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What Are the Total-Tract Digestibility and Glycemic Responses of Processed Corn in Sedentary Horses?By Kentucky Equine Research Staff · May 23, 2017

In the process of extracting starch from corn for food manufacturing, the co-product corn germ dehydrated (AAFCO 48.32) is produced. This fraction is known commercially as Golden Max (GM).

A study was conducted to investigate the nutritional value of GM for horses and compare it to the typical forms of processed corn commonly fed to horses, cracked (CC) and steam-flaked corn (SF). Diets consisted of a control (no corn) and 3 processed corn diets fed with added fiber sources. The four diets were formulated to supply similar intakes of neutral detergent fiber (NDF) and acid detergent fiber (ADF) from a combination of corn bran, alfalfa cubes, and alfalfa meal.  CC, SF, and GM diets were fed to provide a starch intake of 6 g/kg BW/d, offered in 3 equal meals.

Four mature Thoroughbred geldings with an average body weight of 552 ± 10 kg were used in a 4x4 Latin square digestibility trial. Each experimental period was 21 d made up of 5 d adaptation, 11 d on treatment diet, and 5 d total fecal collection. Fecal pH was measured on the last day of each period. The area under the glucose-concentration time curve was used to categorize the pre-cecal starch digestibility of GM, CC, and SF based on 1 kg corn and starch intake per meal (1 g starch/kg BW). Plasma samples were taken pre-feeding and every 30 min post feeding for 240 min and analyzed for glucose.

Apparent total-tract digestibilities (mean % ± SE) were determined for dry matter (DM), crude protein (CP), starch, ADF, NDF and gross energy (GE). All 3 corn diets had significantly higher DM digestibility than the control (P ˂ 0.05). CC had lower CP digestibility (P ˂ 0.05). NDF and ADF digestibility coefficients were not different between diets (P > 0.05). Total-tract starch digestibility was high in all diets ranging from 92 ± 5 for the control, 97 ± 1 for CC, 99 ± 0.4 for SF, and 99 ± 0.4 for GM. Mean DE (Mcal/kg DM) values for CC, SF, and GM estimated by difference from the control diet were 3.22 ± 0.12, 3.84 ± 0.11, and 3.87 ± 0.06, respectively. DE in CC was lower than GM or SF (P < 0.05). Horses fed 1 kg of SF had a larger glycemic response than GM and CC (P < 0.05). On an equal starch-comparison, there was no difference in response between CC, SF, and GM (P = 0.12). Horses fed CC had a lower fecal pH than control and GM (P < 0.05). GM contained highly digestible starch that did not alter fecal pH even when fed at high levels of intake. Compared to SF, GM contained less starch (54.9% vs 73.8%), higher fat (9.8% vs 3.1%), and similar DE content.

GM is a suitable alternative source of carbohydrate and fat compared to traditionally used processed corns. 

This report of KER’s research was published in Proceedings of the 2015 Equine Science Society Symposium.

Read the entire research paper, titled Evaluation of Apparent Total-Tract Digestibility and Glycemic Responses to Processed Corn in Non-Exercised Thoroughbred Horses.