Effect of time of artificial insemination and supplemental estradiol on reproduction of lactating dairy cows

Our objectives were to compare reproductive responses of dairy cows receiving timed artificial insemination (AI) either at 48 or 72 h after induction of luteolysis and supplemented or not with estradiol cypionate (ECP). Holstein cows (971) had their estrous cycles presynchronized with injections of PGF_2α at 37 and 51 d in milk (DIM) and then received an injection of GnRH at 64 DIM and an injection of PGF_2α at 71 DIM. Cows were then assigned to a 2 × 2 factorial randomized block experiment; cows in the CoSynch 48 h (CoS48) received a final injection of GnRH concurrent with timed AI 48 h after PGF_2α, whereas cows in the CoSynch 72 h (CoS72) received GnRH and timed AI 72 h after PGF_2α. Half of the cows in each CoSynch protocol received an injection of 1 mg of ECP 24 h after PGF_2α. Therefore, the 4 treatments were as follows: CoS48-NECP (n = 240), CoS72-NECP (n = 246), CoS48-ECP (n = 245), and CoS72-ECP (n = 240). Blood was sampled at 7 d before and at the first GnRH of the CoSynch from all cows for analysis of progesterone concentration in plasma. Cows were classified as anovular when progesterone was less than 1.0 ng/mL in both samples. Blood was also sampled during proestrus from a subset of 123 cows to measure concentrations of estradiol and at 7 d after timed AI to measure concentrations of progesterone. Ovaries from the same subset of 123 cows were examined by ultrasonography to determine ovulatory follicle diameter and incidence of ovulation. Pregnancy was diagnosed at 40 and 68 d after AI. Prevalence of cyclic cows was 72.4% and was similar among treatments. Concentrations of estradiol increased after ECP treatment and at 72 h of proestrus with CoS72. Pregnancy at 40 and 68 d after AI and pregnancy loss were not affected by timing of AI or supplemental ECP. Delaying timed AI to 72 h and supplementation with ECP increased the proportion of cows displaying estrus at AI, and cows detected in estrus had increased pregnancy per AI associated with improved ovulation and increased postovulatory progesterone concentration. These results indicate that extending the proestrus by delaying timed AI from 48 to 72 h plus supplemental ECP, despite increased expression of estrus at timed AI, did not improve reproductive performance of lactating dairy cows at first AI.     

Double insemination and gonadotropin-releasing hormone treatment of repeat-breeding dairy cattle

Our objective was to determine if double inseminations during the same estrous period of dairy cattle eligible for their third or fourth service (repeat breeders) would improve pregnancy rates equivalent to injections of GnRH given at the time of AI. Repeat-breeding, lactating cows from six herds (five herds in the San Joaquin Valley of central California and one herd in northeast Kansas) were assigned randomly to four treatment groups when detected in estrus: 1) single AI plus no injection, 2) single AI plus 100 micrograms GnRH at AI, 3) double AI plus no injection, or 4) double AI plus 100 micrograms of GnRH at AI. Inseminations were performed according to the a.m.-p.m. rule. The second AI for the double AI treatment was given 12 to 16 h after the first AI. Injections of GnRH were given intramuscularly immediately following the single AI or the first AI of the double AI. Pregnancy rates of cows given a single AI and hormone injection were numerically higher in all six herds than those of their herdmates given only a single AI. In five of six herds, the pregnancy rates of cows given a double AI and hormone injection were numerically higher than pregnancy rates of their herdmates given only a double AI. Overall pregnancy rates for the four treatments were 1) 112/353 (32.1%), 2) 165/406 (41.6%), 3) 119/364 (33.5%), and 4) 135/359 (37.5%). Gonadotropin-releasing hormone increased pregnancy rates of repeat breeders compared with controls given only a single AI. No further benefit beyond the single AI was accrued from the double AI treatment, with or without concurrent hormone administration.     

