Making & Feeding Quality Forage – Principles

September 1, 2016

Making & Feeding Quality Forage – Principles

Maximising growth and utilisation of high quality home grown forages is a key component in driving dairy farm profitability, particularly with low milk prices.  This includes both grazed and conserved pastures and crops, as dairy farmers will need to feed both to match forage supply with herd requirements.

This is the first in a series of articles considering making and utilising silages, and covers key principles in the ensiling process.  Subsequent articles will discuss tools to assist in silage making, and returns on investment from making quality silage, including using an inoculant.

There are two aspects of quality with silages being, the nutrient value of the crop at harvesting, and how well it is preserved.  The first relates to type of crop, fertiliser strategy and crop maturity, as these will determine predicted metabolisable energy (ME), protein, fibre (NDF), sugar or starch and mineral values.

Silages are preserved by bacteria consuming sugars to produce volatile fatty acids (mainly acetic, butyric, lactic) thus pickling the crop to a stable acid pH.  The longer this process takes, more sugars are used (dry matter losses (DM)), more protein is broken down (increased ammonia nitrogen production), the less stable the resulting silage (increased aerobic losses at feeding out), and the less efficiently it is utilised (lower feeding value).  Very slow fermentations can result in over heating resulting in lower nutritive value, even though stock might like the “tobacco” smell and taste. A slow fermentation can also allow negative bacteria such as clostridia to develop, overwhelming the beneficial bacteria and preventing a rapid pH drop which can allow yeasts and mould to take hold.

Very wet crops can result in significant nutritive and dry matter losses due to effluent production, a highly potent pollutant, so cutting drier crops (>25% DM, ideally 32-35% DM) or wilting will help reduce this, and concentrate sugar levels.  Wetter silages stabilise at lower pH levels than drier silages, so require more acids to be produced, using up more sugars to achieve this (increased DM losses).

Good silage making practices, such as short chop length, sufficient compaction and rapid sealing (excluding oxygen ingress) are key to preserving as much crop in as good condition as possible.  Next month’s article will discuss useful tools such as inoculants and oxygen barriers.

As featured in NZ Dairy Farmer

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