Challenges in feeding the modern sow

As little as 25 years ago, it was relatively easy to feed replacement females in a commercial piggery. Gilts could be reared to first service on a normal finisher (or baconer) diet and only a single diet was fed to dry sows and lactating sows. Whilst the dry sow diet has not changed dramatically over the last twenty years, rearing the modern gilt and catering for the demand on the lactating sow has required the development of special feeds for these animals.

The challenge in feeding gilts and sows is largely influenced by genotype of the animals, general environment, management and disease status of the herd under consideration. The Nutritionist is required to design feeds that give optimum performance for a given set of these influences and often decisions need to be made on subjective assessments.

Examples of this include judgements of levels of management and assessment of herds with mixed genetics. Fairly good information exists on nutrient requirements for changes in environmental temperature and humidity, but there is little consensus on the nutrient partitioning in animals that need to mount an immune response to a disease challenge. All the feeds then need to be designed to give maximum profitability per piglet weaned per sow per year.


Gilt Rearing

Modern gilt rearing (or developer) diets are high in energy (13.5 MJ/kg DE & total lysine:DE of 0.62) with typical digestible lysine values of 6.9 g/kg in diets on an as-fed basis. The ideal amino acid ratios are based on growing pigs and the crude protein of these diets is usually around 180 g/kg.

Most recommendations advocate an ad libitum feeding schedule up to ovulation and subsequent mating, but genotype must be considered when using such a strategy and if gilts become too fat, either a reduction in diet density or physical feed restriction may be necessary.

Years of selection for low fat levels in pigs, improved growth rates and better feed conversion has reduced feed intakes and compromised the breeding ability of sows. However, feeding to maximum protein gain improves ovulation rate in gilts and the suggested optimum criteria for age and body composition at sexual maturity are:

• 220 to 230 days of age

• 130 to 140 kg's body mass

• 18 to 20 mm P2 backfat

• Mate at the 2nd or 3rd oestrus

For practical purposes, monitor the P2 and body weight of gilts to achieve the best results on your farm (table 1).

Control feed to influence lean and fat growth in the body (2.5 to 4.5 kg feed/gilt per day) and flush feed (i.e. feed ad libitum) for two weeks prior to mating to achieve optimum ovulation rate.


The dry sow

The early developing embryo requires surprisingly low levels of nutrients relative to the sow's requirements for maintenance and growth. A target maternal weight gain of 20 to 25 kg's during pregnancy for mature sows, and 40 to 50 kg's in the hyperprolific first parity sow is suggested.

Energy intake during gestation remains the most important nutrient in monitoring maternal weight change. Changes in P2 in response to energy intake are less clear although there is usually an increase in P2 during early to midgestation and then a decrease during the final stages of pregnancy. Embryo survival (ES) is a complex phenomenon and the critical time is during the first 21 days of pregnancy. High feed intake (energy levels) during this time can be detrimental to embryo survival and ultimate litter size (table 2).

Typical dry sow diets are 13.0 MJ/kg DE, with crude protein of 140 g/kg and a Lysine:DE of 0.5. Depending on environmental temperature and humidity, feeding levels from 2.0 kg's to 2.5 kg's per sow per day are recommended and increasing feeding levels 2 to 3 weeks pre-partum may have a positive influence on piglet birth weight. Several reviews suggest that piglet weight increases by about 8 g for each 1 MJ/kg increase in DE per day up to a maximum piglet birthweight of around 1.4 kg's.











The lactating sow

By day 11 of lactation, the average sow cannot produce sufficient milk to meet all the nutrient requirements of a 10 pig litter and in the absence of creep feed to piglets, the demand on the sow is enormous. Often, feed intake in lactating sows is the limiting factor and if this is exacerbated by diets that are low in energy and/or protein, it has been shown that there would be adverse effects on return to oestrus, ovulation and embryo survival.

It has been calculated that for a 175 kg sow, a 25% reduction of dietary energy and protein intake below requirements over a 28 day lactation period results in the mobilisation of 4.4 kg's protein and as much as 11.6 kg's of fat from maternal tissues. This is associated with a concomitant liveweight loss of 31 kg's. The higher the relative body weight loss of the animal (i.e. body weight loss as a proportion of body weight), the longer the period between weaning and mating.

Typical lactating rations are high in energy and protein with a DE value of 13.8 MJ/kg, lysine:DE of 0.64 and a protein value of 190 g/kg on an as-fed basis. High, nutrient-dense diets are often low in fibre and recent work suggests that use of purified fibres reduces incidence of MMA (mastitis, metritis, agalactia) in lactating sow rations. Modern feeding strategy encourages feed intakes to be as high as possible after 7 to 10 days post partum and ideal conditions for the sow to achieve this are:

• Adequate supply of water - 2 litres/minute (sow consumes 40 litres/day)

• Ideal environmental temperature of 18°C

• Highly palatable, nutrient dense feed

• Feed often - At least three times per day if possible

• Soaking feed can improve intakes

• Follow a set feeding curve

• Never over-feed during pregnancy

Several lactation feeding systems have been proposed and figure 1 shows a suggested, practical feed intake. The Nottingham System is based on 1.8 kg's feed for the sow and 0.5 kg's for each piglet suckled. Food is introduced at a rate of 2 kg's on day one and increased by 0.5 kg's per day until maximum has been achieved. The Stotfold Feeding Strategy developed by Baker, based on the work of Close suggests feeding a standard scale to 10 days post partum.

Sows are offered 2.5 kg's on day 1, increasing by 0.5 kg's to 7 kg's on day 10 and thereafter fed individually to litter size and piglet weight.

References

Challinor, C.M., Dams, G., Edwards, B., Close, W.H. (1996) The effect of body condition of gilts at first mating on long-term sow productivity. Animal Science, 62, 660.

Hughes, P.E. (1989) Nutrition - Reproduction, Interactions in the breeding sow. Manipulating Pig Production II, 277-280.

Moughan, P.J., Fuller, M.F., (2003) Modelling amino acid metabolism and the estimation of amino acid requirements. Amino Acids in Animal Nutrition, 2nd Editition, 11, 187-202.

Varley, M.A., (2004) Feeding the sow. Proceedings from Kanhym pig conference, Johannesburg, South Africa.

Author: Peter Chrystal
NRM, New Zealand

The previous article is a special collaboration from AFMA South Africa (Animal Feed Manufacturers Association) and their magazine AFMA Matrix. We thank AFMA for their continuous, kind support!