Effects of GnRH administered to cows at the onset of estrus on timing of ovulation,endocrine responses,and conception

Two experiments examined effects of GnRH administered within 3 h after onset of estrus (OE) on ovulation and conception in dairy cows. In experiment 1, 46 cows received either saline, 250 microg of GnRH, or 10 microg of the GnRH analogue, Buserelin. Cows were observed for estrus, blood samples were collected, and ovulations were monitored by ultrasound. In controls, 76% of cows had intervals from estrus to ovulation of < or = 30 h and 24% had intervals > 30 h. Treatment with either GnRH or GnRH analogue (data combined) increased magnitude of LH surges and decreased intervals from estrus to LH surge or to ovulation. Treated cows all ovulated < or = 30 h after OE. Among control cows, plasma estradiol concentrations before estrus correlated positively with amplitudes of LH surges. Higher plasma progesterone was observed in the subsequent estrous cycle in GnRH-treated cows compared to control cows with delayed ovulations. Experiment 2 included 152 primiparous and 211 multiparous cows in summer and winter. Injection of GnRH analogue at OE increased conception rates (CR) from 41.3 to 55.5% across seasons. In summer, GnRH treatment increased CR from 35.1 to 51.6%. Across seasons, GnRH increased CR from 36.0 to 61.5% in cows with lower body condition at insemination and GnRH increased CR (63.2 vs. 42.2%) in primiparous cows compared to controls. Use of GnRH eliminated differences in CR for cows inseminated early or late relative to OE and increased CR in cows having postpartum reproductive disorders. In conclusion, GnRH at onset of estrus increased LH surges, prevented delayed ovulation, and may increase subsequent progesterone concentrations. Treatments with GnRH increased conception in primiparous cows, during summer, and in cows with lower body condition.     

Blood metabolites and hormone-based programmed breeding treatments in anovular lactating dairy cows

The objectives were to (1) compare blood metabolites and reproductive outcomes in lactating dairy cows not inseminated before (early) and after (late) 100 d in milk (DIM) because of prolonged anovulation or anestrus; and (2) evaluate reproductive responses of cows ≤100 DIM to GnRH + PGF_2α treatments after a fixed-time artificial insemination (AI; Ovsynch) or after induced estrus (Select Synch). In blood samples collected before initiating hormone-based breeding programs, anovular cows ≤100 DIM had the greatest serum total protein and globulin concentrations and the lowest tri-iodothyronine concentrations. Anovular and ovular cows >100 DIM had the greatest serum urea concentrations. Ovaries in cows (n = 40) >100 DIM were examined by transrectal ultrasonography, and those without a detectable corpus luteum (CL; anovular) were given GnRH and then PGF_2α 7 d later (Select Synch), whereas cows with a CL (ovular) were given 2 PGF_2α injections 12 d apart. Cows were inseminated at observed estrus after the second or only PGF_2α injection. More ovular (79%; 15/19) than anovular cows (24%; 5/21) were detected in estrus. No differences were detected between ovular and anovular cows in DIM at first AI, conception rate to first AI, cumulative pregnancy rates, number of services per conception, or days open. Cows (n = 93) ≤100 DIM were assigned randomly to 3 treatments: (1) control (n = 20) AI at estrus; (2) GnRH and then PGF_2α on 7 d (Select Synch; n = 42) and monitored for signs of estrus for 5 d and AI accordingly; or (3) 2 GnRH injections 9 d apart with PGF_2α given 48 h before second GnRH injection and AI at 16 h after the second GnRH injection (Ovsynch; n = 31). Among cows ≤100 DIM, controls had more days to first service (149 ± 16 d) than Select Synch cows (117 ± 7 d). Ovsynch cows had the fewest days to first service (84 ± 10 d) compared with control (149 ± 16 d) and Select Synch (117 ± 7 d) cows. Conception rates in control (25%) and Select Synch (26.2%) cows did not differ from those in Ovsynch cows (29%). Ovsynch cows had greater cumulative pregnancy rates and fewer days open than control (161 ± 20 vs. 258 ± 29 d), but did not differ from Select Synch (233 ± 19 d). Timed AI produced comparable fertility and superior cumulative pregnancy rates, fewer days to first service, and fewer days open than AI at observed estrus in cows inseminated ≤100 DIM.     

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.     

