Physiology refers to the function of reproduction and involves;

Environmental influence of the season on reproduction

The role of hormones on reproduction
Environmental Influences
Breeding cycles are governed by environmental influences. The main one is the length of day light hours
In sheep the breeding season is started by shorter day length in autumn. In poultry sexual maturity is hastened by increasing day length in spring.
Day length acts on the brain via the retina of the eye. Here is the sequence.
The brain has an internal clock that is set by the light level. Decreasing hours of daylight stimulate the pituitary gland, a small structure just below the brain, to produce gonadotrophins - hormones that stimulate the reproductive organs.
In rams these gonadotrophins cause the testes to enlarge, producing sperm and male hormones. In ewes the follicles mature in the ovaries and hormones are released.
Breeding Cycles
Breeding cycles vary greatly from animal to animal. There are three main types

Monoestrus (mono = one) animals such as dogs and cats where the female has one period of sexual activity per cycle. A bitch will come on heat once every six months

Polyoestruc(poly = many) animals like rabbits and pigs which breed the whole year

Seasonally polyoestrus animals like sheep goats horses and cattle where breeding is confined to one season of the year. There are many periods of heat during this season
Male breeding cycles are not so clearly defined as the female cycle, but three main types can be distinguished.

Where there is a definite rutting season as in deer, wild ox, and mountain breeds of sheep. Outside of this season they will not breed.
 Where the males are most efficient during the female’s season as in sheep

Where the males are equally efficient at any season, as in cats dogs pigs and cattle.
The Pituitary gland produces hormones called gonadotrophins. Which stimulate the reproductive organs. In rams the gonadotrophins cause the testes to enlarge, producing sperm and male hormones. In ewes the follicles mature in the ovaries and hormones are released.
Hormones are chemical substances that stimulate the sex glands into activity causing the testes to make sperm and the ovaries to shed eggs.

The Female Hormones
1. During the Oestrus cycle all the hormones are present in the blood, but the amounts vary during the cycle. Each hormone has a specific function and is essential to maintaining the reproductive cycle.
Name of Hormone Function of Hormone
FSH
(Follicle stimulating

Stimulates several follicles are to grow

Only one or two follicle reaches full maturity hormone)
Luteotropic

Triggers one or two follicles to rupture, releasing the ova into the fallopian tube to begin the journey to the
Oestrogen
Progesterone
Uterus.

This is called ovulation

Produced by the growing follicles

Triggers the animal to come into heat

Produced by the corpus luteum

Triggers the animal to go out of heat
2. Diagram Refer to Understanding Farm Animals J A Sutherland page 92.
3. Mating animals at a time close to ovulation is essential so that sperm will still be alive when the eggs are shed. It is necessary to know the length of the cycle (ewe 16 days cow 21 days) and also when ovulation occurs in relation to oestrus.
Animal
Mare
Cow
Ewe
Sow
Length of Cycle
16 days
21 days
16 – 17 days
21 days
When ovulation occurs
1 day before the end of heat
13 -15 hours after heat has ended
Towards the end of heat
36 -48 hours after onset of heat
4. Synchronization of Oestrus occurs when females in a herd are given regular doses of progesterone which halts the oestrus cycle. When the farmers stops using the hormone all the females will come into oestrus at one time. This is a common practice on dairy farms where the farmer is undertaking an artificial insemination (AI) programme. It means that he is able to inseminate all the cows at one time. It also means that calving can be condensed into a specific time frame.
5. Super ovulation is often used on New Zealand farms. For example when a dairy farmer is collecting eggs from high producing cows for transplanting into donor cows, or a sheep farmer wants to increase his lambing percentage by producing more twins or multiples
Females are injected with FSH hormone which causes the ovaries to shed a greater number of eggs.

Name of Hormone Function of Hormone
FSH

Triggers the testis to produce sperm
Testosterone

Responsible for the male characteristics
The sheep breeding system is brought about by changes in the length of the day. In
Autumn when day light hours are decreasing the amount of sunlight shining on the eyes and faces of the sheep causes a small gland called the Pituitary Gland to produce hormones called Gonadotrophic hormones that stimulate the male and female reproductive organs.
This process occurs in a cycle with egg production and egg release following on from a highly specialised process that prepares the body for pregnancy.
Use resource number 3B to help explain the following sequence of events.
The egg or ova lie in small sacs (bags) called Follicles. The follicles are very small when immature and enlarge as they develop.
When the follicles have grown to the full size they break through (rupture) the skin, and set the egg free to travel down the fallopian tube and into the Uterus. The egg breaking free is called ovulation. While the follicle is rupturing and the egg is being freed the ovary produces a hormone called Oestrogen. Oestrogen causes the ewe to come on heat and seek a mate. It also stimulates the growth of the Uterus and Udder.
The ruptured follicle heals over and begins to produce its own hormone called progesterone. The follicle is now given a special name called the Corpus Luteum.
Progesterone acts to prevent another heat taking place this gives the egg time to be fertilised. If the egg is not fertilised the Ovary stops making Progesterone and the ewe has another heat period in about 2 days time.
If the egg is fertilised the ovary continues to produce progesterone which stops all further heat periods until after the lamb is born.
This progression from periods of quiet to periods of heat is called the Oestrus Cycle.
Give students a copy of the flow chart Resource (3C) and go over it verbally, so that students have a good understanding of it. Students carry out activity 3 C and make a human flow chart.

SUMMARY
Key functions of the main hormones.
Function of FSH is to tell the sex organs (testes and ovaries) to start working
Function of testosterone is to initiate the male reproductive system, secondary male characteristics at puberty, initiates sperm production
Function of oestrogen is initiate the female reproduction system, secondary female characteristics at puberty, initiates ovulation
Function of progesterone is to initiate and maintain the pregnancy