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

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

Post-insemination milk progesterone concentration and embryo survival in dairy cows

Logistic regression analysis was used to evaluate the relationship between post-insemination milk progesterone concentration and embryo survival, and between milk yield and milk progesterone concentration. Milk samples were collected on Days 1, 4, 5, 6, and 7 (insemination=Day 0) following 871 inseminations in spring-calving dairy cows. Milk progesterone concentrations were measured by enzyme-immunoassay and pregnancy diagnosis was conducted with transrectal ultrasonography at approximately Day 30. There was a negative linear relationship (P<0.01) between milk progesterone concentration on Day 4 and embryo survival while, in contrast, there was a positive linear and quadratic relationship between milk progesterone concentration on Days 5, 6 and 7 (P<0.05) and also between the rate of change in progesterone concentrations between Days 4 and 7 inclusive and embryo survival (P<0.05). There was a weak negative linear relationship between average daily milk yield at the time of insemination and milk progesterone concentrations (P<0.001). There was no association between many production parameters, including liveweight and body condition score measured at various stages between calving and insemination, and milk progesterone concentration between Days 4 and 7 inclusive (P>0.05). In conclusion, low progesterone during Days 5-7 (after insemination) was associated with low fertility in dairy cows and there were indications of a range of progesterone concentrations within which embryo survival was maximal.     

Associations between milk progesterone concentration on different days and with embryo survival during the early luteal phase in dairy cows

The relationships between the concentration of milk progesterone and early embryo survival on Days 4-8 inclusive and between the concentration of progesterone on different days from Days 0-8 inclusive following ovulation and insemination were examined in dairy cows. The relationships were examined following 77 randomly chosen artificial inseminations to cows in standing oestrus. There was a significant (P < 0.05) linear and quadratic relationship between the concentration of milk progesterone on each of Days 4-6 after ovulation and the probability of embryo survival. There was no association (P > 0.05) between milk progesterone concentration and probability of embryo survival on Days 7 and 8 after ovulation. There were no associations between milk progesterone concentration on Days 0-2 and the concentrations on Days 4-7, however, progesterone concentrations on Days 4 and 5 were highly predictive of the concentration on Days 6 and 7, respectively. Overall, the results indicate that suboptimal progesterone support during the early luteal phase is likely to deleteriously affect embryo viability and in addition, that it is possible to predict milk progesterone concentrations during the early luteal phase based on earlier stage concentrations and thus identify cows at risk of early embryo loss.     

Plasma progesterone profiles and factors affecting embryo-fetal mortality following embryo transfer in dairy cattle

The relationship between plasma progesterone (P4) levels and embryo survival, and the value of P4 profiles for the selection of cattle embryo transfer recipients is still a matter of controversy. This study reports a comparison between lactating cows and heifers (n = 407) from a single dairy herd, after transfer of either fresh or frozen-thawed good quality embryos, of their ability to sustain embryo-fetal development to term. Plasma P4 concentrations on the day of estrus (Day 0 = D0), Day 4, Day 7 and on Day 21 were measured and related to embryo survival. Plasma P4 levels on Days 0, 4 and 7 were similar in recipients later found pregnant or open. Plasma P4 levels on Day 7 were significantly higher (P < 0.01) in heifers than in cows, but they were similar in pregnant and nonpregnant heifers and in pregnant and nonpregnant cows. Pregnancy rates for fresh and frozen-thawed embryos were higher in heifers than in cows, but the differences did not reach significance. However, the overall late embryonic mortality was significantly higher (P < 0.01) and the calving rate for frozen-thawed embryos was significantly lower (P < 0.05) in cows than in heifers. As expected, plasma P4 on Day 21 was significantly higher (P < 0.001) in pregnant than in nonpregnant recipients, but there was no difference between pregnant cows and pregnant heifers. Plasma P4 levels on Day 7 of recipients presumed pregnant on Day 21 and later found pregnant or nonpregnant were similar, but plasma P4 levels on Day 21 were significantly higher (P < 0.001) in pregnant than in nonpregnant recipients. The results of this study suggest that plasma P4 levels until the day of transfer, except for the rejection of recipients with abnormal luteal function, are of limited practical use for embryo transfer recipient selection. However, in lactating cows low plasma P4 values on Day 7 might negatively affect embryo survival, while in heifers this effect is not noticeable. Lactating cows are more prone to embryo loss than heifers, especially in the case of frozen-thawed embryos; this is associated with a lower competence of the corpus luteum at Day 7.     

