No abstract

Lactating dairy cows (n = 228) in a semiseasonal, grazing-based dairy were subjected to artificial insemination (AI) to start the 23-d breeding season (d 0 to 22) followed by natural service (d 23 to 120). Cows were randomly assigned to: 1) Ovsynch (GnRH, d -10; PGF2,, d -3; GnRH, d -1; timed AI, d 0) followed by AI at estrus (tail paint removal) on d 1 to 22 (Ovsynch; n = 114); or 2) AI at estrus (tail paint removal) throughout 23 d of AI breeding (tail paint; n = 114). Days to first AI service were greater and the 23-d AI service rate was less for tail paint vs. Ovsynch cows (12.0 +/- 0.6 d vs. 0 d; and 84.2 vs. 100%, respectively). However, conception to first AI was greater for tail paint vs. Ovsynch cows (47.3 vs. 27.3%, respectively). Cows in the tail paint group received only one AI, during 23 d of AI, but 46.4% of Ovsynch cows received a second AI, with similar conception (43.1%) to that of tail paint cows at first AI (47.3%). Based on serum progesterone, incomplete luteal regression after PGF2alpha, and poor ovulatory responses to GnRH contributed to lower conception to timed AI in the Ovsynch group. Cumulative pregnancy rates for tail paint and Ovsynch cows did not differ after 23 d of AI breeding (47.3 vs. 46.3%, respectively) nor after 120 d of AI/ natural service breeding (80.5 vs. 83.3%, respectively). Lactating cows in this grazing-based dairy synchronized poorly to Ovsynch resulting in reduced conception to timed AI compared with AI after tail paint removal.

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.

No abstract

The Early Conception Factor (ECF) test is a commercially available qualitative assay that reportedly detects a pregnancy-associated glycoprotein present in bovine serum within 48 h after conception. One concern with previous assessments of this test is that animals with viable embryos early during pregnancy that subsequently undergo embryonic loss before pregnancy diagnosis increase the rate of false-positive results and bias the assessment. To preclude this possibility, noninseminated Holstein cows (n = 9) and heifers (n = 8) were evaluated as an unequivocal source of nonpregnant animals, and Holstein cows (n = 17) and heifers (n = 1) inseminated at estrus and in which at least one embryo of transferable quality was recovered at a nonsurgical flush 6 d after artificial insemination were evaluated as an unequivocal source of pregnant animals. Blood samples were collected from all animals 6 d after estrus, which was immediately before embryo collection in pregnant animals. Each serum sample was evaluated using two ECF test cassettes (tests 1 and 2), and the result of each test cassette was interpreted by two independent readers (readers 1 and 2). Test sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 86, 4, 49, 23, and 46%, respectively. Although the observed agreement between readers (91% for test 1; 89% for test 2) and between tests for the same serum sample (94% for reader 1; 91% for reader 2) was high, the overall rates of false-positive and false-negative ECF test results were 96 and 14%, respectively. We conclude that the ECF test is an unreliable method for determining pregnancy status of dairy cattle on day 6 after estrus.