When you have read through this page try the comprehension exercise on oestrus in sheep.
Remember that oestrus in most animals is seasonal. Remember also that many animals (including sheep and pigs) will produce more than one egg at once. Males may detect which females are in oestrous (in 'heat') by their sensitivity to pheromones.
Dancing in pigs is not a reliable sign of oestrus.
http://www.unipr.it/~fderensi/rip_pig/rip_pig.htm for more information about oestrus in pigs
http://sps.nus.edu.sg/~seohkahh/pig/cycle.html tells you all you need to know about artificial insemination in pigs and has some cute photographs of pigs.
Oestrus in a farm animal
(Text adapted from material provided by AQA)
Welsh sheep being brought down off the Kerry hills in spring for lambing. Sheep only have oestrus cycles during one season of the year, autumn.
Oestrus: the distinctive pattern of behaviour displayed by some mammals around the time of ovulation.
Many female mammals live solitary lives and are only fertile for a short period of time. If they are to conceive, it is essential that they advertise their reproductive condition to potential mates. This is the purpose of oestrus. Oestrus may involve: ·
changes in the normal behaviour pattern. Cattle, for example, are generally restless, walk about more and feed less. ·
the intense coloration and swelling of patches of skin such as those on the chest and around the reproductive area in some monkeys. ·
the production of chemical signals or pheromones such those produced by a female dog.
Detecting Oestrus in farm animals
Generally speaking, farmers do not want to keep large numbers of male animals. Not only can they be very aggressive and difficult to handle but they are not as productive as females as they do not produce any young. A farmer will therefore either keep as few males as possible or rely on artificial insemination. In either case, it is important that the precise timing of oestrus is known as this is the only time in the reproductive cycle when mating or artificial insemination is likely to result in conception.
Pigs
Female pigs in oestrus may show the following signs:
· a red, swollen vulva
· clear mucous produced from the vagina
· they may sniff the genital areas of other pigs in the pen · make a characteristic grunt or "roar".
· show what is called the "standing reflex". They stand rigid when pressure is applied to the lower back.
The most reliable sign of oestrus is the standing reflex. Farmers need to know when a sow is in oestrus so that she can either be artificially inseminated or the male pig put in with her.
The intensity of the reflex can be increased by the presence of a male pig or boar, or by using a spray of 'boar odour' . This spray has the pheromones made by male pigs (N.B. pheromone is a chemical produced by one animal that effects the behaviour of animals).