Veterinary · Pre-clinical and foundation · also MSVE LPM-121
Growing, conserving and grazing the forage that feeds ruminants: fodder crops, hay and silage, pasture management and toxic plants.
In the exams: ICAR AICE-JRF core group 05 (LPM and Nutrition units)
Fodder production and grassland management is the part of livestock science that grows, conserves and grazes the forage that ruminants eat. Forage means the leaves and stems of plants eaten by animals, either cut and carried to them (fodder, soilage, hay, silage) or grazed where they grow (pasture and range). In most ruminant systems forage supplies the larger share of dry matter in the diet, and in smallholder and pastoral systems it is often almost the whole diet. Feed is usually the largest single cost of milk and meat production, and of that feed bill the forage is the part a farmer can most directly control by choosing crops, cutting at the right stage and conserving surplus for the lean months.
The subject sits between agronomy and animal nutrition. A veterinarian meets it every week: a herd whose milk yield falls every May because the green fodder runs out; a buffalo that dies within an hour of grazing a wilted sorghum regrowth; a flock of sheep with photosensitised ears on a pasture invaded by lantana; silage that smells of rancid butter and a cow with listeriosis that circles in the pen.
This manual follows the units of the Indian MSVE course LPM-121 (Fodder Production and Grassland Management) and widens them for a global reader. Tropical C4 grasses, cut-and-carry Napier systems of East Africa and South Asia, temperate ryegrass-clover grazing of New Zealand and north-west Europe, lucerne hay of North America and the rangelands of Australia, Africa and the Thar are treated side by side. Where practice, legal standards or numerical values differ by country, soil, cultivar or climate, the text says so rather than choosing one value.
Examiners ask the same core things everywhere: fodder crops and their special features, hay and silage making and quality, grazing systems and stocking-rate arithmetic, nutritive value, and toxic plants. Indian PG, PhD and state service papers carry the subject inside Livestock Production Management; licensing papers abroad ask mainly the toxic-plant and conservation-hygiene parts.
Forage resources fall into five groups. Cultivated fodder crops are sown on arable land specifically to be cut and fed green or conserved: maize, sorghum, oats, berseem, lucerne, cowpea and perennial grasses such as hybrid Napier. Permanent pastures and grasslands are grazed areas of grass and legume that are not ploughed each year, from improved irrigated ryegrass paddocks to village common lands. Rangelands are large areas of native vegetation, often semi-arid, used for extensive grazing and browsing, where management works with the existing plant community rather than resowing it. Crop residues are the straw, stover and haulms left after grain harvest; in South Asia and much of Africa wheat and rice straw and sorghum and maize stover provide a large share of the dry matter fed to cattle and buffalo. Tree and shrub fodders (top feeds) complete the list and become critical in dry seasons. A sound feeding plan for a farm or district accounts for all five sources together, because a shortage in one is normally met by another.
Which fodder grows where is decided first by temperature and rainfall. In India the Planning Commission divided the country into 15 agro-climatic regions, and the National Agricultural Research Project further divided it into more than a hundred agro-climatic sub-zones; internationally FAO uses agro-ecological zones based on length of growing period. The practical rule is simple. In the humid and sub-humid tropics, perennial C4 grasses (Napier, guinea, para, signal and Rhodes grass) and tropical legumes (stylo, centro, desmodium, leucaena) dominate. In the semi-arid and arid tropics the choice moves to drought-hardy annuals such as sorghum, pearl millet and cluster bean, and to perennial range grasses such as Cenchrus and Lasiurus. In the subtropical north Indian plains the kharif (monsoon) season grows maize, sorghum, pearl millet and cowpea and the rabi (winter) season grows berseem, oats, lucerne and Indian clover. Temperate and highland zones grow ryegrass, cocksfoot, fescue, timothy and white and red clover.
Grasses fall into two photosynthetic groups. C3 species, the temperate grasses such as ryegrass, oats, fescue and wheat, fix carbon directly through the Calvin cycle; they grow best at moderate temperatures, and their herbage usually has higher digestibility and soluble sugar content. C4 species, the tropical grasses such as maize, sorghum, pearl millet, Napier and guinea grass, first fix carbon into a four-carbon acid in mesophyll cells and concentrate it in bundle-sheath cells. This makes them more efficient in heat, high light and moisture stress, and gives them much higher potential dry matter yield, but their leaf anatomy has more vascular and bundle-sheath tissue, so their digestibility at a given age is generally lower and falls quickly as they mature. All legumes are C3. The consequence for the nutritionist is that a tropical grass fed alone often limits intake and production through its fibre, and a legume is added for protein.
A forage plant passes from a vegetative stage, through stem elongation (jointing in grasses, branching in legumes), to the boot or bud stage, flowering and seed set. As it matures, yield of dry matter per hectare rises but the proportion of leaf falls, the cell wall thickens and lignifies, and crude protein and digestibility fall. Every cutting or grazing decision is a compromise between quantity and quality. The usual rule is to cut grasses between boot stage and early heading, legumes between late bud and one-tenth (early) bloom, and cereal fodders at the stage that balances the two, such as 50 per cent flowering for sorghum or milk to early dough for maize. Perennial plants also need enough leaf left after cutting or grazing, and enough root carbohydrate reserve, to regrow; cutting too low and too often runs those reserves down and thins the stand.
Maize is the most widely grown cereal fodder in the world and the standard silage crop. It is a C4 annual grown in the kharif and, where winters are mild, in spring and summer. It has no hydrocyanic acid problem and is highly palatable at every stage. For green feeding it is cut from tasselling to the milk stage; for silage it is harvested at the dent stage when the whole plant is at roughly 30 to 35 per cent dry matter, which in the field corresponds to the kernel milk line about half to two-thirds of the way down the kernel. At that stage the grain contributes starch and fermentable sugar, the plant has enough soluble carbohydrate for a good lactic fermentation, and moisture is low enough to limit effluent. Seed rates for fodder are higher than for grain because a dense stand with thinner stems is wanted; the exact rate depends on cultivar and region. Maize is commonly intercropped with cowpea to raise the protein of the mixture. Under heavy nitrogen fertiliser and drought, maize can accumulate nitrate.
