The effect of intrauterine and cervical manipulation on the equine oestrous cycle and hormone profiles.

This research examines the effects of intrauterine and cervical manipulation on a horse’s oestrous cycle and hormone profiles, highlighting how post-oestrus endometrial biopsy or biopsy combined with uterine culture can cause lysis of the corpus luteum, leading to reduced progesterone levels and shortened intervals between oestrous cycles.

Introduction

• The study looks into the impacts of endometrial biopsy or endometrial biopsy combined with uterine culture on the oestrous cycle and hormone profiles of horses. The study was conducted on Day 4 after oestrus and observed the effects on lysis of the corpus luteum (CL), a temporary structure involved in the reproduction and the secretion of the hormone progesterone.

Manipulations Impact on the Oestrous Cycle

• The results showed that these manipulations resulted in CL lysis, causing a significant drop in the progesterone concentration in the serum. This led to shortened interoestrous intervals in 8 out of 12 oestrous cycles and 32 out of 33 cycles across two different experiments.

Effect of Cervical Dilatation

• Cervical dilation carried out four days after oestrus also shortened the interoestrous interval in half of the 10 cycles studied. However, in a different set of five cycles, cervical dilation had no effect on the interoestrous interval.

Manipulations Impact on Hormone Profile

• The study also showed that endometrial biopsy and uterine culture done on Days 1 and 3 after oestrus also induced CL lysis during 4 of 7 cycles.
• Moreover, total estrogen levels (represented by sums of oestrone and oestradiol) showed an increase at the onset of subsequent oestrus in the mares that were biopsied on Day 4 of dioestrus.
• Similar effects were also observed in control cycle oestrous periods.

Lysis of the CL

• Endometrial biopsy also induced lysis of the CL in mares with persistent luteal function. This finding suggests that even in mares with ongoing luteal activities, an endometrial biopsy can still cause the disintegration of the CL.

Intracervical or Intrauterine Manipulations Effects

• The research concludes by hypothesizing that intracervical or intrauterine manipulations done during luteal phase of the oestrous cycle may directly, or indirectly, trigger the release of an endogenous luteolysin (a type of prostaglandin) which results in CL regression. This then follows by oestrus and ovulation in the mare.