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Published 1 February 10
A wide variety of fresh and conserved forages are available for dairy feeding. In addition to the mainstays of grass and clover, buffer crops like stubble turnips, kale, forage rape, forage rye, forage peas, turnips, swedes and lucerne can all be grazed or zero-grazed. Most buffer crops can also be stored or ensiled for winter feeding, where they are joined by a vast range of conserved forages - most commonly grass silage, maize silage, wholecrop cereal silage, alkalage, hay and straw.
Forages are valuable for:
- Providing excellent, generally dilute sources of nutrients,
- Supplying particularly valuable fibre for rumen digestion,
- Being home grown and, in many cases, more sustainable and economic than other feeds.
Providing they are well-managed forages can be more cost-effective sources of nutrients for dairy feeding than concentrates in many circumstances. Feeding a mixture of forages rather than grass silage alone will generally give higher dry matter intakes resulting in higher yields or allowing savings in concentrate supplementation.
While forages are the ideal natural basis for ruminant feeding, on their own their nutrient concentrations are generally insufficient to support modern dairy herd production levels. Care is required in supplementing grazed grass with forages as they can easily displace more dry matter from the diet than they add and so reduce performance.
Grazed pasture is the single most cost-effective dairy feed if grown and utilised efficiently.
Ryegrass swards can be highly productive, yielding large amounts of palatable and nutritious feed over an extended growing season. The inclusion of white clover in swards has been shown to improve overall pasture yields, consistency of production and protein content markedly, while reducing nitrogen fertiliser requirements and enhancing soil structure. The nutritive value of swards varies widely and essentially depends upon their degree of maturity, with younger, leafier pastures supporting far higher levels of production than older, stemmier ones.
Buffer crops can play a valuable role in filling gaps in grazed pasture supply or extending the grazing season for some or all classes of dairy stock in either spring or autumn. Most are able to produce high yields of nutritious feed per hectare. However, variable and often relatively low feeding values can make buffer crops unreliable and better suited to late lactation or dry cow feeding. Buffer crops need to be managed correctly if yields and utilisation are both to be maximised.
Kale can be particularly useful for late summer strip-grazing, especially if a spread of sowing dates gives good continuity of supply.
Kale Key Points:
- Goitrogen levels in flowering plants make then unsuitable for dry cows,
- Feeding large amounts is likely to taint milk,
- High selenium or iodine minerals may be required.
At normal rates of 20kg/cow/day 1.0 ha of kale feeds 100 cows for one month.
Stubble turnips can provide useful late season strip-grazing from a short 10 week growing period.
Key Stubble Turnip Points:
- Yields can be very variable, especially in dry seasons,
- Very low fibre and protein levels mean only low production levels can be supported.
- A grass 'run-back' area may be advisable.
At normal rates of 40 kg/cow/day 1.0 ha of stubble turnips feeds 100 cows for 10 days.
Forage rape provides a further catch crop opportunity for late season strip-grazing.
Key Forage Rape Points:
- Yields can be very variable,
- Low fibre levels means only low production levels can be supported,
- Supplementation with baled silage or another source of fibre is important.
At normal rates of 45kg/cow/day 1.0 ha of forage rape feeds 100 cows for one week.
Swedes and Turnips
Although not as popular as in the past, both swedes and turnips can produce large quantities of high energy DM for winter grazing or lifting and yard feeding.
Key Swede and Turnip Points:
- Swedes tend to be consistently higher yielders and energy producers,
- Both crops can suffer from high levels of soil contamination and wastage,
- Swedes can taint milk if fed excessively prior to milking,
- Both crops are highly palatable and can be successful grazed by older cattle.
At normal rates of 20 and 25kg/cow/day respectively, 1.0 ha of swedes or turnips feeds 100 cows for 2 weeks.
Various hybrids of both swedes and turnips are available for feeding in a similar way to kale or forage rape.
Fodder beet is potentially the best buffer crop available, producing significant yields of highly digestible dry matter for winter grazing or lifting and yard feeding.
Key Fodder Beet Points:
- High sugar levels need long fibre supplementation for the best results,
- Soil contamination can cause significant digestive upsets in lactating cows,
- Beet tops can cause tainting of milk and should be wilted before feeding if possible.
At normal rates of 25kg/cow/day 1.0 ha of fodder beet feeds 100 cows for a month.
Very similar to Westerwolds or Italian ryegrass, forage rye is a useful provider of early spring grazing, although it can quickly run to stem and lose feeding value.
Key Forage Rye Points:
- Grazing should start early and fertilisation should be controlled to avoid excessive growth,
- Zero grazing can improve intakes and reduce waste,
- Low protein levels and modest energy values can limit crop value.
At normal rates of 30kg/cow/day 1.0 ha of forage rye feeds 100 cows for a week.
While grass silage can only be as good as the sward from which it is made, there will inevitably be some losses in both quantity and quality in the whole process of harvesting, fermentation and feeding.
