IN-VITRO RUMINAL STARCH DIGESTIBILITY IN OPAQUE-2 AND REGULAR CORN HYBRIDS

Opaque-2 corn (Zen 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. Objec tives 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 ma turity, and five high lysine and five normal hybrids harvested after f ield drying. All grain was ground prior to starch and in vitro analyse s; dry grain was both coarsely and finely ground to examine the intera ction between particle size and corn type. Starch content of normal co rn 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 digesti bility of high lysine and normal hybrids at blacklayer was 55.8% and 3 9.1%, respectively, following 6 h of fermentation (P<0.01) and 95.8% a nd 89.2% after 12 h (P<0.01). For fine-ground dry corn, starch digesti bility of high lysine and normal hybrids was 40.2% and 29.6%, respecti vely, after 6 h(P<0.01) and 89.0% and 78.5% after 12 h (P<0.01). For c oarse-ground dry corn, no difference in digestibility between hybrids was observed after 6 h, however, high lysine corn was 48% more digesti ble than normal corn after 12 h (70.6% vs. 47.7%; P<0.02). Although di gestibility was variable between different opaque-2 corn hybrids, in v itro starch digestibility was consistently higher for all opaque-2 hyb rids compared with normal corn. (C) 1998 Elsevier Science B.V.