Use of estradiol cypionate as a substitute for GnRH in protocols for synchronizing ovulation in dairy cattle

Our purpose was to determine whether estradiol cypionate (ECP) could be substituted for the second GnRH injection of the standard Ovsynch protocol (injection of GnRH given 7 d before and 48 h after PGF(2alpha), with timed AI [TAI] 12 to 20 h after the second GnRH injection). Lactating dairy cows ranging from 61 to 82 d in milk at TAI were studied in 14 replicates. Main effects were hormone (ECP vs. GnRH) to induce ovulation and exposure to progesterone (P4) or not during the week preceding PGF(2alpha)-induced luteolysis. Four treatments were: 1) 100 microg of GnRH at 48 h after PGF(2alpha) (Ovsynch; n = 27); 2) same as Ovsynch, plus a P4-releasing intravaginal insert (CIDR) placed for 7 d beginning at the first GnRH injection (Ovsynch + CIDR, n = 20); 3) same as Ovsynch, but substituting 1 mg of ECP for GnRH, and injecting ECP at 24 h after PGF(2alpha) (Heatsynch; n = 33); or 4) Heatsynch + CIDR (n = 26). The largest follicle was identified by ultrasonography 24 h after PGF(2alpha) and was monitored every 6 h until ovulation. Incidence of estrus was less after GnRH (54%) than after ECP (87%), but more GnRH-treated cows had LH surges detected (95 vs. 65%) and ovulated (100 vs. 86%). Duration of LH surges, but not peak concentrations, was less after GnRH than after ECP (6.1 +/- 0.7 vs. 12.2 +/- 0.9 h). Pre-treatment with P4 reduced the incidence of LH surges but had no effects on incidence of estrus or ovulation. Intervals to the LH surge and ovulation were less after GnRH than after ECP, but intervals between onset of the LH surge and ovulation did not differ (26 +/- 2 vs. 30 +/- 3 h). We concluded that substituting ECP for GnRH resulted in more cows in estrus and slightly fewer ovulating.     

Stage of cycle, incidence, and timing of ovulation, and pregnancy rates in dairy cattle after three timed breeding protocols

In experiment 1, 705 cows were assigned to three treatments: 1) the Ovsynch protocol (a GnRH injection given 7 d before and another 48 h after one PGF2alpha injection); 2) PGF2alpha + Ovsynch (one PGF2alpha injection given 12 d (d -22) before initiating Ovsynch (d -10); and 3) 2xPG12 (two PGF2alpha injections 12 d apart; d -15 and -3, followed 48 h later by a GnRH injection. All cows were inseminated (d 0) 16 to 20 h after the GnRH injection on d -1. Cyclic status was estimated by serum progesterone. More cows were in early diestrus at d -10 for PGF2alpha + Ovsynch (36%) and 2 x PG12 (29%) versus Ovsynch (19%). Multiparous cows receiving PGF2alpha + Ovsynch had greater pregnancy rates via ultrasonography at d 28 after AI (42%) than contemporaries after Ovsynch (28%) or 2xPG12 (27%) but did not differ significantly at palpation 10 to 30 d later (28, 19, and 17%, respectively). Pregnancy of first-parity cows was similar across treatments at 28 d (41%) or at palpation (33%). Pregnancy rates for 128 anestrous cows were lower, regardless of treatment. Overall embryo survival from d 28 until palpation was 72% but was only 44% in 2xPG12 cows that were anestrus through d -10. Experiment 2 included the three treatments above plus controls (one GnRH injection 7 d before PGF2alpha and AI after estrus). Preovulatory follicles were 6 to 11% larger near estrus in controls than on d -1 in cows receiving GnRH. More controls ovulated by 32 h after onset of estrus than were treated cows by 32 h after GnRH, but percentages (79 to 94%) were similar by 40 h. In multiparous cows, PGF2alpha before Ovsynch increased pregnancy rates, whereas the 2xPG12 protocol produced similar pregnancy rates as Ovsynch across parities. Ovulation was effectively induced by 40 h after GnRH.     

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.     

Reproductive performance of dairy cows in various programmed breeding systems including OvSynch and combinations of gonadotropin-releasing hormone and prostaglandin F2 alpha

