Induction of ovulatory estrus and fertility in non-cycling buffaloes with norgestomet during low breeding season

Field trials were designed to evaluate use of norgestomet treatment to induce ovulatory estrus in non-cycling buffalo cows and heifers during low breeding season. Twenty-five buffalo cows and 50 heifers under village management were given a 9-day treatment with a polymer implant containing 6 mg norgestomet with IM injections of 5 mg estradiol valerate + 3 mg norgestomet at the time of implantation and 600 IU PMSG when the implant was removed. Fifty animals served as controls without any treatment. Seventy-four treated animals showed estrus during the period between 36 to 80 hours after removal of the implant. Twenty-five buffalo cows and 40 heifers that could be further followed up were inseminated twice at 8-hour intervals, 12 hrs after induction of estrus with chilled semen by recto-vaginal method. Of these, 15 (23.1%) conceived, 9 (36%) among buffalo cows and 6 (15%) among heifers. Fourteen buffalo cows and 30 heifers that did not conceive manifested cyclic estrus at an interval of 22.4 and 20.6 days. The conception rate in the cyclic estrus was 57% and 23.3%, respectively, for buffalo cows and heifers. The overall conception rate over two inseminations was 46.2%, 68% in buffalo cows and 32.5% in heifers. In the control group, five (10%) showed spontaneous estrus and two (40%) conceived during the period of the experiment.     

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.     

Effect of estrous cycle stage at Syncro-Mate B treatment on conception and time to estrus in cattle

Two trials involving 85 heifers and 67 cows were conducted to determine the effect of estrous cycle stage at the time of Syncro-Mate-B((R)) (SMB) treatment on interval to estrus following implant removal and on conception rate at the synchronized estrus. In Trial 1, 57 beef and 28 dairy heifers were treated with SMB on each representative day of a 22-d estrous cycle (estrus = Day 0). Beef heifers were artificially inseminated approximately 48 h after implant removal, whereas dairy heifers were inseminated 0 to 12 h after detection of estrus. Inseminations were scored by the inseminator according to their difficulty. Interval to the onset of estrus was not different between heifers treated early ( Day 11) in the cycle (35.2 +/- 7.2 h). Conception rate at the synchronized estrus was slightly higher in early-cycle heifers (22 47 = 47% ) compared to late-cycle heifers (14 38 = 37% , P = 0.2). Heifers that were difficult to inseminate had lower (P < 0.01) conception rates (2 11 = 18% ) at the synchronized estrus than heifers considered normal (21 51 = 41% ) or easier than normal to inseminate (13 23 = 57% ). In Trial 2, of the 131 beef cows synchronized, 67 that were estimated to be either early or late in the estrous cycle by progesterone analysis were utilized. Cows were treated with SMB and inseminated without regard to estrus 48-h after implant removal. Inseminations were scored as in Trial 1. Calves were separated from cows from the time of implant removal to insemination. Conception rate was higher (P < 0.05) in cows treated with SMB early ( Day 11, 16 35 = 46% ). Cows that were difficult to inseminate had a lower (P < 0.01) conception rate (0 8 = 0% ) than cows that were normal (43 94 = 46% ) or easier than normal to inseminate (13 29 = 45% ).     

Syncro-mate B induces estrus in ovariectomized cows and heifers

Eleven ovariectomized Hereford x Simmental cows and 10 ovariectomized crossbred heifers (primarily Angus and Hereford) were given the Syncro-Mate B (SMB) estrous synchronization treatment. The SMB treatment consisted of a 2 ml i.m. injection containing 5 mg of estradiol valerate and 3 mg of norgestomet plus a hydron ear implant containing 6 mg of norgestomet. The ear implant was removed 9 d later. Cows and heifers were considered in estrus only if they stood for mounting by a herdmate or a bull. Observations for estrus were made four or six times each day for 3 d after implant removal. The 21 animals were used in eight trials. Each trial involved 9 or 11 cows or 5 or 10 heifers. Four days to three weeks elapsed between implant removal and implant insertion for the next trial. No ovariectomized cow or heifer was observed in estrus for 21 d before treatment with SMB. In the eight trials, 3 of 9, 7 of 9 and 6 of 11 cows exhibited estrus, whereas 5 of 10, 1 of 5, 3 of 5, 3 of 5 and 5 of 5 heifers exhibited estrus after treatment. When data were pooled, 16 of 29 (55.2%) cows and 17 of 30 (56.7%) heifers exhibited estrus after treatment. Our data indicate that the SMB treatment can induce estrus in cows and heifers, independently of the ovaries.     

