Factors Affecting Forage Consumption14 October 2013
Palatability and the birds' foraging behaviour are the main factors affecting the consumption of poultry kept outside, according to 'Pastured Poultry Nutrition and Forages' from the National Sustainable Agriculture Information Service, ATTRA.
Common experience among pastured poultry producers is that the birds will readily consume large amounts of forages, even if they have good rations available: poultry crave greens and eat them readily even if a balanced ration is provided (Blair, 2008). Just because poultry have access to pasture, though, does not necessarily mean that the birds will consume the available forages.
There are several factors that determine how appealing a plant is to a bird (called the plant’s palatability), including the plant type/species; the nutritional content, height, and stage of growth of the plant; as well as the nutritional needs of the bird, how hungry it is, and its foraging instincts. These factors are explored below.
Poultry Foraging Behaviour
One of the main factors that determines the amount of plant matter that chickens and other poultry consume while foraging is the actual behaviour of birds. Several factors affect a bird’s ability to forage, including:
Different breeds of poultry have different foraging habits and consumption rates. On two separate ends of the spectrum, geese are able to meet nearly all their nutritional needs with the vegetation they graze on, whereas modern broilers like the Cornish Cross can only make modest (though still economically and nutritionally important) supplements to their diet from pasture. Turkeys are voracious foragers, and will forage as a flock, forming a line and cleaning a pasture of insects, tasty forages and seeds with almost military precision. Among chickens, laying hens forage much more than their meaty broiler cousins.
Many pastured poultry farmers who have experience with both modern layer hybrids and heritage breeds of hens see little general difference between the two in terms of foraging, but quite a difference in feed conversion and production from the more modern breeds.
Additionally, producers notice variability in grazing ability from hatchery to hatchery, flock to flock, and even among individuals within the same breed (Salatin, 2001).
Pousga et al. point to research that suggests genetics also play a role in chickens’ ability and efficiency in balancing their nutritional deficiencies, at least in free-choice feeding systems (2005). They report that brown-egg layers seem to be able to adapt more readily to free-choice feeding systems than white- or tinted-egg layers. Within a flock, individuals show a range in their capability to select for their own needs, along the same lines as the experiences mentioned above.
Time of day
Poultry are most active during the morning and evening hours. Of the two times, poultry are most active right before sunset (Dawkins et al., 2003). Danish research has found that laying hens with constant access to forages consumed the most vegetation prior to sunset (Horsted et al., 2007). The birds really prefer to fill up before they head off to the roost for a good night’s sleep.
Filling up their crops enables them to digest the seeds, feed, insects, plants and other food items overnight. Likewise, the birds will be out foraging first thing in the morning, looking to get food into their empty stomachs but not to the same extent as they do at night.
Long-time pastured poultry producer and innovator, Joel Salatin, with decades of pastured poultry experience under his belt, advised in the 1990s of the importance of providing chickens fresh pasture early in the morning, noting that “the birds’ most aggressive grazing period is two hours pre-daylight, which occurs long before the sun rises. Every quarter hour, we wait to move pens after daylight reduces the grazing time period. As the dew comes off and the day gets warmer, the birds begin lounging not because they have grazed their fill, but because physiologically they demand a rest period” (Salatin, 2001).
The results of research and experience are clear: give access to forages in the morning and evening if you want to maximise forage utilisation.
It takes time for a flock of birds to adapt to new types of feed (Jones, 1986). Novel food types require time for the birds to figure things out. Some producers give their birds a head start by placing a tray of chopped forages daily in the brooder (lawn clippings work well). Others dig a chuck of sod and place it in the brooder for the chicks to investigate and pick through.
Broiler intake is positively correlated with age (de Almeida et al., 2012). When broilers are first put on pasture, they may pick half-heartedly at forages or totally ignore them. This will change over time, but with the short lifespan of broiler chickens (as short as seven weeks), the sooner they get on pasture, the faster they learn that forages are food.
Poultry raised in pens tend to learn faster than those in day-range-style systems because the birds feel a competitive drive to eat fresh forages before their flockmates gobble them up first.
Laying hens seem to learn to eat forages faster than their broiler kin but it must be remembered that meat birds grow much faster than layers and although their body size is large, they are still essentially chicks in terms of instincts and habits that they are developing.
Shade/protective cover encourages foraging (Dawkins et al., 2003), most likely from the protective effect of shelters (Rivera-Ferre et al., 2007). Shade, whether from trees or shelters, especially encourages layers to roam.
Chickens originated in the jungles of Southeast Asia, and turkeys in the hardwood forests of Eastern America. Staying hidden under tree or plant cover seems to afford the flock an instinctive sense of protection from predators (a false sense when it comes to hawks!). Brightly lit, open areas are among the least desirable habitats for most poultry and for centuries, farmers have noticed that poultry will often overgraze the areas immediately surrounding their housing even if undergrazed forages are available just a little further away.