In Experiment 1, 308 Holstein cows were assigned randomly to four treatments: 1) GnRH injection followed in 7 d by PGF2 alpha injection, then another GnRH injection 33 h later, and artificial insemination (AI) 16 to 18 h after the second GnRH injection; 2) GnRH injection followed in 7 d by PGF2 alpha injection and AI only after detected estrus; 3) injections of PGF2 alpha 14 d apart, GnRH injection 33 h after the second PGF2 alpha injection, and AI 16 to 18 h later; and 4) injections of PGF2 alpha 14 d apart, AI only after detected estrus following the second PGF2 alpha injection or, in the absence of detected estrus, at 80 h after the second PGF2 alpha injection. In Experiment 2, 227 Holstein cows were assigned randomly to two treatments: 1) GnRH injection followed in 7 d by PGF2 alpha injection, then another GnRH injection 48 h later, and AI 16 to 18 h after the second GnRH injection; and 2) GnRH injection followed in 7 d by PGF2 alpha injection and AI only after detected estrus. Although conception rates in both experiments resulting from AI made after detected estrus either tended to be greater or were consistently greater than those following GnRH injection and one fixed-time AI, pregnancy rates were of greater magnitude after fixed-time AI because of poor expression or detection of estrus.     

Impact of gonadotropin-releasing hormone administration at the time of artificial insemination on conception risk and its association with estrous expression

Cows with reduced estrous expression have compromised fertility. The aim of this study was to determine whether the administration of GnRH at the time of artificial insemination (AI) would affect ovulation rates and the fertility of animals expressing estrous behavior of lesser intensity. Cows were enrolled at the time of estrus from 3 farms (n = 2,607 estrus events; farm A: 1,507, farm B: 429, farm C: 671) and randomly assigned to receive GnRH at AI or not (control). The intensity of estrous expression, monitored through leg-mounted activity monitors, was determined using the maximum activity during estrus; estrous expression was categorized as greater or lower relative to the farm median. On farm A, cows were assessed at alert, and 24 h, 48 h, and 7 d post-alert for ovulation using ultrasonography. Pregnancy per AI was confirmed at 35 ± 7 d post-estrus for cows that were inseminated. Differences between treatments were tested using the GLIMMIX procedure of SAS. Treatment with GnRH at the time of AI increased pregnancy per AI (41.3 ± 1.6 vs. 35.7 ± 1.7%). An interaction between treatment and estrous expression on pregnancy per AI was found. Control cows with greater estrous expression had greater pregnancy per AI than those with lesser expression, whereas GnRH administration increased pregnancy per AI for cows with lesser estrous expression but not those with greater expression (GnRH, greater intensity: 43.5 ± 2.1; GnRH, lesser intensity: 37.8 ± 2.2; control, greater intensity: 42.6 ± 2.2; control, lesser intensity: 31.0 ± 2.2%). A higher proportion of cows with greater estrous expression that were administered GnRH at AI were found to ovulate by 48 h and 7 d post-estrus; however, ovulation of cows with lesser estrous expression was unaffected by GnRH administration. In conclusion, fertility of cows with reduced estrous expression may be increased using GnRH at the time of AI; however, increased ovulation rates do not seem to be the direct mechanism behind this relationship.     

Effects of method of presynchronization and source of selenium on uterine health and reproduction in dairy cows

The objectives of this study were to evaluate the effects of method of presynchronization and source of supplemental Se on uterine health and reproductive performance of lactating dairy cows. Holstein cows (n = 512) were assigned randomly to 2 methods of presynchronization, Presynch (2 PGF_2a given 14 d apart) or CIDR-PS (controlled internal drug releasing inserted for 7 d with an injection of PGF_2a at removal) and 2 sources of Se, sodium selenite (SS) or selenized yeast (SY) supplemented at 0.3 mg/kg from 25 d before calving to 80 d in milk (DIM) arranged in a 2 × 2 factorial. Cows were inseminated following the Ovsynch protocol (d 0 GnRH, d 7 PGF_2a, d 9 GnRH, timed artificial insemination (AI) 12 h after the final GnRH) starting at 12 and 3 d after Presynch and CIDR-PS, respectively. Cows were diagnosed for pregnancy at 28, 42, and 56 d after AI. Source of Se did not influence uterine health and resumption of cyclicity, but fewer CIDR-PS than Presynch cows were cyclic at the beginning of the Ovsynch, although differences in the proportion cyclic may have been caused by the timing when corpus luteum evaluations were performed in the different pre-synchronization treatments. Ovulatory responses were not influenced by source of Se. However, the CIDR-PS increased ovulation to the first GnRH, double ovulation to the final GnRH, and size of ovulatory follicle at PGF_2a and final GnRH of the Ovsynch, but did not influence ovulation at the final GnRH of the Ovsynch. Concentrations of estradiol during the Ovsynch increased with follicle diameter and were greater for cows receiving CIDR-PS than Presynch, but they were not influenced by source of Se. Pregnancy per AI on d 28 (32.7%), 42 (28.5%), and 56 (25.9%) after AI, and pregnancy loss (20.5%) from 28 to 56 d were not influenced by source of Se or method of presynchronization. Although cows receiving CIDR-PS had an increased incidence of ovulation to the first GnRH (73.2 vs. 57.8%) and double ovulation to the final GnRH of the Ovsynch (18.7 vs. 9.0%), both of which enhanced pregnancy, the CIDR-PS protocol did not improve pregnancy per AI or reduce pregnancy loss compared with presynchronization with PGF_2a alone.     

