Use of prostaglandin F2α as ovulatory stimulus for synchronizing dairy cattle.

The aim of this study was to evaluate if prostaglandin F2α (PGF) can be used to induce ovulation in a GnRH-progesterone based protocol. In Experiment 1 crossbred dairy cows (n=32) were synchronized with a progesterone-GnRH based protocol for seven days, where the luteolytic dose of 150µg PGF was given 24h prior progesterone device removal (CIDR). On Day 8 cows were separated into two groups to receive: 1) 2mL of Saline (Control Group, n=15) or 2) 150µg of PGF (PGF Group, n=17). Ovulation rate was higher in the PGF than Control group (100% vs 53.3%, P=0.001, Odds ratio=30.88). The percentage of cows that ovulated synchronously tended to be higher in the PGF than Control group (P=0.1, Odds ratio=9.6). Experiment 2 was performed in a cross-over (3×3) design. Crossbred dairy cows (n=25) received a CIDR for seven days and GnRH on Day 0. Seven days later 150µg of PGF was given and the progesterone device was removed, and 24h later cows were distributed into three groups to receive: 1) 2mL of Saline (Control Group, n=25), 2) 150µg of PGF (PGF Group, n=25) or 3) 1mg of ECP (ECP Group, n=23). Diameter of ovulatory follicle was larger in the PGF and Control than ECP Group (P=0.002, Effect size>4.0). Synchronized ovulation rate (between 72 and 96h after CIDR removal) tended to be higher in PGF group in Control group (P=0.1, Odds ratio=0.35). Results suggest that PGF is equally efficient to ECP to induce synchronized ovulation in dairy cows subjected to progesterone-GnRH based protocols.

Comparison between two estradiol-progesterone based protocols for timed artificial insemination in blocks in lactating Nelore cows.

The aim of this study was to compare the use of artificial insemination in time blocks (Artificial Insemination Blocks, AIB) using an 8 and 9 d estradiol-progesterone based protocol. In this experiment, lactating Nelore cows (n=253) were subjected to two estradiol-progesterone based TAI protocols. On the morning of Day 10 (8d group, n=124) or Day 11 (9d group, n=129), cows were examined by ultrasonography to evaluate the diameter of the preovulatory follicle and were inseminated once at one of the following time points, according to the diameter of the pre-ovulatory follicle (POF): Block 0 (POF≥15mm, TAI 0h after conventional TAI), Block 1 (POF 13.0-14.9mm, TAI 6h later), Block 2 (POF 10.1-12.9mm, TAI 24h later), and Block 3 (POF≤10.0mm, TAI 30h later). The pregnancy per AI (P/AI) did not differ between 8d and 9d groups (P>0.05). Considering only multiparous cows, however, P/AI tended to be greater in the 8d (64.1%) than in the 9d group (49.3%; P=0.08). Cows from the 9d group tended to have a larger POF than cows from the 8d group (P=0.07). In conclusion, these results provide evidence that there is no difference between 8d or 9d protocols when using the AIB technique. Use of the 8d estradiol-progesterone based protocol, however, tended to increase pregnancy in multiparous cows.

Timed artificial insemination in blocks: A new alternative to improve fertility in lactating beef cows.

The aim of this study was to evaluate whether changing the interval from CIDR removal to timed artificial insemination (TAI) according to the diameter of the preovulatory follicle (POF) would improve pregnancy per AI in cows. In Study 1, a retrospective analysis of TAI experiments (n=96 cows) was performed to characterize the time of ovulation according to the diameter of the dominant follicle. It was observed that cows with a larger POF had ovulations earlier than cows with smaller POF, according to the equation: y=0.72x(2)-26.74x+264.54 (R(2)=0.63; P<0.001). In Study 2, lactating Nelore cows (n=412) were subjected to an EB-CIDR based TAI protocol. On the morning of Day 10 (time of TAI), cows were randomized into Control (n=209) and Block (n=203) groups; (1) Cows in the Control Group were TAI 48 h after CIDR removal (08:00 am on Day 10), and; (2) Cows in the block group were inseminated once at one of the following time points, according to the diameter of the POF on Day 10: B0 (POF≥15mm, TAI 0 h after convetional TAI), B1 (POF 13-14.9 mm, TAI 6h later), B2 (POF 10.1-12.9 mm, TAI 24h later) and B3 (POF≤10mm, TAI 30 h later). The cows of the Block Group had greater pregnancy rates per AI than the Control Group (129/203, 63.5% when compared with 102/209, 48.8%, respectively; P<0.01). In conclusion, results of the present study demonstrate that adjusting the timing of TAI according to the diameter of the POF can be an effective practice for improving fertility of cows in TAI protocols.