Early pregnancy diagnosis in cattle by means of linear-array real-time ultrasound scanning of the uterus and a qualitative and quantitative milk progesterone test

We compared three methods for diagnosing early pregnancy in cattle: 1) a trans-rectal ultrasound scan of the uterus, 2) a cow-side enzymeimmunoassay (EIA) milk progesterone test 3) a radioimmunoassay (RIA) milk progesterone test. Scanning of the uterus was performed in 148 cows. These cows were not detected in estrus before scanning, which took place between Days 21 and 33 after insemination (AI). A considerable difference was noted between the reliability of the scannings performed at an early stage (Days 21 to 25) and those performed at a later stage (Days 26 to 33). The sensitivity and specificity of the ultrasound examination between Days 21 and 25 were only 44.8% and 82.3%, respectively, but were 97.7% and 87.8% between Days 26 and 33, respectively. Milk samples were collected on the day of AI. (Day 0) and 21 days later. Samples that were positive in the EIA test always contained more than 1 ng/ml progesterone (P4); however, 20% of the negative EIA samples contained also more than 1 ng/ml P4. Only 59% of the animals showing a negative EIA test on Day 0 and a positive test on Day 21, indicating pregnancy, calved, while 16% of the cows with a negative test on Day 0 and Day 21, indicating nonpregnancy, turned out to be pregnant. Of the 82 animals with P4 levels lower than 1 ng/ml on Day 0 and higher than 1 ng/ml on Day 21, only 61.0% calved. All 14 cows with low levels both on Day 0 and Day 21, indicating nonpregnancy, were found to be not pregnant. The influence of both early embryonic death and the accumulation of intrauterine fluids on the accuracy of these tests are discussed.     

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.     

Accuracy of ultrasonography for pregnancy diagnosis on days 10 to 22 in heifers

Two operators independently conducted ultrasonic pregnancy examinations on nulliparous Holstein heifers on Days 10, 12, 14, 16, 18, 20 and 22, and assigned a diagnosis (pregnant or nonpregnant) and a score for degree of certainty in the diagnosis (1, 2 or 3 for low, intermediate or high, respectively). Pregnancy was retrospectively confirmed by the ultrasonographic detection of an embryo proper and embryonic heartbeat on Day 24 in 20 25 bred heifers; the five nonpregnant heifers were excluded from the analyses. Eleven nonbred heifers were included as an unequivocal source of nonpregnant heifers. Accuracy was not significantly greater than a guess (50%) before Day 18, but reached 100% on Days 20 and 22. Mean accuracy was higher (P<0.005) for nonpregnant (65 77 , 84%) than pregnant heifers (91.5 140 , 65%). For certainty score, there were main effects of day (P<0.0001), reproductive status (pregnant or nonpregnant, P<0.003), and an interaction of day and reproductive status (P<0.0001). The certainty score increased in all heifers among days and was higher (P<0.05) in pregnant than nonpregnant heifers on Days 16 to 20. For luteal area (area of corpus luteum, excluding area of fluid filled center, if present), there were significant main effects of day, reproductive status and a day by status interaction (P<0.0001 for each). Luteal area was approximately constant in pregnant heifers, but in nonpregnant heifers it was lower (P<0.05) on Days 16 to 22 than on Days 10 to 14. Uterine echotexture was scored on a scale of 1 to 3, characteristic of a diestrus, intermediate and estrus uterus, respectively. There were main effects of day and reproductive status (P<0.0001 for each) and an interaction of day and reproductive status (P<0.025). Uterine echotexture was approximately constant in pregnant heifers, but in nonpregnant heifers it was higher (P<0.05) on Days 16 to 22 than on Days 10 to 14. Pregnancy diagnosis on Days 10 to 14 was based on detection of the conceptus; however, detection of the conceptus was not accurate prior to visualization of the embryo proper (mean Day 22, range Days 20 to 24). In nonpregnant heifers, a correct diagnosis with high certainty was made when a small corpus luteum and uterine echotexture characteristic of estrus were detected. In the absence of these changes on Days 18 to 22, a diagnosis of pregnancy was made with high accuracy and intermediate or high certainty.     

