Postponing TAI in beef cows with small preovulatory follicles.

The aims of this study were (1) to establish an optimal cut-off point for evaluating the effect of the preovulatory follicle (POF) diameter in timed AI (TAI) programs, and (2) to evaluate the effect of postponing TAI in cows with smaller follicles on pregnancy per AI (P/AI). In Study 1, Nelore cows (n = 426) were subjected to an estradiol-progesterone (P4) based TAI protocol. The diameter of POF was measured at TAI, 48 h after P4 insert removal.

GnRH34: An alternative for increasing pregnancy in timed AI beef cows.

Two experiments evaluated the effects of gonadotropin releasing hormone (GnRH) treatment on fertility of suckled Nelore beef cows treated with an estradiol/progesterone (P4)-based protocol for timed artificial insemination (TAI). Experiment 1 was designed to determine the effect of GnRH administered 34 h after P4 insert removal (GnRH34) on time of ovulation. Suckled cows (n = 34) were treated with 2 mg estradiol benzoate (EB) and an intravaginal insert containing 1.

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).

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.

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.