Sorghum (jowar, chari in north India) is the main kharif fodder of the semi-arid tropics because it tolerates drought and heat far better than maize. Single-cut types are tall and sweet-stemmed; multi-cut types and sorghum-sudangrass hybrids regrow after cutting and give several harvests. Its great hazard is the cyanogenic glucoside dhurrin, which releases hydrocyanic acid (HCN, prussic acid) when plant cells are crushed and the glucoside meets plant enzymes. Dhurrin is highest in young plants, in new regrowth after cutting or grazing, in leaves more than stems, in plants stunted by drought or frost, and where nitrogen is heavy and phosphorus is low. The standard advice is to cut single-cut sorghum at or after 50 per cent flowering, not to graze or cut young or stressed growth, and to let regrowth reach a safe height and age before use. Ensiling and haymaking reduce, but do not always eliminate, the HCN content. Sorghum also accumulates nitrate under drought and heavy nitrogen.
Pearl millet (bajra, Pennisetum glaucum, now often placed in Cenchrus) is the fodder of the hottest, sandiest and driest soils, such as those of Rajasthan, Gujarat and the Sahel. It is fast-growing, can be cut more than once, and contains little or no HCN, so it is safer than sorghum at a young stage; it can accumulate nitrate and oxalate. Oats (Avena sativa) are the main rabi cereal fodder of north India and temperate countries. Single-cut and multi-cut types exist; multi-cut oats are cut first at about 50 to 60 days and the regrowth is cut at flowering or left for seed. Oats are palatable and make good hay, but oat hay from drought-stressed or heavily fertilised crops is a recognised source of nitrate poisoning. Barley is grown as a rabi fodder on saline or less fertile soils and is widely used for hydroponic sprouted fodder. Teosinte (Zea mexicana), a wild relative of maize, is grown in some humid regions for its tillering and regrowth.
Legumes (family Fabaceae) carry root nodules in which bacteria of the Rhizobium group fix atmospheric nitrogen. This gives them high crude protein without heavy nitrogen fertiliser, enriches the soil for the following crop, and makes them the natural partner of cereals and grasses. Their herbage is generally richer than grasses in protein, calcium and magnesium, and is eaten in larger quantity because the cell wall breaks down quickly in the rumen. Their weaknesses are frothy bloat when lush herbage is grazed, a low content of fermentable sugar and a high buffering capacity that make them harder to ensile, and leaf shatter during haymaking. Seed of a legume sown on land where it has not grown before should be inoculated with the specific Rhizobium strain for that crop; the inoculant groups are crop-specific. Cowpea (Vigna unguiculata) is the main kharif legume fodder of the tropics, grown alone or with maize or sorghum. Cluster bean (guar, Cyamopsis tetragonoloba) suits dry sandy areas. Indian clover or senji (Melilotus indica) and shaftal or Persian clover (Trifolium resupinatum) are rabi legumes. Sweet clovers (Melilotus) contain coumarin, which moulds convert to dicoumarol, so spoiled sweet clover hay or silage causes haemorrhagic disease. In the humid tropics perennial pasture legumes include stylo (Stylosanthes species, notably S. hamata and S. scabra in dry areas), centro (Centrosema pubescens), siratro (Macroptilium atropurpureum), butterfly pea (Clitoria ternatea) and desmodium. In temperate pastures white clover (Trifolium repens) spreads by stolons and is the classic grazing partner of perennial ryegrass; red clover (T. pratense) is a short-lived hay and silage legume; subterranean clover (T. subterraneum) is central to Mediterranean-climate pastures of southern Australia.
Berseem or Egyptian clover (Trifolium alexandrinum) is the principal rabi fodder of the north Indian plains, Pakistan and Egypt. It is sown in October to November, usually by broadcasting seed into standing water on a puddled seedbed, and gives several cuts (commonly four to six) from about December to April, the first about 45 to 60 days after sowing and later cuts at intervals of roughly 30 to 40 days depending on temperature. It is succulent, highly palatable and rich in protein; it is low in dry matter and can cause bloat, so it is fed with straw or a cereal fodder. Seed is commonly mixed with a little oats or mustard to raise yield of the first cut. Berseem seed is often contaminated with chicory (Cichorium intybus), whose seed is similar in size, so certified clean seed matters. Lucerne or alfalfa (Medicago sativa) is a deep-rooted perennial legume, called the queen of forages, grown for green feed, hay and haylage across the world. It lasts several years under good management, tolerates drought once established, needs well-drained, neutral to alkaline soil, and is damaged by waterlogging and acid soils. Cutting at early bloom lets the root reserves recover; cutting repeatedly at the bud stage thins the stand. Dodder (Cuscuta), a parasitic plant, is its notorious seed-borne weed.
Tree fodder, also called top feed or browse, is critical in arid, semi-arid and hill regions where it may be the only green feed in the dry season. Leucaena (Leucaena leucocephala, subabul) is a fast-growing leguminous tree with leaves high in protein but containing mimosine, a toxic amino acid; ruminants convert it to 3,4- and 2,3-dihydroxypyridine (DHP), which is goitrogenic. Ruminants without DHP-degrading rumen bacteria (Synergistes jonesii was the first identified) show alopecia, excess salivation, poor growth and goitre when leucaena is a large part of the diet, so it is usually limited to a fraction of the ration unless the animals carry the bacteria. Gliricidia (Gliricidia sepium), sesbania (Sesbania grandiflora and S. sesban), mulberry (Morus alba), moringa, Albizia species, Ficus species, khejri (Prosopis cineraria, the pride of Rajasthan's top feeds), ardu (Ailanthus excelsa) and many acacias are fed in different regions. Many browse leaves contain condensed tannins, which at moderate levels protect protein from rumen degradation and can reduce bloat and nematode burdens but at high levels depress intake and digestibility. Silvopasture is the deliberate integration of trees, forage and grazing livestock on the same land; it provides shade, browse, timber or fruit and soil protection, and is discussed further in chapter 8.
