Anestrous Cows Research Articles

Hypothalamic proopiomelanocortin mRNA levels in suckled or nonsuckled beef cows: A preliminary study

This study was conducted to determine proopiomelanocortin (POMC) mRNA levels in the preoptic and hypothalamic brain regions of postpartum anestrous cows. An additional objective was to determine if calf suckling influences POMC mRNA concentration in these regions. Twenty cows were randomly assigned to suckled and nonsuckled treatment groups and slaughtered between 30 and 36 days postpartum. Serum luteinizing hormone (LH) concentrations were determined from blood collected every 15 minutes for 8 hours, starting 20 hours prior to slaughter. POMC mRNA levels in brain tissues were determined by dot blots. Serum LH concentrations between nonsuckled and suckled cows were 1.3 ± 0.2 and 0.9 ± 0.1 ng·ml −1 (mean ± SEM; P = 0.19), respectively. The POMC gene is expressed in the hypothalamus of postpartum anestrus cows with POMC mRNA levels higher (P<0.05) in the hypothalamus than in the preoptic region. Hypothalamic POMC mRNA levels tended (P = 0.12) to be lower in nonsuckled (14.9 ± 3.8 ADU) than in suckled cows (23.5 ± 3.6 ADU). Covariate analysis indicated (P = 0.10) that as mean serum LH concentrations increased, hypothalamic POMC mRNA levels decreased.

Norgestomet and gonadotropin-releasing hormone enhance corpus luteum function and fertility of postpartum suckled beef cows.

In Exp. 1,101 suckled beef cows were administered two injections of prostaglandin F2 alpha (PGF2 alpha) 11 d apart. Cows in Group 1 received no additional treatment. Cows in Groups 2 and 3 received 250 micrograms of GnRH plus 47-h calf removal. Cows in Group 3 also received a norgestomet ear implant that was inserted 4 d after the first PGF2 alpha injection and left in situ for 8 d. The second PGF2 alpha injection was administered approximately 28 h before the time of norgestomet implant removal. The GnRH was administered approximately 30 h after the time of norgestomet implant removal (or 58 h after the second PGF2 alpha injection). Calf removal was the period from the time of implant removal to AI. All cows were artificially inseminated once 75 h after the second PGF2 alpha injection (47 h after implant removal). Reproductive status before the time of GnRH treatment (presynchronization) was determined by multiple sampling (2, 13, and 23 d before GnRH treatment) for blood progesterone concentrations (62% anestrous and 38% cyclic). The GnRH treatment increased (P < .01) the ovulation response and norgestomet reduced (P < .01) the incidence of short luteal phases in the presynchronization anestrous cows. Norgestomet treatment increased (P < .05) the timed breeding pregnancy rates for both presynchronization anestrous and cyclic cows. In Exp. 2, 174 suckled beef cows were administered Syncro-Mate B (which includes norgestomet). Cows in Group 1 received no additional treatment, whereas cows in Group 2 received 250 micrograms of GnRH (30 h after norgestomet implant removal).(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrasound-guided cannulation of the caudal vena cava in the bovine for selective sampling of ovarian effluent

The accuracy of real-time, B-mode ultrasonography was assessed in the visualization and placement of the cannula tip, cranial to the entrance of the ovarian veins as they enter the caudal vena cava of the bovine. A cannula containing a wire guide was introduced into the coccygeal vein via a 14-gauge needle, and was then directed cranially into the caudal vena cava. Once the caudal vena cava was successfully cannulated (7 of 14 cows), ultrasonography allowed for the visualization of the cannula in 7 out of 7 cows. The tip of the cannula was successfully placed cranial to the entrance of the ovarian effuent into the vena cava in 6 of these 7 animals using ultrasound guidance. This was confirmed using progesterone or prostaglandin F 2α radioimmunoassay (RIA). The primary limitation to this technique was the initial catherization of the coccygeal vein which was not achieved in 7 of 14 cows attempted in this study. Successful cannulation was limited to large framed Holstein cows that had at least one calf. Results from this study indicate that real-time, B-mode, ultrasonography is an effective tool for the visualization and accurate placement of the cannula tip within the caudal vena cava. This finding could have implications for research in ovarian hormonal physiology in the cyclic, postpartum or anestrous cow.