Plasma progesterone profiles and fertility status of anestrus Zebu cattle treated with norgestomet-estradiol-eCG regimen

Zebu cattle are notorious for poor fertility characterized by late maturity and long intercalving intervals attributed to a variety of factors, including genetic, nutritional and climatic. The aim of the present investigation, therefore, was to induce fertile estrus in acyclic pubertal heifers and postpartum anestrous Zebu cows by hormonal intervention. Pubertal Hariana and Sahiwal anestrous heifers (n=51) and postpartum cows (n=55) were either assigned a placebo (controls, N=6 for each breed and parity) or treated with 10-d norgestomet (3 mg) subcutaneous ear implants, with an initial injection of 3 mg, im norgestomet + 5 mg estradiol valerate, followed by 500 IU eCG at implant withdrawal (NOR-treated groups). Jugular venous plasma samples were obtained from a total of 28 animals (controls : 4 heifers and 4 cows; NOR-treated : 12 heifers and 8 cows) on Days 0 (implant insertion), 3, 7, 9 and Day 10 (implant withdrawal), every 12 h on Days 11 and 12, and then once daily on Days 17, 24 and 31. All the samples were assayed for progesterone. Almost all (97%) heifers and 81% cows were induced to estrus, the majority (92% heifers and 79% cows) within 120 h of implant removal. Synchrony of the induced estrus was better in cows, but interval to estrus and estrus duration were significantly longer in heifers (P<0.05). Post-treatment fertility, based on Day 28 nonretum rate, first service, and overall conception rates, was better in heifers (78.9, 60.5 and 73.7%, respectively) than cows (77.1, 48.6 and 62.9%, respectively), but the differences were significant only for the overall pregnancy rate (71.8% for heifers and 51.2% for cows; P<0.05). Low pre-treatment plasma progesterone values (<0.5ng/mL) were consistent with ovarian inactivity, confirming the true anestrus status of experimental animals. Controls failed to exhibit estrus and maintained low progesterone concentrations throughout the study. In treated animals, high progesterone values from Day 17 onwards suggested ovulatory estrus. These early luteal phase progesterone concentrations in nonpregnant (P=0.06) and nonpregnant, nonretum (P<0.05) animals were low in comparison with those of pregnant animals. Good fertility resulting from breeding according to estrus, inspite of variable intervals to estrus and estrus duration, advocates its advantage over fixed-time insemination in norgestomet-treated anestrous Zebu cattle.     

Luteotrophic influence of early bovine embryos and the relationship between plasma progesterone concentrations and embryo survival

This study was carried out to evaluate the luteotrophic influence of early (before Day 7 as well as after Day 7; Day 0=estrus) bovine embryos and the relationship between plasma progesterone (P4) concentrations and embryo survival. Virgin Holstein dairy heifers (n=325) from a single herd were randomly allocated to be nonbred, bred by artificial insemination (AI) or by embryo transfer (ET). Bred heifers were either treated with 1500 IU human chorionic gonadotrophin (hCG) on Day 7 of the estrous cycle or received no hCG treatment. Plasma P4 concentrations on Days 0, 5, 7, 10, 13, 15, 17, 19 and 21 were similar in pregnant AI- and ET-bred heifers and, this was observed in both hCG-treated and untreated females. Nonbred, AI- and ET-bred nonpregnant heifers (both hCG-treated and untreated) presented similar plasma P4 concentrations. Plasma P4 concentrations of pregnant heifers significantly deviated from those of nonpregnant and nonbred heifers on Day 17. In hCG-treated heifers, plasma P4 concentrations and Day 28 pregnancy rate were significantly higher in females with an induced accessory corpus luteum (CL) than in those females without an induced accessory CL. Treatment with hCG, although inducing the formation of accessory CL and significantly increasing plasma P4 concentrations had no significant effect on Day 28 pregnancy rate. In conclusion, this study does not support the existence of any peripherally detectable luteotrophic influence from early embryos (Days 5-7). Plasma P4 was only significantly related to embryo survival on Day 17, the time of expected onset of luteolysis.     