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.     

Effect of bST and reproductive management on reproductive performance of Holstein dairy cows

The objective was to determine the effects of bovine somatotropin (bST) and two artificial insemination (AI) protocols on reproductive performance of Holstein cows. Lactating cows (n = 840) were assigned at 37 d in milk (DIM) to one of four treatments in a 2 x 2 factorial arrangement. Treatments consisted of either bST (500 mg/14 d) starting at 63 +/- 3 DIM or no bST (control), with cows either submitted for timed AI following a synchronized ovulation (Ovsynch) protocol or assigned to receive AI based on estrus detection (ED). Two injections of PGF2, at 37 +/- 3 and 51 +/- 3 DIM were used to presynchronize estrous cycles. Cows then received an injection of GnRH at 63 +/- 3 DIM, followed 7.5 d later by PGF2. Cows assigned to ED treatments were inseminated after observed estrus during a 7-d period. Cows in Ovsynch treatments received a second GnRH injection 48 h after the last PGF2alpha and received timed AI 16 to 18 h later. Pregnancy was diagnosed by ultrasound at 31 d after AI and confirmed 14 d later. Frequency of anovulation (18.5%) at 63 DIM was similar across treatments, but proportions of anovulatory cows decreased quadratically as body condition at 70 DIM increased from 2.25 to 3.75. Estrus detection rate after PGF2alpha tended to be lower in multiparous cows receiving bST, and bST reduced returns to estrus in nonpregnant cows. Conception rates were higher in cows receiving AI after ED and bST improved conception rates to first AI in cyclic cows by reducing embryonic mortality. Pregnancy loss was similar for cows inseminated following ED or the Ovsynch protocol. There was a positive impact of bST on fertility of cyclic cows inseminated at fixed time or at detected estrus, but effective resynchronization protocols are needed to optimize reinsemination of non-pregnant bST-treated cows.     

Estrus synchronization of lactating dairy cows with GnRH, progesterone, and prostaglandin F2 alpha

The reproductive performance of synchronized cows was compared with that of nonsynchronized cows. In trial 1, cyclic cows in five seasonal herds were randomly divided into two groups. Cows in one group (n = 515) were treated with a GnRH agonist and an intravaginal progesterone device, followed in 7 d by a PGF2 alpha injection, and the device was removed 1 d after PGF2 alpha. Cows in the other group (n = 512) did not receive any treatment and acted as control. In trial 2, the treatments were similar to those used in trial 1 except that the progesterone device was removed at the time of PGF2 alpha injection (synchronized: n = 516; control: n = 512). The estrus synchronization rate was 92.8% in trial 1 and 92.2% in trial 2. Conception rate to first artificial insemination (AI) was lower for synchronized cows than for control cows in trial 1 (56.5 vs. 62.7%), but similar in trial 2 (64.6 vs. 63.3%). Across both trials, the pregnancy rate during the AI breeding period was greater for the synchronized cows (85.6%) than for the control cows (81.2%). The synchronization treatment reduced the interval from start of the breeding season to conception for cows conceiving by AI (8.9 vs. 14.8 d) or by AI or natural mating (14.1 vs. 21.6 d). The synchronization protocol used in trial 2 achieved better conception rate than that used in trial 1, but the precision of estrus was less in trial 2 than in trial 1.     

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.     