Nutritional Anestrus in Beef Cows: Effects of Body Condition and Ovariectomy on Serum Luteinizing Hormone and Insulin-Like Growth Factor-I1

The objectives of this experiment were to determine if a postcastration increase in concentrations of LH occurs in nutritionally anestrous beef cows and to examine the relationship between body energy reserves and secretion of LH and insulin-like growth factor-I (IGF-I). Nonpregnant, nonlactating, Hereford cows were fed to maintain (M) body weight (BW), body condition score (BCS), and normal estrous cycles (n = 5) or were fed a restricted (R) diet for 26 wk to lose BW and BCS and to become anestrus (n = 10). At 5-7 wk after the initiation of anestrus, R cows were randomly allotted to be ovariectomized (OVX) via flank incision (n = 5) or to remain intact (INT, n = 5). OVX was performed when R cows became anestrous. All M cows were OVX. Serum was collected frequently the day before and during the first 10 days after OVX, and concentrations of progesterone, estradiol, LH and IGF-I were quantified. On Day 10 after OVX, 1 mg of estradiol was injected into 3 cows from each group and serum was collected for 30 h. After OVX, there was a treatment-by-day effect for mean serum LH and IGF-I concentrations. Concentrations of LH increased (p less than 0.01) and concentrations of IGF-I decreased (p less than 0.05) in M-OVX cows when compared with R-OVX and R-INT cows. Concentrations of LH and IGF-I were similar for R-OVX and R-INT cows. The number of LH pulses was similar for M and R cows.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical masking of neurosensory pathways at the calf-teat interface: Endocrine, reproductive and lactational features of the suckled anestrous cow

A mammary somatosensory mask was employed in suckled anestrous beef cows to attenuate signals that were hypothesized to play a direct regulatory role in postpartum anestrus. Cows (n = 20) were randomly assigned to one of three treatment groups on Days 15 to 20 postcalving. The three treatments were: 1) masked (n = 7); 2) suckled (negative control, n = 6); and 3) weaned (positive control, n = 7). Four layers of surgical glove latex were used to cover the teats and ventro-lateral prominence of the udder of masked cows with a nonhardening, nontoxic adhesive (Day 0). Masks were designed to prevent direct contact between the skin of the teat/udder and the mouth of the calf and to allow normal suckling and milk removal. Masks were left in place for 7 d, with calves in the weaned group removed to a remote location for 7 d. Calves in the suckled group were allowed ad libitum suckling. Calves in the masked group tended (P < 0.1) to suckle longer than calves in the suckled control group (11.3 ± 1.3 vs. 7.8 ± 1.3 min/suckle) posttreatment; however, suckling frequency and calf weight gains did not differ due to treatment. Weaned cows exhibited a four-fold increase (P < 0.01) in the frequency of luteinizing hormone (LH) pulses on Day 2 relative to suckled and masked cows. The percentage of animals ovulating within 12 d after treatment differed (P < 0.05) and was 100, 50 and 0% for weaned, suckled and masked cows, respectively. Presence of the latex mask allowed essentially normal suckling and lactation, but failed to attenuate (and may have potentiated) the negative effects of suckling on secretory patterns of LH, ovulation and estrus.