Extent, pattern and factors associated with late embryonic loss in dairy cows

Intensive genetic selection for increased milk production, coupled with increased dry matter intakes has led to significant improvements in cow milk yield, however, this increase in milk output has been accompanied by a decline in cow fertility. It has been suggested that there is a higher increment of late embryonic loss in high-yielding than in moderate yielding cows or in heifers. The objectives of this study were to establish the extent and pattern of embryonic loss, from days 28 to 84 of gestation, and to examine possible relationships between cow milk yield, cow genetic merit, parity, calving to insemination interval and embryonic loss in dairy cows managed mainly under pasture-based milk production systems. Multiparous dairy cows (n=1046) located on 8 farms and nulliparous dairy heifers (n=162) located on five of these farms were used in this study. The extent and timing of embryonic loss was measured by ultrasound scanning of the cows and heifers at 14-day intervals between days 28 and 84 of gestation. Positive diagnosis of pregnancy was based on the presence of an embryo or foetus with a visible heartbeat and, at the later scans, visible movement, whose size was compatible with stage of gestation and also on the presence of clear amniotic fluid of the cows and heifers presented as presumed pregnant on day 28 after insemination, 67 and 81%, respectively had a viable embryo. The subsequent embryonic loss rate between days 28 and 84 of gestation was similar (P>0.05) for cows (7.2%) and heifers (6.1%) and the pattern of loss over this period was also similar (P>0.05) for cows and heifers. There was no significant association (P>0.05) between level of milk production or milk energy output measured to day 120 of lactation and embryonic loss rate. Similarly, there was no significant relationship (P>0.05) between % milk fat, % milk protein and % milk lactose and embryonic loss rate. The extent and pattern of embryonic loss were not related (P>0.05) to either cow or to cow sire genetic merit. There was no significant (P>0.05) relationship between the calving to first service interval and embryonic loss. The extent of embryonic loss was greater (P<0.05) in cows that lost body condition between days 28 and 56 of gestation compared with cows than either maintained or improved in body condition.     

Effects of administering progesterone at selected intervals after insemination of synchronized heifers on pregnancy rates and resynchronization of returns to service

In 3 separate trials at 2 locations, dairy heifers (n = 396) were treated with a Controlled Internal Drug Release (CIDR) progesterone device for 9 d. On Day 7 of CIDR treatment, all heifers were injected with PGF(2alpha). Synchronized estruses were detected using a tailpaint and chalk (TPC) scoring system. An animal's tailhead was painted at device insertion, and this strip was covered with a contrasting color of chalk at device removal. Over all trials, 85.1% of the heifers were detected in estrus and were inseminated at 48 or 72 hours after CIDR removal. These synchronized and inseminated heifers were divided into the following treatment groups: 1) untreated controls, receiving no further treatment (n = 138); 2) post-insemination progesterone supplementation with a new (n = 59) or used (n = 29) CIDR device for Days 1 to 8 or 2 to 9, respectively, following insemination; or 3) resynchronization of return to service with a used CIDR device for Days 17 to 22 after insemination (n = 112). The pregnancy rate to first insemination in the control and resynchronized groups (Groups 1 and 3) was 46.4%, but decreased to 18.2% with the post-insemination progesterone supplementation. Resynchronization of returns to service (estrus detected 1 to 4 d following removal of second CIDR) occurred in 58.9% of all nonpregnant heifers in Group 3. In summary, CIDR devices used in conjunction with PGF(2alpha) effectively synchronize estrus in dairy heifers. Progesterone supplementation within 2 d of first insemination for 7 d suppressed fertility. Used CIDR devices inserted for Days 17 to 22 after first insemination resynchronized heifers not pregnant to first insemination.     