Evaluation of two hormonal protocols for synchronization of ovulation and timed artificial insemination in dairy cows managed in grazing-based dairies

To evaluate the efficacy of two hormonal protocols for synchronization of ovulation and timed artificial insemination (TAI) in dairy cows managed in grazing-based dairies, lactating dairy cows (n = 142) from two grazing-based dairies were randomly assigned to one of three treatment groups. Cows in the first group (Ovsynch) received 50 microg of GnRH (d -10); 25 mg of PGF2alpha (d -3), and 50 microg of GnRH (d -1) followed by timed AI on d 0. Cows in the second group (PGF + Ovsynch) received a modified Ovsynch and timed AI similar to Ovsynch but with the addition of 25 mg of PGF2alpha 12 d (d -22) before initiation of Ovsynch. Cows in the third group (control) received standard reproductive management in place on each farm. Luteolysis occurred in 90.5% of cows exhibiting luteal function on d -22 in the PGF + Ovsynch treatment group, whereas none of the cows in the Ovsynch group underwent luteolysis on d -22. Synchronization rate (i.e., ovulatory response at 48 h after the second GnRH injection), conception rates at TAI and pregnancy rates after 35 d of breeding were similar for cows in the Ovsynch and PGF + Ovsynch groups. The proportion of anovular cows at the first GnRH injection of the synchronization protocols (d -10) was similar for cows receiving Ovsynch (28.0%) and PGF + Ovsynch (30.7%), and conception rate at TAI was similar for cycling (45.8%) and anovular (30.0%) cows. The cumulative pregnancy rate was greater for cows receiving TAI compared with control cows after 7 d of breeding (41.2 vs. 20.0%) but did not differ at 35 d of breeding (54.9 vs. 60.0%). Administration of PGF2alpha 12 d before initiation of Ovsynch did not improve synchronization, conception, or pregnancy rate compared with the standard Ovsynch protocol. Synchronization of ovulation to initiate timed AI at the onset of the breeding season resulted in earlier establishment of pregnancy compared with standard reproductive management.     

Targeted reproductive management for lactating Holstein cows: Reducing the reliance on exogenous reproductive hormones

Adoption of automated monitoring devices (AMD) affords the opportunity to tailor reproductive management according to the cow's needs. We hypothesized that a targeted reproductive management (TRM) would reduce the use of reproductive hormones while increasing the percentage of cows pregnant 305 d in milk (DIM). Holstein cows from 2 herds (n = 1,930) were fitted with an AMD at 251.0 ± 0.4 d of gestation. Early-postpartum estrus characteristics (EPEC; intense estrus = heat index ≥70; 0 = minimum, 100 = maximum) of multiparous cows were evaluated at 40 (herd 1) or 41 (herd 2) DIM and EPEC of primiparous cows were evaluated at 54 (herd 1) or 55 (herd 2) DIM. Control cows received the first artificial insemination at fixed time (TAI; primiparous, herd 1 = 82 and herd 2 = 83 DIM; multiparous, herd 1 = 68 and herd 2 = 69 DIM) following the Double-Ovsynch (DOV) protocol. Cows enrolled in the TRM treatment were managed as follows: (1) cows with at least one intense estrus were inseminated upon AMD detected estrus for 42 d and, if not inseminated, were enrolled in the DOV protocol; and (2) cows without an intense estrus were enrolled in the DOV protocol at the same time as cows in the control treatment. Control cows were re-inseminated based on visual or patch aided detection of estrus, whereas TRM cows were re-inseminated as described for control cows with the aid of the AMD. Cows received a GnRH injection 27 ± 3 d after insemination and, if diagnosed as nonpregnant, completed the 5-d Cosynch protocol and received TAI 35 ± 3 d after insemination. Among cows in the TRM treatment, 55.8 and 42.9% of primiparous and multiparous cows, respectively, received the first insemination in spontaneous estrus. The interaction between treatment and parity affected pregnancy 67 d after the first AI (primiparous: control = 37.6%, TRM = 27.4%; multiparous: control = 41.0%, TRM = 44.7%). The TRM treatment increased re-insemination in estrus (control = 48.3%, TRM = 70.5%). Pregnancy 67 d after re-inseminations tended to be affected by the interaction between treatment and EPEC (no intense estrus: control = 25.3%, TRM = 32.0%; intense estrus: control = 32.9%, TRM = 32.2%). The interaction between treatment and EPEC affected pregnancy by 305 DIM (no intense estrus: control = 80.8%, TRM = 88.2%; intense estrus: control = 87.1%, TRM = 86.1%). Treatment did not affect the number of reproductive hormone treatments among cows that had not had an intense estrus (control = 10.5 ± 0.3, TRM = 9.1 ± 0.2 treatments/cow), but cows in the TRM treatment that had an intense estrus received fewer reproductive hormone treatments than cows in the control treatment (2.0 ± 0.1 vs. 9.6 ± 0.2 treatments/cow). Selecting multiparous cows for first AI in estrus based on EPEC reduced the use of reproductive hormones without impairing the likelihood of pregnancy to first AI. The use of AMD for re-insemination expedited the establishment of pregnancy among cows that did not display an intense estrus early postpartum.     

