RUMEN DEGRADATION CHARACTERISTICS AND FIBER COMPOSITION OF VARIOUS MORPHOLOGICAL PARTS OF DIFFERENT MAIZE HYBRIDS AND POSSIBLE CONSEQUENCES FOR BREEDING

The rumen dry matter degradability (DMD) of different morphological parts of eight maize hybrids was studied to assess the suitability of nylon bag technique for selecting hybrids for maize silage production. DMD was measured by incubating samples in nylon bags in three rumen fistulated sheep for 6, 12, 18, 24, 48 or 72 h. The data were fitted to the equation p = a + b (1 -e(-ct)) and effective dry matter degradabilities (EDMD) were calculated using a theoretical rumen outflow rate of k = 0.05 h(-1). DMD of all morphological parts varied significantly (P < 0.05) between hybrids in at least three of six incubation times. EDMD (g/kg) of the hybrids ranged from 362 to 470 for stalks, 377 to 446 for leaves, 393 to 455 for husks, 286 to 348 for cobs and 548 to 717 for grain. The average degradation rate (h(-1)) and EDMD (g kg(-1)) were respectively 0.039 and 555 for flint grain and 0.063 and 684 for the dent type of grain. Compared with leaves and husks, stalks had a higher soluble, and lower insoluble but degradable fraction. EDMD was similar in all three morphological parts. Differences in EDMD of stover were attributed to variation within morphological fractions and not to the differences in their proportions. EDMD of stover was positively correlated with the proportion of grain in the whole plant (r = 0.44, P > 0.05). Using multiple regression analysis, 0.99 of the variability in EDMD of stover was explained by the concentration of detergent fibres, particularly by the acid detergent fibre (ADF). It was concluded that nylon bag degradability or concentration of fibre components may be used to assess differences in nutritive value between maize hybrids.