Online

Ordaz Puga, Salvador

Animal Sciences

2017

M.S.

Ensiling is one of the most common processes used as a conservation method for forages on farms and plays an important role in farm economics. Therefore, with the aim to improve the conservation and the nutritive value of silage, the utilization of silage additives such as fibrolytic enzymes (FE) and lactic acid bacteria (LAB) inoculants has been a common on-farm practice. FE are enzymes capable of breaking down complex polysaccharides such as cellulose and hemicellulose. The latter results in an increased substrate availability for epiphytic and inoculated LAB during silage fermentation, thus promoting a higher production of organic acids such as lactic acid and volatile fatty acids such as acetic acid, which are key acids to improve the conservation of the forage by reducing dry matter losses and improving aerobic stability. The degradation of cellulose and hemicellulose results in a partial degradation of fiber measured by the neutral detergent fiber (NDF) and acid detergent fiber (ADF) extraction technique. Therefore, FE could have the potential to improve ruminal fiber digestibility of treated forages. Alternatively, LAB inoculants are used as silage additives with the primary objective to dominate over the epiphytic bacteria present in silage, to accelerate the fermentation process, and to reinforce aerobic stability of the forage at feed out. Additionally, recent research has shown that certain strains of LAB might have the potential to partially degrade NDF and ADF during ensiling, therefore improving fiber digestibility. The first objective of this research project was to evaluate the effects of different mixtures of FE (a mixture of cellulase and xylanase (C+X); xylanase (X); ss-glucanase (G); a mixture of ss-glucanase and xylanase (G+X); and a negative control) on alfalfa harvested at early and late maturity, and stored for 40 or 120 d of ensiling. Alfalfa harvested at early maturity, treated with FE and ensiled for 40 d did not show significant improvements during ensiling in fiber degradability, fermentation characteristics or fiber digestibility in vitro assessed by the Tilley and Terry methodology. However, when harvested at late maturity and treated with a mixture of C+X; X and G+X, the NDF and ADF content at 40 d of ensiling tended to decrease. FE improved total volatile fatty acid production at 40 and 120 d of ensiling. Improvements in fiber digestibility were observed in vitro at 24 h for the C+X treatments. The results of this study suggest that the effects of FE are more pronounced in silages higher in fiber concentration, such as in the late-maturity alfalfa cut. The second objective of this research was to evaluate the effects of two homofermentative LAB (hoLAB) strains, and two heterofermentative LAB (htLAB) strains on alfalfa harvested at late maturity and stored for 40 or 120 d of ensiling. At 40 d of ensiling, hoLAB-treated silages had the greatest DM recovery and the lowest ADF concentration. Lactic acid production was greater for hoLAB-treated silages. At 120 d of ensiling, hoLAB-treated silages had the highest concentration in lactic acid whereas htLAB had the highest concentration in acetic acid and hoLAB-treated silages had the lowest ADF and NDF concentrations while htLAB tended to have higher NDF concentrations. Overall, it appears that the fiber degradation promoted during ensiling influenced digestibility depending upon hoLAB or htLAB inoculation, with hoLAB showing improved digestibility levels. The presented work suggests that certain FE can have the potential as a management resource on farms aiming to improve the nutritive value of forages with a high fiber concentration. As expected, hoLAB and htLAB inoculants improved the fermentation characteristics of alfalfa silage, but it was shown that LAB may exert a differential effect on fiber digestibility depending on their specific metabolism.