Abstract: The aim of this study was to investigate the fermentation performance and combination effect of high-quality forages treated with beef cattle rumen fluid in vitro. The four forages studied were packaged silage of maize, oat and alfalfa, and alfalfa hay. The feeds were sourced from the Loess Plateau region. Seven mixtures of the four forages were also tested: C₁ (50% maize silage+50% oat silage), C₂ (50% maize silage+50% alfalfa silage), C₃ (80% maize silage+20% alfalfa hay), C₄ (50% oat silage+50% alfalfa hay), C₅ (70% maize silage+10% oat silage+20% alfalfa silage), C₆ (65% maize silage+15% oat silage+25% alfalfa silage) and C₇ (50% maize silage +20% oat silage+30% alfalfa silage). It was found that: at each time point, the gas production (GP) was highest for maize silage and lowest for alfalfa silage, among the four forages tested singly (P<0.05). For the seven mixtures, the highest and lowest GP was from C₃ and C₄, respectively (P<0.05). Gas production was partitioned into a rapid degradation component (a), a slow degradation component (b), and a gas production rate constant (c). Among the four single feeds, maize silage had the highest value of a, while alfalfa hay had the highest value of c, and values differed significantly (P<0.05) between the four single feeds for both a and c. Among the seven feed mixtures, the highest values of a and c occurred in mixture C₂, while values of c, and potential gas production (a+b) were higher (P<0.05) in mixture C₃, than in the other mixtures. Among the four single feeds, the highest dry matter digestibility (DMD) after 48 h was for maize silage, and there were also significant differences among the other three forages (P<0.05); the pH values differed among the four feeds (P<0.05), and ranged from 6.27 to 6.72; while the NH₃-N concentration was the highest in oat silage (P<0.05). For the seven feed mixtures, the DMD of C₂ was lower than C₅ and C₇ (P<0.05); the pH values ranged from 6.40 to 6.69, and the pH value of C₃ was significantly lower than that of the other six feed mixtures (P<0.05); The NH₃-N concentration of C₁ and C₂ was higher than that of the other five feed mixtures (P<0.05). Among the four single forages, the total volatile fatty acids (TVFA) alfalfa silage and hay were significantly lower than for maize and oat silage (P<0.05). Among the feed mixtures, the TVFA concentrations of C₂ and C₄ were significantly lower than those of C₅ and C₆ (P<0.05). In conclusion, the GP, DMD, TVFA and acetic acid production from maize silage was the highest, while the lowest GP occurred in alfalfa silage. For the seven feed mixtures positive associative effects were detected, and according to the ‘MAFEI’ index, these effects ranked C₄>C₂>C₅>C₁>C₃>C₆>C₇.

Key words: beef cattle, corn silage, oat silage, alfalfa silage, combination effect