In vitro ruminal starch digestibility in opaque-2 and regular corn hybrids

Opaque-2 corn (Zea mays L.), more commonly known as high lysine corn, contains more lysine than normal corn. However, little is known about the digestibility in ruminants of different high lysine hybrids. Objectives were to determine in vitro ruminal starch digestibility of corn grain from high lysine and normal hybrids. Samples included grain from seven high lysine and one normal hybrid harvested at physiological maturity, and five high lysine and five normal hybrids harvested after field drying. All grain was ground prior to starch and in vitro analyses; dry grain was both coarsely and finely ground to examine the interaction between particle size and corn type. Starch content of normal corn was slightly higher than high lysine for both blacklayer (67.1% vs. 65.0%; P<0.01) and dry corn (70.9% vs. 66.9%; P<0.03). Starch digestibility of high lysine and normal hybrids at blacklayer was 55.8% and 39.1%, respectively, following 6 h of fermentation (P<0.01) and 95.8% and 89.2% after 12 h (P<0.01). For fine-ground dry corn, starch digestibility of high lysine and normal hybrids was 40.2% and 29.6%, respectively, after 6 h (P<0.01) and 89.0% and 78.5% after 12 h (P<0.01). For coarse-ground dry corn, no difference in digestibility between hybrids was observed after 6 h, however, high lysine corn was 48% more digestible than normal corn after 12 h (70.6% vs. 47.7%; P<0.01). Although digestibility was variable between different opaque-2 corn hybrids, in vitro starch digestibility was consistently higher for all opaque-2 hybrids compared with normal corn.