Effects of Particle Size Difference in Two Different Sweet Bran Products on Total Tract Digestibility and Rumen pH

Authors: Emily K Hoefling, Graduate Student; Anna M. Kobza, Research Technician; Jessica L. Miller, Research Technician; Maggie E. Youngers, Cargill Branded Feeds, Blair, NE; Galen E. Erickson, Professor; Jim C. MacDonald, Professor, Animal Science, Lincoln.

Summary with Implications

Seven ruminally fistulated heifers were utilized in a 6 x 7 row-column design to evaluate two different Sweet Bran particle size products (1.8 or 2.5 mm) included at 13%, 18%, or 23% of the diet (DM) on total tract digestibility and rumen fermentation parameters. The treatment design was a 2 x 3 factorial. Rumen pH was reduced and organic matter digestibility tended to be reduced with the small particle size when Sweet Bran was included at 13% of the diet. Both NDF digestibility and dietary digestible energy concentration tended to improve with the larger particle size. The large particle size of Sweet Bran appears to aid in improving diet digestibility and moderating rumen pH, which is more marked with low dietary inclusions (less than 18%). 

Introduction

Sweet Bran is known to moderate ruminal pH while increasing intake and gain when replacing corn in finishing diets. Distillers grains is also known to improve gain but not always intake. While distillers grains are high in NDF, feeding distillers does not increase rumen pH in corn-based finishing diets like Sweet Bran does. We hypothesized that the particle size of Sweet Bran is important for maintaining rumen pH and controlling acidosis in feedlot cattle. The objective of this study was to evaluate the particle size of Sweet Bran on rumen pH, total tract diet digestibility, and digestible energy in corn-based finishing diets.

Procedure

Seven ruminally cannulated, crossbred heifers were used in a 6 x 7 row-column design with 21-d periods consisting of 16-d adaptation period followed by a 5-d collection period. The study was conducted over 124 d. Dietary treatments were designed in a 2 x 3 factorial arrangement. Factor one was Sweet Bran product: either Sweet Bran-SP (small particle size; geometric mean diameter = 1.79 mm) or Sweet Bran-LP (large particle size; geometric mean diameter = 2.51 mm; Table 1). The geometric mean diameters were determined via wet sieving (American Society of Agricultural Engineers. 1969. ASAE Standard: ASAE S319) from samples collected at the time of delivery to the feedlot. Factor two was dietary inclusion of Sweet Bran product: 13%, 18%, or 23% of diet DM. All diets contained 15% modified distillers grains as a protein source, and 7% corn stalks as a roughage source (Table 2). The Sweet Bran products replaced steam-flaked corn (SFC) in the diets. All supplements were formulated to provide 33 g/ton of monensin (Rumensin, Elanco Animal Health) and 9.7 g/ton of tylosin (Tylan, Elanco Animal Health).

Diets were offered once per day in amounts allowing for ad libitum intake at 0700 h. Refusals collected from d 16 to 19 were dried in forced-air oven at 60ºC for 48 h to determine DM content and saved for further nutrient analysis. Individual feed ingredients were dried in a 60ºC forced-air oven weekly to ensure that accurate DMs were used when mixing dietary treatments.
 

Results

Particle Size

Each Sweet Bran product had a different particle size, as designed. The geometric mean diameter of Sweet Bran-SP was 1.79 mm (Table 1), and the geometric mean diameter of Sweet Bran-LP was 2.51 mm. The goal was to obtain a particle size smaller than the commercially marketed Sweet Bran product, targeting a size more similar to corn distillers grains. The Sweet Bran-SP product was not as small in particle size as corn DGS (1.2 mm). Sweet Bran-LP has a particle size similar to the commercial Sweet Bran product currently on the market.

Intake

There were no changes in OM intake for the Sweet Bran products (P = 0.15; Table 3). Feeding Sweet Bran increases intake as the dietary inclusion of Sweet Bran increased from 0 to 40% (2022 Nebraska Beef Report, pp. 46-49), but within the range of 13-23% DM inclusions in the current experiment, an increase in DMI was not detected. Neutral detergent fiber intake increased linearly for both Sweet Bran products (P < 0.01), while starch intake for both Sweet Bran-SP (P ≤ 0.05) and Sweet Bran-LP linearly decreased as inclusion increased from 13 to 23% which was expected as increasing the dietary inclusion Sweet Bran increased NDF and displaced starch from SFC.
 