Progesterone profiles in postpartum Holstein dairy cows as an aid in the study of retained fetal membranes, pyometra and anestrus

This study was carried out to investigate the utility of enzymeimmunoassay (EIA) - derived progesterone profiles in the investigation of postpartum reproductive abnormalities and the effect of their use on reproductive performance in Holstein cows. Whole milk samples, collected twice weekly from parturition until confirmation of pregnancy or removal from the herd, were assayed for progesterone (P4) concentration using a commercially available microtitre plate EIA. The sensitivity, specificity, precision and accuracy were satisfactory to distinguish cyclic changes of P4 reflecting ovarian activity. The P4 profiles indicated that retained fetal membranes and anestrus were associated with increased mean intervals to first ovulation and first estrus (P < 0.05). The first luteal phase of cows with pyometra was prolonged compared with that of normal herdmates (P < 0.05). Anestrus cows had an increased number of ovulations before first service and before pregnancy (3.9 and 5.9) in comparison with normal herdmates (2.1 and 3.5; P < 0.05). Calving to pregnancy interval was increased above normal (74.8) for pyometra (125.0) and anestrus (152.7) (P < 0.05). Pregnancy rate for anestrus cows (82%) was lower than for normal cows (100%) and more anestrous cows were culled (27%) than normal cows (5%) (P < 0.5). The P4 profiles indicated that the major problem in the herd studied, anestrus (32% incidence rate), was most likely due to the failure to observe estrus rather than acyclicity.

Ovarian Ultrasonographs, Milk Progesterone Profiles, hCG Treatment and Sexual Behavior for Better Diagnosis of Ovarian Follicular Cysts in Cows.

Sixteen Holstein cows with ovarian follicular cysts diagnosed by rectal palpation were used to correlate changes in ultrasonographic image of the ovaries, sexual behavior and skim milk progesterone profiles. Of 16 cases, 4 cows exhibited typical nymphomaniac symptoms, 3 had recurrent nymphomaniac symptoms, and the remaining 9 showed anestrus. Neither corpora lutea nor luteal tissues on the cystic wall were detected by ultrasonography during a 20 days of observation period. On the 20th day the animals were treated with hCG 10, 000 IU. Following hCG treatment, 5 of the 7 nymphomaniac cows no longer showed the symptoms and 3 of the 7 cows showed the formation of corpora lutea or luteal cysts, while 6 of the 7 cows showed an upward tendency of skim milk progesterone levels. Of the 9 anestrous cows, 7 cows responded to hCG with an increase in skim milk progesterone levels and luteinization of co-existing medium-sized follicles and newly-formed follicular cysts. The results indicate that ultrasonography in addition to careful observation of sexual behavior and skim milk progesterone measurement is helpful for an accurate diagnosis of bovine ovarian follicular cysts.

Effects of cloprostenol sodium and clenbuterol HCl on reproductive performance in postparium anestrous cows

Two experiments were conducted to study effects of cloprostenol sodium (cloprostenol) and clenbuterol HCl (clenbuterol) during postpartum anestrus on subsequent reproductive performance in cows. In Experiment I, 96 cows received either 0.5 mg cloprostenol (PGF, n = 25), 364 mg clenbuterol (CLEN, n = 24), 0.5 mg cloprostenol and 364 mg clenbuterol (CLEN+PGF, n = 21) or no treatment (Control, n = 26) on Day 20 post partum. Treatments failed to influence postpartum interval, pregnancy rate or the incidence of short estrous cycles preceding the first normal estrous cycle. In Experiment II, anestrous cows were administered cloprostenol (0.5 mg) on either Day 20 (PGF20, n = 27) or Day 35 post partum (PGF35, n = 25), or served as untreated controls (Control, n = 26). Neither postpartum interval nor pregnancy rate were affected by cloprostenol treatment. In conclusion, treatment of postpartum cows with PGF did not alter the resumption of normal estrous cycles following parturition.

Serum concentrations of IGF-I in postpartum beef cows.

Four experiments assessed changes in serum IGF-I under various physiologic conditions in postpartum cows. In Exp. 1, anestrous suckled cows (n = 25) were infused for 6 d with either saline or glucose at two different infusion rates. In Exp. 2, anestrous cows (n = 29) received either a saline (weaned and suckled controls) or 3 g/d phlorizin (weaned phlorizin) infusion for 3 d. Calves from the weaned groups were removed from 15 h before and throughout infusions. In Exp. 3, cycling suckled cows (n = 20) received prostaglandin F2 alpha (PGF2 alpha) when the 5-d saline or phlorizin infusion began. In Exp. 4, suckled cows (n = 20) had ad libitum access to feed or received 50% of control feed consumption from 30 to 40 d postpartum. Increasing glucose availability (Exp. 1) increased (P less than .05) serum IGF-I by 30 to 35%. IGF-I remained stable after weaning (Exp. 2) in phlorizin-infused cows (128.8 +/- 12.7 ng/ml), but increased (P less than .05) by 3 d after calf removal in weaned control cows (152.2 +/- 7.5 ng/ml). IGF-I also remained stable in phlorizin-infused cows following PGF2 alpha injection (Exp. 3), but increased in control cows by 2 d after PGF2 alpha (156.8 +/- 18.3 on d 2 vs. 133.7 +/- 9.8 ng/ml pre-injection; P less than .05) and remained elevated (P less than .05) during the periovulatory period. In cows receiving restricted feed intake (Exp. 4), IGF-I decreased by approximately 50% within 4 d of feed restriction (71.3 +/- 9.4 vs 137.4 +/- 16.6 ng/ml; P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Quantification of naloxone binding sites in brains from suckled beef cows during postpartum anestrus and resumption of estrous cycles.

Thirty beef cows, approximately 3 yr of age, were randomly assigned to be slaughtered on d 7, 14, 28, 42 or 56 postpartum. Each cow suckled one calf until slaughter. Data from cows slaughtered on d 42 and 56 were pooled and further classified as anestrous or cyclic based on the presence of a corpus luteum and elevated serum concentrations of progesterone at slaughter. Specific binding of [3H]naloxone (3H-NAL) to homogenates of tissue from hypothalamus (HYP), preoptic area (POA) and basal forebrain (BF) was assessed using multiple-point Scatchard analyses. Nonspecific binding was estimated in the presence of 10(-6) M naloxone. Separation of bound from free 3H-NAL was achieved by centrifugation at 20,000 X g. Concentration (fmol/mg original tissue wet wt) of 3H-NAL binding sites in POA tissue was higher (P less than .05) on d 28 postpartum in anestrous cows than in cyclic cows on d 42 + 56 postpartum (2.58 +/- .32 vs 1.58 +/- .10). When all anestrous cows were compared with cyclic cows, concentrations of 3H-NAL binding sites in POA tissues and in BF tissue were higher (P less than .05) in anestrous cows (anestrous POA, 2.12 +/- .17, cyclic POA, 1.58 +/- .10; anestrous BF, 2.94 +/- .41, cyclic BF, 2.19 +/- .16). Compared across brain regions for all cows, the concentration of specific binding sites for 3H-NAL was greater (P less than .01) in BF (2.5 +/- .2) than in POA (1.9 +/- .1) and greater (P less than .01) in POA than in HYP (1.5 +/- .1).(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of pre- and post-ovulatory gonadotropin concentrations to subnormal luteal function in postpartum beef cattle.

