FEEDING MECHANICALLY PROCESSED CORN TO NURSERY PIGS

The removal of fiber fractions in corn could significantly impact its nutrient composition and enhance its nutritional value to pigs.

Dietary fiber reduces energy and nutrient utilization in swine and, therefore, increases waste production and nutrient excretion (Shi and Noblet, 1994; Canh et al., 1998). Dehulled, degermed corn, a product of the corn dry milling process, is reported to have superior dry matter, energy, and nitrogen digestibility, compared to regular corn, and provides a potentially valuable feed ingredient for swine diets (Moeser et al., 2002). In addition, extrusion has been reported to improve the digestibility of ingredients, which may be related to restructured physical components due to heat (Hongtrakul et al., 1998). The present study aims to evaluate mechanically processed corn products and extruded corn in nursery pig diets with the goal of reducing nutrient excretion without negatively affecting growth performance.

Materials and Methods
One hundred and fifty-nine crossbred pigs ([Landrace x Yorkshire] x [Hampshire x Duroc]) were weaned at 21 d of age, blocked by weight, and assigned to one of three dietary treatments based on body weight and litter origin. When pigs of the same litter were allocated to the same pen, pigs were switched within a block to ensure that littermates were distributed across treatments as much as possible. Treatments consisted of 1) a control diet containing corn as the major grain source, 2) a diet of extruded corn replacing regular corn, and 3) a diet of dehulled, degermed corn replacing regular corn.

Pigs were housed in 42 pens—9 pens of 3 pigs and 33 pens of 4 pigs—resulting in 14 replicates per treatment (53 pigs per treatment). Temperature in the nursery was initially 27°C and was lowered by 1°C each week. Feed and water were freely available throughout the study. Pigs were fed a complex Starter I diet for 14 days and a Starter II diet for 3 weeks (Table 1). Pig body weights and feed consumption were measured weekly for the experimental period.

Fecal grab samples were taken on d 28 (during Phase II) from at least two pigs in each pen to determine the digestibility of N, P, and GE (gross energy). Chromium oxide (0.10 percent; calculated to provide 684 ppm Cr in the diet) was used as an indigestible marker. Fecal samples for digestibility measurements were dried at 60°C and subsequently ground through a 1 mm screen in a Retsch grinder (model ZM 100, Irvine, CA). GE and N analysis were conducted according to AOAC (1997) procedures. Phosphorus concentrations were analyzed colorimetrically using the vanadomolybdate procedure (AOAC, 1997). GE was determined by adiabatic bomb calorimetry (Model 5001, IKA Works, Wilmington, NC). Analysis of Cr was conducted by wet ashing, followed by Cr determination by ICP.

Data were analyzed as a randomized complete block design using the GLM procedure of SAS (SAS Institute Inc., Cary, NC). The model included the effects of block and diet type. Pen served as the experimental unit. Least squares means were presented and considered statistically significant at P < 0.05.

Results and Discussion
Pigs fed extruded corn weighed less (P < 0.05) at the end of the experiment, compared to pigs fed regular corn-based diets, whereas pigs fed dehulled, degermed corn were intermediate in final weight (Table 2). Daily gain during the Starter I phase (d 0 to 14) tended to be reduced for pigs fed dehulled, degermed corn (P < 0.10), compared to control pigs. During the Starter II phase (d 14 to 35; P < 0.01) and overall (P < 0.05), pigs fed extruded corn gained less weight, compared to pigs fed corn, whereas daily gain of pigs fed dehulled degermed corn was intermediate. Feed intake during the Starter I phase was lower (P < 0.05) for pigs fed extruded corn, but not for pigs fed dehulled, degermed corn. Similarly, during the Starter II phase, feed intake was less for pigs fed extruded corn, compared to control pigs and pigs fed dehulled, degermed corn (P < 0.05); and pigs fed dehulled, degermed corn consumed less feed than control pigs (P < 0.05). This resulted in a reduction in feed intake for the entire experimental period of 13.1 percent for the extruded corn and 8.1 percent for the dehulled, degermed corn (both P < 0.05), compared to the control diets.

The reduction in feed intake in pigs fed extruded corn is surprising, considering the observations by Mercier (1980) and Bjorck et al. (1985) that extrusion of ground corn increased starch gelatinization and improved flavor and palatability in weanling pigs. Pigs fed extruded corn diets had greater gain:feed (P < 0.05) compared to control pigs and pigs fed dehulled, degermed corn during the Starter I phase. During the Starter II phase, pigs fed extruded corn continued to have a better gain:feed ratio than control pigs (P < 0.01). In addition, pigs fed dehulled, degermed corn had improved gain:feed compared to control pigs (P < 0.01). For the entire experimental period, pigs fed extruded corn had superior gain:feed compared to control pigs and to pigs fed dehulled, degermed corn (P < 0.05); and pigs fed dehulled, degermed corn had greater gain:feed than control pigs (P < 0.05). Moeser reported that pigs fed the dehulled, degermed corn diet tended to consume less feed and had a 4 percent improvement in gain:feed, compared to pigs fed diets based on corn. Diets based on dehulled, degermed corn were lower in fiber content. Kass et al. (1980) reported reduced growth rate and feed efficiency in pigs when dietary fiber level was increased.

