TECHNICAL ARTICLES Swine

Heat Spotting In Pigs

No-one needs reminding that sow productivity contributes significantly to profit margins and that an important component of such productivity is the farrowing index or litters farrowed per sow per year. Most units aim to achieve an average of 2.2 litters or better but for some this figure is seldom achieved.

The index is determined by the gestation length (constant), the period of lactation (flexible) and the interval from weaning to effective service (highly variable). Better understanding of the oestrus cycle and control mechanisms could benefit many when inducing and detecting oestrus in the gilt and sow.

When the subject of reproduction is discussed it is often stated that ‘Sex is all in the mind’. In part this statement is true because three sections of the brain, namely the higher brain centre, hypothalamus and anterior pituitary gland together with the reproductive tract and mammary gland in the female are involved in the reproductive process.

Portions of the higher brain centre act as sensory organs and conduct information on the immediate environment to other centres for monitoring and co-ordination.

The relevant information is further relayed to the hypothalamus where releasing or inhibitory hormones feed into the anterior pituitary gland situated immediately below it. These hormones control the production, storage and secretion of a number of reproductive and metabolic hormones from this rather small gland. Only three of these assist with the control of reproduction.

Follicle stimulating hormone (FSH) and luteinising hormone (LH) target the ovaries via the blood stream stimulating the growth of follicles or blister like structures containing the ova or eggs and subsequently inducing ovulation during which time the mature eggs are released for fertilisation.

The third hormone prolactin is responsible for stimulating and maintaining lactation.

As the follicles attain their mature size just prior to ovulation, increasing amounts of oestrogens are secreted. These act on the reproductive tract in preparation for mating and subsequent pregnancy. Oestrogen is also primarily responsible for the behavioural and outward physical signs observed during oestrus, ie reddening and swelling of the vulva, discharge of mucous from the tract, and the ability of the boar or stockperson to elicit the ‘standing reflex’. Other signs include restlessness, lowered appetite, mounting behaviour and the periodic ‘honking’ noise.

The feedback systems between the ovaries, uterus, hypothalamus and pituitary gland govern a cycle of events that takes 18-21 days. This is known as the oestrus cycle. If conception occurs this cyclic pattern is interrupted and pregnancy is maintained for approximately 114 days. Removal of the sucking stimulus at weaning triggers a new sequence of events.

The inhibitory effect of prolactin is removed when lactation ceases and FSH and LH then initiate a new cycle as they stimulate ovarian activity. For prepubertal gilts, age and the external environment in combination with feedback systems controls the commencement of oestrus activity.

So, we are now either confused or understand a little about the physiology of reproduction in the female pig. We are not endocrinologists (hormone specialists) though some of us try to take on this role when in desperation we use PG600 (combination of FSH and LH) to stimulate the onset of oestrus.

Most of us are ordinary people with some knowledge of animal husbandry and stockmanship. For some reason we like the pig as an animal but even more so we would like to improve the reproductive performance of the sow without having to go back to school. So instead of taxing our brains let’s allow the animals brains to work for us instead.

As discussed earlier, the trigger for most of the functions is provision of an ideal external environment. The smell (boar older than 10 months) sound, sight and touch of a boar daily, reduction in levels of stress, presence of other females in oestrus, adequate nutrition, light and care all are received by the higher centre of the brain to enhance oestrus activity and ovulation. In other words by modifying the animal’s immediate surroundings we can promote oestrus activity in the gilt and sow. In an endeavour to create what we believe to be the right environment for the breeding pig we sometimes overlook nature’s intentions.

If we don’t get the sow to concieve, lets consider the financial implication

21 day oestrus x 2.2kg of feed per day = 46.2 kg of feed wasted

46.2 kg of feed x R 1.33 = R 61.45, money lost per sow in one missed oestrus cycle.

Date published: 2003-10-20

Author:
Jose Smith

Publication: N/A