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33
Editorial Information

Richard Cooper, EVBC Ltd.

Published 2009

Nutrition of Dairy Herds
Part 4 - Conserved Forage Management


The importance of forage in dairy farming should not be underestimated. Ruminants have evolved to effectively utilise low quality forages through slow anaerobic  fermentation  by  a  diverse  variety  of enteric microorganisms. For the modern dairy cow, the metabolic demands of lactation are substantial, and the need for rapidly digestible, high energy and protein feedstuffs in order to support milk production are very much at odds with her evolutionary design. If dairy cattle are to thrive, and indeed survive, a substantial proportion of their diet must be from forage. Maximising the quality of this forage is one of the greatest determinants of dairy productivity and economic viability, and this is especially true of conserved forage sources.

There are several critical points in the process of silaging and feeding out,  that can have substantial bearing  on  forage  quality  and  subsequent production. These are:

 

Preparing the crop

For general purpose leys, it is desirable to have around 70% ryegrass content, although productivity can be acceptable at even 50%. The presence of weeds, such as docks and thistles, will decrease sward output  and silage quality. Weeds are often a symptom of pasture problems such as soil pans (a dense, compressed  layer of soil),  incorrect  pH (target 6.0-6.5), poor drainage or poor soil fertility

(e.g. low K+ or P-). Under optimal growing conditions grass  species  usually  limit  weed  infiltration  by competitive growth, but occasionally a selective herbicide may be needed. Where pastures appear poor - e.g. significant ingress of weeds or excessive poaching - referral to an agronomist is advised, who will be able to advise on whether a partial or full reseed is needed.

If land has been churned up by machinery or contains a significant amount of molehills, rolling pastures prior to silaging will reduce the risk of soil contamination of the crop. Soil contamination in silages with high terminal pHs increases the risk of undesirable organisms such as Listeria monocytogenes (can cause 'silage eye' and encephalitis) or clostridia spp.

 

Comparative costs of forage

 

Feed

Cost per tonne of dry matter

1st cut grass silage

£54

2nd cut grass silage

£69

Maize silage

£53

Wholecrop (winter barley)

£59

Wheat

£110

18% dairy compound

£197

 

1 a well managed clamp face

Fig 1: A well-managed face prevents spoilage and subsequent degradation of essential nutrients.

2 a poorly managed clamp face

Fig 2:    A poorly managed clamp face.

3 silage analyses

Fig 3:     Silage analyses.

 

A good silage is an extremely nutritious feedstuff - if made well it can provide ME 11.0MJ/kgDM and 15% crude protein , and, aside from grazed grass,  is probably  the  cheapest  feedstuff  available  to  the farm.

 

Minimising harvesting losses

The process of harvesting is a crucial point influencing the quality of the end product.

  • The ideal time to cut silage with respect to subsequent quality and milk production is pre- bloom, i.e. just before the flowering.
  • Grass should be mown leaving at least 5cm length. Even and rapid spreading within an hour of cutting is advised, and with no more than 24 hours wilt.
  • Chop  length  should  be  adjusted  to  the  dry matter of the crop: 1.5-2.0cm for 28-35% DM, 2.0-2.5cm  for  20-28%  DM,  >2.5cm  for  crops <20% DM
  • Trials within the US have shown that dry matter losses  and  subsequent  milk response  have been improved by rapid wilting. Crops are cut in the morning in good weather and wide swaths made. This increases drying rates and the crop is collected in the afternoon chopped and clamped. The challenges of this practice are its heavy demands on personnel and machinery - crops may become too dry if the processing is not quick enough. The advantages of getting silaging completed within a day - given the changeability of the UK weather - are easily appreciated.
  • The  harvesting  of  crops  for  conservation requires an experienced and dedicated team: cutting corners is a false economy.

