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(167) To maintain a viable pregnancy requires constant daylight length. Ideally this should be 12-16 hours per day. Light intensity experienced by the sow can be affected by a number of environmental inadequacies, for example, poor lighting in the first place, followed by fly faeces and dust on lamps gradually reducing the availability of light. High walls surrounding animals, or automatic feeders in front of sows producing shadows. A simple tip here is to make sure that you can read a newspaper in the darkest parts of the building at sow eye level. If not, then problems may start. Painting the roofs and walls white to increase the reflection of light is one way of improving the environment and on a number of occasions abortions have ceased after such simple improvements.

What you need to know about light
Gilts exposed to 14-18 hours light:
- Reach puberty earlier.
- They are a lighter weight at puberty.
- There is no difference in ovulation rate.
- Both gilts and the boar are sexually more active.

In lactation:
- 16 hours of light increases weaning weights.
- There is no effect on numbers weaned.
- Milk yield is increased.
- 16 hours is recommended at a 360 lux level.

  • The weaning to service interval is reduced if 16 hours of light is given after weaning with a continuous light intensity of 250 lux
  • Sows are on heat longer when exposed to more light.
  • Light has no effect on litter size but absorption of embryo and foetuses may occur in poor lighting during early pregnancy.
  • During the dry period a minimum of 220 lux is required for 14 hours a day.
  • Fluorescent light is nearer to natural light than incandescent lighting.
  • In a building 2.4m high and 4.9m wide a continuous row of fluorescent lights is necessary. As a guide 150 watts is required for every 1.5m.
  • The light must be placed over the sow's heads.
  • Make sure sows are not exposed to decreasing daylight lengths.
  • Provided 8-10 hours of darkness after a period of light.
Anoestrus in the sow
The act of weaning the sow or even removing just 3-4 piglets increases the pressure of milk in the mammary gland and this causes the udder or relevant gland to stop production. This mechanism causes the hormones that promote milk production to cease, thus allowing the development of the follicle stimulating hormone and luteinising hormones, to bring the sow back into oestrus or heat. Provided the sow comes into heat and is served within 6 or 7 days of weaning then she is likely to have a high conception rate, good fertility and litter size. The length of the weaning to service interval is now recognised as being associated with reproductive efficiency and some sows mated 7 and 14 days after weaning are sub fertile with poor litter size and farrowing rates. A high proportion of single matings also occur at this time. If you have a reproductive problem associated with poor litter size and high numbers of repeat matings check the average weaning to first service interval across the herd (5.5 days is ideal) and analyse the results by parity or litter number. The farrowing rate loss in the sub fertile period may be as much as 10% and litter size may drop by up to a pig a litter. The first litter gilt is often a major problem in this respect and the delay in the weaning to service interval can compromise litter size by up to three pigs per litter. If the weaning to service interval is extended and associated with lowered fertility always check the newly weaned gilt, then follow through the checklist below to identify those factors that may be important on your farm.

Anoestrus in the sow - A checklist:

  • Identify from records whether this relates to a particular parity.
  • Make sure during lactation that the sow does not lose body weight if possible and certainly no more than 15kg. Weigh sows after farrowing and again at weaning to check this. Try to achieve weight gain.
  • The most common cause of anoestrus or delayed oestrus is loss of body condition, particularly in the first two - three weeks of lactation. Feed intake here drives the weaning to service interval and subsequent fertility and stimulates the primordial follicles to determine ovulation rate into the next litter.
  • Feed the sow from three days post farrowing to appetite, with a high energy diet, particularly if she is of a lean genotype.
  • The diet should contain at least 14.2 MJ DE/kg, 18% protein and 1.1 lysine. A good grower type diet could be used.
  • Make sure that overfeeding in lactation does not cause inappetence.
  • Make sure that there is easy access to water, with a nipple flow of at least 2 litres per minute. Sows will drink up to 40 litres a day. Test the nipple drinkers and see how long it would take the sow to stand and drink. She could stand for 2 hours per day! Give the sow 4.5 litres twice daily into her trough.
  • Always remove uneaten feed from the trough because in a warm farrowing house fermentation takes place within 3-4 hours.
  • If there is a second litter problem, feed a weaner ration to the lactating gilts as half the daily total intake.
  • If the sow is correctly fed and managed during lactation, she should come into heat in the fertile period.
  • Are sows comfortable in the farrowing house? A too low temperature will cause the sow to lose weight in spite of possibly eating slightly more. Experience shows that there are no advantages to cold farrowing houses. Aim for around 20ºC (68-70ºF).
  • Avoid any environmental factors that will cause the sow to lose weight, for example wet farrowing pens, high airflow and evaporative cooling, water shortage and inappetence associated with disease and spoiled feed.
  • Avoid weaning more than 10% of piglets from the sow during lactation because this may stimulate oestrus and poor ovulation with delayed oestrus again at weaning and sub-fertility. Feed the sow from weaning to point of service ad libitum with the lactator diet.
  • Do not mix first litter females with older sows if group housing is practised.
  • If group housing is practised, introduce a large quiet boar into the group on the day of weaning.
  • Where sows are weaned into stalls, maintain a temperature of 20ºC (70ºF), provide plenty of close nose contact with boars, check there is no evidence of mastitis at weaning time and provide a dry environment with low air flow. Assess the comfort of the sow, by her looks and posture.
  • In loose-housed sows allow at least 3.4 sq.m per sow at mixing and from weaning to service.
  • If sows are exposed to temperatures above 24ºC (75ºF) feed intake becomes compromised. For continual temperatures above 26ºC(79ºF) it is necessary to adopt drip cooling or other evaporative cooling techniques.
  • If you think a gilt or sow is on heat and she will not stand always try another boar but leave a gap of half an hour before doing so, because gilts in particular may only show a high, intense oestrus for 10-15 minute periods
  • If litter size is poor in the first litter gilt it may be worth while to skip or miss the first heat after weaning and serve on the next one, particularly if such animals are coming into heat in the sub fertile period.

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