Napier or elephant grass (Pennisetum purpureum, now Cenchrus purpureus) is a tall perennial C4 grass of the humid and sub-humid tropics and the backbone of cut-and-carry dairying in East Africa and much of South Asia. Hybrid Napier, also called bajra-Napier hybrid, is a cross of pearl millet and Napier. It is a triploid, so it produces little or no viable seed and is planted vegetatively from root slips or stem cuttings with two or three nodes. It combines the vigour and perenniality of Napier with softer, more leafy, more palatable herbage, and under irrigation and good nitrogen supply it gives some of the highest green fodder yields of any crop, over several cuts a year. Cutting is usually done at a height of roughly 1 to 1.5 metres every six to eight weeks; letting it grow taller gives more bulk but stemmy, less digestible fodder. Like other tropical grasses it can contain soluble oxalate, and fed alone as the only roughage over long periods it may contribute to calcium imbalance, especially in horses.
Guinea grass (Megathyrsus maximus, formerly Panicum maximum) is a tufted, shade-tolerant perennial suited to orchards, coconut gardens and silvopasture. Para grass (Brachiaria mutica, now often Urochloa mutica) spreads by long stolons and tolerates waterlogging, so it is the grass for low-lying and seasonally flooded land. Signal grass (Brachiaria decumbens) and related Brachiaria (Urochloa) species dominate the improved pastures of tropical Latin America and are expanding in Africa; B. decumbens contains steroidal saponins that can cause hepatogenous photosensitisation, particularly in sheep and young animals. Rhodes grass (Chloris gayana) is stoloniferous, moderately saline-tolerant and good for hay. Setaria (Setaria sphacelata) tolerates wet, acid soils but accumulates enough oxalate to cause hypocalcaemia in cattle and nutritional secondary hyperparathyroidism in horses. Several native perennial grasses are the basis of rangeland and pasture development in arid and semi-arid zones. Buffel grass or anjan (Cenchrus ciliaris) is deep-rooted, drought-hardy and widely sown from India to Australia and the Americas. Birdwood grass or dhaman (Cenchrus setigerus) is closely related and similarly hardy. Sewan (Lasiurus sindicus) is the outstanding grass of the most arid, sandy tracts of western Rajasthan and Sindh and is often called the king of desert grasses. Marvel grass (Dichanthium annulatum) and Sehima nervosum dominate the Sehima-Dichanthium grasslands of peninsular India. Dinanath grass (Pennisetum pedicellatum) is an annual of the sub-humid tropics. Spear grass (Heteropogon contortus) is palatable when young but its sharp awned seeds injure sheep later. Bermuda grass or doob (Cynodon dactylon) is a creeping, hardy grass of lawns and grazing lands.
In temperate climates and Indian hill regions the main sown grasses are perennial ryegrass (Lolium perenne), Italian ryegrass (L. multiflorum), cocksfoot or orchardgrass (Dactylis glomerata), tall fescue (Festuca arundinacea, now Lolium arundinaceum), timothy (Phleum pratense) and Kentucky bluegrass (Poa pratensis). Perennial ryegrass is the most digestible and palatable and responds strongly to nitrogen; it is the standard grazing grass of New Zealand, Ireland and the UK. Some ryegrass and tall fescue plants carry fungal endophytes (Epichloe species) that live inside the plant. These protect the grass against insect pests but produce alkaloids: lolitrem B in ryegrass causes ryegrass staggers, and ergovaline in tall fescue causes fescue toxicosis. Selected 'novel' or 'safe' endophyte strains keep the insect protection with much less toxin.
Fodder supply is seasonal; animals eat every day. In the north Indian plains green fodder is usually short in two transition periods: in late autumn, between the end of the kharif crops and the first cut of berseem, and in the hot summer between the end of the rabi crops and the establishment of kharif crops after the monsoon. Equivalent gaps exist everywhere, such as the dry season in the tropics, winter in temperate regions and the summer dry in Mediterranean climates. A fodder calendar is a month-by-month plan that lists which crop will be cut in each month, the area under each, the expected yield and the herd's requirement, so that gaps are seen in advance. Gaps are closed by choosing crops with different sowing and cutting windows, by perennials such as hybrid Napier and lucerne that yield through most of the year, and by conserving surplus as hay or silage in the flush season for use in the lean season.
Several systems are used to keep land producing fodder all year. Sequential cropping grows two or three fodder crops one after another on the same land within a year, for example maize or sorghum plus cowpea in the kharif followed by berseem with oats in the rabi, and a quick summer crop such as maize, cowpea or pearl millet before the monsoon. Intercropping grows two crops at the same time in rows on the same land, typically a cereal with a legume (sorghum with cowpea, maize with cowpea, oats with berseem), which raises the protein of the mixture and makes better use of nitrogen. Relay cropping sows the next crop into the standing current one before it is harvested, so the land is never empty. Overlapping cropping, developed at Indian research stations for irrigated land, combines a perennial grass such as hybrid Napier, planted in widely spaced rows, with seasonal legumes such as berseem in winter and cowpea in summer sown between the rows, giving a near-continuous supply of a balanced cereal-legume mixture.
