In the midst of the Edinburgh Fringe Festival, poultry nutritionists debated the latest thinking on feed.
Nutritionists and researchers have for many years focused on feeding birds for meat and egg production, in particular looking at ways of supplying nutrients more efficiently and cost effectively.
But this emphasis has changed in recent years. This was reflected at the 17th European Symposium on Poultry Nutrition, organised by the World Poultry Science Association and held in Edinburgh during the world famous Fringe Festival. The organisers had broadened its scope to include aspects of the environment, litter quality, biofuels and plant breeding.
Maintaining good litter quality is set to become more crucial after the implementation of the new EU broiler welfare Directive. Under the rules, flocks will be routinely monitored at abattoirs for signs of poor welfare and acted upon. Where a problem is identified, such as poor welfare due to wet litter, producers may be forced to stock at a lower density until the problem is solved.
Stephen Lister of Crowshall Veterinary Services, Norfolk, said: “There is seldom one isolated cause of wet litter, so unravelling the causes can be difficult.”
“For instance, a high stocking density is associated with an increased incidence of footpad dermatitis. But it is not clear whether this is due to increased faecal output, lower ventilation at high stocking rates, or changes in bird activity.
“Probably it is due to a complex interaction of all of these plus other factors”, he remarked.
Tips on avoiding litter problems
The causes of wet litter can be broadly divided into infectious and non-infectious factors. One key non-infectious cause is water quality, including total bacterial count, pH and mineral content. The other important factors relate to diet. These include physical properties of the feed (such as grist size), dust content, heat treatment of feeds, electrolytes, proteins, fats, cereals and the presence of mycotoxins.
For infectious causes, the most important causes include parasites like coccidiosis, and some bacterial challenges. Viral infections of concern include Gumboro disease, certain strains of infectious bronchitis, astroviruses, rotaviruses and enteroviruses.
The most significant effects of wet litter are in relation to skin problems, mainly pododermatitis, hock burn and breast blisters. Wet or caustic litter can lead to contact dermatitis or burns, and the resulting injury to the skin surface can lead to a range of bacterial lameness problems.
“On the other hand,” warned Dr Lister, “excessively dry litter can lead to a greater risk of scratches and skin tears in very active birds. This can lead to downgrading at processing due to skin trauma and major lesions or through the skin necrosis.” In this condition, skin damage allows a range of bacteria to cause infections that are often not detected on farm.
Dr Lister outlined his recommended strategy (see panel) which includes using high quality feed rations and supplements, minimising feed changes and related stresses and aiming for good intestinal integrity.
Looking at the role of nutrition in more detail, Steve Collet, assistant professor at the University of Georgia, Athens, Georgia, warned of the risks associated with the shift to all-vegetable diets.
“This has led to an increased risk of wet litter because of higher levels of dietary potassium, which increases water output. In addition, higher levels of non-digestible carbohydrate and protein fractions increase faecal moisture.
“Inefficient protein assimilation increases nitrogen excretion which negatively affects litter quality and can elevate ammonia levels in the house to dangerous levels.”
Litter moisture content should not exceed 25%, above this wet litter problems occur. Dietary non-starch polysaccharides (NSP) such as pentosans in wheat, beta glucans in rye and barley, and raffinose and stachyose in soya, also contribute to wet litter. Enzyme additions to alleviate some of these problems have become standard practice.
The type and quality of dietary fats should also be considered. Lipids are susceptible to oxidation and, therefore, require careful storage and quality control. Rancid fats are less digestible, reduce the efficiency of fat soluble nutrient absorption, cause intestinal inflammation and alter the composition of the gut microflora.
“These changes inevitably cause wet litter,” concluded Dr Collet.
Henk Enting of Trouw Nutrition added that while increased dietary sodium, potassium or magnesium increases litter moisture, the role of chloride is less clear and may depend on the mineral that is used to replace sodium chloride.
Data showed that a moderate reduction of chloride by substitution with bicarbonate or sulphate did not greatly affect excreta moisture, but further reducing chloride levels and substituting with sulphate caused a significant increase in moisture.
Biofuels are having a dramatic effect on feed supply and prices, having doubled the annual rate of growth in global demand for grains and vegetable oils.
Julian Bell of the Scottish Agricultural College, near Edinburgh, said that this explosion in demand has made it difficult for production to keep up and has contributed significantly to higher feed prices. “Higher grain and oilseed prices are a strong incentive for farmers worldwide to maximise production.”
According to SAC figures, the total use of grain and vegetable oil feed stocks (excluding sugar and molasses) has risen by 225% (64m tonnes in 2005 to 145m tonnes in 2009). This growth has up to now been driven by a wide range of incentives from governments seeking benefits for environmental, fuel security and agricultural support reasons.
“High [crude] oil prices over much of this period have further supported biofuel use,” added Dr Bell. “However, the pace of expansion has slowed sharply in the last two years as ethanol production margins have declined and capital availability has decreased due to the credit crisis.”
Biofuels have also led to shifts in the profitability and production of different crops. In 2007 expansion of the US ethanol sector led to high maize prices and resulted in US farmers increasing maize plantings by 22% to a record 35m hectares. This displaced other crops particularly soya and affected the price of feeds such as soyabean meal.
In terms of feed availability and price, the development of a UK biofuel industry has two main impacts; increased competition for feed materials (grains and oilseeds) and increased production and interest in by-products such as rapeseed meal and dried distillers grains with solubles (DDGS).
So far, the reliance on imported feed ingredients has meant a limited local impact. However, this could change given the large scale increase in UK ethanol processing currently under way.
Dr Bell added: “Global growth in biofuel demand is expected to continue to support grain and oilseed prices in the future, although the pace of growth is expected to slow.”
“Politically”, he pointed out, “Biofuels are facing growing scrutiny over greenhouse gas savings and their potential impact on food prices.”
He predicted that prices will continue to be driven by weather and economic factors such as exchange rates and the price of crude oil. Longer term price trends will also depend in part on whether technology can help raise agricultural production to meet additional demands for biofuel and food.
One benefit to the poultry industry is the use of DDGS in poultry diets. Researcher Jean Noblet of INRA (French National Institute for Agricultural Research) in north-west France has been investigating the nutritional value of DDGS in poultry diets.
“The chemical composition of DDGS has been found to be much more variable than in the original cereals, with large differences between ethanol plants,” he warned.
The colour of DDGS can also vary from light yellow to dark brown. Only light- coloured DDGS has a sweet and fermented smell. Dr Noblet recommended that while DDGS from cereals can be used in diets for poultry, only the light products should be used, and if using high inclusion rates, this is possible only in low density diets.
It appears that the composition of maize DDGS is more stable than wheat DDGS and most results on performance in poultry describe maize. Researchers speculate that a performance reduction with higher DDGS inclusions is due to an overestimation of the essential amino acid lysine in the product.
“More accurate lysine estimation would allow higher inclusion levels,” suggested Dr Noblet. Indeed, trials have shown no negative effect even when DDGS was included up to 25% in the grower/finisher diet of broilers, when low density diets were formulated based on digestible amino acids.”