Methods of identifying and inseminating nonpregnant beef females after synchronization of second estrus with norgestomet implants

Beef females (547) were included in three experiments to evaluate methods of identifying and inseminating nonpregnant beef females after synchronization of second estrus with norgestomet implants. In the first experiment, heifers not pregnant to the first insemination were identified for insemination via estrus (inseminated via the a.m./p.m. rule or 48 h after implant removal). In the second experiment, females not pregnant to the first insemination were identified for insemination via estrus (inseminated via the a.m./p.m. rule) or progesterone concentrations < 1.5 ng/mL at implant removal (inseminated 48 h after implant removal). In the third experiment, heifers not pregnant to the first insemination were identified for insemination via progesterone concentrations (as in experiment 2) or anterior vagina electrical resistance values < 81 ohm resistance 48 h after implant removal (inseminated after resistance measured). All methods of identifying and inseminating nonpregnant females were equally effective (P > 0.10) and did not effect (P > 0.10) calving rates from the first and second AI.     

Concentrations of progesterone in milk as a monitor of early pregnancy diagnosis in dairy cows

The objectives of the experiment were to evaluate the efficacy of using progesterone concentrations in milk and palpation per rectum on days 21 or 22 postbreeding to estimate pregnancy and evaluate management practices; and to investigate physiological occurrences leading to incorrect diagnosis of pregnancy when serial samples of milk were collected. Of particular interest were indications of early embyronic death and insemination of cows not in estrus. Milk samples were collected at the afternoon milking of days 0 or 1 (day 0 = day of estrus), 9 or 10, 21 or 22 and 27 or 28 following breeding in 200 lactating dairy cows. Tentative diagnosis of pregnancy was made based on concentrations of progesterone in milk on days 21 and 22 alone and on days 21 or 22 and 27 or 28. In addition all cows were palpated per rectum on days 21 or 22 postbreeding and a tentative pregnancy diagnosis was made. Pregnancy was confirmed by examination of the genital tract per rectum between 35 and 50 days after breeding. Values of 4 ng/ml or greater and/or the presence of a mature corpus luteum were considered positive signs of pregnancy. Progesterone in milk ranged from 0.1 to 18 ng/ml. On days 0 or 1, 9 or 10, 21 or 22 and 27 or 28 concentrations of progesterone in milk averaged 1.5 +/- 0.3, 11.1 +/- 0.5, 12.0 +/- 0.4 12.5 +/- 0.5 ng/ml for pregnant cows. Corresponding samples from nonpregnant cows averaged 1.2 +/- 0.2, 10.3 +/- 0.4, 3.0 +/- 0.4, 6.8 +/- 0.6 ng/ml, respectively. Ninety-six and 104 cows were classified as pregnant and nonpregnant on days 21 or 22 as compared to 78 and 118 cows diagnosed as pregnant and nonpregnant on days 21 or 22 and 27 or 28 combined. Pregnancy detection by progesterone in milk on days 21 or 22 with pregnancy determined via rectal palpation 35 to 50 days postbreeding was 77 and 100% accurate for positive and negative diagnosis, respectively. The percent agreement using progesterone in milk on days 21 or 22 and 27 or 28 combined was 95 and 100%, respectively, for positive and negative diagnosis. Diagnosis based on rectal palpation 21 or 22 days postbreeding was 63 92 (69%) and 76 88 (87%) for pregnant and nonpregnant cows, respectively. Ten of the 200 cows had progesterone concentratins in milk of > 4 ng/ml at the time of breeding. Six of these cows were pregnant from a previous insemination. The other four cows were nonpregnant and were inseminated during the luteal phase of the cycle. In conclusion, measurement of progesterone in milk is a useful tool in early detection of pregnant and nonpregnant cows and may be useful in detecting reproductive problems in a dairy herd. It will probably be most useful when used in combination with later pregnancy diagnosis per rectum .     

