Conception rates and calving intervals after prostaglandin F2 alpha or prebreeding progesterone in dairy cows

Two experiments were performed in two different herds to determine if utilizing prostaglandin F 2 alpha to induce estrus for first services would be effective in reducing the duration and variability of calving intervals. In Experiment 1, cows were assigned randomly as controls (n = 217) to be inseminated as they were detected in estrus (beginning d 42 to 53 postpartum depending on replicate) or treated with prostaglandin F2 alpha (n = 185). In Experiment 2, the same treatments were utilized, except control cows (n = 124) were inseminated at their first detected estrus after d 40 postpartum, and treated cows received either one injection of prostaglandin F2 alpha between d 54 and 63 (n = 116) or were given progesterone (via a progesterone-releasing intravaginal device) for 7 d, with the device removed 24 h after prostaglandin F2 alpha (n = 116). More cows were inseminated and pregnancy rates were higher within 5 d after treatment with prostaglandin F2 alpha, and interval from prostaglandin F2 alpha to first service was reduced compared with that of control cows. Duration and variation of calving intervals were unaffected in either experiment, despite the fact the elective waiting period was 6 to 23 d longer for treated cows than for controls. Prebreeding treatment with progesterone failed to improve conception rates, but the efficiency of estrous expression increased from 54% in prostaglandin F2 alpha-treated cows to 71% in those cows also receiving prebreeding progesterone. We conclude that prostaglandin F2 alpha was ineffective in improving reproductive performance of these herds under good herd management. However, prostaglandin F2 alpha offers the convenience of inseminating small groups of cows, controlling when breedings occur during the work week, and prolonging the elective waiting period without extending the calving interval.     

Comparison of two timed artificial insemination (TAI) protocols for management of first insemination postpartum

Two estrus-synchronization programs were compared and factors influencing their success over a year were evaluated. All cows received a setup injection of PGF2alpha at 39 +/- 3 d postpartum. Fourteen days later they received GnRH, followed in 7 d by a second injection of PGF2alpha. Cows (n = 523) assigned to treatment 1 (modified targeted breeding) were inseminated based on visual signs of estrus at 24, 48, or 72 h after the second PGF2alpha injection. Any cow not observed in estrus was inseminated at 72 h. Cows (n = 440) assigned to treatment 2 received a second GnRH injection 48 h after the second PGF2alpha, and all were inseminated 24 h later. Treatment, season of calving, multiple birth, estrual status at insemination, number of occurrences of estrus before second PGF2alpha, prophylactic use of PGF2alpha, retained fetal membranes, and occurrence of estrus following the setup PGF2alpha influenced success. Conception rate was 31.2% (treatment 1) and 29.1% (treatment 2). A significant interaction occurred between protocol and estrual status at insemination. Cows in estrus at insemination had a 45.8% (treatment 1) or 35.4% (treatment 2) conception rate. The conception rate for cows not expressing estrus at insemination was 19.2% (treatment 1) and 27.7% (treatment 2). Provided good estrous detection exists, modified targeted breeding can be as successful as other timed artificial insemination programs. Nutritional, environmental, and management strategies to reduce postpartum disorders and to minimize the duration of postpartum anestrus are critical if synchronization schemes are used to program first insemination after the voluntary waiting period.     

Fertility of postpartum dairy cows after administration of gonadotropin-releasing hormone and prostaglandin F2 alpha: a field trial

Our objective was to examine further the potential profertility effects of gonadotropin-releasing hormone and prostaglandin F2 alpha in postpartum Holstein cows. Reproductive performance was monitored in 843 cows milked thrice daily. One group of cows (n = 218) was untreated, while three groups received either 100 micrograms gonadotropin-releasing hormone administered once between d 11 and 25 (n = 211); 25 mg prostaglandin F2 alpha given once between d 11 and 25 (n = 215); or 25 mg prostaglandin F2 alpha given once between d 25 and 40 postpartum (n = 190). No profertility effects were detected in cows, regardless of their health status during the periparturient period, except cows given gonadotropin-releasing hormone between d 11 and 18 had shorter intervals to first estrus and to first service than controls. Cows with reproductive disorders (abnormal health status) in the concurrent lactation had longer intervals from calving to conception after receiving gonadotropin-releasing hormone between d 18 and 25 or prostaglandin F2 alpha between d 33 and 40. Abnormal health status adversely affected every reproductive trait measured. Early postpartum treatments with either hormone failed to improve reproductive performance of dairy cows, in contrast to several reports of profertility effects for gonadotropin-releasing hormone, and a few reports for prostaglandin F2 alpha.     

Short communication: presynchronization using a single injection of PGF2alpha before synchronized ovulation and first timed artificial insemination in dairy cows

Conception to synchronized ovulation (Ovsynch) using injections of GnRH and PGF2alpha and timed artificial insemination has been shown to be maximized when the program is initiated 5 to 12 d after estrus. The objective of this double-blinded field trial was to assess the effect of one injection of PGF2alpha, 10 d before the Ovsynch program, on the probability of pregnancy at first insemination in lactating dairy cows. The hypothesis was that cows that underwent luteolysis in response to PGF2alpha would be between 5 and 8 d postestrus at the start of Ovsynch. In five commercial dairy herds in Ontario, Canada, at 52 +/- 12 d in milk, 506 cows were assigned at random to receive either one i.m. injection of 500 microg of cloprostenol or saline. Ten days later, all cows received 100 microg of GnRH i.m., followed in 7 d by 500 microg of cloprostenol i.m. and 100 microg of GnRH i.m. 48 h later. All cows were artificially inseminated 0 to 20 h after the second injection of GnRH, without regard to detection of estrus. Pregnancy was diagnosed by transrectal palpation at least 35 d after insemination. The probability of pregnancy after first insemination was modeled with logistic regression, accounting for the correlation of cows with herd and the effect of season of calving. There was no difference in pregnancy risk between cows that received PGF2alpha presynchronization and controls (37.3 and 36.6%, respectively; odds ratio = 1.03, 95% confidence interval, 0.88 to 1.20). Parity and days in milk at insemination were not significant covariates.     

Dairy herd reproductive management programs with or without synchronization of estrus

Reproductive efficiencies were compared among herds with (treated, n = 25) or without (visited control, n = 25) routine synchronization of estrus and herds without investigator visits (unvisited control, n = 22). Treatment groups were subdivided based on participation in veterinary herd health programs. Reproductive tracts were palpated rectally at 21-d intervals for 6 mo in two sets of treated and visited control herds. Data were collected during the visitation period and from the 6-mo period before visits. In treated herds, cows more than 40 d postpartum with a corpus luteum received prostaglandin F2 alpha. In visited control herds, cows received prostaglandin F2 alpha after 82 d postpartum if they were not observed in estrus. Routine synchronization of estrus did not enhance herd reproductive efficiency compared with no synchronization of estrus in visited herds. Small changes in reproductive efficiency occurred during visits in herds with an established reproductive health program. However, herds not using a health program had 15.2 fewer d from calving to insemination, and the pregnancy rate at 120 d postpartum was 13.0 percentage units higher than before herd visits. Consequently, reproductive performance of those herds during visits was similar to that of contemporaries under a herd health program.     

Gonadotropin-releasing hormone and prostaglandin F2 alpha for postpartum dairy cows: estrous, ovulation, and fertility traits

A study of 234 Holstein cows was conducted to determine if early postpartum treatments of gonadotropin-releasing hormone, prostaglandin F2 alpha, or both would alter frequency and occurrence of estrus and ovulation as well as subsequent fertility. Cows in groups 1 and 2 received gonadotropin-releasing hormone (200 micrograms) between 10 and 14 d postpartum, and cows in groups 3 and 4 received saline. Ten days later, cows in groups 2 and 3 received prostaglandin F2 alpha (25 mg), and cows in groups 1 and 4 received saline. Treatment with gonadotropin-releasing hormone reduced intervals to first ovulation and first detected estrus as well as increasing the proportion of cows with three or more ovulations before first service from 57% for saline-treated controls to 83%. Treatment with prostaglandin F2 alpha reduced intervals to second and third ovulation and shortened the first estrous cycle. Treatments for cows in groups 1 and 3 increased the proportion of cows having estrous cycles of normal duration. Interval from calving to conception was reduced by 43 to 48 d for cows with an abnormal puerperium treated with either gonadotropin-releasing hormone or prostaglandin F2 alpha compared with controls (group 4) and by 27 to 29 d overall in all cows in groups 1 and 3. Cows with normal or abnormal puerperium in groups 1 and 3 required 26 to 41% fewer services per conception than controls. We conclude that treatments of gonadotropin releasing hormone or prostaglandin F2 alpha, but not the treatment combination, improved fertility of dairy cows, especially those that experienced puerperal problems.     