In addition to these nutritional parameters, silage chop length should not be too short as this can impair fibre digestion and promote sub-clinical acidosis.It is the combination of dry matter and nutrient (ME or CP) content rather than either individually that is the key determinant of a silage's overall feeding value.
Excess nitrogen in the crop should be avoided in silage making wherever possible as it can lead to reduced sugar levels and poor preservation. Good silage-making should also maximise palatability if high daily intakes are to be possible.
Forage maize has become British dairy farmers' main alternative to grass silage in recent years. It produces a high yield of relatively high dry matter silage with a good energy but relatively poor protein content from a single late season harvest.Providing forage maize is grown and managed correctly it can be an extremely valuable home-grown feed resource for many dairy herds.
Key Forage Maize Points:
- A source of long fibre should generally be included in diets,
- Low protein content makes protein supplementation essential,
- Relatively high starch levels help boost milk proteins,
- Adequate dietary Rumen Degradable Protein (RDP)? will be particularly important.
Considerable interest has recently been shown in harvesting maize with a combine and either ensiling it as 'grain ear maize' or treating it by crimping. Although relatively new, these techniques have been reported to produce very high energy concentrate-type feeds with attractive nutritive values.
Crimped maize, , can be 69% DM with an ME content of 14.0 MJ/kg DM, CP of 100 g/kg DM and starch content of 680 g/kg DM.
Rather than being harvested conventionally for grain, cereal crops mown and harvested with a forager before they are fully ripe can produce valuable wholecrop feeds. They boast generally high dry matters and reasonable combinations of energy and protein, although actual feeding values vary with the stage at which the crops are harvested and the way in which they are preserved. Well-produced wholecrop can be particularly valuable in forage mixtures which trials have shown can improve both dairy cow intakes and performance - primarily milk quality rather than volume.
A true silage, fermented wholecrop is cut at around 35-45% DM and ensiled in exactly the same way as high dry matter grass or maize silage. Inclusion of the straw means a generally mediocre energy value, and the grain needs to be adequately cracked if it is to be digested.
Made from more mature 50-65%+ DM crops nearer to combining time, this involves mixing with urea at 1.5-2.0% before ensiling to preserve the crop without fermentation.
The urea is broken down to release ammonia which then preserves the crop. On higher dry matter crops (60-80%) an additive containing urea with an enzyme to aid urea breakdown should be used, producing what is commonly known as Alkalage. Starch contents tend to be higher than fermented wholecrop due to greater grain fill, and the urea preservative increases both the CP levels and pH of the feed.
Hay is generally of a lower nutritive value than silage but with far higher DM and fibre contents. The very best hay has an energy value comparable to good silage with an additional physical 'scratch factor' benefit in stimulating rumination. In contrast, poorly made hay can be a very poor feed and high fibre contents together with low palatability (from moulding) can seriously limit intakes.
Measuring Hay Quality:
- The type of sward cut,
- The maturity of the sward at cutting,
- How quickly the crop is dried,
- Whether the crop was rained on in the field,
- The amount of leaf left on the crop,
- How well it is stored.
Barley straw, in particular, can be a useful filler for cattle feeding, its low nutritive value making it suitable only for low yielding late lactation and dry cow diets. Like hay, it can be valuable for its scratch factor, especially where included in mixed diets. There is no recognised method for the laboratory evaluation of straw, assessment of feed quality being related mainly to the ratio of leaf to stem, the more leaf (with a typical ME of around 9 MJ/kg DM) to stem (4 MJ/kg DM) the better. Palatability is also critical feeding straw should have no mould and bales should spring apart when the strings are cut.
Legume silages invariably have relatively low energy contents (typically 9-10 MJ ME/kg DM for pure legumes) due to generally high fibre levels. However, as this fibre is digested very rapidly, the effective ME provided is much higher than the laboratory analyses suggest as a result of higher than expected overall feed intakes. Laboratory analysis of legume silages is, however, valuable as their protein content can vary widely depending on species, levels in sward mixtures and harvesting.
Crops which are turned in the field or harvested too dry (over 35% DM) can experience a high degree of leaf shatter with loss of high protein leaf. Legume silages can make an especially valuable contribution to the protein requirements of organically-fed cows. High buffering capacities make legume silages more resistant to acidification, demanding greater care and attention in ensiling to ensure stable fermentations and good preservation.
Mycotoxins are toxic compounds which are produced naturally from fungal species or moulds. The majority of mycotoxins are derived from three main mould groups: Fusarium, Aspergillus and Penicillium. Penicillium and Aspergillus derived mycotoxins are often associated with the storage of feedstuffs and ensiled forages. Penicillium based mycotoxins can often affect the sensory quality of the forage and can affect the palatability of forages, often leading to a reduction in feed intakes.
For more information on Mycotoxins, the symptons and how to deal with them please click here.