Height of forage
Poultry like their forages relatively short. Virginia producer, Joel Salatin, prefers forages under four inches (Salatin, 2001) but ideally around two inches. Before his birds get to the pastures, he grazes ruminants until the pastures are the preferred height for the birds (Salatin, 1996). Meanwhile, Oregon producer Aaron Silverman prefers a sward height of six to eight inches for his chickens (Silverman, 2000).
Producer and research observation have noted that chickens go for shorter forages over longer plants when given the choice (Horsted, 2006). Turkeys do not seem to be nearly as picky, eagerly ingesting long strands of grass either in pieces or whole, like slurping noodles.
It is worth considering, though, that forage height usually correlates with palatability, as younger, more succulent plants tend to be shorter.
The term “palatability” refers to how “tasty” a bird finds a particular plant to eat at a particular time. Whether or not a plant is palatable is one of the most critical factors for birds on pasture: if the bird won’t eat a plant, the benefits of the plant - no matter how nutritious - are worthless.
Several factors directly affect palatability:
Like people, poultry find some plants highly palatable, while others are completely unappealing and will not be eaten. Some plants have strong flavourings that poultry love, like the tart taste of yellow wood sorrel or clover seed pods, or despise, like the bitter fluid from milkweed.
Generally, legumes and young, soft grasses are appreciated, while forbs and shrubs can be hit or miss.
Clovers and alfalfa have long been considered among the best forages for a variety of reasons: high protein content (legumes), lush leaves, perennial growth and, importantly, because these legumes mature slower and stay palatable much longer than grasses. Grass leaves on average contain twice the fibre of legume leaves. Fibre content in alfalfa and crimson clover leaves at the mid-blooming stage is around 25 per cent, compared to fescue and orchardgrass leaves that have fibre contents near 50 per cent and up to 70 per cent in big bluestem and bermudagrass as the plants go to seed.
Given their structural purpose of supporting seeds, it comes as no surprise that stems are typically much higher in fibre than leaves (Buxton and Redfearn, 1997).
The specific variety of a plant can affect the amount of grazing a bird does on pasture. For instance, alfalfa varieties high in bitter tannins or saponins are less palatable than varieties with little of these compounds. The tannins can also depress protein digestibility and reduce overall feed intake, which can reduce feed conversion. Therefore, in the case of alfalfa, variety can play a significant role in the amount of vegetation consumed.
Feeding Poultry, a poultry nutritional text from 1955, makes the following suggestion on desirable species for poultry production: 'For poultry pastures, plants capable of forming a dense, hard-wearing, and lawn-like turf are desirable. Wild white clover and ladino clover are suitable legumes. Grasses suitable for poultry turf are perennial rye grass, meadow grasses, the fescues, creeping bent, and crested dog’s tail. However, poultry does not like the plants after they have become aged and woody and will then only eat them as a last resort. Turkeys prefer ladino clover, but other grasses can be satisfactorily used for grazing.” (Heuser, 1955)
Aaron Silverman from Oregon has settled on a complementing blend of highly palatable clovers and more persistent grasses, “a balanced mixture of orchard-grass, perennial ryegrass, tall fescue, annual ryegrass, subclover and New Zealand white clover” (Silverman, 2001).
Stage of growth
As pasture forage plants near maturity, they will direct energy and nutrients away from producing nutrient-dense leaf mass and into producing the next generation of seeds. Funnelling nutrients into the seeds, which includes pulling nutrients from existing leaf mass, greatly decreases the livestock feed value of the forage.
Additionally, the lignin content (roughly, the “woodiness”) of the plant increases as the plant gets closer to producing fruit or seeds, especially in the stems (resulting in higher fibre content).
As an example, alfalfa’s nutritive qualities plummet after the blooming stage (see Table 1). It makes sense that the younger the forage, the more tender and palatable it will be. Plant stems become lignified faster than leaves, and rapidly become indigestible and unattractive to poultry.
|Table 1. Changes in alfalfa quality due to maturity|
|Alfalfa Stage of Maturity||% Total Digestible Nutrients||% Crude Protein||% Acid Detergent Fibre|
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Source: Nutrient Requirements of Dairy Cattle, 3rd edition. National Research Council. 1966.
Although grasses can be higher in several nutritive qualities, other plants may be preferred as forages because they stay palatable for a longer time during the growing season. It was noted in the 1950s that “clover and alfalfa ranges are preferred [for poultry], primarily because the green stuff is available over a longer period of the year. They do not grow up and become tough and unavailable, as grass does. Frequent mowing of grass, either with ruminants or machinery, however, will help keep it tender.” (Heuser, 1955).