Most fodder in the developing world is produced on farms whose main business is food or cash crops, so fodder systems must fit into crop rotations. Options include dual-purpose cereals, where cultivars are chosen for both grain yield and stover quality; growing fodder legumes in fallows and on field bunds; cutting a fodder crop of berseem or oats before leaving it for seed or grain; and growing fodder trees on boundaries. In East Africa, the push-pull system intercrops maize with the legume Desmodium and surrounds it with a border of Napier or Brachiaria grass, which together control stem borers and the parasitic weed Striga while providing fodder. Crop residues are improved by chopping, by urea treatment (described in chapter 7) and by feeding with a legume or green fodder. Hydroponic sprouted fodder (usually barley or maize grown in trays for about seven to ten days) is promoted where land and water are scarce; it is green and palatable, but sprouting loses dry matter rather than creating it, the product is very wet, and cost per kilogram of dry matter is high, so its economic value is disputed.
A fodder budget compares the herd's demand with the supply from each source. Demand is the number of animals of each class multiplied by their daily dry matter intake and the number of days. A common working figure for dry matter intake is about 2 to 3 per cent of body weight for cattle and buffalo, higher in high-yielding dairy cows and lower in dry or low-producing stock; it is lower with poor-quality roughage. Supply is the area of each crop multiplied by its yield and by a factor for wastage. Because green fodder is mostly water, budgets should be done on a dry matter basis wherever possible, and converted to fresh weight only at the end, using the measured dry matter content of each crop. For example, a herd of 20 adult cows each fed 30 kilograms of green fodder a day for 365 days needs 219 tonnes of green fodder; at a yield of 60 tonnes per hectare per year, that needs about 3.65 hectares, before any allowance for wastage.
Hay is forage dried enough to be stored without spoiling. Freshly cut green forage usually contains 70 to 85 per cent moisture; hay must reach a moisture content low enough to stop plant respiration and the growth of bacteria and moulds. As a general guide, loose hay is stored at or below about 20 per cent moisture and baled hay at roughly 15 to 18 per cent, with drier targets for large dense bales because they shed heat poorly. The exact safe figure depends on bale size, density and climate. The amount of water removed is large: 1,000 kilograms of fresh grass at 20 per cent dry matter contains 200 kilograms of dry matter, and as hay at 15 per cent moisture it weighs 200 / 0.85 = 235 kilograms, so about 765 kilograms of water must be evaporated. Crops for hay should have thin stems and plenty of leaf; lucerne, berseem, cowpea, oats, Rhodes grass and fine range grasses make good hay, while thick-stemmed maize, sorghum and Napier dry slowly and unevenly.
Hay quality is set mainly by the stage at which the crop is cut. Legumes are cut at late bud to early bloom and grasses at boot to early heading; later cutting gives more tonnes but less protein and digestibility. In the field the crop is mown, then spread or tedded to dry faster, and raked into windrows when partly dry. Mechanical or roller conditioning crushes or crimps the stems so they dry at nearly the same rate as the leaves. Legume leaves, which carry most of the protein, become brittle and shatter when very dry, so legumes are raked and baled while the leaves are still slightly moist, often in the early morning with dew. In humid climates or with legumes, drying on tripods, fences or racks improves air flow and reduces rain damage. Barn drying with forced air, and preservatives such as propionic acid applied at baling, allow baling at higher moisture.
Losses in haymaking come from four sources. Plant respiration continues after cutting and burns soluble sugar until the moisture falls below about 40 per cent. Mechanical losses, mostly of leaf, occur during tedding, raking and baling and are much larger in legumes. Rain on cut hay leaches soluble nutrients and prolongs respiration. Storage losses come from heating and moulding when hay is baled too moist, and from weathering of bales stored outdoors. Hay baled too wet heats; moderate heating causes Maillard browning, in which sugars bind amino acids and lower protein availability (heat-damaged hay may smell sweet like caramel or tobacco); severe heating can cause spontaneous combustion of the stack. Good hay is leafy, green, soft, free of mould and dust and has a pleasant aroma. Mouldy, dusty hay is a source of the actinomycete and fungal spores that cause farmer's lung in people and recurrent airway obstruction (heaves) in horses, and of mycotic abortion in cattle.
Silage is forage preserved by fermentation in the absence of air. Lactic acid bacteria present on the crop ferment its water-soluble carbohydrates (sugars) mainly to lactic acid, which lowers the pH until microbial activity stops. Ensiling passes through four phases. In the aerobic phase, plant respiration and aerobic microbes use the oxygen trapped in the mass; this should last only hours, which is why rapid filling, fine chopping, firm packing and immediate airtight sealing matter. In the fermentation phase, which lasts days to a few weeks, lactic acid bacteria dominate and the pH falls. In the stable phase, the sealed silage changes little as long as air is kept out. In the feed-out phase, the face is exposed to air, and yeasts and moulds can grow on residual sugars and lactic acid, causing heating and spoilage (aerobic instability). Homofermentative lactic acid bacteria such as Lactobacillus plantarum produce almost only lactic acid and give a fast, efficient pH fall; heterofermentative species such as Lentilactobacillus (formerly Lactobacillus) buchneri produce acetic acid as well, which loses some dry matter but inhibits yeasts and improves aerobic stability.
Three crop properties decide how easily a forage ensiles: its water-soluble carbohydrate content, its buffering capacity (resistance to a fall in pH, high in legumes because of protein and organic-acid salts) and its dry matter content. Maize and sorghum, with high sugar and low buffering capacity, ensile easily and are the classic silage crops. Grasses are intermediate. Legumes such as lucerne and berseem have low sugar and high buffering capacity and, if ensiled wet, often undergo a clostridial fermentation in which butyric acid is produced, protein is broken down to ammonia and amines, and the silage smells rancid and is poorly eaten. The remedies are to wilt the crop to a higher dry matter, to add a source of sugar such as molasses, to mix the legume with a cereal fodder, or to use an acid or inoculant additive. Conventional chopped silage is commonly made at about 30 to 35 per cent dry matter; very wet crops lose nutrients in effluent and risk clostridia, while very dry crops pack poorly and heat.