Digestibility

The percent OM digestibility of Sweet Bran-SP increased linearly (P = 0.01; Table 3) with increasing inclusion while Sweet Bran-LP’s OM digestibility remained relatively constant. Heifers fed 13% Sweet Bran-SP exhibited lower OM digestibility than cattle fed any inclusion level of Sweet Bran-LP. The Sweet Bran feed with the larger particle size (Sweet Bran-LP) showed no significant change in NDF digestibility (P > 0.16) across inclusions. In contrast, the smaller particle size Sweet Bran (Sweet Bran-SP) resulted in the greatest reduction in NDF digestibility at a 13% inclusion level, the lowest among all treatments. Accordingly, NDF digestibility increased linearly with greater inclusions of Sweet Bran-SP (P < 0.01). Starch digestibility tended to increase quadratically with the 18% inclusion providing the greatest starch digestibility for Sweet Bran-SP (P = 0.06). Starch digestibility was unaffected by changes in the inclusion of Sweet Bran-LP (P > 0.34).

Digestible Energy

Digestible energy (%) linearly increased (P = 0.01; Table 3) with increasing inclusion of Sweet Bran-SP. Cattle fed Sweet Bran-SP linearly increased in digestible energy per day, digestible energy per lb, and total digestible nutrients (P ≤ 0.03). At 13% inclusion of Sweet Bran-SP, acidotic events may have occurred due to the smaller particle size of Sweet Bran-SP alongside having the greater SFC inclusion among the treatments. Sweet Bran has been shown to increase DMI up to 37-40% of the diet DM due to its highly digestible fiber, but the larger range in Sweet Bran inclusion in other studies would make these differences much easier to detect. The 13% inclusion of the smaller particle size Sweet Bran (Sweet Bran-SP) resulted in the most pronounced negative impact on energy values, whereas cattle fed the 18% and 23% Sweet Bran-SP diets exhibited energy levels comparable to those fed any inclusion of the larger particle size Sweet Bran (Sweet Bran-LP).

Ruminal pH

Average rumen pH increased linearly (P < 0.01; Table 4) and tended to increase quadratically (P = 0.10) with increasing concentrations of Sweet Bran-SP whereas average rumen pH remained constant for Sweet Bran-LP (P > 0.29). Cattle fed Sweet Bran-LP at any inclusion had pH which was greater than pH from cattle fed 13% Sweet Bran-SP. The 18% and 23% Sweet Bran-SP inclusions behaved similarly to the Sweet Bran-LP product. For Sweet Bran-SP, this is the only instance where a quadratic response approaches significance. The results indicate that the smaller particle size reduced pH at the lowest inclusion level. As Sweet Bran increase in the diet, so did the pH. Average pH (5.81-5.94) and maximum pH (6.51-6.77) for Sweet Bran-LP appear to be consistently greater than the average pH (5.55-5.83) and maximum pH (6.27-6.66) of Sweet Bran-SP. Minimum pH (5.21-5.51) for Sweet Bran-LP is on average greater than the minimum pH (5.02-5.42) of Sweet Bran-SP, with the exception of 18% inclusion of the Sweet Bran products. 
 

Conclusions

Digestibility tended to be reduced at 13% inclusion with the smaller particle size Sweet Bran (Sweet Bran-SP) with no differences at 18 or 23% inclusion. Both NDF digestibility and DE concentration tended to increase with the larger particle size Sweet Bran (Sweet Bran-LP). Increasing both types of Sweet Bran increased NDF digestibility and tended to increase DE concentration of the diet. Rumen pH was reduced with the smaller particle size Sweet Bran at 13% compared to all other inclusions of both Sweet Bran-SP and Sweet Bran-LP. Furthermore, the larger particle size Sweet Bran appears to be important to improving diet digestibility and moderating rumen pH, especially when fed at low dietary inclusions. Therefore, the particle size of Sweet Bran appears to be important in controlling ruminal acidosis and impacts diet digestibility and energy density. 

Acknowledgment

This research was funded by a grant provided by Cargill Branded Feeds. Rumensin was provided by Elanco Animal Health.

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