Advantages of Forage Consumption by Poultry23 September 2013
Feed savings and a ready supply of a whole range of nutrients are the advantages of free-range systems, according to 'Pastured Poultry Nutrition and Forages' from the National Sustainable Agriculture Information Service, ATTRA.
Forages can provide a significant amount of poultry nutrition, reducing the amount of feed that a poultry farmer feeds a flock. Although poultry are not ruminants - they’re monogastric - a good pasture is still a valuable resource for the flock. Jeff Mattocks, a livestock nutritionist with decades of experience in pasture-based and sustainable/organic farming, estimated in 2002 that, after “gathering data from year to year and producer to producer, I have come to the conclusion that pastured poultry eat five to 20 per cent [of their diet] from pasture, depending on type and age of poultry, and the quality of forage growth”.
In many areas, feed savings are typically greatest in the late spring and early fall, when lush pasture provides plenty of high-quality forages to offset a significant amount of the cost of feeding poultry. Additionally, insect and other invertebrate populations (poultry favourites) in the pasture are booming at the same time. The amount of plant forages consumed by the flock, or even an individual bird, depends on a variety of factors that will be further explored below.
The primary benefit of forage consumption is that plant matter is typically high in both vitamins and minerals. Besides the vitamins and minerals, forages also contain components such as fibre, protein, energy (calories), and other compounds like carentoids and omega-3 fatty acids that are important for metabolic functions in all animals, especially humans. The specific benefits that poultry gain from forages are explored below for each nutritional group.
Vitamins are complex organic compounds required by animals for normal growth. Many of the vitamins added to modern-day poultry rations can lose their potency over time because they are not as shelf-stable as other components of the poultry ration.
Pasture intake by poultry acts as a form of nutritional insurance, as the living forages provide a back-up “bank” of nutrition to prevent any vitamin deficiencies of the feed from affecting the birds.
Vitamins are classified as either water-soluble or fat-soluble. Fat-soluble vitamins dissolve in body fat and when excess vitamins are consumed, they are able to be stored in the liver and fatty tissues. The fat-soluble vitamins are vitamins A, D, E and K. Forages are high in all the fat-soluble vitamins except D and are an important natural source of these nutrients for poultry. In confinement production, vitamin D must be added to the poultry ration to prevent the nutritional disease rickets. For pastured poultry production, however, vitamin D deficiency is not a problem because pastured poultry are exposed to ample amounts of sunshine and readily synthesise vitamin D in their skin. With access to plenty of forage and sunlight, poultry on pasture should not have problems with fat-soluble vitamin deficiencies.
Water-soluble vitamins are not able to be stored in the body and need to be consumed regularly. The water-soluble vitamins include several important vitamins grouped together and collectively called the vitamin B complex, as well as vitamin C. Poultry can synthesize vitamin C in their own bodies, and generally don’t need to supplement with dietary intake. The B vitamins consist of vitamins like riboflavin, folic acid, and B6, which are found in ample amounts in pasture vegetation. Vitamins such as niacin, thiamine, and B12 are found in animals (think insects) that poultry eagerly hunt on pasture. Some of the water-soluble vitamins are also produced by bacteria in a healthy poultry gut. Forage consumption plays a significant role in poultry gut health, as will be discussed in the section ofn Fibre.
Poultry feed can often be deficient in vitamins A, D, riboflavin and B12 due to the perishable nature of these vitamin sources in the feed. As mentioned above, pasturing poultry and giving them access to high-quality forages will help in balancing out any deficiencies.
Forages are rich in vitamin A and riboflavin; when exposed to sunshine, a bird’s body manufactures all the vitamin D the bird needs; and vitamin B12 can be supplemented by grasshoppers, crickets, worms, and other invertebrates (and the occasional vertebrate) that are commonplace in healthy pastures.
Minerals are inorganic compounds, typically found as salts, that are critical for bone and eggshell formation in poultry, as well as important in many biochemical processes like hormone production and fluid balance in the bird’s body. Many of the minerals needed by poultry can be supplemented by forages.
By far, the most common mineral deficiency is calcium, especially for laying hens. Calcium plays a critical role in poultry health, comprising approximately 70 per cent of the mineral content in a bird. Calcium works hand-in-hand with phosphorous inside of the bird to build strong bones and eggshells. The calcium content of grains is very low, and typically sources like oyster shells, limestone, or calcium salts are added to feed.
Forages can provide supplemental minerals, and the calcium found in plants like alfalfa is highly bioavailable. A bird’s digestive system is able to utilise calcium from forages as efficiently as calcium from more common sources like limestone or oyster shell (Blair, 2008). Although pasture can supply around 25 per cent (Horsted, 2006) of the calcium required by layers, it cannot serve as the long-term sole source of calcium. Good pasture with access to supplemental limestone or oyster shell, however, will provide all the calcium the flock needs.
Proteins are used by animals to build muscles, organs and all other tissues. Crude protein is a basic measure of what percentage of a particular feed item is protein. Proteins are comprised of amino acids, of which there are over a dozen types. An easy way to understand protein nutrition is to imagine crude protein as a completed wall made up of individual amino-acid bricks. Each type of amino acid is like a different type of brick, and each animal requires a completed wall (crude protein) with a certain pattern of amino acid bricks, i.e. particular types and numbers of amino acids. When looking at the crude protein of a feed, it is important to understand that not all proteins are the same, and that different animals have different levels of amino acid requirements.
Of particular importance in raising poultry, there is one amino acid that can often be limiting: methionine. In grains, methionine is found only in relatively low levels, and the best natural source for methionine is animal proteins – typically fish (fed as a meal), or insects and other animals found while ranging. In the modern poultry industry (including organic), most methionine is supplied in poultry diets by synthetically produced protein powders - the only way that so-called vegetarian poultry diets are possible.