Early weaning of calves from anestrous cows results in formation of short-lived corpora lutea (CL) unless the animals are pretreated with a progestagen (norgestomet). This study was conducted to investigate the relationship between pre- and post-ovulatory gonadotropin secretion and luteal lifespan. Postpartum beef cows were assigned randomly into two groups, control (n = 5) and norgestomet (implant given at weaning for 9 d; n = 7). Calves from all cows were weaned 30 to 33 d postpartum. Coccygeal artery cannulas were placed into cows in the control group 1 d prior to weaning and 2 d before implant removal in cows in the norgestomet group. Plasma for determination of luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol-17 beta (E) and progesterone (P) was collected daily at 10-min intervals for 6 h from weaning (control) or the day prior to implant removal (norgestomet) to estrus (d 0) and on d 2, 4 and 6 following estrus. Average interval (X +/- SE; P less than .05) from weaning to estrus or implant removal was 4.2 +/- .8 and 2.3 +/- .2 d for the control and norgestomet groups, respectively. Estrous cycle length for the control group was 12.4 +/- 1.8 d compared with 20.4 +/- .3 d for the norgestomet group (P less than .05). Four of five control cows had an estrous cycle length of 7 to 14 d; all cows in the norgestomet group and the remaining control cow had an estrous cycle of normal length (16 to 21 d).2+ estrus.(ABSTRACT TRUNCATED AT 250 WORDS)

The postweaning rise of tonic luteinizing hormone secretion in anestrous cows is not prevented by chronic milking or the physical presence of the calf.

The objective of the following study was to examine the ability of frequent milking, the physical presence of the calf, and their combination to prevent a postweaning rise in tonic luteinizing hormone (LH) secretion, estrus, and ovulation. Thirty Hereford cows were allowed to suckle their calves ad libitum until 17-21 days post partum and confirmed as anestrus. They were then assigned alternately by order of calving to 1 of 5 treatment groups: (1) Suckled (S) ad libitum; (2) Nonsuckled (NS)--calf removed for 102 h; (3) Nonsuckled--calf present (NSC)--calf remained with cow, but muzzled to prevent suckling for 102 h; (4) Nonsuckled--milked 8 times a day (NSM)--calf removed for 102 h and cow hand-milked for 10 min every 2 h from 0700 to 2100 h; (5) Nonsuckled--calf present--milked 8 times a day (NSMC)--combination of 3 and 4. Luteinizing hormone secretion patterns, estrous activity, and ovulation were monitored throughout the experiment. Prior to treatment (Day 0), mean pulse frequency (pulses/6 h), mean concentrations (ng/ml), and median concentrations (ng/ml) of LH did not differ (p greater than 0.45) between groups, and were 0.7 +/- 0.15, 2.8 +/- 0.14, and 2.6 +/- 0.11, respectively. Marked rises (p less than 0.01--p less than 0.03) in LH pulse frequency were observed in all groups except S between 48 and 54 h after onset of treatment. Mean and median concentrations of LH were lower (p less than 0.02) in S cows than in all other groups at 48-54 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Descriptive epidemiology of anestrus in Michigan Holstein-Friesian cattle

Twenty-two Michigan Holstein-Friesian herds were studied to determine the incidence and epidemiology of anestrus. In 3,309 lactations studied, 42% were classified as having exhibited preservice anestrus (no estrus detected by 70 d after calving). Organic reasons (pyometra, cystic follicles, static ovaries) were identified by palpation per rectum for 237 (23%) of the cows with preservice anestrus that were examined by a veterinarian. Postservice anestrus, defined as failure to show estrus within 35 d after an unsuccessful insemination, was identified in 790 (47%) of 1,691 lactations. Veterinary examination identified 104 (20%) of postservice anestrous cows as having this condition because of organic causes. The average cow with preservice anestrus had an increase of 30 d open compared to her herdmates, and the average cow with postservice anestrus had an increase of 37 d open. Anestrous cows produced more milk than their unaffected herdmates in both the current and the previous lactation. Analysis of composite lactation curves indicates that, for preservice anestrus, this additional milk production was obtained gradually over the entire lactation. Anestrous cows were culled at a significantly higher rate than their herdmates. Cows with preservice anestrus were more likely to have begun their lactation in the spring months.

Synchronization of estrus in postpartum beef cows with melengestrol acetate and prostaglandin F2 alpha.

