How good is that silage?

The best silage comes from good quality pasture. Conditions at harvest together with the practices used in the process dictate the quality of the silage made.

Too often the silage analysis results that we see indicate that the grass has been harvested too late in the growing season - for whatever reason. Samples often have low protein, high fibre and low digestibility with resultant low metabolisable energy (ME). This analysis profile is a consequence of plant maturity as grasses grow past the vegetative stage and start to produce stalk and seed-head.

Fig 1 shows the frequency of this occurrence from a simple qualitative data analysis of a group of 200 pasture silage samples analysed at Hill Laboratories recently. Less than 20% of these samples fell into the 'good' category, with nearly 40% rated 'poor' and less than half falling into an 'adequate' category.

While this simple analysis is only desktop and does not consider associated animal production data, it does point out a lost opportunity for farmers in that the operational cost of making good silage is pretty much the same as making lesser quality feed. An increase in silage digestibility (achieved by harvesting at an earlier growth stage) will increase milk production by improving intake and utilisation of nutrients in the silage. The converse is true whereby silage with low digestibility reduces intake and milk production response. Silage digestibility is largely a function of the Neutral Detergent Fibre (NDF) component which represents the total insoluble fibre content of the feed.

As well as protein, NDF and ME results, a silage analysis will provide information on fermentation quality by way of pH, ammonium-N and lactic acid. If the fermentation quality is poor this may lead to unpalatable silage with depressed intake and poor animal response to feeding. Additionally, a volatile fatty acid (VFA) profile provides analysis for acetic, butyric, propionic and formic acids. The proportion of fermentation acids in the silage can greatly influence the proportions of rumen VFA e.g. lactic acid in silage has an effect on the propionate levels in the rumen of cattle. The amount of fermentation acids produced is largely dependent on dry matter and sugar content of the grass at harvest (together with chop length, inoculant, compaction and covering of the stack or bales). Higher dry matter silages will not produce as much acid as lower DM silages (see Fig 2) and storage and feeding practices need to be managed accordingly. Very low dry matter silages are undesirable however, in that they produce large amounts of effluent which is not only a waste of nutrients but also an environmental contaminant. They also may result in an undesirable fermentation.

The key message

The message is to have whatever silage you have bought or made analysed for feed quality. Good quality silage may reduce the requirement for expensive concentrates, while poorer quality silages can be used with other better quality feed to balance the ME and protein requirements of the livestock being fed. A silage test is in very low cost when compared to the value of the stack and its potential production value

For further details contact our agricultural client service managers

Contact us today on 07 858 2000 (North Island) or 03 377 7176 (South Island) or click below for the contact details of: