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Effect of grass maturity and wilting on the nitrogen fractions in silage, their rate and extent of degradation in the rumen

University of British Columbia

The available literature indicates that, silages containing more undegraded protein will be better feeds for high levels of production from ruminants. Ensiling excessively wet herbage will increase degradation of both protein and energy. Ensiling wilted herbage will increase aerobic losses initially, during compaction and later, during removal which decreases digestibility. This study was carried out, to evaluate the effect of grass/legume maturity and wilting on the nitrogen fractions in silage, their rate and extent of degradation in the rumen and to determine the availability of undegraded silage protein and microbial protein to the animal. At the beginning of this study, laboratory assessment of the nutritional composition of both grass/legume parent material, and their ensiled products was carried out. The results for both parent herbage and silage were then compared on DM basis. While, silage crude protein (CP) (p<0.05), water soluble carbohydrates (WSC) (p<0.001), ash (p<0.001), acid detergent fibre (ADF) (p<0.05), and grass/legume ammonia-N (NH₃N) (p<0.001), were significantly increased by wilting, silage hot water insoluble nitrogen (HWIN) was significantly reduced (p<0.001). Significantly lower pH (p<0.05), NH₃N (p<0.05), and ash (p<0.01) contents were observed in mature silage. The composition of silage nutrients was found to be governed by that of the standing crop, at the time of cutting and by modifications which take place during wilting and ensiling. Although, wilting increased WSC content, it had the undesirable effect of reducing silage hot water insoluble nitrogen. Maturity had desirable effects of reducing volatile NH₃N and silage pH. The fermented herbage contained lower levels of nutrients than the parent material. In the second part of this study, the nylon bag technique was used to determine the rate and extent of protein degradation (in the rumen) of immature unwilted and wilted, mature unwilted and wilted silages. Estimates of effective protein degradation as a function of rumen outflow rate and degradation rate were also evaluated. The study showed that wilting and maturity significantly reduced (p<0.05) the soluble nitrogen fraction of the grass/legume silage. DM disappearance was significantly reduced (p<0.05) by wilting. The insoluble protein fraction was increased (p<0.05) in the mature silages. At an estimated rumen outflow rate of 0.02%, effective DM and CP degradation were significantly reduced (p<0.05) by wilting. From these findings, it is likely that supplementation of both protein and energy is required most for the unwilted and immature silages. Also, when silages are wilted more undegraded protein leaves the rumen compared with unwilted silage. In the final part of the study, the effect of wilting and maturity on rumen degradation of silage N fractions were estimated using four rumen and duodenal cannulated steers and heifers fed on grass/legume silage, at maintenance level. Solute, particulate, and RNA markers were used to determine digesta flow rate and microbial N respectively. Measurements of digestibility of DM, CP and ADF, proportions of duodenal bacterial N, amount of undegraded protein entering the duodenum, degradability of silage protein, rumen NH₃N and plasma urea nitrogen (PUN) were made. This showed that, there were no significant differences (p<0.05) in PUN and rumen NH₃N among silages. Significant increases (p<0.05) in duodenal and fecal CP and reduced (p<0.01) fecal ADF were observed in animals given wilted silages. The degradability and digestibility results were much lower than expected and no apparent differences (p<0.05) were observed among silages.

Text

2010-08-31

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http://hdl.handle.net/2429/28024

Animal Science

University of British Columbia

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