Effects of Hybrid and Maturity on Maize Stover Ruminai Degradability in Cattle Fed Different Diets

Abstract

The effect of maize hybrid (Suco and Dekalb 765, DK 765), maturity stage (milk, R3 and 1/2 milk line, R5) and animal diet (Diet 1: 70% lucerne hay+30% maize silage; Diet 2: 50% maize silage+20% sunflower meal+30% maize grain) on ruminai stover dry matter (DM) degradability was studied. Additionally, morphological and chemical plant composition was evaluated. Fodder samples ground at 2 mm were incubated in three Holstein steers (400 kg body weight) using the in situ technique. Ruminal degradation kinetics was studied and the effective degradability (ED) was estimated for an assumed kp of 5%/h. The in situ data was analyzed in a complete randomized block design with the animals as blocks. Significant interactions between hybridxdiet and maturityxdiet on kinetic digestion parameters were detected. In Diet 1, hybrids did not differ in degradable fraction, kd or ED, although a minor difference (p<0.05) in the soluble fraction was found (25.5 and 23.2% for Suco and DK 765, respectively). In Diet 2, the DK 765 had greater degradable fraction (p<0.001) but smaller (p<0.01) kd than Suco, without differences in the soluble fraction or in ED. Anticipating the harvest increased ED of stover from 37.5% in R5 to 44.6% in R3 (average values across hybrids and diets) due to the increase (p<0.001) in the soluble fraction (R5: 22.6%, R3: 28.8%). It is concluded that hybrids had similar stover in situ DM degradability and that soluble fraction represent the main proportion of degradable substrates. Advancing the date of harvesting may not improve the in situ DM degradability of whole maize plant silage since the increase in stover quality is counteracted by the depression in the grain-to-stover ratio. The diet of the animal consuming silage might not improve stover utilization either.