicular PG levels between the LH-treated and control ovaries is, however, not reflected in the perfusion medium.     

Increase of pregnancy rate in dairy cattle after preovulatory follicle palpation and deep cornual insemination

A total of 334 first-service lactating cows in natural estrus were used in the study. Semen was deposited into the uterine body of 174 cows and deep into the uterine horn ipsilateral to the side of impending ovulation of 160 cows. In both groups, insemination was performed within the interval of 50 to 100 d postpartum at 8 to 15 h after estrus detection and after preovulatory follicle palpation. Pregnancy rates were determined by palpation per rectum 50 d post insemination. The pregnancy rate was higher (P < 0.05) for deep uterine horn insemination (70.62%) than for uterine body insemination (60.34%).     

The effect of PGF-2 alpha on reproductive performance of naturally bred dairy cows with or without pyometra

Five hundred thirty-four naturally bred Holstein dairy cows from two Colorado dairies were examined $\text{per}$$\text{rectum}$ between 21 and 36 days after calving. Alternate cows in each herd received either 25 mg PGF-2 alpha or no treatment at the time of initial examination. No differences were found in days open or pregnancy rates between groups (P>0.25).Days open in 23 cows with pyometra were 98.7 ± 9.4, and 77.0 ± 2.2 in 493 herdmates without pyometra. The large inequalities in numbers precluded valid statistical comparisons between these groups. No overall difference (P>0.25) in reproductive performance was found in cows with pyometra treated at the initial examination compared to those not treated until two to four weeks after the initial examination. Contributing to the lack of significance were a number of cows with pyometra that had spontaneous cures before treatment was considered. Untreated cows that recovered spontaneously had better (P<0.05) reproductive performance than herdmates that required later treatments to initiate uterine evacuation. No overall advantage in reproductive performance was obtained by the routine treatment of postpartum dairy cows with PGF-2 alpha but treatment of cows with pyometra should not be delayed.