Sunflower silage (SS) is being promoted as an efficient forage for feeding dairy cattle in the face of shortages of irrigation and erratic rainfall. The objective was to compare, through the in vitro gas production technique, the kinetics of ruminal fermentation of SS and its mixtures with maize silage (MzS) to know its nutritional characteristics before its inclusion in feeding strategies. Five combinations of SS with MzS were assessed (MzS%: SS%); T1) 100:0, T2) 75:25, T3) 50:50, T4) 25:75 y T5) 0:100. Combining MzS with 25% SS decreased neutral detergent fiber and acid detergent fiber contents (P<0.05), which resulted in a digestibility of dry mather, organic matter, neutral detergent fiber and metabolizable energy similar to MzS (P>0.05), and with a CP content not statistically higher than MzS. The MzS had the highest total gas production (GP) but at a lower fermentation rate (P<0.05) when compared to T2 that had a better fermentation rate of 0.0530 %/h, with Lag time of 3.4 h. Before ensiling, sunflower supplies 31.8 % more CP, 11.8 % less metabolizable energy and 11.9 % less in vitro digestibility of organic matter than maize plant. Compared to T1, the T2 supplied 1.6 % more crude protein, 2 % less metabolizable energy and 4.4 % less of in vitro digestibility of organic matter. Therefore it is concluded that sunflower silage could be an alternative to substitute up to 25 % of maize silage as the crude protein and metabolizable energy supply are similar to maize silage.

El ensilado de girasol forrajero (Helianthus annuus L.) es promovido para la alimentación del ganado lechero ante escasez de riego y lluvias erráticas. El objetivo fue valorar al ensilado de girasol, solo y en diferentes proporciones con ensilado de maíz mediante degradación in vitro y la cinética de producción de gas. Se realizaron micro-silos, abiertos a los 80 días para el ensilado de maíz (EMz) y 50 días para el ensilado de girasol (EG), evaluándose los siguientes tratamientos (EMz%: EG%); T1) 100:0, T2) 75:25, T3) 50:50, T4) 25:75 y T5) 0:100. En el T2 la fibra detergente neutra y ácida disminuyeron significativamente (P<0.05), resultando en una digestibilidad in vitro de materia seca, materia orgánica, fibra detergente neutra y contenido de energía metabolizable y proteína cruda (P>0.05) similar a T1. Hubo mayor producción de gas total en T1, pero con una menor tasa de fermentación (P<0.05) al compararlo con T2 cuya tasa de fermentación fue de 0.0530/h, con un tiempo Lag de 3.4 h. El girasol aporta 31.8 % más de PC, 11.8 % menos de energía metabolizable y 11.9 % menos de digestibilidad in vitro. Comparado con el T1, el T2 aportó 1.6 % más de proteína, 2 % menos de energía metabolizable y 4.4 % menos de digestibilidad in vitro. Se concluye que el ensilado de girasol podría ser una alternativa para sustituir al ensilado de maíz hasta un 25 %, ya que el aporte de proteína y energía es similar al ensilado de maíz solo.

O uso da análise de cinética de produção de gases, em conjunto com a análise de prova de curva e as propriedades químicas da forragem permitem uma melhor descrição das características nutritivas das forragens. Objetivou-se estudar a composição nutritiva e características de fermentação de ruminal de três gramíneas, uma leguminosa e uma mistura composta de pastagens do Planalto Montanhoso Central do México. As amostras representativas de Pennisetum clandestinum (kikuyu grama), Sporobolus indicus (rabo de rato), Eleocharis dombeyana (cana), Trifolium amabile (trevo asteca) mais uma amostra composta foram coletadas durante os meses de Julho, Setembro e Novembro de 2003. Foi utilizada a técnica de produção de gás in vitro (GP). Os perfis de GP foram ajustados ao modelo descrito por PALMER et al. (2005). As diferenças (P<0.001) foram observadas entre espécies e períodos quanto à composição química, matéria orgânica e digestibilidade da fibra em detergente neutro. As diferenças (P<0.05) dos parâmetros de fermentação e cinética de produção de gases mostraram T. amabile e P. clandestinum com fermentação mais intensa, ao passo que S. indicus e E. dombeyana tiveram fermentação limitada. Concluiu-se que a combinação da análise de cinética de produção de gases e o perfil de GP ajustado ao modelo matemático ajudou a descrever as características nutritivas das gramíneas, da leguminosa e da amostra composta de forma mais acurada do que quando um dos métodos foi utilizado de forma isolada.

This paper has two objectives, the first is to determine the chemical composition, gas production parameters and the gas release kinetics, at different stages of maturity, of three grasses and a legume commonly found in long established pastures in Mexico central highland plateau. The second is to combine the gas release kinetics analysis and the GP fitted to a mathematical model in order to improve the biological understanding of the fermentation kinetics obtained from the GP technique. Representative samples of Pennisetum clandestinum (kikuyu grass), Sporobolus indicus (mouse tail), Eleocharis dombeyana (reed), Trifolium amabile (Aztec clover) plus a composite sample were collected in the growing season (July, September and November 2003) and analysed using an in vitro gas production (GP) technique. The accumulated GP was fitted to the model described in PALMER et al. (2005). Significant differences (P<0.001) were observed among species and periods for chemical composition, organic matter and neutral detergent fibre digestibility. Significant differences (P<0.05) were observed regarding fermentation parameters and gas release kinetic, with T. amabile and P. clandestinum being the species with the highest fermentability, whereas S. indicus and E. dombeyana were poorly fermented. P. clandestinum and T. amabile showed higher nutritive value than S. indicus and E. dombeyana. Composite samples were influenced by the chemical and fermentation characteristics of all species. It was concluded that the use of gas release kinetics analysis was useful for differentiating the fermentation kinetic of the soluble and insoluble fraction in the grasses and legume. Therefore by performing both approaches, the gas release kinetics analysis and the GP fitted to a mathematical model, gave a better description of the fermentation kinetic of grasses and the legume was achieved when only one approach had been used.