Comparison of reproductive performance in lactating dairy cows bred by natural service or timed artificial insemination.

The objective of this study was to compare reproductive performance of lactating dairy cows bred by natural service (NS) or timed AI (TAI). One thousand fifty-five cows were blocked by parity and enrolled to receive either NS or TAI. Cows in both groups were presynchronized with 2 injections of PGF(2alpha) given at 42 and 56 d postpartum. Fourteen days after the last PGF(2alpha) injection, cows in the TAI group were enrolled in an Ovsynch protocol (d 0 GnRH; 7 d later, PGF(2alpha); 56 h after PGF(2alpha) injection, second dose of GnRH; and 16 h after second GnRH cows were TAI). Cows in the TAI group were resynchronized with an intravaginal insert containing progesterone inserted 18 d after TAI and removed 7 d later when GnRH was given. Cows were examined by ultrasonography on d 32 after TAI; nonpregnant cows received PGF(2alpha) and GnRH 56 h later followed by TAI 16 h after the GnRH injection. Nonpregnant cows in TAI group were reinseminated up to 5 times using the same scheme. Cows in the NS group were exposed to bulls 14 d after the second PGF(2alpha) injection, and ultrasonography was performed 42 d after exposure to bulls to determine pregnancy status. Nonpregnant cows in the NS group were reexamined by transrectal palpation combined with ultrasound every 28 d until diagnosed pregnant or 223 d postpartum, whichever occurred first. Cows diagnosed pregnant in TAI or NS were reconfirmed 28 d later to determine pregnancy loss. All bulls underwent an evaluation of breeding soundness and were rested for 14 d after 14 d of cow exposure. Health disorders were evaluated up to 70 d postpartum, and body condition score was evaluated at d 70 postpartum. Blood was collected on d 56 and 65 postpartum and analyzed for progesterone to determine cyclicity. The proportion of pregnant cows in the first 21 d of breeding did not differ between groups. The overall 21-d cycle pregnancy rate (PR), which included a total of 8 and 5 service opportunities for NS and TAI, respectively, was not different between groups (25.7 and 25.0% for NS and TAI, respectively). The daily rate of pregnancy was 15% greater for NS than TAI because cows in NS had a greater PR, which resulted in fewer median days open (111 vs. 116 d). Proportion of pregnant cows at 223 d postpartum was greater in the NS than TAI group (84.2 vs. 74.8%, respectively). Cyclicity did not affect reproductive performance. Cows with body condition score >/=2.75 had greater proportion of pregnant cows in the first 21 d of breeding and daily PR in the first 223 d postpartum Primiparous cows had greater proportion of pregnant cows and daily PR than multiparous cows at 223 d postpartum. In conclusion, the greater proportion of pregnant cows in the NS group was attributed to more opportunities for breeding than in the TAI group.

Rectal temperature, calving-related factors, and the incidence of puerperal metritis in postpartum dairy cows.

The objectives of this study were as follows: 1) to evaluate the association among abnormal calving, parity, and season on the incidence of puerperal metritis (PM) and clinical endometritis (CE) during d 3 to 13 and 20 to 30 postpartum, respectively; 2) to describe the rectal temperature (RT) of cows with PM before diagnosis; and 3) to document associations among PM, CE, and reproductive performance in lactating dairy cows. This study followed a prospective observational study design. Cows were classified as having an abnormal calving status (AC), i.e., cows calving with dystocia, twins, retained fetal membranes, or some combination of these conditions, and having a normal calving status (NC). Daily RT was recorded from d 3 to 13 postpartum for all cows, and health examinations were performed on cows that appeared not well. A total of 450 calvings were evaluated. Cows with an AC had greater odds of PM than cows with NC [adjusted odds ratio (AOR) = 4.8; 95% confidence interval (CI) = 2.9 to 8.0). A season by parity interaction showed that primiparous cows that calved during the warm season had lower AOR of PM than during the cool season (0.24; 95% CI = 0.09 to 0.62), whereas multiparous cows did not have seasonal effects on PM (1.43; 95% CI = 0.65 to 3.18). Cows with AC have greater AOR for CE than cows with NC (2.8; 95% CI = 1.7 to 4.9), and greater AOR of CE were detected in cows diagnosed with PM than in cows without PM (2.2; 95% CI = 1.1 to 3.9). Rectal temperature in cows with PM increased significantly 24 h before diagnosis of PM, reaching 39.2 +/- 0.05 degrees C on the day of diagnosis. In cows with PM and fever at diagnosis, the RT began to increase from 72 to 48 h before the diagnosis of PM and continued to increase to 39.7 +/- 0.09 degrees C on d 0 (day of diagnosis). Nonetheless, cows with PM without fever at diagnosis had no daily increases in RT before diagnosis of PM. Still, the RT on d 0 was different from cows without PM. Cows without PM had a stable RT (38.6 +/- 0.01 degrees C). There were no detected differences in first-service conception risk or cumulative pregnancy risk by 150 d postpartum between cows with or without PM. Still, a season effect on first-service conception AOR (warm vs. cool = 0.98; 95% CI = 0.18 to 0.72) and accumulated pregnancy AOR by 150 d postpartum was detected (warm vs. cool = 0.18; 95% CI = 0.10 to 0.33).