Treatment of Cycling and Noncycling Lactating Dairy Cows with Progesterone During Ovsynch

Pregnancy rates to timed artificial insemination in Holstein heifers given prostaglandin F2alpha twenty-four hours before or concurrent with removal of an intravaginal progesterone-releasing insert

The objective was to compare pregnancy rates in nulliparous Holstein heifers given PGF(2alpha) 24 h before, or concurrent with, removal of an intravaginal progesterone-releasing (CIDR) insert in 3 timed artificial insemination (TAI) protocols. Heifers (from 2 herds) were assigned randomly, over 11 mo, to 1 of 3 modified Ovsynch protocols. On d 0 (without reference to the stage of the estrous cycle), all heifers were given 100 microg of GnRH i.m. and a CIDR insert (containing 1.9 g of progesterone). In the PG-7/P4-8 protocol (n = 99), PGF(2alpha) was given on d 7, and CIDR inserts were removed on d 8. In the PG-7/P4-7 (n = 98) and PG-8/P4-8 (n = 102) protocols, PGF(2alpha) administration and CIDR removal occurred concurrently, on d 7 or 8, respectively. In all 3 protocols, a second GnRH treatment (100 microg) was given 48 h after PGF(2alpha) with TAI 16 to 20 h later. Blood samples were collected (subset of 124 heifers) on d 0, 7, 10 or 11 (i.e., at TAI), and 17. Pregnancy rates (32 d after TAI) for protocols PG-7/P4-8, PG-7/P4-7, and PG-8/P4-8 were 61.8, 55.6, and 54.1%, respectively. Pregnancy rate was higher when synchronization was initiated during diestrus than when initiated at other stages (57.0 versus 34.8%). Although pregnancy rates were not affected by season, there was an interaction between protocol and season; pregnancy rates were significantly lower in summer in heifers subjected to PG-7/P4-7 and PG-8/P4-8, but season did not affect pregnancy rates in heifers subjected to PG-7/P4-8. In summary, giving PGF(2alpha) 24 h before CIDR removal, followed by TAI (PG-7/P4-8 protocol), resulted in consistent pregnancy rates, regardless of season, relative to protocols involving PGF(2alpha) treatment concurrent with CIDR removal.

Assessment of a Practical Method for Identifying Anovular Dairy Cows Synchronized for First Postpartum Timed Artificial Insemination

Our objective was to determine whether a single examination of ovaries using transrectal ultrasonography at the first GnRH injection of a Presynch + Ovsynch protocol is a useful method for assessing cyclicity status and thereby enabling differential management of anovular vs. cyclic cows. Lactating Holstein cows (n = 842) receiving a Presynch + Ovsynch protocol to initiate first postpartum timed artificial insemination (TAI) were used to compare 2 methods for assessing cyclicity status before TAI. For the standard method (using RIA), blood samples were collected at the second PGF2alpha injection of Presynch and the first GnRH injection of Ovsynch, and cows with serum progesterone > or = 1.0 ng/mL in one or both samples were classified as cycling, whereas cows with serum progesterone < 1.0 ng/mL in both samples were classified as anovular. For the practical method, transrectal ultrasonography (U/S) was used to determine the presence or absence of a corpus luteum (CL) at the first GnRH injection of Ovsynch, and cows without CL were classified as anovular, whereas cows with CL were classified as cycling. Statistical agreement (kappa) between the RIA and U/S methods to identify cycling cows was 0.66. Sensitivity, specificity, positive predictive value, and negative predictive value of U/S to identify anovular status were 85.7, 87.7, 64.7, and 95.9%, respectively. We conclude that assessing the presence or absence of CL at the first GnRH injection of a Presynch + Ovsynch protocol using U/S is a reliable and practical method for identifying the cyclicity status of cows before first TAI, but may slightly overestimate the proportion of anovular cows compared with the RIA method.