 

Minimising clamp losses

Once harvested, retaining as many of the nutritive properties of the crop is desirable:

  • The clamp should be filled, consolidated and sealed as soon as possible after harvesting. Consolidation is best achieved by thoroughly rolling  the  crop  with  an  appropriately  sized tractor between every load.
  • Where a clamp has to be left overnight, it is best practice to cover it with a plastic sheet. Do not roll the settled silage before the next layer is added the following morning - this will increase air ingress.
  • Once filled, cover with a double plastic sheet; a thin, flexible layer in contact with the crop and a thick   protective   layer   on  top.   A   very   thin adhesive plastic film is now available as a contact layer, and has demonstrated very positive benefits   in   reduction  of   top   and shoulder wastage.
  • Once   filled,   the   clamp   should   remain undisturbed for at least 21 days where possible. Systems should be in place to allow adequate and appropriate drainage of effluent from the clamp.

4 cutting silage pre bloom

 

Fig 4:  Cutting silage pre-bloom, and especially before seed head formation, significantly increases the subsequent nutritive value of the silage made.

 

5 harvesting of crops for conservation

 

Fig 5:  Having a dedicated, experienced team is critical in producing good quality silage

 

6 forage should be cut at an appropriate length

Fig 6:  Forage should be cut at an appropriate length for its dry matter to achieve good clamp consolidation, and with the potential subsequent effects on animal health carefully considered.

 

Minimising feed-out losses

The nutritive losses at feed-out can be extremely significant and may be up to 10% of the original crop dry matter. As soon as the silage face is exposed to air, the crop starts deteriorating by aerobic (oxygen driven) fermentation. Much of this will be driven by moulds and yeasts, although bacteriological degeneration also plays a significant part. As dairy cows have a very refined sense of smell and taste, these nutritive losses are compounded by reduced dry matter intake by animals. The result is that a very  different  ration  can end  up  being consumed than the one derived from the clamp analysis.

  • Using a block cutter, auger or sheer grab allows silage to be removed cleanly from the face and reduces the depth into which air is introduced, slowing aerobic losses. Purchase of the correct machinery is considered a wise investment.
  • Ideally it should take no more than 5 days to go across the length of the silage face. Removing no more than a single grab deep will reduce the time a given section of the face is exposed.
  • Crops that failed to reach a low pH in the clamp (typically dry silages) undergo a more rapid aerobic fermentation when fed out. In addition, clamps faces are less easy to manage .
  • The act of feeding out is an extremely effective way of aerating the crop. Fungal and bacterial contaminants   are   able   to   reproduce   and metabolise substrates much quicker at higher temperatures. During summer months it may be neccessary to revert to twice daily feeding to prevent excessive deterioration.
  • Removing old silage (or TMR) from dairy feed bunks every day prevents new silage being contaminated as it fed out. Remaining mouldy feed makes an excellent 'starter culture' and has negative effects on cow dry matter intakes.

fig7

Source: Institute of Grassland and Environmental Research, Aberystwyth, Ceredigion

 

Planning ahead

There is arguably no greater error in dairy nutrition than running out of winter forage reserves; buying in forage or forage extenders is both expensive and logistically difficult. It is crucial, for farmers, feed advisors and nutritionists alike, to constantly review remaining forage, and this is easily achievable by regular basic calculations.

  1. The  volume  of  the  silage  clamp  should  be calculated; the sloping front of a clamp can be estimated by basic trigonometry.   e.g. 20m x 15m x 2m = 600m3
  2. The  fresh-weight  density  of  silage  can  be assumed   under   most  circumstances   to   be 600kg/m3;   poorly   compacted,   long-chop   is approximately  500kg/m and  well-compacted short-chop 700kg/m e.g. 600m x 700kg/m = 420,000kg or 420 Tonne
  3. The silage feed-rate per head per day should then be taken from the ration and used to calculate the number of days remaining. Silage wastage of 10-15% must be budgeted for.  e.g. 150 cows fed 12kg /head /day = (420,000 x 0.85) / (150 x 12) = 193 days
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