Use of bovine somatotropin in lactating dairy cows receiving timed artificial insemination

Objectives of the research were to examine the effect of bovine somatotropin (bST) on pregnancy rates to a timed artificial insemination protocol and to test a resynchronization system with two consecutive synchronized services. Lactating Holstein cows (n = 403) were assigned to the following treatments: bST treatment (500 mg) was initiated at 63 +/- 3 d postpartum concomitantly with initiation of the timed artificial insemination protocol or bST treatment was initiated at 105 +/- 3 d postpartum. At 63 +/- 3 d postpartum, all cows received GnRH (100 microg), an injection of PGF2alpha (25 mg) 7 d later, and a GnRH injection at 48 h after PGF2alpha and were inseminated 16 to 20 h later. Cows were reinseminated at detected estrus or resynchronized with a GnRH injection at 20 d after insemination. At 27 d after insemination, cows were examined for pregnancy. Resynchronized cows diagnosed nonpregnant received an injection of PGF2alpha and were inseminated at detected estrus or received an injection of GnRH at 48 h after PGF2alpha and inseminated 16 to 20 h later. Cows pregnant at d 27 were reexamined for pregnancy at 45 d after insemination. First-service pregnancy rates at d 45 were increased in cows not resynchronized that initiated bST treatment at 63 +/- 3 d postpartum, compared with cows initiating bST treatment at 105 +/- 3 d postpartum (37.7 +/- 5.8% and 22.1 +/- 4.2%, respectively), but the effect of bST treatment was not observed when cows were resynchronized (25.6 +/- 4.3% and 25.8 +/- 5.5%, respectively). Thus, bST increased pregnancy rates to a timed artificial insemination protocol.     

Prostaglandin in milk, days open, and estrus detection in dairy cows treated with prostaglandin F2 alpha

Prostaglandin F2 alpha was used to induce estrus in postpartum dairy cows to decrease calving interval and time spent on heat checks. The amount of prostaglandin residue in milk after treatment also was investigated. Twenty-two control cows, checked for heat twice daily, were bred at estrus after 55 days postpartum. Sixty-three cows checked on days 55 to 60 were either bred if in estrus or treated with 30 mg of prostaglandin F2 alpha injected intramuscularly on day 60 and bred at induced estrus or at 75 h posttreatment. Twelve cows were in heat between days 55 and 60 and were bred. Twenty-nine of 51 treated cows were seen in estrus; all of these were bred and 51.7% conceived at this time. Treated cows had fewer days to first service than did controls, but days open were not different, 105.7 versus 101.8. Fertility was similar. Controls required more heat checks than did treated cows (39 to 8.2). Milk from 17 cows at two milkings before and ten milkings after treatment had similar concentrations of prostaglandin (698 +/- 27 pg/ml) except for the first posttreatment milking when prostaglandin concentration almost doubled (1.293 +/- 143 pg/ml).     

Timed artificial insemination with estradiol cypionate or insemination at estrus in high-producing dairy cows

A total of 799 Holstein cows from 3 herds were randomly assigned at 37 +/- 3 d in milk (DIM) to timed artificial insemination (AI) or insemination at detected estrus. Cows were presynchronized with injections of PGF(2alpha) at 37 and 51 DIM. At 65 DIM, cows received an injection of GnRH, followed 7 d later by PGF(2alpha). Cows in the estrus-detected group were inseminated after being observed in estrus during the 7 d after the last PGF(2alpha). Cows in the timed AI group received an injection of 1 mg of estradiol cypionate (ECP) 24 h after the last PGF(2alpha). If detected in estrus or=1 ng/mL; L = <1 ng/mL), resulting in 8 combinations (LLL, LHL, LLH, LHH, HHH, HHL, HLH, and HLL). Conception rates and pregnancy rates were higher for cows in the timed AI group than in the estrus-detected group at 30, 44, and 58 d (e.g., at 58 d, pregnancy rates were 42.2% for multiparous cows or 34.4% for primiparous cows in the group receiving ECP and timed AI compared with only 20.8 or 18.8% for respective parity subgroups for the treatment group inseminated only at detected estrus). Pregnancy losses were 11.5% from 30 to 58 d and did not differ between treatments. Cyclic cows within both treatments had higher estrous responses, conception rates, and pregnancy rates. Cows that responded to presynchronization and to luteolysis (HHL) had the highest conception and pregnancy rates, followed by cows classified as LHL. Use of 1 mg of ECP to induce ovulation as part of a synchrony regimen improved reproduction at first postpartum insemination in dairy cows.     