Apparent fecal digestibility of P (Table 3) was improved (P < 0.05) for pigs fed extruded corn and dehulled, degermed corn, compared to control pigs. The germ in a corn kernel provides 78 percent of the whole-corn minerals and contains P in the form of phytate, which is indigestible in the digestive tract of a pig (Lei and Stahl, 2000; Kim and Baker, 2003). Thus, removal of the germ and its associated phytate P, in conjunction with the increased inclusion of dicalcium phosphate (which contains highly digestible P), to compensate for the lower P content in dehulled, degermed corn was expected to improve P digestibility. Digestibility of energy was greater (P < 0.05) for pigs fed dehulled, degermed corn, compared to pigs fed corn or extruded corn diets. These results are similar to Moeser, who reported increased DM and GE digestibility when dehulled, degermed corn was fed at 96.4 percent of the diet. The improvement in digestibility in dehulled, degermed corn may be related to its reduced fiber content. Just et al. (1983) reported a 1.3 percent increase in energy digestibility for every 1 percent reduction in dietary fiber content. Similarly, Noblet and Perez (1993) reported that every 1 percent decrease in dietary fiber resulted in an improvement in energy digestibility of 1.1 percent. Nitrogen digestibility, on the other hand, was not affected (P > 0.10) by dietary treatments in the current experiment.

The results of this study indicate that the mechanically processed corn products used here reduced feed intake and may compromise growth rate, while improving feed efficiency. Reductions in fecal volume and P excretion can be expected because of improvements in energy and P digestibility, respectively.

Literature Cited

1. AOAC. 1997. Official methods of analysis. 16th ed. Association of Official Analytical Chemists, Arlington, VA.
2. Bjorck, I., T. Matoba, and B. M. Nair. 1985. In vitro enzymatic determination of the protein nutritional value and the amount of available lysine in extruded cereal-based products. Agric. Biol. Chem. 49:945-951.
3. Canh, T. T., A. L. Sutton, A. J. A. Aarnink, M. W. A. Verstegen, J. W. Schrama, and G. C. M. Bakker. 1998. Dietary carbohydrates alter the fecal composition and pH and the ammonia emission from slurry of growing pigs. J. Anim. Sci. 76:1887-1895.
4. Hongtrakul, K., R. D. Goodband, K. C. Behnke, J. L. Nelssen, M. D. Tokach, J. R. Bergstrom, W. B. Nessmith Jr., and I. H. Kim. 1998. The effects of extrusion processing of carbohydrate sources on weanling pig performance. J. Anim. Sci. 76:3034-3042.
5. Just, A., J. A. Fernandez, and H. Jørgensen. 1983. The net energy of diets for growth in pigs in relation to the fermentative processes in the digestive tract and site of absorption of nutrients. Livest. Prod. Sci. 10:171-186.
6. Kass, M. L., P. J. Van Soest, and W. G. Pond. 1980. Utilization of dietary fiber from alfalfa by growing swine. I. Apparent digestibility of diet components in specific segments of the gastrointestinal tract. J. Anim. Sci. 50:192-197.
7. Kim, S. W., and D. H. Baker. 2003. Use of enzyme supplements in pig diets based on soyabean meal. Pig News Info. 24:91N-95N.
8. Lei, X. G., and C. H. Stahl. 2000. Nutritional benefits of phytase and dietary determinants of its efficacy. J. Appl. Anim. Res. 17:97-112.
9. Mercier, C. 1980. Structure and digestibility alterations of cereal starches by twin-screw extrusion cooking. In: P. Linli, Y. Malkki, J. Olkku, and J. Larinkari (Ed.). Food Process Engineering. Vol. I. Food Process Systems. pp. 795-807. Applied Science Publishers, New York.
10. Moeser, A. J., I. B. Kim, E. van Heugten, and T. A. T. G. van Kempen. 2002. The nutritional value of degermed, dehulled corn for pigs and its impact on the gastrointestinal tract and nutrient excretion. J. Anim. Sci. 80:2629-2638.
11. Noblet, J., and J. M. Perez. 1993. Prediction of digestibility of nutrients and energy values of pig diets from chemical analysis. J. Anim. Sci. 71:3389-3398.
12. NRC, 1998. Nutrient requirements of swine. 10th revised edition. National Academic Press, Washington, D.C.
13. Shi, X. S., and J. Noblet. 1994. Effect of body weight and feed composition on the contribution of the hindgut to digestion of energy and nutrients in pigs. Livest. Prod. Sci. 38:225–235.

—E. van Heugten and T. van Kempen

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Last modified July 18, 2006.