At the beginning of the breeding season, most beef herds consist of a population of cyclic and anestrous postpartum cows. To be most effective and economical, an estrous synchronization method for postpartum beef cows must be capable of synchronizing estrus in cyclic cows and inducing estrus in anestrous cows. In the first of two experiments, the combination of melengestrol acetate (MGA) fed for 9 d and prostaglandin F2 alpha (PGF2 alpha) administered on the last day of MGA feeding synchronized estrus in cyclic cows (94%) and induced estrus in anestrous cows (66%) as effectively as combining PGF2 alpha with a progestin implant (97 and 75%, respectively). In the second experiment, MGA treatment was necessary for 7 d prior to administering PGF2 alpha to maximize the expression of estrus in cyclic and anestrous cows. In both experiments the proportion of cows exhibiting a synchronized estrus and the pregnancy rates tended to be higher for cows that were cyclic prior to treatment. However, the MGA-PGF2 alpha treatments consistently induced estrus in more than 50% of the anestrous cows and approximately one-third of the cows that were anestrous prior to treatment conceived during the synchronized breeding period. The MGA-PGF2 alpha treatment was 33 to 46% less expensive than a comparable estrous synchronization method that is approved by the U.S. Food and Drug Administration. If feeding MGA and administering PGF2 alpha is approved, it may be the treatment of choice for synchronizing estrus in cyclic cows and inducing estrus in anestrous cows when supplemental feeding is feasible.

Response to synthetic gonadoliberin (GnRH) in anestrous cows

Fifty-three anestrous cows of Hariana crossed with Holstein, Friesian, Brown Swiss or Jersey half-breed crosses were treated with Buserelin acetate aqueous solution 0.0042 mg/ml, administered as a single intramuscular (i.m.) dose of 21 ng. Twelve (22.64%) animals exhibited complete follicular development, ovulation and behavioural expression of oestrus. Twenty-eight (52.83%) cows showed only partial follicular development with no ovulation or oestrous manifestations. Thirteen (24.53%) animals did not respond. Of eight control animals, three (37.50%) showed partial follicular development and no ovulation or symptoms of oestrus while five (62.50%) did not respond. In GnRH-treated cows showing follicular development, oestrous manifestation, and ovulation, nine animals responded between 4 to 10 d after administration. Three animals took from 14 to 155 d. The mean time from treatment to response for this group was 29.17 d. In animals showing partial follicular development and no oestrous behaviour, the interval was 3 to 11 d in 28 animals. In the control group, three animals showed partial follicular development on 94 d average. The administration of GnRH in anestrous cows promoted the development of follicles to a certain stage as evident from the clinical observations, but the follicles failed to grow beyond a particular stage. The reasons for failure of follicular development beyond a particular stage in GnRH-treated animals are not clear. It appeared that the response to GnRH may be expected to peak by the eleventh day and a second dose may then be tried for a favourable response.

Progesterone and prostanoid production by bovine binucleate trophoblastic cells.

A procedure for preparing highly enriched suspensions of bovine binucleate trophoblastic cells was developed and data showing that these cells produce progesterone, prostacyclin (PGI2), and prostaglandin E2 (PGE2) were obtained. Approximately 200 X 10(6) enzymatically dissociated cells from bovine cotyledons were applied to the surface of a density gradient of 2% to 4% Ficoll-400 using the Wescor CELSEP sedimentation chamber. After 90-120 min of sedimentation at unit gravity, fractions containing binucleate trophoblastic cells were obtained and washed in HEPES-buffered Medium 199. Preparations of 90% to 100% binucleate trophoblastic cells were obtained routinely; viability was 50% to 80%. After incubation at 37 degrees C, concentrations (ng/10(5) cells) of progesterone were greater in those fractions containing binucleate cells than in those containing primarily smaller, mononucleate cells. Total progesterone secreted (mean +/- SEM) after 4 h by 1 X 10(5), 2 X 10(5), 4 X 10(5), 8 X 10(5), and 1.6 X 10(6) binucleate cells was 0.27 +/- 0.03, 1.01 +/- 0.09, 4.02 +/- 0.37, 10.31 +/- 0.92, and 20.96 +/- 2.23 ng, respectively (r = 0.997). Addition of 10% fetal bovine serum (FBS) or normal anestrous cow serum increased (P less than 0.05) production of progesterone by binucleate trophoblastic cells. Luteinizing hormone, follicle-stimulating hormone, prolactin, thyrotropin, and 8-bromo-adenosine 3',5'-cyclic monophosphate had no effect. Binucleate trophoblastic cells also produced PGI2 in relation to number of cells incubated (r = 0.996). Time courses for production of PGI2, PGE2, and progesterone were similar. Aspirin inhibited production of PGI2 and PGE2 by about 50% at a dose of 100 microM; FBS stimulated production of both prostanoids.

