Year of Publication

2014

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Agriculture, Food and Environment

Department

Animal Science

First Advisor

Dr. Robert J. Coleman

Abstract

Determining digestibility of feed ingredients is a challenge. While forage type feeds may be fed as the sole dietary component, concentrates cannot. To determine the apparent digestibility of these ingredients a by difference method can be utilized. The study was conducted to investigate the nutritional value of corn germ dehydrated (AAFCO 48.32) for horses in comparison to two processed corns commonly fed to horses. The second objective was to compare total tract digestibility of the treatments to determine differences in digestibility of the various fiber fractions due to added concentrate and to use the difference method to determine nutrient digestibility of the three corn treatments. In addition, glycemic responses and fecal pH changes were used to assess and quantify the presence of associative effects in fiber digestibility and differences in site of digestion.

A 4x4 Latin square digestibility trial was conducted using a starch intake level of 6 g/kg BW/day, offered in three equal meals. The control diet consisted of hay cubes, alfalfa pellets, corn bran and corn oil. The treatment diets contained the control diet plus one of the three processed corn treatments, cracked, steam flaked or corn germ dehydrated. Cracked corn was selected as a negative control and steam flaked corn as a positive control based on previous research showing differences in pre-cecal starch digestibility coefficients. The four diets were formulated to have equal starch, NDF and ADF components. Each experimental period was 21 days made up of 5 days adaptation, 11 days on feed and a 5 day total fecal collection. Indirect methods for estimating small intestinal starch digestion (glycemic response) and changes in the hindgut environment (fecal pH and acid concentrations) were used due to the use of non-surgically modified experimental animals.

Mean total tract starch digestibility for all diets was high, control 92.2±4.9, cracked corn 96.6±1.0, steam flaked corn 99.2±0.4 and corn germ dehydrated 98.8±0.4 % (P>0.05). The process of steam flaking compared to cracking or dry corn milling resulted in a greater area under the blood glucose time curve in response to 1kg of corn treatment meal, suggesting increased pre-cecal starch availability. No statistical differences were observed on an equal starch basis between the three corn products (P>0.05). Cracked corn significantly lowered fecal pH compared to the control and corn germ dehydrated diets (P0.05) when comparing the control diet and the combined diets (control diet plus processed corn) and the three individual corn ingredients by the difference method. Even though mean digestibility of fiber fractions were not affected by diet, individual horse data suggests that negative impacts on fiber fraction digestion occurred. Surprisingly, the steam flaked diet did not appear to act as a positive control in limiting changes in fermentation kinetics when fed at this intake level. The process of steam flaking improves small intestinal starch availability but the reduction in particle size may increase the rate of microbial fermentation prompting the development of acidosis. The study findings suggest the corn germ dehydrated product to be a good feedstuff for horses requiring additional calories and high feed intakes. The DE value is comparable to steam flaked corn, without the negative impacts observed on fecal fermentation end products.

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