Fertility of Bos indicus and Bos indicus x Bos taurus crossbreed cattle after estrus synchronization

Ninety-five cows (79 Boran and 16 Boran-Brahman crossbreeds) and 107 heifers (55 Boran and 52 Boran x Friesian F1 crossbreeds) were used to determine estrus response, estrus response interval and pregnancy rate following synchronization with prostaglandin (PGF(2)alpha), a progesterone-releasing intravaginal device (PRID) and Synchro-mate B (SMB). The proportion of cattle responding to synchronization treatment was 62.5, 43.5 and 57.7% for cows and 85.7, 68.0 and 81.5% for heifers using PGF(2)alpha, PRID and SMB, respectively. The overall mean response was 59 and 81.8% for cows and heifers, respectively. The estrus response of the control animals over a 45-d breeding period was 72.7 and 90% for cows and heifers, respectively. The estrus response interval for cows was 31.8, 22.1 and 18.0 h and it was 51.1, 38.0 and 21.6 h for heifers with PGF(2)alpha, PRID and SMB treatment, respectively. Mean pregnancy rate for cows was 50.0, 34.8, 46.2 and 68.8% and for heifers it was 60.7, 40.0, 55.6 and 77.8% in the PGF(2)alpha, PRID, SMB and control groups, respectively. Based on these findings, it was concluded that both PGF(2)alpha and SMB produce a satisfactory estrus response and pregnancy rate in the cattle studied.     

Reproductive performance of lactating dairy cows and heifers resynchronized for a second insemination with an intravaginal progesterone-releasing device for 7 or 8d with estradiol benzoate injected at the time of device insertion and 24h after removal

One aim of this study was to compare the reproductive performance of cows and heifers when resynchronizing returns to estrus for a second insemination by treating with an intravaginal progesterone-releasing device (IVD) for 7 or 8d when estradiol benzoate (EB) was administered at the start of treatment and again 24h after device removal. An additional aim was to document the pattern of onset and characteristics of estrus with each resynchrony treatment. Lactating cows in three herds were synchronized for a first estrus and AI by treatment with an IVD for 8d, starting on Day 0, cloprostenol (0.5 mg im) at device removal and EB at device insertion (2.0 mg im) and 24h after removal (1.0 mg im). Cows were resynchronized for a second estrus starting on Day 23 by reinsertion of IVDs for 7 (IVD-7-EB; n=449) or 8d (IVD-8-EB; n=445) with EB (1.0 mg im) administered at device insertion and 24h after removal. Cows were resynchronized for a third estrus by administration of EB (1.0 mg im) on Day 46, but subsequent treatments (no further treatment, reinsertion of CIDR or administration of EB on Day 55) varied among herds as part of separate studies. Maiden heifers (7-Day, n=68; 8-Day, n=69) were similarly treated as cows in a separate herd, but doses of EB were always 1.0 mg im at device insertion and 0.75 mg im 24h after removal. Heifers were not resynchronized for a third estrus. Cattle were inseminated on detection of estrus at each synchronized estrus. Cumulative pregnancy rates 4 week (66.0%, 276/418 versus 59.1%, 247/418) and 7 week (72.7%, 304/418 versus 67.7%, 283/418) after the start of AI were greater (P<0.05) in the IVD-7-EB cows compared to the IVD-8-EB cows, respectively; this was associated with a 9% increase in conception rates at the second estrus (P=0.051) in the IVD-7-EB cows. Treatment did not significantly affect reproductive performance in heifers. Characteristics of estrus measured with radiotelemetry did not differ significantly between the two treatment groups, but more cows were detected in estrus 36 h after removal of IVDs in the IVD-8-EB cows compared to the IVD-7-EB cows (P<0.05). We concluded that reproductive performance in resynchronized dairy cows but not heifers was greater following resynchronization of estrous cycles after AI with an IVD for 7 compared to 8d when EB was injected at the start of treatment and 24h after device removal.     

Estrous behavior and the estrus-to-ovulation interval in Nelore cattle (Bos indicus) with natural estrus or estrus induced with prostaglandin F2 alpha or norgestomet and estradiol valerate

Estrous behavior and the estrus-to-ovulation interval are essential for estimating the best time to artificially inseminate cattle. Because these parameters are not well characterized in the Nelore breed (Bos indicus), the main purpose of the this study was to determine the estrus-to-ovulation interval in Nelore heifers and cows with natural estrus or with estrus induced by treatments with PGF2 alpha or norgestomet and estradiol valerate (NEV). The cows and heifers were observed continuously (24 h a day) to determine the onset of estrus and to study estrous behavior in the cows. Ten hours after the start of estrus the ovaries were scanned every 2 h by ultrasonography to monitor the dominant follicle until ovulation. Blood samples were collected periodically to determine progesterone levels by RIA. Administration of PGF2 alpha (2 injections, 11 days apart) did not induce estrus in most Nelore females in spite of the presence of functional CL, indicated by progesterone concentrations above 6.0 ng/ml in 25 of 28 animals. Treatment with NEV induced high sexual receptivity in cows (10/11), but only 66% ovulated. Cows with natural or induced estrus exhibited behavioral estrus of 10.9 +/- 1.4 h, and ovulation occurred 26.6 +/- 0.44 h (n = 26) after the onset of estrus. In most of the cows (53.8%) estrus began at night (between 1801 and 600 h), and 34.6% it started and finished during the night. It is concluded that in Nelore females ovulation occurs approximately 26 h after the onset of estrus. Additionally, estrous behavior is shorter than in European breeds, and there is a high incidence of estrus at night, which makes it difficult to detect and, consequently, impairs Al in Nelore cattle. The observation that a high percentage of Nelore females with an active CL did not respond to usual dosages of PGF2 alpha warrants further investigation.     

Synchronization of estrus after treatment with Luprostiol in beef cows and in beef and dairy heifers

Four trials were conducted to study synchronous estrous response in beef cows and in beef and dairy heifers to Luprostiol (13, thia-PG-F(2)alpha analog) in comparison with other prostaglandin products. In Trial 1, 60 virgin beef heifers were observed for estrus for 5 d and artificially inseminated. Heifers not observed in estrus within 5 d were randomly assigned to receive 15 mg Luprostiol or 25 mg Lutalyse. In Trial 2, 75 multiparous, lactating beef cows were randomly assigned to receive either 15 mg Luprostiol, 25 mg Lutalyse or 500 mcg Estrumate. All cows received a second injection of the respective treatment 11 d later. In Trial 3, 96 multiparous, lactating beef cows were randomly assigned to receive 15 mg Luprostiol or 25 mg Lutalyse. All cows received a second injection of the respective treatment 11 d later. In Trial 4, virgin dairy heifers were palpated per rectum. Seventy-seven heifers with a palpable corpus luteum (CL) were randomly assigned to receive 15 mg Luprostiol or 500 mcg Estrumate. In all trials animals were artificially inseminated 12 h following observed estrus. Estrous response during the 5-d synchronized period was 44% for Luprostiol and 42% for Lutalyse treated heifers in Trial 1. It was 52, 56 and 60%, respectively, for Luprostiol, Lutalyse and Estrumate treated cows in Trial 2; 23% for Luprostiol and 19% for Lutalyse treated cows in Trial 3; and 68% for Luprostiol and 70% for Estrumate treated heifers in Trial 4. Treatment with Luprostiol results in a similar synchronous estrous response as with the other prostaglandin products used in these studies.     

Synchronization of estrus in beef cows and heifers with fenprostalene, cloprostenol sodium, and prostaglandin F2 alpha

The effects of fenprostalene, cloprostenol sodium and prostaglandin F(2) alpha (PGF(2alpha)) on estrus, conception rate, pregnancy rate, and the interval from Day 1 of the breeding season to calving were studied on 135 purebred Angus cows and heifers. The cows and heifers were randomly allotted within age to the three estrus synchronization treatments and a control group. The calving percentages (for cows and heifers combined) that resulted from artificial insemination (AI) were 32.3, 31.4, 43.6, and 51.1% for the control, fenprostalene, cloprostenol sodium, and PGF(2alpha) groups, respectively. The calving percentage during the AI period by ages of dam at breeding were 54.2% for yearling heifers, 30.5% for two-year-olds, 47.6% for three-year-olds, and 26.1% for four-year-old or older cows. The percentage of cows and heifers detected in estrus and the percentage that conceived after the first injection for control, fenprostalene, cloprostenol sodium, and PGF(2alpha) groups were 51.6 and 22.3%, 59.3 and 32.1%, 76.8 and 44.1%, and 66.6 and 50.2%, respectively. The intervals from Day 1 of the breeding season to calving and from Day 1 of the calving season within each treatment to the birth of each calf were control, 285.9 and 23.8 d; fenprostalene, 283.6 and 13.4 d; cloprostenol sodium, 285.5 and 6.5 d; and PGF(2alpha), 284.0 and 11.1 d.     

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.     

Recovery rate and quality of embryos collected from suckled cows and beef heifers after superovulation with PMSG

Recovery rate and embryo quality were investigated in beef heifers and suckled cows following superovulation induced by 2000 IU pregnant mare serum (PMSG) combined with different methods of estrus cycle synchronization (Norgestomet, Prid, Dinolytic, Norgestomet combined with Dinolytic). Genital tracts were flushed upon slaughter with Dulbecco's medium 6.5 to 7.5 days after insemination. Of the heifers, 42 out of 43 responded to treatment. The mean embryo recovery rate, based on the number of corpora lutea, was only 14.8%. Of the 83 embryos recovered, 54.2% had developed to the expected stage and only 40% appeared normal. Of the adult cows, 55 out 58 responded with an embryo recovery rate of 39.5%. Of the 149 embryos recovered, 48.9% had developed to the expected stage and 67.1% of these appeared normal. In both heifers and adult cows, the different methods of estrus synchronization produced no significant differences in recovery rate or embryo quality.     

The variability in the interval between estrus and ovulation in cattle and its determinants

Fertility of Holstein cows has been decreasing for years and, to a lesser extent, the fertility of heifers too but more recently. A hypothesis to explain this phenomenon may be that the chronology of events leading to ovulation is different for those animals bred nowadays when compared to what was reported previously; this would result in an inappropriate time of insemination. Therefore, two experiments were designed to investigate the relationships among estrus behavior, follicular growth, hormonal events and time of ovulation in Holstein cows and heifers. In the first experiment, the onset of estrus, follicular growth, patterns of estradiol-17beta, progesterone and LH, and the time of ovulation were studied in 12 cyclic Holstein heifers that had their estrus synchronized using the Crestar method; this was done twice, 3 weeks apart. The intervals between estrus and ovulation, estrus and the LH peak, and between the LH peak and ovulation were, respectively, 38.5 h +/-3.0, 9.1 +/- 2.0 and 29.4 h +/-1.5 (mean+/- S.E.M). The variation in the interval between estrus and the LH peak explained 80.6% of the variation in the interval between estrus and ovulation. The intervals between estrus and the LH peak, and estrus and ovulation were correlated with estradiol-17beta peak value (r=-0.423, P <0.04 and r=-0.467, P<0.02, respectively). Positive correlation coefficients for the number of follicle larger than 5 mm, and negative correlation coefficients for the size of the preovulatory follicle with the intervals between estrus and LH peak, LH peak and ovulation, and estrus and ovulation suggest an ovarian control of these intervals. In respect to its role to explain the variation in the interval between estrus and ovulation, the variation in the interval between estrus and the LH peak was evaluated further in a second set of experiments utilizing 12 pubertal Holstein heifers and 35 Holstein cows. The duration of the interval between the beginning of estrus and the LH peak was longer in heifers than in cows (4.15 h versus -1.0 h; P <0.002); the variation for this interval was higher in cows than in heifers (S.E.M.= 1.2 h versus 0.8 h; P=0.01). According to the results of these studies it can be proposed that estradiol and other product(s) of ovarian origin regulate not only the duration of intervals between the onset of estrus and the LH surge but also between the LH surge and ovulation. From the results obtained in the first experiment, it may be postulated that differences observed between cows and heifers for the duration of the interval between onset of estrus and the LH surge as well as for the variation of this interval would be observed also for the interval between the onset of estrus and ovulation. Therefore, on a practical point of view, the long interval between the onset of estrus and ovulation and the high variation of this interval, especially in cows, may be a source of low fertility and should be considered when analysing reproductive disorders.     

Follicular dynamics and concentrations of steroids and gonadotropins in lactating cows and nulliparous heifers

Differences in follicular development and circulating hormone concentrations, between lactating cows and nulliparous heifers, that may relate to differences in fertility between the groups, were examined. Multiparous, cyclic, lactating Holstein cows (n=19) and cyclic heifers (n=20) were examined in the winter, during one estrous cycle. The examinations included ultrasound monitoring and daily blood sampling. Distributions of two-wave and three-wave cycles were similar in the two groups: 79 and 21% in cows, 70 and 30% in heifers, respectively. Cycle lengths were shorter by 2.6 days in heifers than in cows, and in two-wave than in three-wave cycles. The ovulatory follicle was smaller in heifers than in cows (13.0+/-0.3 mm versus 16.5+/-0.05 mm). The greater numbers of large follicles in cows than in heifers corresponded well to the higher concentrations of FSH in cows. The duration of dominance of the ovulatory follicle tended to be longer in cows than in heifers. Estradiol concentrations around estrus and the preovulatory LH surge were higher in heifers than in cows (20 versus 9 ng/ml). Progesterone concentrations were higher in heifers than in cows from Day 3 to Day 16 of the cycle. Circulating progesterone did not differ between two-wave and three-wave cycles. The results revealed differences in ovarian follicular dynamics, and in plasma concentrations of steroids and gonadotropins; these may account for the differences in fertility between nulliparous heifers and multiparous lactating cows.     

Estrus synchronization and superovulation with a subcutaneous gestagen implant (Norgestomet, Intervet) in suckler cows and heifers

Four trials were conducted to investigate the suitability of a gestagen implant (Norgestomet, Intervet) for estrus synchronization and superovulation in suckler cows and heifers kept under field conditions in Germany. In trial 1 out of 17 heifers treated 12 responded with one ovulation each. In trial 2 57 suckler cows were treated at the University experimental farm. Of 23 cows treated sooner and 34 cows treated later than 50 days post partum one (4 %) and 16 (47 %) respectively calved at the expected time. Trial 3 was a field trial involving 126 suckler cows and 21 heifers. Of 24 cows treated sooner and 102 cows treated later than 50 days post partum 17 % and 52 % respectively calved at the expected time. Of the 21 heifers only 19 % calved at the expected time. In trial 4 superovulation of 13 cows and 17 heifers resulted in 62 % and 94 % responding with 10.0 +/- 2.5 and 11.1 +/- 3.0 (x +/- SD ) ovulations per animal respectively.     

Effect of stage of the estrous cycle on interval to estrus after PGF(2alpha) in beef cattle

Effect of stage of the estrous cycle at the time of prostaglandin F(2alpha) (PGF(2alpha)) injection on subsequent reproductive events in beef females was studied in four trials involving 194 animals. Cycling animals were given two injections of 25 mg PGF(2alpha) 11 days apart or, in some cases, the interval was altered to allow the second injection to fall on a specific day of the cycle. Day of estrous cycle at time of the second injection was determined by estrous detection. Interval from the second PGF(2alpha) injection to the onset of estrus (interval to estrus) was shorter (P<.01) in heifers than in cows. Both cows and heifers injected on days 5 to 9 (early cycle) had a shorter (P<.01) interval to estrus (estrus = day 0) than did those injected on days 10 to 15 (late cycle). Conception rate was lower (P<.05) for early-cycle heifers than for late-cycle heifers inseminated by appointment at 80 hours. There was no significant difference in conception rate of early-or late-cycle heifers or cows inseminated according to estrous detection or early- or late-cycle cows inseminated at 80 hours. Progesterone concentrations in blood samples collected in heifers at 4-hour intervals after the second PGF(2alpha) injection on either day 7 or day 14 declined linearly (P<.05) through 36 hours. Day of the estrous cycle at PGF(2alpha) injection had no effect on rate of progesterone decline, even though heifers injected on day 7 had a shorter (P<.05) interval to estrus. All animals whose cycle length was not affected by the second PGF(2alpha) injection were treated on days 5 through 8 of the cycle, indicating that PGF(2alpha) was less effective in regressing the corpus luteum between days 4 and 9 of the cycle than later in the cycle.     

Control of estrus in dairy cows with a synthetic analogue of prostaglandin F2 alpha

Trials were carried out on 1184 dairy cows calved at least six weeks before treatment and 255 heifers to determine effectiveness of the prostaglandin analogue, cloprostenol to control estrus. In trial 1, following two injections of cloprostenol given 12 days apart, there was no difference in calving rate following AI either at 72 and 96 hr after treatment (71 163 ) or at a detected estrus (53 118 ) compared to control cows bred at estrus (54 110 ). In trial 2, treated cows were injected once after 5 to 7 days of estrous detection and AI. The calving rate following AI either at 72 and 96 hr after cloprostenol (46 100 ) or at a detected estrus (39 71 ) was similar to that in control cows bred at estrus (45 86 ). In trial 3, cows were bred at a detected estrus after the first cloprostenol injection. Twelve days after this injection, cows not bred were given a second injection and bred 72 and 96 hr later. The calving rate in treated cows bred at estrus after the first injection (66 138 ) was similar to calving rate in controls (55 95 ). However, calving rate in cows given a second injection and bred 72 and 96 hr later was significantly (P angle 0.05) lower (30 98 ). Similar results were obtained in heifers, except calving rate in trial 3 after the second cloprostenol injection was not reduced.     

Embryo production from superovulated Holstein-Friesian dairy heifers and cows after insemination with frozen-thawed sex-sorted X spermatozoa or unsorted semen