Silos range from pits and trenches dug in the ground, through above-ground bunkers and clamps, to tower silos, plastic tube bags and round bales wrapped in stretch film. The best silo for a small farm is often a lined trench or a sealed plastic bag; what matters is that the forage is chopped short, packed hard in layers, and covered airtight with weighted plastic sheet. Capacity is estimated from silo volume and packed density; for example a trench 10 metres long, 3 metres wide and 2 metres deep holds 60 cubic metres, and at an assumed packed density of 600 kilograms of fresh silage per cubic metre it holds about 36 tonnes. Additives are of two kinds: fermentation stimulants (sugar sources such as molasses, and bacterial inoculants) and fermentation inhibitors (acids such as formic acid). Good silage of a cereal crop is greenish-yellow to light brown, firm, with a pleasant acidic smell, no mould and a low pH (often about 3.8 to 4.2 for wet silage; haylage and high dry matter silages are stable at a higher pH). Laboratory measures include dry matter, pH, lactic, acetic and butyric acid, and ammonia nitrogen as a proportion of total nitrogen, where a low value indicates little protein breakdown.
Haylage is wilted forage, typically 40 to 60 per cent dry matter, ensiled usually in wrapped bales; it ferments less and relies more on air exclusion, so any hole in the wrap leads to mould. Silage has specific hazards. Silo filler's disease is caused by nitrogen dioxide and other oxides of nitrogen released from nitrate-rich forage in the first days to weeks after filling; the yellow-brown gas collects in enclosed silos and over the silage surface and damages the lungs of people and animals who enter. Poorly fermented or soil-contaminated silage with a high pH can carry Listeria monocytogenes, causing encephalitis (circling disease), abortion and septicaemia in ruminants. Bale silage that contains carcasses or soil can carry Clostridium botulinum toxin. Silage effluent has an extremely high biochemical oxygen demand and must be kept out of watercourses. Low-quality straw can be improved by urea treatment: urea solution is sprayed on straw, which is then sealed for some weeks; urease converts urea to ammonia, which breaks lignin-hemicellulose bonds, raising digestibility and adding nitrogen. A commonly used rate is about 4 kilograms of urea per 100 kilograms of straw dissolved in water, sealed for about three weeks in warm weather and longer in cold weather; details vary by programme.
Several terms are often confused. Stocking rate is the number of animals (or animal units) per unit area of land over a whole grazing period or year, for example 2 cows per hectare. Stocking density is the number of animals on a given area at one moment, which in rotational systems can be very high on the paddock being grazed even when the overall stocking rate is moderate. Carrying capacity is the stocking rate that a pasture or range can sustain over the long term without damaging vegetation or soil, given its forage production. Grazing pressure is the ratio of animal demand to forage available at a point in time; its inverse is forage allowance, the kilograms of forage dry matter available per animal or per kilogram of live weight. An animal unit (AU) is a standard animal used to compare classes; in the United States it is usually a 1,000-pound (about 454 kilogram) cow with or without a calf, and an animal unit month (AUM) is the forage one AU eats in a month. Other countries and range agencies use different reference animals, so AU equivalents for sheep, goats or buffalo must be taken from the local standard.
Carrying capacity is calculated from forage supply and animal demand. Supply is the annual dry matter production per hectare multiplied by area and by a utilisation factor, also called the proper use factor or harvest efficiency, which is the fraction of production animals may safely eat; the rest is lost to trampling, insects, decay or must be left to protect the plants and soil. The classic range rule 'take half, leave half' corresponds to a utilisation of about 50 per cent, and lower values are used for arid or fragile ranges. Demand is daily intake per animal multiplied by the days of grazing. For example, 20 hectares producing 6,000 kilograms of dry matter per hectare per year at 50 per cent utilisation supply 60,000 kilograms of usable dry matter. A 450-kilogram cow eating 2.5 per cent of body weight eats 11.25 kilograms a day, or about 4,106 kilograms a year. The pasture therefore carries about 14.6 such cows for a year. Forage production is estimated by clipping quadrats: herbage from a known area is cut, dried and weighed, so 60 grams of dry matter from a 0.25 square metre quadrat equals 240 grams per square metre, or 2,400 kilograms per hectare.
Continuous grazing keeps animals on the same area for the whole season; it is simple and cheap but lets animals repeatedly graze the most palatable plants, which decline. Rotational grazing divides the pasture into paddocks grazed in turn, each grazed for a short period and then rested to regrow. The number of paddocks needed is the rest period divided by the grazing period, plus one for the paddock being grazed; with a 30-day rest and a 3-day graze, 11 paddocks are required. Strip grazing gives animals a fresh strip of pasture each day or half-day behind a movable electric fence, often with a back fence to protect regrowth; it suits high-yielding dairy cows on intensive pasture. Deferred grazing keeps animals off part of the range until key plants have set seed; rest-rotation rests one unit for a whole year in turn. Creep grazing lets young stock pass through openings into better pasture ahead of their dams. Leader-follower grazing puts high-producing animals first on fresh pasture and lower-demand animals after them to clean up. Mixed grazing of cattle with sheep or goats uses different plant species and heights and can reduce parasite loads for each species. Zero grazing (cut and carry, soiling) brings cut fodder to housed animals; it saves trampling losses but costs labour.
The two decisions that matter most are stocking rate and timing. Too high a stocking rate is the commonest cause of pasture degradation everywhere. Timing means grazing when the plant has enough leaf to regrow quickly and stopping before it is grazed so low that regrowth depends on root reserves. In ryegrass-based temperate pastures a widely used guide is to graze when plants have regrown about two and a half to three new leaves per tiller and to leave a set residual height or post-grazing mass; tropical tall grasses have their own target heights. Pasture health is also animal health: rotational rest periods do not by themselves break most nematode life cycles, because infective larvae survive for weeks to months depending on climate, but integrating grazing with other species, hay or crop phases, and young stock grazing ahead of older stock, can lower worm exposure. Lush, rapidly growing grass pastures heavily fertilised with potassium and nitrogen predispose cattle and sheep to grass tetany (hypomagnesaemia), and lush legume pastures to frothy bloat.
