Forage Quality and Nutrition’s
By Muh.Salman Naeem & Muh. Shahbaz

Forage quality is defined in many ways but is often poorly understood.

Usually forage quality receives less concern as it justify.

Adequate animal nutrition is essential for high rates of gain,ample milk production, efficient reproduction and maximum profits.

Pakistan has no normal pasture appropriate for dairy sector, so dairy stocks, mostly buffaloes, depends on cultivated annual forage for green feed.

 A large number of dairy stocks are kept in and around cities and feed have to be brought in.

Most dairy animals are in and around intensively cultivated and irrigated regions, except for some rain-fed areas such as Rawalpindi, Attock and Islamabad.

There is no land for grazing, so animals are kept at farmstead and stall-fed on cultivated forage, crop residues and concentrates.

Pakistan has a total cropped area of 22.54 million hectare. But only 2.35 million hectare area is under fodder crops. Due to increased requirement, improved forage crops such as multi-cut Oats, Rhodes grass, Berseem, Lucerne, Sorghum- Sudan grass hybrids, Maize and Millet have been developed.

Analyzing forages for nutrient content can be used to determine whether quality is adequate and to guide proper ration supplementation. The vast irrigated tracts of the Punjab, the North West Frontier Province and Sindh, which are the major source of forage for urban dairies, are at low altitude with a sub-tropical monsoon climate and hot summers.

Cash crops such as wheat, sugar cane, maize, rice, and forage crops like sorghum, Rhodes grass, alfalfa, clover, and oats are commonly supply the grain and forage requirements for urban dairies.

Due to suitable temperatures and availability of irrigation, green forage is produced year the round. Improved forage varieties and technology have been slow to reach the small scale farms which account for the bulk of forage production.

Palatability: Animals select one type of forage over another forage type on the basis of smell, feel and taste. palatability may therefore be influenced by texture, leafiness, fertilization, crop fall, dung or urine patched in field, moisture content, pest problem, fungal infestation and compounds present in it to taste sweet, sour or salty. High quality forages are generally highly palatable.

Intake: Animals must consume adequate quantities of forage to perform well. Typically, higher the palatability and forage quality, higher the intake.

Digestibility: The extent to which forage is absorbed as it passes through an animal’s digestive track varies greatly. Immature, leafy plant tissues may be 80% to 90% digested, while less than 50% of mature stem material is digested. Approximately 0.5% digestibility goes down within a day after crop maturity.

Nutrient content: Living forage plants usually contain 70 to 90% water. To standardize analyses, forage yield and nutrient content are usually expressed on a dry matter (DM) basis.

Forage dry matter can be divided into two main categories: (1) cell contents (the non-structural parts of the plant tissue such as protein, sugar and starch); and (2) structural components of the cell wall (hemicelluloses and lignin). Rhodes grass has more DM% on equal age rather than barseem and alfalfa.

Anti-quality factors: Various compounds may be present in forage that can lower animal performance, cause sickness, or even result in death. Such compounds include tannins, nitrates, alkaloids, cyanoglycosides, estrogens, and mycotoxins.

The presence or their severity of these elements depends on the plant species present, time of year, environmental conditions, and animal sensitivity. High-quality forages not contain harmful levels of anti-quality components.

■ Animal performance is the ultimate test of forage quality, especially when forages are fed alone and free choice. Forage quality encompasses “nutritive value” (the potential for supplying nutrients, i.e., digestibility and nutrient content), how much animals will consume, and any anti-quality factors present.

Animal performance can be influenced by any of several factors associated with either the plants or the animals. Failure to give proper consideration to any of these factors may reduce an animal’s performance level, which in turn reduces potential income.

Factors affecting forage quality
Many factors influence forage quality. The most important are forage species, stage of maturity at harvest, and (for stored forages) harvesting and storage methods. Secondary factors include soil fertility and fertilization, temperatures during forage growth, and variety.

Legumes vs. grasses: Legumes generally produce higher quality forage than grasses. This is because legumes usually have less fiber and favor higher intake than grasses. One of the most significant benefits of growing legumes with grasses is improvement of forage quality. But production may affect intercropping due to different dormant season of crops.

Cool-season vs. warm-season grasses: There is considerable variation in forage quality among the grasses used as cultivated forages. Forage grasses are divided into two broad categories: cool season and warm season. Cool-season grasses include perennial and annual ryegrass. Rhodes grass is example of warm-season grasses.

Cool-season species are generally higher in quality than warm-season grasses. The digestibility of cool season grass species averages about 9% higher than warm-season grasses. Minimum crude protein levels found in warm-season grasses are also lower than those found in cool-season grasses.

Within each category, annual grasses are often higher in quality than perennials. Due to differences in leaf anatomy, warm-season grasses convert sunlight into forage more efficiently than cool-season grasses, but their leaves contain a higher proportion of highly lignified, less digestible tissues.

