The method of feeding-out silage can directly impact both the aerobic stability of the silage and the feed value of the silage.
Final silage quality is defined by the timing of forage harvesting, the control of the forage microbiology and the control of air during ensiling, storage and feedout.
During feedout silage is exposed to oxygen which allows yeast to become metabolically active, to grow and to generate heat, which means energy and feed value losses. Every 10°C rise in temperature of 1 ton of silage over a 24-hour period is the equivalent of 30MCal, or 5 liters of lost milk production. Silage as been recorded as reaching temperatures excess of 70°C through the action of yeast. In the absence of air, the silage maintains a relatively constant temperature until the bunker is opened, with only a slight decline in temperature occurring from the ensiling temperature.
The initial packing density defines how far air can penetrate into the silage face – generally somewhere between 20cm and 1m behind the face. The higher the density, the less the air can penetrate the silage and the more temperature-stable the silage will be at feed-out.
The method adopted to feedout silage can significantly impact the density and pore space of the face of the silage, potentially allowing air to penetrate in greater volumes and to greater depths behind the face of the silage, allowing yeast to become active further behind the face and for the silage in turn to start to heat.
Various methods to feed-out silage from bunkers, piles, and bags:
The defacer may be a “stand alone” piece of equipment or integrated within a mixer wagon which removes a thin layer of silage from the face. Removal of the silage maintains the density of the face and reduces air from entering into the forage, therefore limiting the growth of yeast in the silage, protecting up to 3% DM from feeding losses as well as maintaining the optimal feed value of the silage. Removal of the silage can be relatively slow however the feeding method ensures the face is crossed rapidly and that the animal is fed a daily uniform silage aiding rumen stability. This is the optimal feedout method for all silages though it must be recognized that the defacer reduces the silage particle length and therefore the physical effective fiber.
The silage rake is attached to a telehandler and scrapes the silage from the face, allowing the removal of a relatively narrow layer of silage to be removed without reducing the silage face density. The effectiveness is not as great as with the defacer and the feedout is slower with the silage then requiring bucket collecting however the system is a good bunker management tool suitable for use on all bunkers and piles but not for use on silage bags.
Block cutters maintain the major integrity/density of the face, but generally lead to a slight loosening of the silage at the base of the block that is removed even with the best management practice. Block cutters may remove an entire section of the face or a defined block volume (see photo). The depth of the block that is removed is significant (varying between 50cm and 1m deep) which means that the face may be crossed relatively slowly, and, if the entire face is not crossed daily variability exists within the ration.
Use of a grab or a bucket leads to very significant disruption of the face of the silage, the level of disruption being dependent on the feeder. As the face is disrupted more air is allowed behind the face of the silage and the yeast numbers start to grow, which leads to an ongoing instability of the silage and a constant reduction in the feed value of the silage, a reduction in the animal dry matter intake of the silage ─ as the palatability lowers with rising ammonia and volatile acids ─ and an increased imbalance of the rumen as the animal is fed a constantly changing feed structure. Feeding with a grab or a bucket is the least recommended method of feeding silage.
To ensure maximum feed value, silage should only be removed from the bunker when it is about to be fed, and only the silage that is going to be immediately fed should be removed – loose silage at the face of the bunker will nutritionally deteriorate and any silage that has been excessively removed from a previous feeding should be collected and fed as soon as practical.