Nutrition: Bulking up with wheat straw improves sow and litter performance

Tuesday, June 2, 2009

Research from eight U.S. experimental stations indicates that sows fed a wheat straw diet farrowed and weaned more pigs per litter and had greater litter birth and weaning weights than sows on a control diet

by JANICE MURPHY

It is generally accepted that restricting feed intake during gestation is necessary to limit excessive weight gain and fat deposition, stimulate lactation feed intake and increase overall sow productivity.

However, limit feeding does not give the sow the chance to feel full or satisfied after eating and can lead to frustration. Given the opportunity, a sow would voluntarily eat almost twice the amount of feed she is offered. As a result, dry sows are excellent candidates for high-fibre diets since they have the capacity to handle less energy-dense diets and, unlike growing pigs, have the ability to derive more energy from fibrous feed ingredients.

A research report was recently published from the North Central Region of the United States, from eight experimental stations with a total of 320 sows. The aim of the experiment was to evaluate the response of sows and litters when 13.35 per cent ground wheat straw was added to a corn-soybean meal gestation diet for three successive reproductive (gestation-lactation) cycles compared with sows fed a standard control diet without straw.

To prepare the wheat straw for inclusion, it was ground in a hammer mill and passed through a screen with 1.25-centimetre openings, yielding a particle size of approximately six to eight millimetres. The specific composition of the diets is outlined in Table 1.

A total of 708 litters farrowed over three reproductive cycles. Intake of the basal gestation diet averaged 1.95 kilograms daily for both treatments, with an additional 0.30 kilograms of straw daily for sows fed the diet with ground wheat straw, for a total intake of 2.25 kilograms per day.

The gestation diets were fed once each morning. For the purpose of the experiment, it was assumed that the wheat straw did not contribute any nutrients to the wheat straw ration. During lactation, all sows on both treatments were fed ad libitum the standard lactation diet used at each experimental station.

The results (summarized in Table 2) indicate that, when averaged over the three reproductive cycles, sows fed the diet with wheat straw farrowed and weaned 0.51 more pigs per litter, and had total litter birth and weaning weights that were 0.87 and 3.59 kilograms heavier, respectively, than sows fed the control diet. Daily intake of the lactation diet increased with increasing reproductive cycle, and was significantly greater for sows fed the diet with wheat straw than for sows fed the control diet during each reproductive cycle and overall.

Sow bodyweight and backfat thickness at breeding increased with increasing reproductive cycle. In addition, sow bodyweight and backfat thickness at weaning were not different for the two treatment groups while being fed the same lactation diet, suggesting that the greater lactation diet intake by sows fed the wheat straw diet might have resulted in increased metabolism to support a higher level of milk production in that treatment group.

The weaning-to-estrus interval decreased numerically with increasing reproductive cycle, but the difference was not statistically significant. As for the rest of the parameters measured in the experimental protocol, there were no significant differences between treatments for sow parity at the beginning of the experiment, lactation length, sow bodyweight (at breeding, day 109 of gestation, farrowing, or weaning), or sow backfat thickness (at breeding, day 109 of gestation, or weaning).

Although not directly measured or reported in this particular study, previous research has suggested that the addition of ground or chopped straw to the gestation diet translates into greater gut fill, as well as more satisfied and less excitable sows that spend more time lying down after consuming the daily meal compared with sows fed a conventional diet.

Other experiments have also shown that feeding high-fibre diets to dry sows reduces stereotypic behaviours, prolongs the feeling of satisfaction, improves sow welfare, and stabilizes blood glucose and insulin levels. In an effort to allow foraging behaviour, providing loose straw in the gestation stall at a rate of 1.0 to 1.5 kilograms per sow per day has also shown similar benefits.

Wheat and barley straw have very low energy values for sows compared with other fibrous feed ingredients, such as sugar beet pulp and wheat bran. However, the energy values for straw increase slightly for sows housed in a cold environment compared with sows housed at their thermoneutral comfort level. Compared to growing pigs, sows have a greater ability to digest and use fibrous feeds, since the hindgut contributes more to their total digestible energy intake than growing animals.

In this experiment, when the sows on both treatments were fed the same standard lactation diet ad libitum at each station, the researchers estimated that the sows fed the control diet consumed approximately 18.5 Mcal of metabolizable energy (ME) per day compared to 19.8 Mcal ME per day for the diet with wheat straw (an average of 5.62 or 5.99 kilograms per day, respectively, with 3.30 Mcal of ME per kilogram of diet). For reference, the daily intake of ME during lactation for both treatment groups exceeded the National Research Council's estimated requirement (NRC, 1998).

As long as daily intake of the basal gestation diet was equalized for both treatments, adding 13.35 per cent ground wheat straw to the gestation diet resulted in improved sow and litter performance, increasing not only litter size but also total litter weight at birth and weaning compared with control sows and litters.

The daily lactation intake of ME by sows previously fed the gestation diet with wheat straw was approximately seven per cent greater than that of sows fed the control diet. The bulkiness of the high-fibre diets required greater daily intakes of those diets during gestation to equalize nutrient intake compared with sows fed the control diets. That appears to have helped those sows adapt to a higher level of feed and nutrient intake during lactation, which ultimately enhanced sow and litter performance.

Not to be ignored is the fact that greater feed intake during lactation is also associated with a longer reproductive life. BP

Source: T. L. Veum, J. D. Crenshaw, T. D. Crenshaw, G. L. Cromwell, R. A. Easter, R. C. Ewan, J. L. Nelssen, E. R. Miller, J. E. Pettigrew, M. R. Ellersieck and the North Central Region-42 Committee On Swine Nutrition. 2009. The addition of ground wheat straw as a fibre source in the gestation diet of sows and the effect on sow and litter performance for three successive parities. J. Anim Sci. 87: 1003-1012. 

Janice Murphy is a former swine nutritionist with the Ontario Ministry of Agriculture, Food and Rural Affairs who now lives and works in Prince Edward Island.