Chickens and turkeys especially crave methionine. One sign of methionine deficiency is an increase in feather pecking or even cannibalism in the flock. One of the major advantages of allowing poultry to forage on pasture is that it allows the birds to hunt and eat insects and other invertebrates that they find while ranging, thus satisfying the bird’s craving for animal protein. Indeed, research has demonstrated that even commercial Cornish Cross broilers are able to make up for some methionine deficiencies by consuming vegetation and insects on pasture (Mortiz et al., 2005; Horsted, 2006).
For decades, poultry farmers have noted that hens given access to pastures full of alfalfa and clover need less protein than hens raised in confinement. Experience has shown that hens purposefully fed protein-deficient diets increased their consumption of pasture forages compared to flocks fed a ration with adequate protein levels (Horsted, 2006). The same behaviour was exhibited by broilers fed a protein-deficient diet (Eriksson, 2010). Horsted (2006) reported a 50 per cent increase in forage consumption in hens fed a restricted diet of wheat and oyster shell compared to hens with access to a balanced layer ration.
Similarly, poultry scientists have found that consumption of forages is inversely tied to protein levels, i.e. a higher protein content (methionine) in the feed ration can result in a lower amount of plant matter consumed on pasture (Heuser, 1955; Mortiz et al., 2005). A study in 2007 demonstrated that poultry are able to utilise the majority of the amino acids that they consume in forages, finding that the amount of methionine and lysine digested was 88 per cent and 79 per cent of the respective amount consumed (Buchanan et al., 2007;). Rivera-Ferre et al. found that broilers on pasture were able to meet around seven per cent of their protein needs from foraging (2007). For more information about methionine in poultry, consult the ATTRA publication Organic Poultry Production: Providing Adequate Methionine.
Among plants, the legume family is the king of protein production. Legumes are unique in the plant world because they house a group of bacteria called Rhizobia in their roots that are able to pull atmospheric nitrogen (which composes roughly 70 per cent of the air we breathe) and are able to convert it as a nitrogen fertiliser source for the legumes. In return, the Rhizobia are able to get shelter, water, and sugars from the cells in the legumes’ roots. The abundant nitrogen production of legumes leads to elevated levels of valuable nitrogen-rich protein in these plants. Legumes important in poultry production are soybeans and various field peas, as well as pasture forages like alfalfa, lespedeza, clovers, and vetches.
|Table 1. Changes in alfalfa quality due to maturity|
|Alfalfa stage of maturity||Total Digestible Nutrients (%)||Crude protein (%)||Acid Detergent FibRE (%)|
|Source: Nutrient Requirements of Dairy Cattle, 3rd edition. National Research Council. 1966.|
As mentioned previously, forages are poor sources of energy but they still contribute some calories to fuel the bird’s need for energy.
Buchanan et al. (2007) reported that a chicken gains anywhere from 129 to 246 calories for each pound of forages consumed (or 285 to 542kcal per kg) and Rivera-Ferre et al. reported that broilers raised on pasture got only three per cent of their energy need from forages (2007). Yellow dent corn, the main supplier of energy in poultry rations, by comparison, supplies around 1,632 calories per pound (3,596kcal per
kg). While grains are obviously one of the most important sources of energy in poultry rations (along with oils), even the small amounts of energy supplied by forages are important when feed prices soar. Forages can play a small but key role in reducing the feed bill in a pastured poultry operation.
Although fibre is often overlooked, research is increasingly showing that it is an important component of poultry diets. Fibre generally falls into two categories: digestible and indigestible. Both types have roles in maintaining a healthy poultry digestive system.
Digestible fibre is fibre that gets broken down by the bacteria in the bird’s digestive tract. Digestible fibre is an excellent food source for beneficial bacteria like Lactobacillus sp and Bifidobacteria. Additionally, lactic acid and other beneficial compounds are produced as these beneficial bacteria ferment digestible fibre, stimulating gut health. The competitive presence of populations of these beneficial bacteria, as well as the lower pH resulting from the fermentation of the fibre, creates a difficult environment for the establishment of Salmonella and other pathogenic populations (Nurmi and Ratala, 1973; Esmail, 2012).
Indigestible fibre does not get broken down as it moves through the bird’s gut. This type of fibre does, however, slow things down considerably by bulking up the food and helping the gut “grip” the feed. Indigestible fibre typically is very water-absorbent, and allows water more time to be absorbed by the digestive system, especially in the large intestines.
When evaluating the nutrition of a particular feed item, it is helpful to understand a few terms that involve fibre:
Crude fibre (CF) – CF expresses the percentage of the feed item that is made of fibre, both digestible and indigestible.
Total Digestible Nutrients (TDN) – this term refers to the sum of all the digestible parts of a feed item, including fibre, fats, proteins, and carbohydrates. Expressed as a percentage, it represents what can be digested by the animal; the remainder is indigestible.
Acid Detergent fibre (ADF) – refers to the indigestible plant parts, including cellulose and lignin, that make up the outer walls of individual plant cells and, on a larger scale, the walls of leaves and stalks.
When building poultry rations, the greatest concern associated with fibre is having too much in the diet, which can cause a drastic drop in poultry performance and health. It is advisable to stick with a ration recipe formulated by a poultry nutritionist, especially in confinement situations. Poultry have the ability to at least partially regulate fibre intake, as birds in confinement have been observed supplementing their fibre intake by eating wood shavings from the litter when fed a fibre-limited diet.
With access to pasture, poultry are able to round out any fibre deficiencies on their own, especially if given a wide variety of forages to choose from. Grasses are more fibrous than legumes, and grasses often have two or three times the fibre concentration of legumes in similar growth stages (Buxton and Redfearn, 1997).