All Silages Are Not Equal

Date: 4 May 2020
Author: Hill Laboratories

It is timely to think about silage testing, given feed supply is short for much of the country and supplementary feeding may be needed to get livestock through the autumn and winter. Maintaining body condition and animal health is going to be challenging, given the summer dry and on-going effects on pasture growth as well as many farms carrying higher stock numbers due to the pandemic restrictions.

Feed testing provides information to generate feed budgets based on quality – so farm managers can suit the feed available to the stock class i.e. check whether a particular silage is fit for purpose, and allocate a suitable allowance per day.

Customers often ask us to share regional results on some of the tests we do for the agriculture sector, to benchmark or provide context for individual farm result data. This is actually quite difficult to do for a number of reasons, and for some regions, we might only have small data sets. However, we do recognise the power of data when there is a reasonably large set to interrogate.

This article explores some findings on an analysis of pasture silage and baleage samples submitted in 2019, being a data set of more than 1600 samples. The focus is on metabolisable energy (ME) - as energy is the key for maintenance of body weight and production. It is immediately clear from Fig 1 that all silages are not equal.

Fig 1: Frequency distribution of Metabolisable Energy (ME) results for samples identified as Pasture Silage or Pasture Baleage, analysed at Hill Laboratories in 2019.

The median value at 9.9 MJ/kgDM means that approximately half of these silages have an ME of less than 10. Various publications, including the DairyNZ Facts & Figures booklet, describe pasture silage as “good” or “poor” according to the guideline criteria shown in Fig 2.

Fig 2: Excerpt from DairyNZ publication “Facts & Figures” for guideline feed values, p66.

The fact that half of the samples tested in 2019 would therefore be considered as fair or poor, does not mean these feeds are of no use at all – it just means that some will suit different livestock classes and feeding needs better than others. The power is in having this information to help make those decisions.

Another finding of interest is that nearly 5% of the samples had an ash result above 13%. The ash result is a measure of the inorganic content in the sample and while some of this is valuable mineral content, high results (>10%) are usually indicative of soil contamination. This soil contamination could have occurred at pasture harvest, during the silage stack management or even at sampling. As ash does not contribute to digestible energy for livestock, these samples have a very low ME. Having an Iron (Fe) test included in the silage analysis by requesting the Extended Silage Profile (EstSil) will be very useful in characterising the ash and mineral content – as high Fe levels are a good indicator of soil contamination. The full range of minerals reported in this test profile will also help livestock managers and nutritionists manage any shortfall in nutrition for optimal animal health.

Silage and other feed testing are made easy through provision of our Animal Feed Testing kit, which has sampling information, sample bags and return courier bags included. Tests and kits can be ordered online or these tests can be arranged through your usual farm advisory channels.