Evaluation of reproductive performance in lactating dairy cows with prostaglandin F2alpha, gonadotropin-releasing hormone, and timed artificial insemination

Nine hundred and twenty Holstein cows from 16 commercial dairy herds to evaluate three systematic breeding protocols: 14-d PGF2alpha, timed artificial insemination (AI), and GnRH-PGF2alpha, relative to AI following estrus detection without hormone intervention. The timed AI protocol involved GnRH, followed by PGF2alpha 7 d later and GnRH again 2 d after PGF2alpha, with AI 6 to 18 h after the second GnRH. The GnRH-PGF2alpha protocol consisted of GnRH followed by PGF2alpha 7 d later. Eight herds relied on visual observation to detect estrus, and eight herds utilized the HeatWatch estrus detection system. The average interval to first postpartum AI was shortest for the timed AI protocol (77.1 d) followed by the 14-d PGF2alpha protocol (81.6 d). There was no difference in days to first AI between the control (86.1 d) and GnRH-PGF2alpha (89.5 d) protocols. Percent pregnant per first AI did not differ among control (45.6%), 14-d PGF2alpha (43.7%), or GnRH-PGF2alpha (44.0%) protocols, but all protocols had a higher percent pregnant per first AI than the timed AI protocol (30.1%). Response to the GnRH-PGF2alpha protocol was limited because 44.0% of the cows submitted to the protocol were not detected in estrus < or = 10 d post-PGF2, administration and had an interval to first AI of 103.8 d. Cumulative percent pregnant by 120 d postpartum did not differ between control cows (53.1%) and hormonally treated cows (50.6%). Visual observation herds had a shorter interval to first postpartum AI (82.8 d) than the HeatWatch herds (84.8 d), with a higher overall rate of estrus detection across all protocols (75.3 and 67.6%, respectively).     

An alternative AI breeding protocol for dairy cows exposed to elevated ambient temperatures before or after calving or both

Our objective was to determine if a timed artificial insemination (AI) protocol (Ovsynch) might produce greater pregnancy rates than AI after a synchronized, detected estrus during summer. Lactating Holstein cows (n = 425) were grouped into breeding clusters and then assigned randomly to each of two protocols for AI between 50 and 70 days in milk. All cows were treated with GnRH followed 7 d later by PGF2alpha. Ovsynch cows then were treated with a second injection of GnRH 48 h after PGF2alpha and inseminated 16 to 19 h later. Controls received no further treatment after PGF2alpha and were inseminated after detected estrus. Pregnancy was diagnosed once by transrectal ultrasonography (27 to 30 d after AI) and again by palpation (40 to 50 d). Based on concentrations of progesterone in blood collected before each hormonal injection, only 85.4% of 425 cows were considered to be cycling. Although conception rates were not different between protocols at d 27 to 30, AI submission rates and pregnancy rates were greater after Ovsynch (timed AI) than after detected estrus. A temperature-humidity index > or = 72 was associated with fewer controls detected in estrus with lower conception than for controls detected in estrus when index values were < 72, whereas the reverse was true for cows after the Ovsynch protocol. We concluded that a timed AI protocol increased pregnancy rates at d 27 to 30 because its success was independent of either expression or detection of estrus. However, because of poorer embryonic survival in Ovsynch cows during heat stress only (39.5 vs. 69.2% survival for Ovsynch and control, respectively), pregnancy rates were not different by d 40 to 50 after timed AI.     

Inseminations at estrus induced by presynchronization before application of synchronized estrus and ovulation

A controlled field study examined conception rates after 2 timed artificial insemination (TAI) breeding protocols conducted on 2 commercial dairy farms. Estrous cycles in postpartum lactating cows were presynchronized with 2 injections of PGF(2alpha) given 14 d apart (Pre-synch) and then, after 12 d, the standard Ovsynch protocol (injection of GnRH 7 d before and 48 h after an injection of PGF(2alpha), with one TAI at 12 to 16 h after the second GnRH injection) or Heatsynch protocol [injection of GnRH 7 d before an injection of PGF(2alpha), followed 24 h later by 1 mg of estradiol cypionate (ECP) and one TAI 48 h after ECP] was applied. Experimental design allowed artificial insemination to occur anytime after the second Presynch injection and during the designed breeding week when estrus was detected. Of the 1846 first services performed, only 1503 (rate of compliance = 81.4%) were performed according to protocol. Numbers of cows inseminated, logistic-regression adjusted conception rates, and days in milk (DIM) were for inseminations made: 1) during 14 d after first Presynch injection (n = 145; 22.6%; 54 +/- 0.4 DIM); 2) during 12 d after second Presynch injection (n = 727; 33%; 59 +/- 0.2 DIM); 3) during 7 d after the first GnRH injection of Ovsynch or Heatsynch (n = 96; 32.1%; 74 +/- 0.5 DIM); 4) after estrus as part of Heatsynch (n = 212; 44.6%; 76 +/- 0.3 DIM); 4) after TAI as part of Heatsynch (n = 154; 21.1%; 76 +/- 0.4 DIM); 5) after estrus as part of Ovsynch (n = 43; 48.7%; 77 +/- 0.7 DIM); and 6) after TAI as part of Ovsynch (n = 271; 24.4%; 77 +/- 0.3 DIM). Conception rates when AI occurred after one Presynch injection were less than when AI occurred after 2 Presynch injections. Conception rates for those inseminated after either Presynch injection did not differ from those inseminated after combined Heatsynch + Ovsynch. Cows in the Ovsynch and Heatsynch protocols inseminated after estrus during the breeding week had greater conception rates than those receiving the TAI, but overall conception rates did not differ between protocols. Among cows inseminated after detected estrus, conception was greater for cows in the Heatsynch + Ovsynch protocol (77 +/- 0.4 DIM) than for those inseminated after either Presynch injection (54 +/- 0.4 or 59 +/- 0.2 DIM). We concluded that conception rates after Heatsynch and Ovsynch were similar under these experimental conditions, and that delaying first AI improved fertility for cows inseminated after detected estrus.     

Ovarian follicular activity in lactating Holstein cows supplemented with monensin

The objective of this study was to determine effects of monensin on ovarian follicular development and reproductive performance in postpartum dairy cows. Forty-eight multiparous Holstein cows were randomly assigned to receive either a control total mixed ration (n = 24) or the same diet plus 22 mg of monensin/kg (n = 24) from 21 d before anticipated calving until cows were either confirmed pregnant or were >180 d postpartum. Monensin had no effect on development of the first dominant follicle postpartum or the numbers of class 1 (3 to 5 mm), 2 (6 to 9 mm), or 3 (10 to 15 mm) follicles. Control cows had more class 4 (>15 mm) follicles at 10 to 13 d postpartum than cows in the monensin group. The first dominant follicle postpartum ovulated, regressed, or became cystic unrelated to differences between diets. However, the first ovulation postpartum occurred earlier in monensin-fed cows than in the control group (27.2 +/- 2.1 d vs. 32.4 +/- 1.5 d), with no dietary effects on the diameter of the ovulating follicle. Similarly, treatments did not differ in the proportion of cows with 2 or 3 waves of ovarian follicular development per cycle, nor in the number of follicles of all classes during the breeding period. Times of ovulation following treatment with prostaglandin F2alpha were not different between dietary groups. Pregnancy rates after timed artificial insemination were similar between diets. Supplementation with monensin resulted in a shorter postpartum interval to first ovulation but did not affect other reproductive measures in healthy, lactating dairy cows.     

Voluntary waiting period and adoption of synchronized breeding in dairy herd improvement herds

Voluntary waiting period and adoption of synchronized breeding (ovulation synchronization followed by timed artificial insemination) were characterized from 33 million services of Holsteins and Jerseys in Dairy Herd Improvement herds. Calving month, calving year, and parity had large effects on days to first service for both breeds. Holstein cows that calved during March and April were bred later than those that calved during other months (February and March for Jerseys), whereas cows that calved during September and October were bred earlier. First-parity cows had longer days to first service than did second-parity cows. Herd-year voluntary waiting period was measured as the days postpartum by which 10% of cows had received a first insemination. Median days to reach 10% of cows bred were 55.5 d. Over 65% of herds had 10% of cows inseminated by 60 d postpartum, the voluntary waiting period assumed for national evaluations for daughter pregnancy rate. Herd-years with synchronized breeding at first insemination were identified through χ² analysis based on deviation of observed frequency of first inseminations by day of the week from an expected equal frequency and by the maximum percentage of cows inseminated on a particular day of the week. Herds that were identified as having synchronized breeding had fewer days to first service (17.0), more services (0.16/cow), and fewer days open (9.1) than did herds that were classified as having traditional estrus detection. Synchronized herds also had a standard deviation for days to first service that was only 38% as large as that for herds that bred on observed estrus. Adoption of synchronized breeding for first services steadily increased from 1.9% of herd-years (2% of cows) for 1996 to 19.9% of herd-years (34.9% of cows) for 2005. Procedures for genetic evaluation of daughter pregnancy rate should be examined to determine if herd regimen for reproductive management affects results.     

Use of estradiol cypionate in a presynchronized timed artificial insemination program for lactating dairy cattle

Experiment 1 evaluated pregnancy rates when estradiol cypionate (ECP) was used to induce ovulation as part of a timed artificial insemination (TAI) protocol in comparison to Ovsynch for lactating dairy cows in Florida (n = 371) and Texas (n = 321). Cows were presynchronized with two injections of PGF2, (25 mg, im) given 14 d apart with TAI protocols beginning 14 d after the second injection of PGF20. The TAI protocols consisted of an injection of GnRH (100 microg, im) followed by PGF2alpha 7 d later. Then, cows either received an injection of GnRH (Treatment I, Ovsynch) at 48 h after PGF2alpha and inseminated 16 to 24 h later or received an injection of ECP (1 mg, i.m.) at 24 h after PGF2alpha, (Treatment II; Heatsynch) and inseminated 48 h later. In Florida, pregnancy rates after TAI were 37.1 +/- 5.8% for Ovsynch compared with 35.1 +/- 5.0% for Heatsynch. In Texas, pregnancy rates were 28.2 +/- 3.6% for Ovsynch and 29.0 +/- 3.5% for Heatsynch. Overall pregnancy rates did not differ between Ovsynch and Heatsynch treatments. In Experiment 2, estrus and ovulation times were determined in lactating dairy cows submitted to the Heatsynch protocol. Frequencies of detected estrus and ovulation after ECP were 75.7% (28/37) and 86.5% (32/37), respectively. Mean intervals to ovulation were 55.4 +/- 2.7 h (n = 32) after ECP and 27.5 +/- 1.1 h (n = 27) after onset of estrus. Estrus occurred at 29.0 +/- 1.8 h (n = 28) after ECP. It is recommended that any cow detected in estrus by 24 h after ECP injection be inseminated at 24 h and all remaining cows be inseminated at 48 h because 75% (n = 24/32) of the ovulations occurred between > or = 48 h to < or = 72 h after ECP. Synchronization of ovulation and subsequent fertility indicated that estradiol cypionate could be used to induce ovulation for successful timed insemination.     

Effects of presynchronization and bovine somatotropin on pregnancy rates to a timed artificial insemination protocol in lactating dairy cows

The objective was to examine the effects of presynchronization and bovine somatotropin (bST) on pregnancy rates to a timed artificial insemination protocol in lactating dairy cows. Lactating Holstein cows (n = 543) were assigned randomly in a 2 x 3 factorial experiment in which cows received a presynchronization treatment or not, and were treated with bST (500 mg) at 63 +/- 3, 73 +/- 3, or 147 +/- 3 d postpartum. The latter group was used as a control. Presynchronization treatment consisted of two injections of PGF2alpha (25 mg) given 14 d apart, with the second injection of PGF2alpha being administered 12 d before initiation of the timed artificial insemination protocol. All cows received GnRH (100 microg) at 63 +/- 3 d postpartum, an injection of PGF2alpha (40 mg) 7 d later, a GnRH injection at 48 h after PGF2alpha and were inseminated 16 to 20 h later. Cows were resynchronized if determined to be nonpregnant at ultrasonography at 32 d after insemination with a GnRH injection (100 microg), an injection of PGF2alpha (40 mg) 7 d later, and a GnRH injection at 48 h after PGF2alpha and were inseminated 16 to 20 h later. Cows were examined for pregnancy at 32 d and reexamined at 74 d after insemination. No differences in pregnancy rates were observed between cows receiving bST treatment at 63 +/- 3 d postpartum or at 73 +/- 3 d postpartum. An interaction between presynchronization and bST treatment indicated that pregnancy rates were increased for cows treated with bST when cows were presynchronized. When anestrous cows were excluded from the analyses, both an effect of bST and of presynchronization were observed, indicating that bST increased pregnancy rates regardless of presynchronization treatment and that presynchronization also increased pregnancy rates independently of bST treatment. Presynchronization and bST treatment may be used to increase first-service pregnancy rates to a timed artificial insemination protocol.     

Supplementation with estradiol-17beta before the last gonadotropin-releasing hormone injection of the Ovsynch protocol in lactating dairy cows

The aim of this study was to determine whether an increase in circulating estrogen concentrations would increase percentage pregnant per artificial insemination (PP/AI) in a timed AI protocol in high-producing lactating dairy cows. We analyzed only cows having a synchronized ovulation to the last GnRH of the Ovsynch protocol (867/1,084). The control group (n = 420) received Ovsynch (GnRH - 7 d - PGF_2α - 56 h - GnRH - 16 h - timed AI). The treatment group (n = 447) had the same timed AI protocol with the addition of 1 mg of estradiol-17β (E2) at 8 h before the second GnRH injection. Ovarian ultrasound and blood samples were taken just before E2 treatment of both groups. In a subset of cows (n = 563), pressure-activated estrus detection devices were used to assess expression of estrus at 48 to 72 h after PGF_2α treatment. Ovulation was confirmed by ultrasound 7 d after timed AI. Treatment with E2 increased expression of estrus but overall PP/AI did not differ between E2 and control cows. There was an interaction between treatment and expression of estrus such that PP/AI was greater in E2-treated cows that showed estrus than in E2-treated or control cows that did not show estrus and tended to be greater than control cows that showed estrus. There was evidence for a treatment by ovulatory follicle size interaction on PP/AI. Supplementation with E2 improved PP/AI in cows ovulating medium (15 to 19 mm) but not smaller or larger follicles. The E2 treatment also tended to improve PP/AI in primiparous cows with low (≤2.5) body condition score, and in cows at first postpartum service compared with Ovsynch alone. In conclusion, any improvements in PP/AI because of E2 treatment during a timed AI protocol appear to depend on expression of estrus, parity, body condition score, and size of ovulatory follicle.     

Effect of early or late resynchronization based on different methods of pregnancy diagnosis on reproductive performance of dairy cows

The aim of this study was to compare the reproductive performance of dairy cows subjected to early (ER) or late (LR) resynchronization programs after nonpregnancy diagnoses based on either pregnancy-associated glycoproteins (PAG) ELISA or transrectal palpation, respectively. In addition, the accuracy of the PAG ELISA for early pregnancy diagnosis was assessed. Lactating Holstein cows were subjected to a Presynch-Ovsynch protocol with timed artificial insemination (AI) performed between 61 and 74 DIM. On the day of the first postpartum AI, 1,093 cows were blocked by parity and assigned randomly to treatments; however, because of attrition, 452 ER and 520 LR cows were considered for the statistical analyses. After the first postpartum AI, cows were observed daily for signs of estrus and inseminated on the same day of detected estrus. Cows from ER that were not reinseminated in estrus received the first GnRH injection of the Ovsynch protocol for resynchronization 2 d before pregnancy diagnosis. On d 28 after the previous AI (d 27 to 34), pregnancy status was determined by PAG ELISA, and nonpregnant cows continued on the Ovsynch protocol for reinsemination. Pregnant cows had pregnancy status reconfirmed on d 46 after AI (d 35 to 52) by transrectal palpation, and those that lost the pregnancies were resynchronized. Cows assigned to LR had pregnancy diagnosed by transrectal palpation on d 46 after AI (d 35 to 52) and nonpregnant cows were resynchronized with the Ovsynch protocol. Blood was sampled on d 28 after AI (d 27 to 34) from cows in both treatments that had not been reinseminated on estrus and again on d 46 after AI (d 35 to 52) for assessment of PAG ELISA to determine the accuracy of the test. Cows were subjected to treatments for 72 d after the first insemination. Pregnancy per AI (P/AI) at first postpartum timed AI did not differ between treatments and averaged 28.9%. The proportion of nonpregnant cows that were resynchronized and received timed AI was greater for ER than for LR (30.0 vs. 7.6%). Cows in ER had a shorter interval between inseminations when inseminated following spontaneous estrus (21.7 ± 1.1 vs. 27.8 ± 0.8 d) or after timed AI (35.3 ± 1.2 vs. 55.2 ± 1.4 d). Nevertheless, the ER did not affect the rate of pregnancy (adjusted hazard ratio = 1.23; 95% confidence interval = 0.94 to 1.61) or the median days postpartum to pregnancy (ER = 132 vs. LR = 140). A total of 2,129 PAG ELISA were evaluated. Overall, sensitivity, specificity, and positive and negative predictive values averaged 95.1, 89.0, 90.1, and 94.5%, respectively, and the accuracy was 92.1%. In conclusion, PAG ELISA for early diagnosis of pregnancy had acceptable accuracy, but early resynchronization after nonpregnancy diagnosis with PAG ELISA did not improve the rate of pregnancy or reduce days open in dairy cows continuously observed for estrus.     

