The presence of two ovulatory follicles at timed artificial insemination influences the ovulatory response to GnRH in high-producing dairy cows

Abstract

This study sought to examine the impact of the presence of two co-dominant (ovulatory) follicles at the time of artificial insemination (AI) on the ovulatory response to GnRH given in a fixed-time AI protocol. The study population comprised 622 lactating dairy cows: 306 (49.2%) with a single follicle, 198 (31.8%) with two bilateral follicles (one follicle per ovary) and 118 (19%) with two unilateral follicles (same ovary). Based on odds ratios, cows with two bilateral or unilateral follicles were less likely (by factors of 0.09 and 0.11, respectively) to undergo ovulation failure compared with cows with one follicle (P = 0.01 and P = 0.02, respectively); the likelihood of ovulation failure decreased 0.75 times with every one-mm increase in follicle diameter for cows with a single follicle, whereas individual follicle diameter was not related to ovulation failure in cows with two bilateral follicles (P = 0.001). The likelihood of double ovulation decreased 0.7 times with every one-mm diameter difference between the larger and smaller follicle for all cows with two follicles (P = 0.001), whereas cows with two unilateral follicles showed a higher (P< 0.05) double ovulation rate than cows with two bilateral follicles. In 116 (58.6%) of the cows with two bilateral follicles, only the larger follicle ovulated in 59.5% cows, whereas only the smaller one ovulated in the remaining 40.5% cows. In these cows, a one-mm size difference between the larger and the smaller follicle gave rise to a 1.12-fold increase in the ovulation failure rate for the larger follicles (P = 0.0001). Cows with two bilateral follicles were more likely (by a factor of 1.5) to conceive than cows with one follicle (P = 0.001). Significant right-left differences were not found in cows with two bilateral follicles, whereas the right ovary was more active than the left in the remaining cows. Our results indicate that cows with two co-dominant follicles at AI show different ovulation patterns to those with one dominant follicle. A higher rate of ovulation failure was observed among cows with one follicle than cows with two follicles, whereas the conception rate was higher for cows with two bilateral follicles than for the remaining cows. In cows with two follicles, double ovulations along with ovulation of the smaller follicle were related to the least size difference between the larger and smaller follicle.

Improved embryo survival following follicular drainage of subordinate follicles for twin pregnancy prevention in bi-ovular dairy cows

“…Further prerequisites were a uterus that was highly tonic and contractile to touch, and a vaginal discharge of copious clear fluid. As double ovulation has been related to the least possible size difference between the larger and smaller follicle, irrespective of the individual diameter of each follicle [17], only bi-ovular cows with a size difference less than 2 mm between the two co-dominant follicles were included in the study.…”

Pre-ovulatory follicular temperature in bi-ovular cows

“…Fluid temperatures within the antrum were 1.54°C cooler than rectal temperatures in cows that ovulated, but no significant depression of temperature was recorded in cows that failed to ovulate [4]. In a recent study on 622 cows, cows with two co-dominant follicles showed different ovulation patterns to those with one dominant follicle [5]. The objective of the present study was to assess whether follicular cooling in bi-ovular cows occurs in a similar manner to that in monovular cows.…”

Effects of twin pregnancy prevention strategies such as GnRH dose and drainage of the smaller follicle on ovulation in dairy cows with two follicles of pre-ovulatory size in the same ovary

“…Further prerequisites for the animals to be included in the study were that they have a uterus that was highly tonic and contractile to touch and a vaginal discharge of copious clear fluid. As double ovulation has been shown to be related to the least possible size difference between the larger and smaller follicle, irrespective of the individual diameter of each follicle [ 14 ], only cows with a size difference of less than 2 mm between the two co-dominant follicles were included in the study.…”