Silage and hay making
How forage is conserved as silage and hay: ensiling science, cutting stage, additives, silos and bales, hay drying, losses, and a clamp sizing sum.
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Pastures and fodder crops grow fastest in the rainy season or spring, when animals cannot eat it all, and slowest in the dry season or winter, when feed is scarce. Conserving surplus forage as silage or hay carries feed from the season of plenty to the season of shortage, keeping milk and meat production steady. Done well, conserved forage keeps much of the nutritive value of fresh grass; done badly, it rots, loses most of its value, or even makes animals sick.
Silage and hay making are standard topics in fodder production, animal nutrition and dairy husbandry exams.
Silage: preserving by fermentation
Silage is moist forage preserved by anaerobic fermentation. Lactic acid bacteria, naturally present on the crop or added as inoculants, convert plant sugars to lactic acid, lowering the pH until spoilage organisms cannot grow. As long as air is kept out, silage keeps for months or years.
The phases
- Aerobic phase: in the first hours, plant respiration and aerobic microbes use the trapped oxygen, producing heat and losing sugars. Fast filling and good compaction shorten this phase.
- Fermentation phase: lactic acid bacteria multiply and pH falls, typically to about 3.8 to 4.2 for grass and maize silage within one to two weeks.
- Stable phase: with the silo sealed, little changes.
- Feed-out phase: once opened, air lets yeasts and moulds grow, heating the silage (aerobic instability) and wasting it.
What makes good silage
- Crop and stage: maize at about 30 to 35 per cent dry matter (kernels at half milk line); grasses and legumes at early heading or early flowering for good digestibility; sorghum and cereal crops also make good silage.
- Dry matter: about 28 to 40 per cent depending on silo type; very wet crops produce effluent and butyric (clostridial) fermentation, with rancid smell and poor intake, so they are wilted first.
- Sugars: enough fermentable sugars; legumes such as lucerne are low in sugar and high in buffering capacity, so they are harder to ensile.
- Chop length of about 1 to 2.5 cm for maize, for good compaction.
- Rapid filling, thorough compaction and immediate airtight sealing with weighted plastic sheets.
Additives
- Inoculants of homofermentative lactic acid bacteria speed fermentation; some heterofermentative strains (such as Lactobacillus buchneri) improve aerobic stability.
- Acids (formic, propionic) and sugar sources such as molasses for difficult crops.
Silo types
Bunker or clamp silos, drive-over piles, tower silos, wrapped round bales (bale silage, haylage) and, for smallholders, bag or pit silos.
Hay: preserving by drying
Hay is forage dried to a moisture content of about 15 to 20 per cent (80 to 85 per cent dry matter), low enough to stop microbial growth. Steps:
- Cutting at the right stage: early flowering for legumes, early heading for grasses, balancing yield and quality.
- Field drying: tedding (spreading and turning) and raking into windrows speed drying; conditioners that crimp stems help stems dry as fast as leaves.
- Baling when dry enough; baling too wet causes heating, mould and even spontaneous combustion in stacks.
- Storing under cover, off the ground.
Losses come from plant respiration during drying, leaf shatter (especially in legumes, whose leaves hold most of the protein), rain leaching and storage moulds. In humid climates, making good hay is difficult, so silage or haylage is often preferred.
Comparing silage and hay
| Silage | Hay | |
|---|---|---|
| Weather dependence | low (short wilting) | high (several dry days needed) |
| Typical losses | about 10–20% of DM if well made | about 15–30% with rain or leaf loss |
| Feeding | needs daily feed-out, heavy | easy to store, transport and sell |
| Capital | silo or bales, plastic, machinery | baler, storage shed |
Feed-out management
Remove enough silage from the face each day, at least about 15 cm in cool weather and more in warm weather, with a clean, smooth face, to prevent heating and spoilage. Discard mouldy silage: it can contain mycotoxins and cause disease, including listeriosis.
Sizing a silage clamp
A dairy farm will ensile 400 t of fresh maize at 33 per cent dry matter.
- Dry matter = 400 × 0.33 = 132 t DM.
- With good compaction, maize silage density is about 230 kg DM per m3: volume = 132,000 ÷ 230 ≈ 574 m3.
- A clamp 8 m wide and 3 m high needs a length of 574 ÷ (8 × 3) ≈ 24 m.
Feed-out rate. The farm feeds 60 cows 12 kg of silage DM each a day = 720 kg DM, or about 720 ÷ 230 ≈ 3.1 m3 a day. The face area is 8 × 3 = 24 m2, so the daily face removal is 3.1 ÷ 24 ≈ 13 cm, slightly less than the 15 cm recommended in warm weather. A narrower clamp, such as 6 m wide and 3 m high (about 32 m long), would give about 17 cm a day.
Duration. 132 t DM ÷ 0.72 t a day ≈ 183 days of feeding, enough for the six-month dry season, before allowing for losses.
Key points
- Silage preserves moist forage by lactic acid fermentation under anaerobic conditions, reaching pH about 3.8–4.2.
- Phases: aerobic, fermentation, stable, feed-out; exclude air by fast filling, compaction and sealing.
- Ensile maize at about 30–35 per cent DM; wilt wet grass and legumes; use inoculants or acids for difficult crops.
- Hay is dried to about 15–20 per cent moisture; losses come from respiration, leaf shatter, rain and moulds.
- Remove at least about 15 cm from the silage face daily; size clamps from DM and density.
What the exams ask
- School-leaving and entrance papers: meaning of silage and hay, and steps in making them.
- Degree and research-fellowship entrances: fermentation biochemistry, factors affecting silage quality, additives, silo types, hay drying and losses, and quality evaluation.
- Professional examinations: forage budgeting, clamp sizing, feed-out management and economics of conservation.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Why does bad silage smell rancid?
Butyric acid from clostridial fermentation, usually because the crop was too wet, low in sugar or contaminated with soil. Such silage is less palatable and less nutritious.
Can smallholders make silage?
Yes. Small bag, drum and pit silos, filled by hand and well compacted and sealed, work well for a few cows and are widely promoted in East Africa and South Asia.
Why does my hay heat in the stack?
It was baled too wet. Microbes and plant respiration produce heat, which can damage the hay and, in extreme cases, start fires.
Sources
- McDonald, P., Henderson, A. R. and Heron, S. J. E. The Biochemistry of Silage, 2nd edition. Chalcombe Publications, 1991.
- Kung, L., Shaver, R. D., Grant, R. J. and Schmidt, R. J. "Silage review: interpretation of chemical, microbial, and organoleptic components of silages." Journal of Dairy Science 101, 4020–4033 (2018).
- Muck, R. E. et al. "Silage review: recent advances and future uses of silage additives." Journal of Dairy Science 101, 3980–4000 (2018).
- 't Mannetje, L. (ed.) Silage Making in the Tropics with Particular Emphasis on Smallholders. FAO Plant Production and Protection Paper 161, 2000.
- Rotz, C. A. and Muck, R. E. "Changes in forage quality during harvest and storage." In Fahey, G. C. (ed.) Forage Quality, Evaluation, and Utilization. ASA, CSSA and SSSA, 1994.
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