Características agronômicas, químicas e degradabilidade ruminal da silagem de cultivares de sorgo

Abstract

Forages for dairy cows should merge the potential for high yield ofdry matter per unit ofárea, allowing a high animal stocking rate, with high nutritive value, capable ofdecreasing the amount of concentrate feedstuffs per unit of milk produced. Eighteen sorghum cultivars were randomly cultivated within three field blocks in four 5 m rows 0.70 m apart. After thinning, 12 plants per linear meter were kept. Plants were harvested 10cm from the soil surface at the milky/pastymaturity stage. One sample from each plotwas ensiled in mini PVC silos. Agronomic characteristics were evaluated in the fresh material (days until flowering, plant height, dry mattercontent, yield offresh material, and yield of dry matter) and chemical analysis were perforrried in silage samples composited by cultivar (percentages of dry matter, NDF, ADF, CP, EE, ash and non-fiber carbohydrates). Silage samples were incubatedin situ for 0, 12, 24, and 72 hours into the rumen of 8 rumen cannulated cows and the effective dry matter degradation (DEF) was calculated assuming a fractional pássage rate of-0.04/h. The yield of dry matter was 13.0 ± 2.3 (mean ± S.D.) rariging from 8.8 to 16.6 ton/hectare. The NDF content was 50.3 ± 3.8 ranging from 44.8 to 60.4 % ofdry matter. The DEF was 48.8 ± 2.8 ranging from 44.0 to 54.0 % ofdry matter. Forage type cultivars were more productive but had greater fiber content and lower DEF than grain and double purpose type cultivars. Among ali the agronomic and chemical characteristics % ADF hadthe greatest correlation with DEF (r = -0.64). The correlation between dry matter yield and % ADF was 0.45. The linear model correlating DEF to productivity was: DEF = -54.694 - 0.4449x tons of dry matter per hectare (r2 = 0.13). Although there are cultivars that conciliate productivity and digestibility, it seems to be difficult to conciliate high nutritional value and high yield ofdry matter per área in the sorghum plant.