Do high fibre diets affect feeding motivation in pregnant sows?

Tuesday, February 5, 2013

Danish researchers tested four different fibre diets on 60 pregnant sows and at different intervals with inconclusive results

by JANICE MURPHY

In order to avoid excessive weight gain during gestation, the swine industry has relied heavily on a protocol that involves feeding dry sows a restricted, concentrated diet. Unfortunately, this feeding regimen is often associated with negative behaviours relating to hunger and boredom.   

These stereotypic behaviours can include bar biting, sham chewing, or nosing or licking the floor or feeder when feed is absent. Producers and researchers alike have tried different remedies, including various sources and levels of dietary fibre as well as increasing the frequency of feedings, in order to reduce hunger pangs and minimize these stereotypic behaviours.

Previous research has indicated that spreading the daily feed allowance over two feedings (morning and afternoon), rather than just one feeding in the morning, tended to reduce feeding motivation in the afternoon. Feeding a diet that is high in fibre in combination with feeding twice daily may stabilize the energy supply, resulting in decreased feeding motivation over a 24-hour period.

Researchers at Aarhus University in Denmark recently investigated the effect of diets high in fibre, and once- versus twice-daily feeding, on feeding motivation and circulating levels of plasma metabolites in restricted-fed sows during early- to mid-gestation (up to day 70 of gestation).

The study involved 60 pregnant sows, with an average body weight of 170 kilograms, allocated to one of five diets. The first four diets were restricted to approximately 35 MJ of metabolizable energy (ME) per day:

1)    a barley and wheat control diet;
2)    a fibre diet formulated to contain 35 per cent dietary fibre (DF) by including pectin residue;
3)    a fibre diet formulated to contain 35 per cent DF by including potato pulp;
4)    a fibre diet formulated to contain 35 per cent DF by including sugar beet pulp;
5)    a mixture including an equal proportion of the three fibre diets, with ad libitum access for one hour intervals starting at 3:00 a.m., 6:00 a.m., 11:00 a.m., 3:00 p.m., 6:00 p.m. and 11:00 p.m. Sows were fed a daily ration of 2.6 kilograms for the control, potato and sugar beet diets, and three kilograms for the pectin residue diet. Table 1 summarizes the resulting dietary fibre composition of the diets.

The experiment ran for two periods of four weeks each. Restricted-fed sows were fed once daily (8:00 a.m.) during the first period and twice daily (8:00 a.m. and 3:00 p.m.) during the second period, or vice versa. Sows fed semi-ad libitum had access to feed six times a day throughout. In each period, feeding motivation was assessed and blood samples were taken at 9:00 a.m., 12:00 p.m., 7:00 p.m. and 7:00 a.m, corresponding to one, four, 11, and 23 hours after feeding for restricted sows fed once daily.

Table 2 summarizes the average body weight gain, energy and fibre intake throughout the experiment (from week one after mating until day 70 of gestation). The average body weight gain throughout the experiment was significantly lower for sows on the potato diet and significantly higher for sows fed semi-ad libitum, while the remaining diets yielded intermediate and almost identical results.

Despite the different diet ingredients, feeding motivation did not differ between the four restricted diets at any of the time points after feeding; however, sows that were fed semi-ad libitum exhibited significantly lower feeding motivation. Among restricted-fed sows, feeding twice daily resulted in significantly decreased feeding motivation at 7:00 p.m. and 7:00 a.m. compared with feeding once daily. This was not true, however, at 9:00 a.m. and 12:00 p.m., suggesting that feeding twice daily provided some degree of satiety during the night compared with feeding once a day.

Among restricted-fed sows, plasma concentrations of short-chain fatty acids (SCFA) were significantly greater in sows fed high-fibre diets compared with the control. Non-esterified fatty acid (NEFA) was lowest in sows on the control diet and greatest in sows on the potato diet, whereas sows on the pectin and sugar beet diets were intermediate. This emphasizes that fibre diets, and especially the potato diet, contributed more energy for fibre fermentation. Providing starch instead of fibre gives the sows a relatively constant supply of energy for the gastrointestinal tract to process over a 24-hour period, even when they are only fed once daily. This was also supported by the observation that there was less diurnal variation in plasma glucose in sows on high-fibre diets in this experiment.

Unfortunately, the researchers realized too late that the high-fibre diets did not all contain the intended level of 35 per cent dietary fibre, making it difficult to determine whether or not the observed differences in plasma metabolites related to the fibre type or the fibre level. The potato diet ended up having higher fibre content than originally intended. The sows on this diet had a lower feed intake and, as a result, gained less weight than sows on the remaining restricted-fed diets.

The researchers did note that, although they gained less weight, sows on the potato diet did not have a greater feeding motivation, suggesting that the potato diet may contain some unknown compound with the ability to satiate the appetite. Although further research is required in order to identify the specific mechanism involved, this may prove to be an important finding.

Characteristically, the fibre diets exhibited greater water binding capacity than the control; this may have translated into delayed gastric emptying compared with the control diet. The researchers expected that this would result in a reduced feeding motivation of restricted-fed sows on fibre diets.

However, there was no effect of diet on feeding motivation in restricted-fed sows; only semi-ad libitum feeding reduced feeding motivation. Evidently, the metabolic, physico-chemical and gastrointestinal effects were not sufficient to reduce feeding motivation in restricted-fed sows.

Feeding frequency had a noticeable effect on feeding motivation at 7:00 p.m., and a lesser effect at 7:00 a.m. These observations correspond to 11 and 23 hours after the morning feeding and four and 16 hours after the afternoon feeding (if sows were fed twice daily). As a result, sows that were fed only once each day were more motivated to eat in the evening and the next morning than the sows that were fed twice.

Based on these results, the researchers concluded that the problem of hunger in pregnant sows may not be solved unless the quantity of fibre is increased above the amount applied in this experiment, or unless additional sources of fibre, such as roughage or straw, are provided ad libitum. BP

Source: M. B. Jensen, L. J. Pedersen, P. K. Theil, C. C. Yde and K. E. Bach Knudsen. 2012. Feeding motivation and plasma metabolites in pregnant sows fed diets rich in dietary fiber either once or twice daily. J. Anim. Sci. 2012, 90:1910-1919.

Janice Murphy is a former Ontario agriculture ministry swine nutritionist who now lives and works in Prince Edward Island.