THE EFFECT OF EXOGENOUS OXYTOCIN ON CORPUS LUTEUM FUNCTION IN THE COW

in Reproduction

Summary.

Seventy-seven Hereford cows were used to study the effects of oxytocin (0, 2, 6 or 18 USP units/100 lb live weight) on corpus luteum function (net weight, progesterone concentration and total progesterone content). Oxytocin was injected in the morning (a.m.) or evening (p.m.) according to four injection regimes. Calling day of oestrus Day 0, oxytocin was injected on Days 2 to 5 and the corpus luteum collected on Day 5 (regime 1) or Day 9 (regime 2). Oxytocin was injected on Days 2 to 7 (regime 3) or 2 to 9 (regime 4), and the corpus luteum collected on Day 9.

There was no effect of time of injection on corpus luteum net weight, progesterone concentration or total progesterone content over all doses and regimes. However, within doses 2 and 6 units, corpus luteum total progesterone was less affected by p.m. than a.m. injection. The opposite effect was observed when 18 units oxytocin injected a.m. in regime 2 did not reduce corpus luteum total progesterone to the same extent as in other high dosage treatment groups.

The 2 units dose of oxytocin stimulated total progesterone content of corpora lutea in regime 2. Increase in the dose or number of days of injections reduced corpus luteum net weight, progesterone concentration and total progesterone. A significant dose-response relation was demonstrated between corpus luteum net weight, progesterone concentration and total progesterone and dose of oxytocin when oxytocin was injected on Days 2 to 5 (p.m.) and the response measured on Day 9 ; or when oxytocin was injected either a.m. or p.m. on Days 2 to 7 or 2 to 9 and the response measured on Day 9.

It was concluded that there may be a diurnal response in corpus luteum functions to oxytocin injections and a critical time on Day 5 through which injections must be made to elicit a maximum dose response in corpus luteum weight, progesterone concentration and progesterone content.

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     An official journal of

    Society for Reproduction and Fertility

 

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