Interventions After Artificial Insemination: Conception Rates, Pregnancy Survival, and Ovarian Responses to Gonadotropin-Releasing Hormone, Human Chorionic Gonadotropin, and Progesterone

We hypothesized that increasing concentrations of progesterone (P4) after artificial insemination would increase fertility. Our objective was to assess changes in ovarian structures, incidence of ovulation, and change in serum P4 in response to GnRH, human chorionic gonadotropin (hCG), or exogenous P4 (controlled internal drug release; CIDR insert) treatment beginning 4 to 9 d after artificial insemination (d 0) and again 7 d later (experiment 1). Blood was collected from 753 cows in 3 herds on d 0 and 7. Ovaries of 162 cows were scanned and mapped to confirm the presence of a corpus luteum (CL), and cows were assigned randomly to serve as controls (n = 41) or to receive a CIDR insert for 7 d (n = 41), 100 microg of GnRH (n = 40), or 3,300 IU of hCG (n = 40). More cows were induced to ovulate in response to GnRH (60%) and hCG (78%) compared with controls (2.4%). Compared with controls, cows treated with GnRH or hCG had more induced CL (d 7) and more total CL (d 7), but serum P4 was increased only in response to hCG. Largest follicle diameters on d 7 were less after GnRH and hCG, but total follicular volume on d 7 was reduced by GnRH, hCG, and CIDR, compared with that of controls. Volume of the original luteal structures was increased by hCG but tended to be reduced by CIDR and GnRH compared with luteal volume in controls. Total CL volume was increased by hCG, but reduced by CIDR, compared with CL volume of controls. Conception rates and pregnancy survival were assessed in response to the same treatments described in experiment 1: controls (n = 708), CIDR (n = 711), GnRH (n = 719), and hCG (n = 714). Tendencies for interactions of treatment x herd and treatment x lactation group were detected, but no 3-way interactions were found. Treatment with hCG increased conception rates in second-lactation cows. The CIDR tended to increase, and hCG increased, conception rates in 2 herds, whereas the CIDR decreased conception rates in 1 herd. Pregnancy survival was reduced by GnRH compared with that in controls. We concluded that GnRH and hCG effectively induced ovulation, and increased number of CL, but only increased serum P4 in hCG-treated cows. Further, treatment with the CIDR or hCG increased conception rates but only in some herds.

Comparison of Two Estrus-Synchronization Protocols and Timed Artificial Insemination in Dairy Cattle

The objective of this study was to evaluate the effect of the Ovsynch protocol with and without exogenous progesterone on pregnancy rate (PR) in cows in which estrous cycles were previously synchronized with 2 doses of PGF(2alpha) and that were not detected in estrus during the presynchronization period. The study was conducted in Chihuahua, Mexico (8,650 Holstein milking cows; 305-d mature equivalent milk yield = 13,790 kg). On d 47 postpartum, estrous cycles in cows were synchronized by using 2 doses of PGF(2alpha) 14 d apart. Any cow detected in estrus during this presynchronization period was inseminated. Cows not detected in estrus were selected at random and assigned to receive progesterone supplementation or to serve as controls. Controls (n = 594) were subjected to the Ovsynch protocol and cows in the progesterone supplemented treatment (n = 594) were subjected to the Ovsynch protocol plus an intravaginal insert containing 1.9 g of progesterone inserted at the time of the first GnRH injection and removed 7 d later. Progesterone-supplemented cows had a greater PR (31.2%) compared with controls (22.7%). Plasma progesterone concentrations at artificial insemination (AI) were <1 ng/mL and did not differ between treatments. At 14 d post-AI, however, more cows that received progesterone supplementation had concentrations of progesterone >1 ng/mL compared with controls. It was concluded that after a presynchronization period, cows subjected to the Ovsynch program and supplemented with exogenous progesterone had a greater PR and greater concentrations of progesterone after AI than those subjected to the Ovsynch protocol and not supplemented with progesterone.