On that basis alfalfa considered best by dairy specialist than Rhodes grass. However, Rhodes grass is many time better as economical and management point of view than Mott grass and alfalfa.

Temperature: Plants grown at high temperatures generally produce lower quality forage than plants grown under cooler temperatures, and cool-season species grow most during the cooler months of the year. However, forage of any species tends to be lower in quality if produced in a warm region rather than a cool region.

For example, in one study annual ryegrass grown at temperatures of 18°C to 24°C produced forage made up of 59% leaf material, but only 36% leaf matter when grown at 32° C to 45°C.

Maturity stage: Maturity stage at harvest is the most important factor determining forage quality. Forage quality declines with advancing maturity. For example, cool season grasses often have dry matter (DM) digestibility’s above 80% during the first 2 to 3 weeks after growth initiation in spring.

Thereafter, digestibility declines by 1⁄3to 1⁄2percentage units per day until it reaches a level below 50%. Maturity at harvest also influences forage consumption by animals. As plants mature and become more fibrous, forage intake drops dramatically. Intake potential decrease and NDF concentration increases as plants age increase.

This is because NDF is more difficult to digest than the non-fiber components of forage. Also, the rate at which fiber is digested slows as plants mature. Therefore, digestion slows dramatically as forage becomes more mature. As I mentioned before nearly 0.5% digestibility loses by fodder after maturity due to late of harvesting.

Leaf-to-stem ratio: Reduced leaf-to-stem ratio is a major cause of the decline in forage quality with maturity, and also the loss in quality that occurs under adverse hay curing conditions. Leaves are higher in quality than stems, and the proportion of leaves in forage declines as the plant matures.

The oldest portion of alfalfa stems had less than 10% CP compared with 24% in alfalfa leaves. Stem had much higher fiber levels than leaves, but the older, lower alfalfa leaves were similar in quality to the upper, younger leaves. However, older alfalfa stem tissue was considerably lower in quality than young stem tissue. Reproductive growth lowers leaf-to-stem ratio, and thus forage quality.

Most cool-season grasses require a period of cool temperatures (vernalization) for flowering, so they produce reproductive stems only in the spring. Thus, the forage quality of re growth of these grasses is greater and changes less over time because they have higher leaf-to-stem ratios than first-growth forage.

Legumes and some grasses such as Bermuda grass can flower several times each season, so their forage quality patterns are less closely linked to season.

Grass–legume mixtures: Grass–legume mixtures generally have higher crude protein concentration and lower fiber concentration than pure grass stands.

Fertilization: Fertilization of grasses with nitrogen (N) often substantially increases yield and also generally increases CP levels in the forage.

Fertilization with phosphorus (P), potassium (K), or other nutrients that increase yield may actually slightly reduce forage quality when growth is rapid. Excessive levels of some elements such as potassium may in some cases decrease the availability of other elements such as magnesium (Mg) in the diet.

Daily fluctuations in forage quality: changes in soluble carbohydrate levels in alfalfa were linked to time of day. Plants accumulate soluble carbohydrates during daylight and then use them overnight. Thus, soluble sugars are lowest in the morning and highest after a day of bright sunshine.

Alfalfa is harvested in the late afternoon rather than in the morning. It appears that the advantage of afternoon harvest is greatest on cool, sunny days and when the forage is highly conditioned to increase drying rates and minimize respiration in the windrow.

However, afternoon harvests may not be advisable in high rainfall areas where every hour of good drying time is needed in curing hay. In summer season, digestibility may also be on lower endin case of cutting at afternoon both in alfalfa and legumes.

Harvesting and storage effects: Leaf shatter, plant respiration, and leaching by rainfall during field drying of hay can significantly reduce forage quality, particularly with legumes. Moderate rain damage reduced alfalfa CP levels slightly and digestibility dramatically, but NDF and ADF levels increased sharply.

Red clover hay quality was also greatly reduced by rain, even though crude protein increased. The total amount of crude protein did not increase; the percentage of crude protein in the remaining dry matter was higher due to leaching of highly soluble constituents. Rainfall during curing damages legume leaves most.

For alfalfa hay exposed to both drying and leaching losses, more than 60% of the total losses of dry matter, CP, ash, and digestible DM were associated with the leaves.

Rain during field drying has less impact on the forage quality of grasses than legumes. In one study, alfalfa hay that received rain was 12 percentage units less digestible than fresh forage, compared with a difference of only 6 percentage units for grass hay produced under similar conditions.

Damage from rain increases as forage becomes dryer, and is especially severe when rain occurs after it is ready to bale. Quality losses also occur due to weathering, plant respiration, and microbial activity during storage. In high rainfall areas, losses can be large for round bales stored outside, due to weathering of the outer layers.

November 2014

Courtesy: Pakissan Report