Estrus synchronization and pregnancy rates in cyclic and noncyclic beef cows and heifers treated with syncro-mate B or Norgestomet and Alfaprostol

Postpartum lactating cows (N=118) and virgin heifers (N=60) were treated with subcutaneous Norgestomet implants for nine days and received either an intramuscular injection (im) of 5 mg estradiol valerate and 3 mg Norgestomet at the time of implant insertion or an im injection of 5 mg Alfaprostol 24 hr before implant removal. Animals were artificially inseminated 12 hr after detection of estrus. Of the cows and heifers, 78% and 88%, respectively, were in estrus within five days after implant removal (P<0.09). There was no difference between treatments in the proportion of animals in estrus or in the timing of estrus (P<0.85). Estrus was detected in a greater (P<0.05) proportion of animals that were cyclic prior to treatment (88%) than among those that were anestrous prior to treatment (77%). Pregnancy rates after five days were similar between heifers that were cyclic (42%) or anestrous (47%) prior to treatment; however, the five-day pregnancy rate in cows that were anestrous prior to treatment was 38% lower than that in cows that were cyclic prior to treatment (17 vs 55%, P<0.01). Although the treatments synchronized or induced estrus in both cyclic and anestrous animals, marked variability in estrous response and fertility among previously cyclic or anestrous postpartum cows limited the effectiveness of the treatments.

Influence of exogenous steroids, nutrition and calf removal on reproductive performance of anestrous beef cows

Methods for inducing a fertile estrus in anestrous beef cows suckling calves were explored in three studies. Trial 1 . Eighty-two primiparous and pluriparous Brahman-Hereford crossbred and Angus cows suckling calves were divided into four groups: 1) good body condition, high level of nutrition (GH); 2) good body condition, low level of nutrition (GL); 3) poor body condition, high level of nutrition (PH); 4) poor body condition, low level of nutrition (PL). All cows received the Shang Treatment (S). Following treatment, more cows (P<0.05) ovulated in the GH group (95%) than either the GL (61%), PH (58%), or PL (53%) group. Pregnancy rates were low and were not different between groups following the insemination taking place 54 hours after implant removal or after cows had been bred for 21 days. Trial 2 . One hundred fourteen two-year-old Santa Gertrudis-Hereford crossbred cows in poor body condition were divided into four groups. Forty-nine cows received S treatment and 65 cows served as controls (C) with approximately half of each group fed a high (H) or a medium (M) level of nutrition (SH, SM, CH, CM). One cow in the SH group ovulated and was pregnant 21 days after breeding. The remaining cows failed to exhibit estrus, ovulate or become pregnant. Trial 3 . Cows used in this trial were those from Trial 2 which did not exhibit estrus nor had a palpable corpus luteum present 21 days after implant removal. Cows were divided into 1) control (C), 2) wean (W), 3) wean + Syncro-Mate-B (W+SMB) and 4) Syncro-Mate-B + wean (SMB+W). The percentage of cows ovulating by 2 and 40 days after the start of breeding was similar (P>0.05) in the W, W+SMB, and SMB+W groups but all were greater (P<0.05) than the percentage of cows ovulating in the C groups. Pregnancy rates of cows in the W+SMB and SMB+W groups were higher (P<0.05) than pregnancy rates of cows in the W and C groups by two days after the start of breeding. Pregnancy rates 40 days after the start of breeding were higher (P<0.05) for cows in the W, W+SMB) and SMB+W groups than for cows in the C group.