Natural grasslands are classified by their dominant species and climate. For India, Dabadghao and Shankarnarayan described five major grass cover types: Sehima-Dichanthium (peninsular India), Dichanthium-Cenchrus-Lasiurus (the arid north-west), Phragmites-Saccharum-Imperata (the moist alluvial Gangetic and north-eastern plains), Themeda-Arundinella (the humid hills) and temperate-alpine grasslands of the Himalaya. Range condition describes how far the present vegetation has departed from the potential of the site. In the approach developed by Dyksterhuis, plants are grouped as decreasers (palatable species that decline under heavy grazing), increasers (less palatable species that at first increase as decreasers decline) and invaders (species not native to the climax community that move in when the range is degraded). The proportion of the climax community remaining places a range in excellent, good, fair or poor condition. Later approaches such as state-and-transition models recognise that degraded ranges may cross thresholds and not return simply by reducing grazing. Grasslands and rangelands degrade through overgrazing, loss of grazing land to cropping and settlement, invasion by unpalatable woody plants and weeds, soil erosion, uncontrolled fire, and the breakdown of traditional controls on common land. In India the village commons (gochar, gauchar, oran in Rajasthan) are often grazed by more animals than they can support, with no one responsible for their upkeep. Invasive species such as Lantana camara, Parthenium hysterophorus and Prosopis juliflora have spread across Indian and African grazing lands; Prosopis juliflora pods are eaten and the plant is useful for fuel, but it suppresses grass beneath it. Signs of degradation include declining ground cover, loss of perennial grasses, more bare soil and annual weeds, gullies, and falling animal performance.
Range improvement starts with grazing control: matching stocking rate to carrying capacity, resting overgrazed areas, and rotating grazing. Physical measures include contour furrows, trenches and bunds to hold rainwater, and enclosures that exclude grazing while vegetation recovers. Reseeding with adapted grasses such as Cenchrus, Lasiurus or Dichanthium, and introducing legumes such as Stylosanthes, raise production and protein. Fertiliser, especially phosphorus for legumes, and lime on acid soils, improve sown pastures where it is economic. Weed and bush control uses grazing management, manual or mechanical removal, biological agents and, where justified, prescribed burning; fire timing must match the ecology of the site because badly timed fire damages perennial grasses. Water points distribute grazing; animals concentrate near water, so too few points cause overgrazing near them and underuse far away. Agreed community rules on who grazes, when and how many often decide whether these measures last.
Silvopasture integrates trees, forage and livestock deliberately on the same unit of land. Trees supply shade that reduces heat stress, leaves and pods as dry-season fodder, timber, fuel or fruit, and they protect soil and store carbon. Forage under trees must tolerate shade, which is why guinea grass, signal grass and some legumes are favoured beneath plantation crops and in coconut gardens. Typical Indian systems include khejri (Prosopis cineraria) with Cenchrus grass in Rajasthan, subabul or Albizia rows with Napier or guinea grass in sub-humid areas, and fodder trees on field boundaries in the hills, where farmers lop oak, Grewia and Celtis leaves in winter. Lopping intensity and timing affect tree survival; lopping the whole crown every year can kill some species. In Latin America, intensive silvopastoral systems combining leucaena at high density with improved grasses are a recognised model. Browse leaves should be introduced gradually because of tannins and other secondary compounds.
Fodder yield is reported as green (fresh) matter or as dry matter per hectare, per cut or per year. Green yield exaggerates the value of watery crops, so comparisons should use dry matter, and better still yield of digestible dry matter or crude protein. Dry matter is found by drying a representative sample to constant weight, commonly in a forced-air oven at a moderate temperature for forage to avoid charring sugars, or at about 100 to 105 degrees Celsius for a standard laboratory determination. If a berseem crop yields 10 tonnes of dry matter per hectare at 18 per cent crude protein, it yields 1.8 tonnes of crude protein per hectare. Typical yields vary enormously with variety, water, fertiliser and climate; under irrigation and good management hybrid Napier is among the highest-yielding fodders, berseem and lucerne give high yields over several cuts, and rainfed range grasses give much less.
Two systems describe forage composition. The proximate (Weende) system divides dry matter into crude protein (nitrogen multiplied by 6.25), ether extract, crude fibre, total ash and nitrogen-free extract (by difference). Its weakness for forages is that crude fibre does not recover all of the lignin and hemicellulose, so nitrogen-free extract, supposedly the soluble fraction, contains some of the least digestible material. The detergent system of Van Soest overcomes this. Neutral detergent fibre (NDF) is the total cell wall (cellulose, hemicellulose and lignin) and relates inversely to intake, because cell wall fills the rumen. Acid detergent fibre (ADF) is cellulose and lignin and relates inversely to digestibility. Acid detergent lignin (ADL) is the indigestible core that limits fibre digestion. Hemicellulose is estimated as NDF minus ADF. As forage matures, NDF, ADF and lignin rise and crude protein falls. Legumes usually have lower NDF than grasses at a similar digestibility, which is why animals eat more of them.
