Characterization of nitrogen transformation dynamics in alfalfa and red clover and their mixture silages

Abstract

The objective of this experiment was to characterize the dynamics of nitrogen (N) transformations in alfalfa and red clover and their mixture during ensiling. Alfalfa, red clover and a mixture of them (1:1 on fresh weight) were ensiled for 3, 5, 7, 14 and 30 days. The fermentation qualities and dynamic change of N components of the three silages were determined. Red clover and mixed silages showed better fermentation qualities, indicated by lower (p < 0.05) pH value, higher (p < 0.05) lactic acid concentration compared with alfalfa silage after ensiling. Retarded N transformation was observed in red clover and mixed silages, as evidenced by lower (p < 0.05) free amino acid concentrations at all intervals of ensiling, higher (p < 0.05) peptide N and lower (p < 0.05) ammonia N concentrations after 14 days of ensiling as opposed to alfalfa silage. Mixing red clover apparently delayed the degradation process of alfalfa protein in mixed silage, as demonstrated by no significant difference in non-protein N (NPN) concentrations in comparison with pure red clover silage at most intervals of ensiling. The results of this study, from the perspective of N transformation, confirmed the lower rate of protein degradation in red clover in contrast to alfalfa during ensiling and potentially provide an effective strategy to reduce protein loss for alfalfa silage production. K E Y W O R D S Alfalfa, mixture, nitrogen transformation, red clover, silage | INTRODUC TI ONAlfalfa (Medicago sativa L.) is the leading legume forage crop, commercially used as feed for dairy cows and other livestock. In some rainy regions such as southern China, alfalfa is commonly preserved as silage. However, low dry matter (DM) and sugar content, as well as high buffering capacity, make ensiled alfalfa often subject to extensive proteolysis. During the ensiling process, between 44% and 87% of alfalfa proteins can be degraded by plant and microbial proteases (Jones, Hatfield, & Muck, 1995). The high extent of protein degradation leads to the low utilization of forage nitrogen (N) by ruminants, thus resulting in high economic losses to farmers and adverse environmental impacts.Red clover (Trifolium pratente L.), a legume forage of similar protein content to alfalfa, has been shown that only 7%-40% of red clover protein is degraded during ensiling. This relatively lower protein degradation has been proven to be related to the activity of polyphenol oxidase (PPO) in red clover (Sullivan & Hatfield, 2006).

Quality of alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.) mixture silages depending on the share in the mixture and additives

“…Fermentation quality could affect the process of proteolysis of ensiled alfalfa, as proteases are sensitive to pH. Treatments which contained any of the used percentages of red clover, as well as the ones which received the higher dose of oak tannin, reduced the ammonia nitrogen (NH3-N) content, which is similar to the results obtained by Herremans et al (2019), and Dong et al (2019). This suggests that the use of oak tannin and red clover in certain proportions had a positive influence on the microbial proteolysis during the process of ensiling.…”

“…In alfalfa, 44 -87% of protein is degraded to non-protein nitrogen (NPN) compounds during silage fermentation, whereas for red clover of similar protein content, only 7-40% of the protein is lost due to plant proteolytic degradation (Jones et al, 1995). The high extent of protein degradation in ensiled alfalfa leads to the low utilization of forage nitrogen (N) by ruminants, thus resulting in economic losses to farmers and adverse environmental impacts (Dong et al, 2019). Inhibited proteolysis in ensiled red clover was connected by various studies with polyphenol oxidase (Mayer, 1986), a coppercontaining enzyme naturally present in red clover (Jones et al, 1995;Sullivan and Hatfield, 2006).…”

“…Inhibited proteolysis in ensiled red clover was connected by various studies with polyphenol oxidase (Mayer, 1986), a coppercontaining enzyme naturally present in red clover (Jones et al, 1995;Sullivan and Hatfield, 2006). Recent studies have shown that red clover through co-ensiling could confer alfalfa the same features of reducing proteolysis as red clover (Li et al, 2018;Dong et al, 2019). Bacterial inoculants are the primary additives used for legume silage in the USA because they usually have a positive effect on the silage more often than enzyme additives and are much safer to use than acid or formaldehyde additives (Muck and Bolsen, 1991).…”

Clarifying Key Cellulase Component Cooperated With Lactic Acid Bacteria for Alfalfa Lignocellulose Degradation to Improve Lactic Acid Production

“…According to the formula reported by Porter et al (1995), DM loss was calculated using the corrected DM content. The pH value, ammonia-N, alcohol, lactic acid, and volatile fatty acids in ensiled alfalfa were determined according to the method reported by Dong et al (2019).…”

Effects of wheat‐legume cultures on the fermentation quality and protein degradation of silage

“…However, in order to pursue high DM yield and starch content, WT harvest at the dough stage might face the risk of decreasing crude protein (CP) content (Xie et al, 2012;Li et al, 2016). A large number of legumes were planted as a green manure crop, which can improve production conditions of the post crops, and some legumes were also often ensiled as forage, while higher buffering capacity and lower watersoluble carbohydrate (WSC) content increased the protein degradation during ensiling (Dong et al, 2019). Some studies have shown that the appropriate ratio of WT and kura clover (Trifolium ambiguum M.…”