Evaluation of nutritional and agronomic characteristics of corn hybrids for silage

Author(s)

Luis Felipe Prada e Silva

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 1998-05-21
• Advisor: Paulo Fernando Machado

Abstract

The agronomic characteristics, stover and silage chemical composition, and the dry matter (DM) and neutral detergent fiber (NDF) "in situ" digestibility of 28 corn hybrids in 1996, and 21 corn hybrids in 1997, was measured with the objective of establishing relationships among this analyzed variables. From the 21 corn hybrids selected in 1997, 13 were hybrids already tested in 1996. In 1996, silages were made with the selected hybrids in 200 L plastic barrels. The mathematic model described by McDonald (1981) was used to describe the DM "in situ" digestibility kinetics, and the model described by Mertens & Loften (1980) to analyze the digestibility kinetics of the NDF fraction. The experimental design utilized in the agronomic experiment was the randomized blocks with 3 plots. In the digestibility trial, the split-plot design was utilized, where the periods were the blocks (3 periods), the ruminal incubation times were the plots, and the corn hybrids were the split-plots. Both the years were analyzed together to determine the environmental effect (year) and the environmental (year) x genetic (hybrids) interactions over the analyzed variables. The occurrence of genetic variability was observed for all the analyzed variables. The total DM production and the cob percentage were not correlated with the stover digestibility, showing the possibility for a selection program based on productivity and digestibility. The cell wall constituents (NDF, ADF, lignin, cellulose and hemicellulose) were negatively correlated with the stover DM digestibility, and among them, ADF was the variable best correlated with effective DM degradability (Deg.ef) during both experimental years, showing that from now on should be utilized as a stover digestibility indicator using this equation: Deg.ef = 100,6077 - 1,4085*ADF (R2=0,86). The cobs DM percentage were positively correlated with the stover NDF and ADF content in 1996, and with the stover ADF content in 1997; possibly a reflection of a soluble carbohydrates translocation from the stover to the grains. There was a greatest environmental effect over the corn hybrid quality variables. The hybrid X year interaction was significant for the agronomic characteristics, as well as for the stover digestibility, showing that the environment had great influence upon the genetic behavior of the corn hybrids, however the interaction were not significant for the stover ADF content. The occurrence of water stress (1996) reduced the DM total production and the percentage of cobs, however improved the com hybrids stover digestibility (AU)