Introduction

These investigations indicate that soybeans are an excellent source of protein and energy for poultry, however the raw grain contains certain antinutritional factors that inhibit productivity, and as a result, prior heating is required. The processing conditions, especially those relating to the milling size, the use of steam, the temperature and the pressure applied, in addition to the process duration, all influence the goodness of the final product and define its nutritional value to a large extent in addition to defining advisable levels of use in commercial diets. Adult birds appear to be less sensitive than younger ones to the antinutritional factors present in the bean, however it is necessary to heat these prior to their use whatever the case.

The use of unprocessed soybeans

There is a substantial amount of information available regarding the use of raw beans in feeds for poultry farming and the majority of investigators indicate that tolerance to antinutritional factors depends on the age of the bird. Saxena et al. (1963a) observe that diets based on autoclaved beans (102 ºC for 30 min.) in 14 day old chicks allowed greater growth (8.5 vs 4.2 g/d) and conversions (1.60 vs 2.10 g/g) than diets based on raw beans. Mogridge et al. (1996) discover that the consumption of raw beans increased the size of the pancreas (0.80 vs 0.37% of live weight) and the duodenum (1.35 vs 1.06% of live weight) and reduced the consumption of the feed and growth of the chick (66 vs 97 g/14 d). Similar results have been discovered by Herkelman et al. (1993) who observe that that the size of the pancreas increases by 260% and broiler growth is reduced by 50% when introducing 37% raw beans to the diet. Renner and Hill (1960) observe that the apparent absorption of oil varied from 72% in raw beans to 80% in autoclaved beans treated for 60 min and using 4 lbs of pressure. The energy values found in the beans were 2,770 and 3,370 kcal ME/kg, respectively.

Rand et al. (1996) estimate a metabolizable energy value of 2,800 kcal/kg for raw beans, far from the value of 3,500 kcal used by industry for processed beans. These authors have discovered that the chickens fed with 20% untreated beans grew by 24% less and had a conversion of 11% worse than the control chickens fed with soybean meal and fat (table 1). Wiseman (1994) discovered that in 18 day old chicks the extruded beans provided 33% more metabolizable energy and 45% more nitrogenous retention than raw beans. Perilla et al. (1997) compared diets with 41.3% raw beans or a combination of soybean meal and oil in chicks between 8 and 35 days old.

The diets based on raw beans reduced consumption and live weights and also decreased the conversion indices by 14, 35 and 53%, respectively. Recently Ordóñez and Palencia (1998) indicated that the use of raw beans in chickens reduces the live weight by 81% (1,118 vs 2,030 g) when compared to beans dry roasted at 130 ºC. Similar data has been published on turkeys (Waldroup, 1982). Scott (1980) indicates that young turkeys are less tolerant to the antinutritional factors of raw beans than adults. Moran et al. (1973a) discovered that 8 to 23 week old turkeys fed on raw soybeans grew 5% less and had a conversion of 8.4% less than turkeys fed with soybean meal and oil.

The results obtained using raw beans on laying poultry are very variable. The oldest data, which relate to low-productivity stock, shows satisfactory results when using up to 20% unprocessed beans, both in chicks (Nesheim, 1967) and in commercial laying hens (Fisher et al., 1957; Saxena et al., 1963b and c; Summers et al., 1966). Arscott (1975) compares diets for laying hens based on raw beans, extruded beans and soybean meal and indicates that the raw beans reduce the laying capacity and the weight of the birds, but improves the Haugh units (table 2). Latshaw and Clayton (1976) observe an increase in the weight of the pancreas and a small reduction in the laying capacity and egg size when including 20% raw beans in the diet, but not with inclusion levels of less than 10% (table 3). Waldroup and Hazen (1978) compare feeds based on raw and processed beans (table 4). The raw beans reduced the consumption of the feed (88 vs 101 g/d), laying capacity (53.8 vs 79.0%) and egg size (58.1 vs 61.7 g), but improved the Haugh units (78.7 vs 70.9).

Hill and Renner (1963) discovered energy values of 2.84 and 3.70 Mcal ME/kg for raw and processed beans, differences that were mainly due to the different absorption levels of the lipid fraction (78% in raw beans and 92% in autoclaved beans). The use of raw beans in this test reduced the laying capacity significantly (46 vs 64%). Scott (1980) indicates that laying hens adapt better than chicks to raw beans and that adaptation improves with the duration of consumption.

The supplementation of diets based on raw beans with methionine often improves productivity but without reaching the results obtained with equivalent quantities of soybean meal and oil (Ogundipe and Adams, 1974; Waldroup, 1982).

Latshaw (1974) indicates that die ts containing 18% raw beans supplemented with methionine allowed acceptable production levels and in many cases comparable to those obtained with roasted beans (table 5). However, Arscott (1975) did not find any benefit in supplementing diets based on raw beans with methionine (table 2). Whatever the case, with or without added methionine, the weight of the pancreas is greater with raw beans than with processed beans (Summers et al., 1966). The most recent investigations indicate that it is not possible to have good beaks nor to maintain the persistence of egglaying with unprocessed beans, even at low inclusion levels during a complete cycle (Zhang et al., 1991). Thus, the use of raw beans in feeds for intensively- farmed poultry is not recommended (Waldroup, 1982; Monari et al., 1996).

The energy value of the treated soybean in poultry farming

The energy content of the soybean depends on the chemical composition of the original seed, the type and conditions of the process used to inactivate the antinutritional factors and to release the oil, characteristics of the diet, and the species and age of the bird that consumes it. The key factor is the influence of the treatment (heat, duration, pressure, milled size and subsequent processing) on the destructio n of the antinutritional factors and the availability of the energy and protein fraction of the bean.

To read the full report, please click here (PDF)

Source: The American Soybean Association - July 2004