Pregnancy rates following RCG administration at the time of transfer in embryo-recipient cattle

The objective of the experiments was to determine the effects of treatment of anestrous lactating beef cows with gonadotropin-releasing hormone (GnRH), 7 d before treatment with prostaglandin F2α (PGF2α), on estrous and luteal activity. Lactating Hereford and Angus x Hereford cows with a body condition score of 4.5 were classified as cyclic or anestrus based on concentration of progesterone in plasma at 7 d before and on the day of GnRH treatment. In Exp. 1, cows (n = 93) were treated with buserelin (GnRH agonist; Receptal®; Hoechst Animal Health, Bucks, United Kingdom; 8 μg, i.m.) or saline on d 0, and all cows received PGF2α (Lutalyse®; Pharmacia and Upjohn Co., Kalamazoo, MI; 25 mg, i.m.) on d 7. In Exp. 2, calves were separated from all cows (n = 88) for 3 d at 7 d before treatment with GnRH (100μg i.m.) or saline on d 0, and PGF2α (25 mg, i.m.) was given to all cows on d 7. Ovarian morphology of anestrous cows was examined by ultrasonography on d 0 and 7 in Exp. 2. At GnRH treatment (d 0), 55 and 50% of cows were anestrous in Exp. 1 and 2, respectively. Treatment of anestrous cows with buserelin or GnRH did not initiate luteal activity during 7 to 35 d after treatment. Buserelin did not influence the percentage of cows in estrus during the first 7 d after PGF2α in Exp. 1. However, in Exp. 2, 34% more cyclic cows treated with GnRH expressed estrus within 7 d after PGF2a compared with cyclic control cows (P<0.02). In Exp. 1, 69% of cyclic cows at the time of treatment with either buserelin or saline had normal luteal cycles following PGF2a treatment, and only 10% of anestrous cows had normal luteal activity after buserelin or saline and PGF2α. In Exp. 2, 98% of cyclic cows treated with either GnRH or saline had normal luteal activity following PGF2α compared with 48% of anestrous cows. Treatment of thin, lactating, anestrous beef cows with buserelin or GnRH at 7 d before PGF2a did not induce luteal activity.

Use of Prostaglandin F2α or Gonadotropin Releasing Hormone in Treating Problem Breeding Cows

Ten veterinarians diagnosed and treated 296 cows for reproductive irregularities on 28 dairy farms. Average interval from treatment with 25mg of prostaglandin F2α (137 cows) to estrus for cows with a corpus luteum (14.6 days) was reduced compared to saline (52 cows) (21.8 days), and a greater percentage (41.6 versus 17.3%) showed estrus within 6 days of treatment. Cows with a cystic corpus luteum (28) were detected in estrus at comparable intervals after prostaglandin F2α or saline (21.8 versus 21.2 days), and similar proportions of cows were detected in estrus within 6 days of treatment (16.7 versus 10.0%). Intervals to estrus among cows with cystic follicles (40 cows) or anestrous cows with follicular ovaries (39 cows) did not differ after treatment with saline or 100 or 200μg of gonadotropin releasing hormone. Within 25 days after treatment, 47.5% of cows with cystic ovaries and 64.1% of anestrous cows showed estrus. Number of cows pregnant after as many as three artificial inseminations of the number examined was 46%, whereas average number of conceptions per service was .32. The long interval from parturition to examination (112 days), the low rate of estrous response after treatment, and the long interval (1.6 estrous cycles) between estruses are consonant with inadequate estrous detection.