Digestibility is measured in vivo with animals, in sacco with nylon bags in the rumen of fistulated animals, or in vitro; the Tilley and Terry two-stage method (rumen liquor then acid pepsin) is the classic in vitro technique, and gas production methods are also widely used. Energy value is expressed as total digestible nutrients (TDN), digestible or metabolisable energy, or net energy, depending on the national feeding system. Near-infrared reflectance spectroscopy (NIRS) predicts composition rapidly once calibrated against wet chemistry. In the hay trade of North America, relative feed value (RFV) combines estimated digestible dry matter and intake: digestible dry matter (per cent) = 88.9 minus 0.779 times ADF; dry matter intake (per cent of body weight) = 120 divided by NDF; and RFV = digestible dry matter times intake divided by 1.29, so that full-bloom lucerne scores about 100. A hay with 35 per cent ADF and 50 per cent NDF has digestible dry matter 61.6 per cent, intake 2.4 per cent and RFV about 115. Relative forage quality (RFQ) is a later refinement that uses measured fibre digestibility.
Nutritive value is decided more by stage of growth than by any other factor. Leaf is more digestible and richer in protein than stem, and the leaf to stem ratio falls with maturity. High temperature during growth lowers digestibility; tropical grasses therefore start lower and fall faster than temperate grasses. Species differ: legumes are richer in protein and minerals, temperate grasses in sugars, tropical grasses in fibre. Nitrogen fertiliser raises crude protein and yield of grasses, and can raise nitrate. Soil determines mineral content; forage grown on deficient soils carries too little phosphorus, copper, cobalt or selenium for grazing animals, while some soils give toxic excesses such as selenium or molybdenum. As rough indicative values, which vary with stage and conditions, lush berseem and lucerne often contain around 15 to 22 per cent crude protein in dry matter, green maize and sorghum fodder roughly 7 to 10 per cent, tropical grasses cut at a reasonable stage roughly 6 to 12 per cent, and cereal straws only about 3 to 4 per cent. Below about 7 per cent crude protein, rumen microbial activity becomes limited by nitrogen and intake falls.
Cyanogenic glycosides (dhurrin in sorghum and Sudan grass, linamarin in linseed and cassava, others in Prunus leaves and some clovers) release hydrocyanic acid when plant tissue is damaged. Cyanide binds the ferric iron of cytochrome oxidase, so tissues cannot use oxygen; venous blood stays bright cherry red, and death can follow within minutes to an hour, with dyspnoea, tremors, convulsions and collapse. Ruminants are more susceptible than monogastrics because rumen microbes release HCN quickly. The classic treatment is sodium nitrite followed by sodium thiosulfate, or sodium thiosulfate alone, given intravenously; doses must be taken from the current formulary and product label. Nitrate accumulates in plants stressed by drought, cloudy weather or herbicide after heavy nitrogen fertilisation, especially in the lower stem; oats, maize, sorghum, pearl millet, Sudan grass and weeds such as pigweed (Amaranthus) are common sources. In the rumen nitrate is reduced to nitrite, which converts haemoglobin to methaemoglobin, giving chocolate-brown blood and cyanosis. The specific antidote is methylene blue intravenously, dose by formulary and label. Nitrate content is reported in different forms (nitrate, nitrate-nitrogen or potassium nitrate), so a value must be converted before comparing it with a guideline: nitrate-nitrogen multiplied by about 4.43 gives nitrate.
Soluble oxalates occur in Setaria, Napier, para grass, Brachiaria, Halogeton and Oxalis, among others. Large intakes by hungry animals cause acute hypocalcaemia and renal damage from calcium oxalate crystals; long-term feeding of high-oxalate tropical grasses to horses binds dietary calcium and causes nutritional secondary hyperparathyroidism (big head). Mimosine in leucaena and its rumen metabolite DHP cause alopecia and goitre, as described in chapter 3. Saponins in lucerne and clovers contribute to the stable foam of frothy bloat, while steroidal saponins in Brachiaria and in Tribulus terrestris cause crystal deposition in bile ducts and hepatogenous photosensitisation. Condensed tannins are a double-edged factor: moderate amounts reduce bloat and protein degradation, but high amounts reduce intake and digestibility. Phyto-oestrogens such as formononetin in some subterranean and red clover cultivars caused 'clover disease' of sheep in Western Australia, with ewe infertility; low-oestrogen cultivars were bred in response. Brassica forage crops such as kale and rape contain S-methylcysteine sulphoxide, which causes haemolytic (kale) anaemia, and glucosinolates that are goitrogenic.
Lantana camara contains pentacyclic triterpenoids (lantadenes) that cause cholestatic liver damage, jaundice and hepatogenous photosensitisation; it is common across India, Africa and Australia and is eaten mainly by hungry or newly introduced animals. Bracken fern (Pteridium aquilinum) contains thiaminase, which causes thiamine deficiency in horses and pigs, and ptaquiloside, which in cattle causes acute bone-marrow damage with haemorrhage and, with prolonged intake, enzootic haematuria from bladder tumours. Pyrrolizidine alkaloids in Senecio, Crotalaria and Heliotropium cause chronic, progressive liver damage with megalocytosis, often appearing months after exposure. Parthenium hysterophorus is an aggressive weed causing dermatitis and bitter milk, and is avoided by stock unless they are hungry. Oleander (Nerium) contains cardiac glycosides and is lethal in small amounts. Water hemlock (Cicuta) causes violent convulsions. Astragalus and Oxytropis (locoweeds) contain swainsonine, which causes a lysosomal storage disease, and some Astragalus species accumulate selenium. Primary photosensitisation is caused by plants such as St John's wort (Hypericum, hypericin) and buckwheat (fagopyrin); secondary (hepatogenous) photosensitisation follows liver damage that stops the excretion of phylloerythrin, a chlorophyll breakdown product.