The aim of this study was to evaluate embryo production in superovulated Holstein-Friesian dairy heifers and cows inseminated with either X-sorted spermatozoa (2 million/dose) or unsorted semen (15 million/dose). Experiment 1 at the research farm involved eight heifers, six cows and semen of one Holstein bull. All transferable embryos were diagnosed for sex. Experiment 2 included embryo collections on commercial dairy farms: X-sorted spermatozoa from three Holstein bulls were used for 59 collections on 28 farms and unsorted semen from 32 Holstein bulls were used for 179 collections on 79 farms. Superovulations were induced by eight declining doses of FSH (total of 12 ml for heifers and 19 ml for cows) starting on days 8-12 of the estrus cycle. Inseminations began 12h after the onset of estrus and were performed two to four times at 9-15 h intervals. Low-dose X-sorted inseminates were deposited into uterine horns and unsorted semen was placed into the uterine body. In Experiment 1, on average 70.3 and 75.0% of embryos recovered from heifers, and 48.4 and 100% of embryos recovered from cows were of transferable quality in X-sorted and unsorted groups, respectively. The proportion of transferable female embryos produced approximately doubled when insemination was with X-sorted spermatozoa compared to insemination with unsorted semen (heifers 96.4% versus 41.1%; cows 81.1% versus 39.8%). In Experiment 2, estimated 53.9 and 65.5% of embryos recovered from heifers, and 21.1 and 64.5% of embryos recovered from cows were of transferable quality in X-sorted and unsorted groups, respectively. Proportions of unfertilized oocytes were 21.1 and 10.6% for heifers and 56.0 and 14.4% for cows in X-sorted and unsorted groups, respectively. Consequently, cows inseminated with X-sorted spermatozoa produced significantly smaller proportions of transferable embryos (p<0.005) and significantly larger proportions of unfertilized oocytes (p<0.001) than those inseminated with unsorted semen. Proportions of quality 1 or degenerated embryos were similar for the two treatments in both heifers and cows. Within treatments, bulls did not significantly affect the proportions of transferable, unfertilized or degenerated oocytes/embryos. It was concluded that using low-dose X-sorted spermatozoa rather than normal-dose unsorted semen for the insemination of superovulated embryo donors can improve the proportion of transferable female embryos produced but this potential may not be achieved in commercial practice, particularly in cows, because of reduced fertilization rates when using low doses of X-sorted spermatozoa.     

A field investigation of the effects of bovine viral diarrhea virus infection around the time of insemination on the reproductive performance of cattle

During a study of methods of synchronizing estrus in Bos indicus cattle, blood was collected from 169 heifers and 38 cows 2 to 3 days prior to artificial insemination (AI), and then again at Day 51 and Day 210 after AI to determine the incidence of infection with bovine viral diarrhea (BVD) virus. Prior to insemination 53 and 68% of the cows and heifers, respectively, were seronegative to the BVD virus. At Day 51 after AI, 70 and 32% of the seronegative cows and heifers, respectively, had seroconverted; but between Day 51 and Day 210, only 17 and 3% of the seronegative cows and heifers, respectively, had seroconverted. The Day- 51 pregnancy rate of cows which were immune (seropositive) to BVD virus infection at the time of AI was similar to the rate of the cows which became infected around the time of AI. However, the pregnancy rate of the immune heifers (44%, n=54) was significantly (P=0.04) greater than the rate of the heifers which became infected around the time of AI (24%, n=37). It was concluded that infection of susceptible females with BVD virus around the time of AI may significantly lower the pregnancy rate.     

Early pregnancy diagnosis by transrectal ultrasonography in dairy cattle

The objective of the present study was to determine differences in time of detection of pregnancy between heifers and cows and the interval after insemination at which the maximum sensitivity and negative predictive value of transrectal ultrasonography were obtained. One-thousand-four-hundred transrectal ultrasonographies (TRUS-1; 1,079 in cows and 321 in heifers) were performed using a 5-MHz linear-array transducer. The cattle were randomly assigned to have TRUS performed once between days 24 and 30 (estrus=day 0) in cows or between days 21 and 27 in heifers. Every TRUS diagnosis was subsequently compared with a second TRUS diagnosis (TRUS-2), performed 3-8 days later, after day 30 (range 31-38) for cows and after day 27 (range 28-35) for heifers. The sensitivity and specificity between cows and heifers for the common days of TRUS (from 24 to 27) were compared. In cows, sensitivity increased gradually from 74.5% at day 24 to 100% at day 29 (P<0.01). Specificity increased from days 24-25 and reached a plateau of 96.6% on day 26 (P<0.01). In heifers, sensitivity increased from 50% at day 21 to 100% at day 26 (P<0.01). Specificity increased from 87.5% at day 21 and remained steady at 94% starting on day 23 (P>0.05). The sensitivity for cows and heifers was 89.2 and 96.8%, respectively (P<0.05) and the specificity was 93.0 and 93.4% (P>0.05). In this study, heifers were diagnosed pregnant earlier than cows, and the maximum sensitivity and negative predictive value were obtained 3 days earlier in heifers than cows (days 26 and 29, respectively).     

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.