Fertility of dairy cattle treated with human chorionic gonadotropin (hCG) to stimulate progesterone secretion

Two experiments were conducted to determine if progesterone secretion and fertility would be affected by administration of human chorionic gonadotropin (hCG) before or after the first insemination. In Experiment 1, 48 Holstein heifers received 1000 IU of hCG or 1 ml of saline on Days 2, 3, and 4 of an estrous cycle. They were inseminated at the subsequent estrus. In Experiment 2, 110 Jersey and 105 Holstein cows received a single injection of 5000 IU of hCG or 5 ml of saline on Day 3 after estrus. These cows were first inseminated either at the estrus immediately preceding treatment or at the subsequent estrus. In both experiments, blood samples for determination of progesterone were collected thrice weekly for 3 to 4 wk following treatment. In Experiment 1, progesterone concentrations during mid-cycle were higher in hCG-treated heifers than in saline-treated controls. Treatment with hCG resulted in an 11% increase in the first service conception rate (P < 0.48). In Experiment 2, hCG-treated cows displayed higher progesterone secretion during mid-cycle than saline-treated herdmates. The conception rate of cows inseminated prior to hCG-treatment was not affected by treatment, but cows inseminated after treatment had a marginally lower fertility rate. The conception rate of cows receiving a repeat insemination following hCG treatment was higher than for the controls. We conclude that treatment with hCG did not improve the conception rate at the first insemination, but it may be beneficial for cows that require a repeat service.     

Effectiveness of administration of gonadotropin-releasing hormone at Days 11, 14 or 15 after anticipated ovulation for increasing fertility of lactating dairy cows and non-lactating heifers

One strategy for improving fertility in cattle is mid-cycle administration of GnRH to increase progesterone secretion and delay luteolysis. This strategy might be especially useful during hot weather because heat stress increases uterine prostaglandin release and reduces development of the elongating embryo. A series of experiments was conducted to test the efficacy of GnRH for increasing fertility. There was no effect of administration of 100 microg GnRH at Day 11 after anticipated ovulation on pregnancy rates in virgin heifers subjected to timed artificial insemination (TAI) during the summer. Similarly, there was no beneficial effect of administration of GnRH at Day 11 after anticipated ovulation on pregnancy rates of lactating cows subjected to TAI in summer and winter. Three experiments tested effects of injection of GnRH at Days 14 or 15 after anticipated ovulation on pregnancy rates of lactating cows. The first experiment used 477 lactating cows subjected to TAI. Cows receiving GnRH at Day 14 had higher pregnancy rates in both summer and winter than cows receiving vehicle (20.3 versus 12.7%, P<0.02). When this experiment was repeated during summer with 137 cows, there was a negative effect of GnRH treatment at Day 14 on pregnancy rate. In the third experiment, lactating cows during summer were inseminated at detected estrus and cows were assigned to treatment with either GnRH or vehicle at Days 14 or 15 after insemination. Pregnancy rates were 25.6% (32/125) for cows receiving vehicle, 20.7% (19/92) for cows receiving GnRH at Day 14, and 20.3% (16/79) for cows receiving GnRH at Day 15. In conclusion, GnRH administration at Days 11-15 after anticipated ovulation or estrus did not consistently increase pregnancy rates in either cool or warm seasons.     

Diagnosis of pregnancy by radioimmunoassay of a pregnancy-specific protein in the plasma of dairy cows