Effect of reducing the period of follicle dominance in a timed artificial insemination protocol on reproduction of dairy cows

Objectives were to determine the effect of reducing the period of follicle dominance in a timed artificial insemination (AI) protocol on pregnancy per AI (P/AI) in Holstein cows. In experiment 1, 165 cows received 2 injections of PGF_2α at 36 and 50 d in milk (DIM). At 61 DIM, cows were assigned randomly to Cosynch 72 h (CoS72: d 61 GnRH, d 68 PGF_2α, d 71 GnRH) or to a 5-d Cosynch 72 h with 1 (5dCoS1: d 61 GnRH, d 66 PGF_2α, d 69 GnRH) or 2 injections of PGF_2α (5dCoS2: d 61 GnRH, d 66 and 67 PGF_2α, d 69 GnRH). Blood was sampled at the first GnRH, first PGF_2α, and at the second GnRH of the protocols and assayed for progesterone. Ovulatory responses to GnRH were evaluated by ultrasonography. Cows were considered synchronized if they had concentrations of progesterone ≥1 ng/mL and <1 ng/mL on the days of the PGF_2α, and the second GnRH of the protocols, respectively, and if they ovulated within 48 h of the second GnRH injection. In experiment 2, 933 cows were assigned randomly to CoS72 or 5dCoS2. Blood was assayed for progesterone and ovaries were scanned as in experiment 1. Plasma on the days of the first PGF_2α and final GnRH of the timed AI protocols was assayed for estradiol in 75 cows. Pregnancy was diagnosed on d 38 and 66 after AI. In experiment 1, the proportions of cows with corpora lutea (CL) regression on the day of AI differed and were 79.0, 59.1, and 95.7% for CoS72, 5dCoS1, and 5dCoS2, respectively. Cows that ovulated to the first GnRH of the Cosynch tended to have lesser CL regression than cows that did not ovulate (73.0 vs. 86.4%). Protocol synchronization differed between treatments and they were greater for CoS72 (69.4%) and 5dCoS2 (78.4%) than for 5dCoS1 (42.3%). In experiment 2, CL regression was lesser (91.5 vs. 96.3%) but detection of estrus at timed AI (30.9 vs. 23.6%) was greater for CoS72 than 5dCoS2, and cows in estrus had increased P/AI (46.2 vs. 31.9%). Cows in CoS72 ovulated a larger follicle and had greater concentrations of estradiol on the day of AI than cows in 5dCoS2, but protocol synchronization tended to increase in cows receiving the 5dCoS2. When all 933 cows were evaluated, P/AI was greater for 5dCoS2 than for CoS72 (37.9 vs. 30.9%). Similarly, when only cows with progesterone <1 ng/mL on the day of AI were evaluated, P/AI was greater for 5dCoS2 than for CoS72 (39.3 vs. 33.9%). Treatment with PGF_2α on d 5 and 6 after GnRH resulted in increased luteolysis and allowed for reducing the interval from GnRH to timed AI, which increased P/AI. Reducing time of follicle dominance in timed AI protocols improves fertility of lactating dairy cows.     