Postpartum ovarian follicular dynamics and estrous activity in lactating dairy cows

The objectives of this study were to characterize early postpartum follicular dynamics in dairy cows in relation to their estrual activity and subsequent reproductive performance using 50 (26 primiparous and 24 multiparous) lactating Holstein cows. Ovaries and uterine horns of postpartum lactating cows were examined by ultrasonography 3 times weekly and continued until first services occurred after a 45-d voluntary waiting period. No differences were detected in fertility between primiparous and multiparous cows. In 40 of 50 cows, first postpartum ovulation was observed within 4 follicular waves, and the follicular wave patterns and ovarian cycles in most cows returned to normal as in cattle having normal estrous cycles after the second postpartum ovulation. Cows with the longest intervals from calving to first ovulation produced the most milk and also had prolonged intervals to first estrous activity. Differences in follicular dynamics before first ovulation altered intervals to first estrus, first service, and uterine involution, but these differences did not affect pregnancy rate, number of services, and days open. First postpartum insemination after 3 follicular waves tended to have greater pregnancy rates than those after 2 follicular waves. First inseminations at first estrus could produce greater pregnancy rates than those at subsequent periods of estrus.     

Effect of time of insemination on number of accessory sperm, fertilization rate, and embryo quality in nonlactating dairy cattle.

Two experiments were conducted to determine the effect of insemination time on number of accessory sperm per embryo (ovum), fertilization rate, and embryo quality. Semen was collected from three fertile Holstein bulls and cryopreserved in egg yolk-citrate-glycerol. In experiment 1, cows were continuously monitored for behavioral estrus by the HeatWatch estrous detection system and were artificially inseminated (AI) with one 0.5-ml straw (25 x 10(6) sperm) at the onset of estrus (AI 0 h), 12 h after onset (AI 12 h), or received natural service at 0 h (Nat 0 h) from one of three bulls. From 150 inseminations, 115 embryos and ova (AI 0 h: n = 39; AI 12 h: n = 39; Nat 0 h: n = 37) were recovered 6 or 7 d after insemination. Fertilization rates differed between treatments (AI 0 h: 67%; AI 12 h: 79%; Nat 0 h: 98%). Median accessory sperm per embryo (ovum) also differed (AI 0 h: 1; AI 12 h: 10; and Nat 0 h: 27) and paralleled the fertilization rate. Embryo quality was not affected by insemination time or natural service. In experiment 2, cows received AI at 0, 12, or 24 h (AI 24 h) after the onset of estrus as determined by HeatWatch. From 154 inseminations, 117 embryos and ova (AI 0 h: n = 39; AI 12 h: n = 39; AI 24 h: n = 39) were recovered 6 or 7 d after insemination. Fertilization rates did not differ in experiment 2 (AI 0 h: 66%; AI 12 h: 74%; AI 24 h: 82%); however, a trend toward a higher fertilization rate accompanied AI 24 h. Median accessory sperm values increased from AI 0 h (1) to AI 24 h (4). Embryo quality declined with AI at increasing intervals after onset of estrus, as percentages of excellent and good, fair and poor, and degenerate embryos were as follows: 77, 15, 8; 52, 38, 10; and 47, 19, 34 for the 0-, 12-, and 24-h inseminations, respectively. Results indicate AI 12 h after the onset of estrus provides a compromise between potential fertilization failure (AI 0 h) and embryo failure (AI 24 h), despite increased accessory sperm per embryo (ovum) after AI 24 h. Artificial insemination 12 h after onset of estrus should optimize fertility of dairy cattle through an acceptable fertilization rate, number of accessory sperm per embryo, and desirable embryo quality.