The accuracy and efficiency of progesterone (P4) and bovine pregnancy-specific protein B (bPSPB) radioimmunoassays (RIA) in detecting pregnant and nonpregnant dairy cows were compared at different stages of pregnancy. The study included 145 French Friesian heifers and cows from a single herd. A total of 175 artificial insemination (A.I.) and blood sampling procedures were performed. Animals were bled 24 d post AI for P4 RIA. They were bled at 24, 26, 30 to 35, and 70 +/- 9 after AI for bPSPB RIA. Females were declared nonpregnant when plasma P4 concentrations were lower than 1.5 ng/ml. With the bPSPB RIA, cows were nonpregnant when at least one of the B Bo x 100 replicates was higher than 95% in the RIA. When compared with palpations per rectum at 70 d, the accuracy of positive diagnoses (no. positive and pregnant/no. positive diagnoses) by P4 RIA at Day 24 was 67.2% (82 122 ). The accuracy of negative diagnoses was 98% (52 53 ). Accuracy of positive diagnoses by bPSPB RIA increased with gestation age (P<0.05) from 86.2% (50 58 ) on Day 24 to 98.8% (83 84 ) at time of palpation per rectum. Accuracy of negative diagnoses increased (P< 0.001) from Day 24 (71.8%; 84 117 ) to Days 30 to 35 (100%, 83 83 ). Efficiency in detecting nonpregnant females was much higher (P < 0.001) with the bPSPB RIA on Days 30 to 35 (90.2%; 83 92 ) than with the P4 RIA on Day 24 (56.5%, 52 92 ). It is concluded that 30 days after AI, the bPSPB RIA is an efficient test both for pregnancy prediction and detection of nonpregnant dairy cows.     

Plasma oestradiol and progesterone during early pregnancy in the cow and the effects of treatment with buserelin

We have monitored plasma concentrations of oestradiol and progesterone after insemination in dairy cows, and investigated the effects of injection with 10 μg of the gonadotrophin-releasing hormone (GnRH) analogue buserelin, a treatment known to result in an improvement in conception rate. Animals were injected intramuscularly on Day 12 after insemination with 2.5 ml of either control saline (n = 29) or buserelin (n = 26). Blood samples were collected from Day 8 to Day 17 and milk samples from the day of insemination until Day 30. On the basis of milk progesterone profiles, in the control group 15 cows remained pregnant (control pregnant) and 11 underwent luteolysis (control not pregnant), whereas in the treated group 13 cows remained pregnant (treated pregnant) and 13 underwent luteolysis (treated not pregnant). Three cows were excluded from the control group owing to high progesterone at insemination or failed ovulation. In both the control and treated groups mean plasma progesterone concentration was significantly (P < 0.05) lower in non-pregnant cows than in pregnant ones from Day 12 post-insemination. However, no significant effect of buserelin treatment on plasma progesterone concentration was detected. In the control group the plasma oestradiol concentration was similar in the pregnant and non-pregnant cows. In the treated group, plasma oestradiol concentration in the non-pregnant cows was similar to that in the control group, whereas in the treated pregnant cows the plasma oestradiol concentration showed a significant (P < 0.05) decline after treatment. As oestradiol is known to stimulate the development of the luteolytic mechanism at this time, we suggest that buserelin is acting to reduce the strength of the luteolytic drive in some cows, thus improving the chance of the embryo being able to prevent luteolysis.     

Evaluation of the early conception factor (ECF) test for the detection of nonpregnancy in dairy cattle

The ability to detect conception and/or conception failure in cattle would be beneficial to producers in formulating reproductive management plans. A new diagnostic test, the early conception factor (ECF) test, has been developed forthis application yetthe accuracy of this test has not been adequately determined. The objectives of this study were to evaluate the effectiveness of the ECF test for detecting the nonpregnant cow, and to compare the reliability of serum versus milk ECF tests relative to actual pregnancy rates. In Trial 1, Holstein heifers were synchronized, the animals were bred (timed-AI), and serum ECF tests were performed 72 h later. Heifers exhibiting a negative ECF test after AI were re-synchronized, bred again, and re-tested for ECF for up to three services. Relative to actual pregnancy rates, a negative ECF test was correct (i.e., true negative) 38.5% of the time over the three services. In Trial II, Holstein heifers were bred (AI) after observed estrus and serum ECF tests conducted between Days 1 and 3 and Days 7 and 9 after AI. In this trial, only 44.4% and 55.6% of the confirmed nonpregnant heifers were identified correctly by serum ECF analysis at Days 1 to 3 and Days 7 to 9 post-AI respectively. In Trial III, 40 lactating cows were synchronized, the animals were bred (AI), and serum and milk ECF tests were performed on Days 3, 9, 15, 21 and 30 after AI. Pregnancy diagnosis (ultrasound on Day 30 and palpation on Day 51) confirmed that 50% of the cows were pregnant to AI, while serum and milk ECF analysis indicated a 100% and 37.5% predicted pregnancy rate, respectively, at 30 d post-AI. Moreover, results of the serum and milk ECF tests disagreed with one another 36.9% of the time overall, while agreement between ECF and actual pregnancy rates were 50.6% and 45.6% for milk and serum respectively. Additionally in Trial III, a negative ECF result only identified 5% and 28.8% of nonpregnant cows overall for serum and milk tests respectively (i.e., true negatives), with a high incidence of false positive ECF results noted (47.5% and 31.3% for serum and milk, respectively). Collectively, these data indicate that the current ECF test cannot accurately identify the nonpregnant cow with the precision needed by the dairy producer.     

