By Atta Agyekum and Denise Beaulieu, University of Saskatchewan
Feeding fiber-rich diets to gestating sows may reduce the behavioral problems associated with restricted feeding and improve sow and litter performance during lactation. However, these beneficial responses are not consistently observed. This probably related to differences in dietary inclusion rates and composition of the fiber, specifically the proportion of soluble to insoluble fiber.

For example, sows offered diets rich in soluble fiber had an extended feeding time, delayed glucose and nutrient absorption, spent less time standing (Ramonet et al., 2000; de Leeuw et al., 2004) and showed reduced aggression (Danielsen et al., 2001) compared to a diet based on a less soluble mixed fiber. However, many of the fiber-rich ingredients available for inclusion in the diet of a gestating sow are high in insoluble fiber. There is work indicating that severe hydrothermal processing of fiber sources increases the solubility and improves the utilization of insoluble of fiber in pigs (de Vries et al. 2012).

The overall objective of this study was to determine if feeding heat-treated straw to sows in late-gestation would provide beneficial effects. We were especially interested in potential benefits to the piglets. 

Experimental approach
This experiment was conducted at the Prairie Swine Centre in Saskatchewan, and utilized 150 sows (86 ± 2 days of gestation; 236.7 ± 32.4 kilograms bodyweight; parity 0-5), 10 sows per week. Gestating sows were maintained in a free-access stall system (Egebjerg International, Denmark) with 32 individual walk-in/lock-in stalls per group pen. Each stall (66 cm x 210 cm) is equipped with a feeder and nipple drinker. Sows were fed individually in stalls once per day, but were allowed to leave, with sows from various treatments mixed within the group.

On Day 110 of gestation, sows were moved from the gestation facility into a farrowing room containing 16 farrowing crates (183 x 244 cm each). Each crate was equipped with an individual bowl feeder and water nipple at the front.

The experiment used five dietary treatments: a standard gestation diet (Control) or the Control supplemented with processed or unprocessed oat or wheat straw at 10% of the daily feed allowance. The straw was ground using a tub grinder followed by further grinding through ¼-inch screen using a hammer mill. The processed straws were produced by hydraulically compressing straw through a briquette maker (Biomass Briquette Systems LLC, Chico, Calif.) at a temperature of about 80 C.

We intended to measure indicators of behavior, such as scratches and marks due to aggression, but this was terminated after the first couple of blocks because there was no indication of fighting with any of the sows. However, as an indicator of treatment effect on satiety, feeding rate was estimated at 1300 hour on Day 18 (about Day 100 of gestation) by measuring the time required to consume 200 grams of the standard gestation diet offered to each sow at six hours post feeding. Blood samples were obtained on Day 100 of gestation at -5 (preprandial) and at 30, 60, 90, 120, 180, 240, 300, and 360 minutes post feeding from a catheter that had been inserted into an ear vein the previous day. Upon weaning, three piglets per litter with the bodyweight closest to the average were selected, placed on standard diets, and followed from weaning to market.

The statistical analysis used two models. The first model assumed a randomized complete block design with five treatments, while the second model also used the RCBD but with four treatments arranged as a 2 × 2 factorial.

Results and discussion
Treatment had no effect on aggression; however, a non-competitive feeding system was used, and the sows were grouped after receiving their morning feeding. This environment results in low overall aggression, making it difficult to detect treatment effects. There was also no effect of treatment on the time required to consume 200 grams of gestation diet provided to the sows six hours post-feeding. This test was used as an indicator of satiety, assuming that “hungrier sows” would consume the 200 grams more quickly. Six hours after the morning feeding may not be sufficient time to adequately measure this response.

As expected, dietary energy content was reduced with the addition of straw (Table 1, trt P < 0.001). Processing increased diet digestibility and thus energy content of the diet and this effect was greater with the oat straw than the wheat straw (S × P, P < 0.01).

Pre- and post-prandial plasma glucose tended to decrease with processing in the wheat, but not the oat straw (P × S, P < 0.10, data not shown) and this effect was more apparent in the preprandial samples. This, combined with the effects on digestibility, indicates that processing had a greater effect on the solubility of fiber in the oat, relative to the wheat straw.

Supplementing the gestation diet with processed straw during late-gestation had no effect on litter size or piglet birth weight (Table 2). However, piglet weaning weights were improved with the oat straw supplementation (S, P < 0.01) and there tended to be a further improvement when the oat straw was processed (S × P, P = 0.06). This observation could be a reflection of the improved feed intake for the sows during the initial seven days post-farrowing that was observed with the oat straw supplementation (S, P < 0.01; Table 2). The improvements observed with straw processing were still evident at nursery exit (P < 0.03); however, piglets on the control treatment had similar nursery exit weights as piglets from sows receiving processed oat or wheat straws.

Finally, treatment had no effect (P > 0.10) on market weight or yield, dressing or carcass yield percent, back fat or loin depth.

Summary and conclusions
Although data on aggression and/or satiety was not conclusive, processing the oat straw increased plasma glucose, whereas the opposite effect was observed with the wheat straw. Moreover, gestating sows fed oat straw from Day 86 of gestation to farrowing had increased feed intake post-farrowing and higher average piglet weaning weights. In our study, oat but not wheat straw provided benefits for gestating sows and there was some indication that further benefits could be obtained through processing.

Acknowledgements
We acknowledge funding for this project from Swine Innovation Pork, part of Agriculture and Agri-Food Canada Agri-Innovation Program. The Prairie Swine Centre Inc. receives program funding from Sask Pork, Manitoba Pork, Alberta Pork, Ontario Pork and the Saskatchewan Ministry of Agriculture.

References

Danielsen, V. and E.-M. Vestergaard. 2001. Dietary fibre for pregnant sows: effect on performance and behaviour. Anim. Feed Sci Tech. 90:71-80.

De Leeuw, J.A., A.W. Jongbloed and M.W.A. Verstegen. 2004. Dietary fiber stabilizes blood glucose and insulin levels and reduces physical activity in sows (Sus scrofa). J. Nutr. 134: 1481-1486

De Vries, S., A.M. Pustjens, H.A. Schols, W.H. Hendriks and W.J.J. Gerrits. 2012.  Improving digestive utilization of fiber-rich feedstuffs in pigs and poultry by processing and enzyme technologies:  A review.  Anim. Feed Sci Technol. 178: 123-138.

Ramonet, Y., S. Robert, A. Aumaitre, J. Y. Dourmad, and M. C. Meunier-Salaun. 2000. Influence of the nature of dietary fibre on digestive utilization of some metabolite and hormone profiles and the behaviour of pregnant sows. Anim. Sci. 70:275-286