Evaluation of Apparent Total-tract Digestibility and Glycemic Responses to Processed Corn in Nonexercised Thoroughbred Horses

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 4×4 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.