Luteal inadequacy during the early luteal phase of subfertile cows

A study was made of early luteal function (up to Day 6) in cyclic and pregnant heifers and also in older, subfertile cows. There were no differences in vivo or in vitro between cyclic and pregnant heifers, indicating no luteotrophic effect of the embryo at this stage, but the increase in postovulatory peripheral progesterone concentrations was delayed (P less than 0.01) and occurred more slowly (P less than 0.001) in the subfertile cows than in the heifers. The corpora lutea of the subfertile cows were heavier (P less than 0.001) than those of the heifers on Day 6. Basal progesterone production by dispersed luteal cells was similar between heifers and subfertile cows, but there was a difference (P less than 0.001) in the pattern of response to exogenous LH and PGE-2. Cells from subfertile cows were less sensitive to the stimulatory effects of PGE-2 and although LH increased (P less than 0.001) progesterone production by all cells, this stimulation by a low dose of LH was inhibited by PGE-2 in luteal cells from subfertile cows. This effect did not occur in the luteal cells from heifers. These results indicate the possibility that luteal inadequacy, due to a diminished response to circulating luteotrophic hormones, may contribute to embryo mortality in subfertile cows.     

Experiments on egg transfer in the cow and ewe: dependence of conception rate on the transfer procedure and stage of the oestrous cycle.

The effects on embryo survival of procedures used in transferring eggs non-surgically were investigated in three experiments in ewes and heifers. In Exp. 1, two techniques for introducing eggs into the uterus through the cervix in heifers were compared; namely (i) deposition of the eggs high into the uterine horn or (ii) into the body of the uterus. Both methods were followed by inflation of the uterus with carbon dioxide. Out of a total of 34 heifers, only one became pregnant by the use of Method (i). Non-surgical egg tansfers early (Days 3 to 5) or later (Days 6 to 9) in the oestrous cycles of heifers were carried out in Exp. 2. Three transfer procedures were compared: (i) pipette transfer of an egg into the body of the uterus through the cervix (control), (ii) the control procedure performed under Fluothane anaesthesia, or (iii) followed by inflation of the uterus with carbon dioxide. Wide transfers carried out early in the cycle, pregnancies resulted in 1/10, 0/10 and 1/10 of the heifers in the control, carbon dioxide and Fluothane groups, respectively. With late transfers, 7/20, 1/10 and 8/20 heifers became pregnant in the respective treatment groups. This trend for pregnancy rate to be improved when late transfers were done in the control and Fluothane groups was significant only at the 10% level of probability when both groups were pooled. It was tentatively concluded, however, that non-surgical transfers of fertilized eggs to heifers may be best done during mid-cycle, after Day 6. Fluothane anaesthesia did not improve conception rate. Inflation of the uterus with carbon dioxide appeared to be deleterious when used at the mid-cycle stage in heifers. In Exp. 3, it was found that inflation of the ewe's uterus with carbon dioxide or nitrogen following the surgical thansfer of an egg did not affect the incidence of pregnancy. The introduction of 50 mul liquid Fluothane into the lumen of the uterus was embryotoxic.