Many pasture poisonings are caused by fungi rather than the plant itself. Ergot (Claviceps purpurea) replaces grass and cereal seeds with dark sclerotia whose alkaloids cause vasoconstriction, gangrene of extremities, convulsions and agalactia. Fescue toxicosis from ergovaline in endophyte-infected tall fescue causes poor summer growth and heat intolerance ('summer slump'), dry gangrene of the feet ('fescue foot') and, in mares, prolonged gestation, thickened placenta and agalactia. Perennial ryegrass staggers from lolitrem B produces tremors and incoordination when animals are disturbed, and usually resolves when they are moved to safe feed. Facial eczema, a disease of New Zealand and parts of Australia and South America, is caused by sporidesmin from spores of Pithomyces chartarum on dead pasture litter in warm humid weather; it damages bile ducts and causes photosensitisation. Lupinosis in Australia is caused by a fungus on lupin stubble. Prevention combines pasture management (avoiding risky growth stages and dead litter), monitoring of spore counts or toxin levels where available, safe endophyte cultivars, and supplementary feeding during danger periods.
Shortage of good seed is one of the main brakes on fodder development in South Asia and Africa. Fodder crops are bred for leaf and regrowth, not for seed, so seed yields are low and unreliable. Grasses flower over a long period, so seed heads ripen unevenly, and many shed their seed (shattering) as soon as it is ripe. Some important grasses, such as hybrid Napier, are sterile and must be propagated vegetatively, and many tropical grasses set seed poorly. Farmers who rely on cutting the crop for fodder are reluctant to leave it for seed. Seed of range grasses such as Cenchrus is borne in fascicles or burrs with bristles that make cleaning and sowing difficult. For multi-cut legumes and cereals the usual practice is to take one or more fodder cuts and then leave the crop for seed. In north India berseem is commonly cut for fodder until about February to early March and then allowed to flower and set seed in April and May; it is cross-pollinated by honeybees, so seed yield depends on bee activity, and placing hives in the field helps. Lucerne is also insect-pollinated; in North America leafcutter bees and alkali bees, as well as honeybees, are managed for lucerne seed production. Multi-cut oats are given one fodder cut and the regrowth is harvested for seed. Seed crops need clean land, isolation from other varieties of the same species according to national certification rules, removal of off-type plants and weeds (roguing), and timely harvest to limit shattering. Weed seeds of similar size, such as chicory in berseem and dodder in lucerne, must be removed by careful cleaning, and certification rules set limits for them.
Seed quality is described by physical purity (the proportion of pure seed of the named species by weight), germination percentage, moisture content and freedom from weeds and disease. Many legume seeds have hard seed coats that do not absorb water, so a proportion fail to germinate promptly; scarification by abrasion or brief hot-water treatment improves germination. Pure live seed (PLS) is the fraction of a seed lot that is pure seed capable of germinating: PLS = purity multiplied by germination. A lot with 90 per cent purity and 80 per cent germination has 72 per cent PLS, so to sow 10 kilograms of PLS per hectare a farmer must sow 10 / 0.72 = 13.9 kilograms of the seed lot. In India seed moves through a generation system of nucleus, breeder, foundation and certified seed, with certification under national seed law; most countries have a similar chain under their own rules or OECD seed schemes. Standards for purity, germination, isolation and weed seeds differ between countries and crops and should be taken from the national seed certification standards.
A student uses this subject to answer two kinds of questions: what a crop or plant is and does, and how to calculate a fodder requirement. Learn each major fodder by season, botanical name, cutting stage and its one special hazard or feature (sorghum: HCN; berseem: bloat and chicory; leucaena: mimosine; hybrid Napier: sterile). Practise the arithmetic of dry matter, hay moisture, silo capacity, carrying capacity and paddock numbers until it is automatic, because the same few formulae appear in every paper. In the clinics, link every pasture poisoning to the plant, the circumstance in which animals ate it and the antidote.
A practitioner five years out is the person farmers ask why milk fell in May, why a cow died after grazing regrowth, or whether last year's silage is safe. The tasks are to draw up a fodder calendar for a 10 to 50 animal dairy unit, estimate how much land or silage is needed for the lean months, judge silage by smell, colour and pH paper, check hay for mould before advising its use in horses or pregnant cattle, and investigate sudden deaths with forage history, cherry-red or chocolate-brown blood, and samples for nitrate or cyanide testing. Advice on rotational grazing and stocking rate prevents more disease than any drug.
A senior officer or consultant with 25 years' experience plans fodder at district, cooperative or company scale: seed procurement and certification for fodder programmes, area targets for berseem, oats and hybrid Napier, silage and baling units, fodder banks for drought and disaster response, and the rehabilitation of common grazing lands with village institutions. Decisions involve trade-offs between irrigated fodder and food crops, the economics of conserved fodder against bought concentrate, and the governance of commons. Such a person also judges which new technology is worth promoting, for example hydroponic fodder or a new silage additive, by asking for dry matter and cost data rather than claims.
A researcher with a PhD and 25 years of experience works on questions that remain open: breeding fodder sorghum with low dhurrin and better stover quality, safe endophyte associations for grasses, rumen microbial adaptation to mimosine and tannins, modelling of rangeland carrying capacity under climate change, greenhouse gas outcomes of grazing and silvopastoral systems, and NIRS calibrations for regional fodders. Such a person designs grazing trials with adequate replication and paddock-level experimental units, avoids confounding stocking rate with grazing system, and reads claims about holistic or adaptive grazing critically, because the evidence on these is contested.
This manual does not give variety-by-variety recommendations, state-wise sowing dates, fertiliser doses or herbicide rates, because these are set by regional agricultural universities and change with new releases; use the current package of practices for your region. It gives no fixed toxic threshold values for nitrate or HCN in forage, because laboratories and authorities use different reporting bases and cut-offs; use your diagnostic laboratory's guidelines. Antidote doses are deliberately omitted; take them from the current formulary and product label. Seed certification standards (isolation distances, purity and germination minimums) are country-specific and are not listed. Regional toxic floras outside South Asia, Australasia, Europe and North America are covered only by example. Rangeland ecology models, grassland carbon accounting and the economics of conserved fodder are introduced but not treated in depth.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
These notes are free to read here, with no account.
What the Laisha app adds:
Free for ten days, then a subscription. We would rather write that here than have you find it later.