Control of the oestrous cycle in farm animals: A review
L.V. Swanson
Department of Animal Science, Oregan State University,
Corvallis, Oregan 97331, USA
Proceedings of the New Zealand Society of Animal Production.
1989, 49: 71-80
Ultrasonography has permitted close visualisation of follicular
development in cattle and has revealed that three waves of follicles
normally develop during the oestrous cycle. Follicle stimulating
hormone is important for the recruitment of follicles but it is not
known how the recruited follicles are selected to become dominant over
other follicles and eventually to ovulate. Hypothalamic, pituitary and
ovarian hormones are secreted and released episodically. During the
luteal phase of the oestrous cycle, the negative feedback of
progesterone prevents any rise in luteinising hormone (LH). As
progesterone levels fall, LH increases, prompting an increase in
oestradiol which triggers the ovulatory LH surge and behavioural
oestrus. LH causes ovulation and luteinisation of follicular cells.
Luteal phase progesterone may be responsible for later increases in
prostaglandin F2a (PG)F2a, a luteolytic hormone in cattle and sheep
which is transferred from the uterus, its site of synthesis, to the
corpus luteum. Oestradiol and oxytocin, synthesised in the ovary, may
be involved in regulation of uterine synthesis of PGF2a, hastening
luteolysis. At this time it is not known how essential these two
hormones are to the process of luteolysis. The discovery and synthesis
of new ovarian hormones should permit superovulation to become a more
exact and a less expensive procedure and for embryonic mortality to be
reduced.
Keywords: NZSAPAB;
Cattle; sheep; oestrous cycle; progesterone; oestradiol;
oxytocin; LH; FSH; follicles; CL
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Last Updated 18-03-1997
