Pigs

Gilt management to improve sow output

By Gerard McCutcheon, Oak Park

14 June 08: Gilts are an investment in the future of your business. When sows are replaced, we should strive to improve herd performance (whether the gilts are home reared or purchased). However, gilt management is not always given the attention it deserves.

In 1992, the Danish pig industry started to include litter size as one of its breeding goals. Since then, Danish litter size has improved by 2.7 pigs per litter. In 1992, the average Irish litter size was 11.5 (including born dead). By 2006, the figure was 12.2 (as per PigSys herds) - a rise of only 0.7 pigs/litter.

We have fallen behind our European counterparts even though Ireland was the European leader in sow productivity in the early 1990s.

This article looks at some areas of management that producers should review in order to improve sow output. This may involve some changes in routine but should result in increased numbers of pigs produced per sow per year.

Sow Replacement

In 2006, the average sow replacement rate was 49% (Teagasc PigSys). On herds with an annual replacement rate of 45% and producing 2.3 litters/sow/year, gilt litters constitute almost 20% of all farrowings. This can have a significant effect on the overall herd output.

If gilts produce small litters, the overall number born alive for the herd is reduced. If the sow replacement rate is high, the overall litter size is further reduced. The aim should be to have good-sized litters from gilts. It is possible to improve the number born with more prolific gilts being brought into the herd (i.e. purchasing gilts) or by using more prolific lines if you are breeding your own.

There are advantages to purchasing gilts (from the genetic companies) but the risk to herd health has to be considered. Purchased gilts (at 90 to 100kg liveweight) should be kept in isolation (400m minimum from the main herd) for a minimum of four weeks after arrival. Controlled contact with culled sows from the main sow herd should occur for the next four weeks, still in the isolation area.

Gilts should be purchased from a single source of known health status, which is similar to, or higher, than your herd. Request health reports from your breeding stock supplier on a routine basis. A suitable vaccination programme should be devised with your veterinary specialist.

Onset of puberty and gilt stimulation

The onset of puberty is one important factor in the potential breeding performance through the sow's lifetime. Puberty can occur over a wide range of ages (131-201 days), weights (80-155kg) and back/fat levels (9.1mm to 34.8mm). There are many advantages to early puberty:

• Formation of gilt pools to be stimulated and cycle together
• Number of non-productive days (NPD) at herd entry is reduced
• More gilts can be bred at third estrus without increasing NPD
• The greatest advantage to early onset of puberty may be that it allows identification of the gilts with innate ability to reach puberty early in life and these are more prolific
• Because lean growth rate slows after gilts reach puberty, early onset of puberty may help to reduce ultimate mature size. Large mature size is becoming more of a cost and a problem so this may be a consideration.

There is considerable evidence showing that when gilts reach puberty early they are more fertile, and, therefore, early response to a boar is a good predictor of lifetime reproductive performance. This leads to fewer empty days and a longer breeding life i.e. "the earlier cycling female is the most prolific female throughout her lifetime''.

Some units suffer problems trying to stimulate gilts to cycle.

Conclusion

The management of sow output is greatly affected by the fertility of the raw breeding stock. Do you have the best potential in your gilts? Are they being managed properly after they are selected or purchased?

Table 1: Gilt litters as a percentage of total farrowings depending on annual sow replacement rate

Annual sow replacement rate %	Gilt litters as % of total litters
35%	15
45%	20
55%	24

Keypoints

• Until gilts reach about 120kg liveweight, they should be reared in isolation from the boar. They should then be moved to a comfortable pen within sight, smell and sound of a mature boar.
• A vasectomised boar is ideal to stimulate gilts. The main chemical substances to stimulate oestrous are pheromones found particularly in the boar's saliva and are more powerful in older boars.
• Provide direct physical contact with boars. Facilities should allow gilts to have full contact for 20 to 60 minutes per day depending on group size.
• Provide 14 to 16 hours of continuous light per day and should be stocked with about 1.4 square meter (15sq. ft) floor space. The intensity of the light is important. It should be 300 lux - if you have a light metre. In the absence of a light metre, the general rule is that you should be able to read a newspaper, at gilt level, in the darkest part of the building. Light intensity is reduced by fly faeces or dust on light covers, and by dark walls or roofs. Paint the roofs and walls white and clean the light covers regularly.
• Gilts should be served on their second or third heat. Ideally, they will be 140kg liveweight and at least 225 days. Ideally, they should have a backfat cover of 18mm (at the P2). This is seldom achieved nowadays with lean stock.
• Gilts that are slow to cycle should be culled.
• Flush gilts with a plentiful supply of feed for two weeks before service.