ABSTRACT The goal of our study was to evaluate the nutritional potential of dented corn hybrids for silage production. We performed a two-location trial in which 19 dented corn hybrids and five corn controls grew in four randomized blocks within two experimental areas located in the Northern (Campos dos Goytacazes) and Northwestern (Itaocara) Rio de Janeiro State, Brazil. We recorded yields of fresh and dry forage matter and yields of fresh and dry grain matter, as well as chemical composition variables. We interpreted variables by assuming a Normal distribution for yield variables and a Beta distribution for chemical composition and ratios. The SAS GLIMMIX procedure fitted the linear model under those assumptions. Dual-pool models fitted the gas production profiles generated by in vitro anaerobic fermentations. We used the nlme of R software to fit the dual-pool models and the information-theoretic approach to evaluate their quality of fit. We did a cluster analysis (NbClust of R) to group corn hybrids based on fresh and DM yields and kinetic parameters of in vitro gas production. Three clusters of corn hybrids stood out, their basic differences relied on fresh and DM yields. Nonetheless, the least-squares means for gas production characteristics among groups did not present disjoint confidence intervals. Therefore, we can infer that dented corn hybrids rank by forage yield, but not by forage quality, and recommend the most productive ones that consistently outstand in both locations (hybrids UENF-2203, UENF-2192, UENF-2193, and UENF-506-11).

RESUMO Este estudo objetivou avaliar o efeito da adubação com nitrogênio (N) e potássio (K) sobre o acúmulo o valor nutritivo da forragem da Urochloa ruziziensis, durante as estações de verão de 2010/2011 (verão 1), outono, inverno, primavera e verão de 2011/2012. Foi utilizado o delineamento em blocos completos casualizados com quatro tratamentos (0, 120, 240 e 360 kg ha-1year-1 de N e K2O) e cinco repetições. Os dados foram analisados pelo PROC MIXED do SAS®. Foram avaliadas as variáveis: altura do dossel, massa de forragem, densidade volumétrica da forragem; porcentagens de massas secas de lâminas foliares, colmos de material morto; relação lâmina: colmo; teores de matéria seca, proteína bruta e digestibilidade in vitro da matéria seca, fibra em detergente neutro, lignina da forragem da Urochloa ruziziensis. Houve efeito de interação entre doses de adubação com N e K e estação do ano para todas as variáveis. Também houve efeito linear positivo de doses de fertilização com N e K sobre a taxa de acúmulo de forragem, o teor de proteína bruta e da digestibilidade in vitro da matéria seca, e efeito linear negativo sobre os teores de fibra em detergente neutro e de lignina durante a primavera e o verão 2. A adubação com N e K e as mudanças climáticas características de cada estação afetam de forma conjunta o acúmulo e valor nutritivo da Urochloa ruziziensis. A adubação com N e K com até 360 kg ha-1ano-1 aumenta o acúmulo de foragem e o valor nutritivo de Urochloa ruziziensis.

ABSTRACT This study aimed to assess the effect of nitrogen (N) and potassium (K) fertilisation on the forage accumulation and nutritive value of Urochloa ruziziensis during the summer of 2010/2011 and autumn, winter, spring and summer of 2011/2012. A complete randomised block design with four treatments (0, 120, 240 and 360 kg ha-1 year-1 N and K2O) and five replicates were used. The data were analysed under the PROC MIXED of SAS®. The following variables were evaluated: sward height; forage mass; forage bulk density; percentages of leaf blade dry matter, stem dry matter, and dead material dry matter; leaf blade:stem ratio; contents of dry matter and crude protein; in vitro digestibility of dry matter; neutral detergent fibre content; and lignin content of Urochloa ruziziensis. There was an interaction between the N and K levels of fertilisation and the season for all variables. In addition, there was a positive linear effect of the N and K levels of fertilisation on the forage accumulation rate, the crude protein content and the in vitro digestibility of dry matter and a negative linear effect these levels on the neutral detergent fibre and lignin contents during the spring and summer of 2011/2012. N and K fertilisation and the climate changes characteristic of each season jointly affected the accumulation and nutritive value of Urochloa ruziziensis. N and K fertilisation up to 360 kg ha-1 year-1 improved the forage accumulation and nutritive value of Urochloa ruziziensis.

ABSTRACT This experiment was conducted to evaluate the degradation kinetics and microbial efficiency of beef cattle grazing on low-quality forage and receiving supplements with different levels of rumen undegradable protein (RUP). The animals grazed on palisade grass pasture solely or this pasture and supplement containing 40 or 60 g of RUP per 100 g of crude protein (CP). The degradation profiles of neutral detergent fiber, fiber carbohydrates, and neutral detergent insoluble protein were interpreted kinetically by using a decreasing logistic model. Treatments (no supplement, or RUP at 40 or 60 g−1 100 g CP) did not affect rumen fill; however, the increase in the indigestible fiber carbohydrate fraction that occurred at the expense of the digestible fiber carbohydrate fraction resulted in a greater rumen fill effect. The palisade grass showed a significant proportion of its nitrogen in the form of slowly degradable protein as neutral detergent insoluble protein, which amounted to 26 g per 100 g CP. Supplementation with 40 g of RUP per 100 g CP decresead the indigestible fraction of the low-quality forage. However, the absence of a rumen-fill effect demonstrates that the additional supply of nutrients contributes greatly to increasing growth efficiency and use of the available energy from the forage by the ruminal microorganisms.