Fertility of lactating dairy cows treated with Ovsynch after presynchronization injections of PGF2 alpha and GnRH

Synchronization of ovulation (Ovsynch) using GnRH and PGF2 alpha allows control of follicle growth, corpus luteum regression, and ovulation, but resulting pregnancy rates vary. This study examined whether presynchronization to allow initiation of Ovsynch during diestrus would improve pregnancy rates at timed artificial insemination (AI). Lactating dairy cows (n = 427), 69 to 75 d postpartum, were randomly assigned to two groups by parity. Control cows received Ovsynch (GnRH, d 0; PGF2 alpha, d 7; GnRH, d 9; timed AI 16 h after second GnRH). Treated cows received presynchronization injections of PGF2 alpha and GnRH, 10 and 7 d, respectively, before starting Ovsynch. Pregnancy diagnoses were performed 36 d after AI. Progesterone (P4) concentrations from a subset of cows (n = 84) were determined in serum samples collected on d 0, 3, and 7 of Ovsynch. Presynchronization increased the percentages of cows with > or = 1 ng/ml serum P4 compared with control cows at first injection of GnRH (d 0; 93 vs. 56%) and on d 3 (90.7 vs. 51.2%) during Ovsynch. On day of PGF2 alpha, d 7 during Ovsynch, percentages of cows with > or = 1 ng/ml serum P4 were similar (95.3%, treated vs. 82.9%, control) but more treated cows had > or = 2 ng/ml serum P4 (95.3 vs. 63.4%). However, pregnancy to timed AI was similar between treated (41.5%) and control cows (38.3%). Cows with above-average milk production had greater pregnancy rate (45.8 vs. 33.8%) compared with lower producing cows. Although presynchrony increased the proportion of cows with luteal function at onset of Ovsynch, pregnancy rate to timed AI was not improved. Cows with above-average milk production had greater fertility at timed AI than herdmates with lower milk production.     

Effect of gonadotropin-releasing hormone administered at the time of artificial insemination for cows detected in estrus by conventional estrus detection or an automated activity-monitoring system

The objectives of this study were to determine the effects of GnRH at the time of artificial insemination (AI) on ovulation, progesterone 7 d post-AI, and pregnancy in cows detected in estrus using traditional methods (tail chalk removal and mount acceptance visualization) or an automated activity-monitoring (AAM) system. We hypothesized that administration of GnRH at the time of AI would increase ovulation rate, plasma progesterone post-AI, and pregnancy per AI (P/AI) in cows detected in estrus. In experiment 1, Holstein cows (n = 398) were blocked by parity and randomly assigned to receive an injection of GnRH at the time of estrus detection/AI (GnRH, n = 197) or to remain untreated (control, n = 201) on 4 farms. The GnRH was administered as 100 µg of gonadorelin acetate. Ovarian structures and plasma progesterone were assessed in a subset of cows (GnRH, n = 52; control, n = 55) in experiment 1 at the time of AI and 7 d later. In experiment 2, a group of 409 cows in an AAM farm were enrolled as described for experiment 1 (GnRH, n = 207; control, n = 202). Data were categorized for parity (primiparous vs. multiparous), season (cool vs. warm), number of services (first vs. > first), DIM (>150 DIM vs. ≤150 DIM), and for AAM cows in experiment 2 for activity level (high: 90–100 index vs. low: 35–89 index). Pregnancy diagnosis was performed between 32 and 45 d post-AI (P1) and 60 to 115 d post-AI (P2). In experiment 1, there was no difference in plasma progesterone at day of estrus detection (control = 0.09 ng/mL vs. GnRH = 0.16 ng/mL), 7 d later (control = 2.03 ng/mL vs. GnRH = 2.18 ng/mL), and ovulation rate (GnRH = 83.2% vs. control = 77.9%) between treatments. There were no effects of GnRH in experiment 1 for P/AI at P1 (control = 43.3% vs. GnRH = 38.6%), P2 (control = 38.4% vs. GnRH = 34.5%), and for pregnancy loss (control = 9.8% vs. GnRH = 8.2%). In experiment 2, there were no effects of GnRH for P/AI at P1 (control = 39.6% vs. GnRH = 40.1%), P2 (control = 35.0% vs. GnRH = 37.4%), and for pregnancy loss (control = 9.5% vs. GnRH = 6.2%). There was a tendency for a parity effect on P/AI for P1, but not P2 or for pregnancy loss. High-activity cows had greater P/AI in P1 (low activity = 27.9% vs. high activity = 44.1%), P2 (low activity = 21.8% vs. high activity = 41.2%), and lower pregnancy loss (low activity = 20.7% vs. high activity = 5.1%), but there were no interactions between treatment and activity level. The current study did not support the use of GnRH at estrus detection to improve ovulatory response, progesterone 1 wk post-AI, and P/AI. More research is needed to investigate the relationship between GnRH at the time of AI and activity level in herds using AAM systems.