Glycine max

Soybean, soya bean, soja bean, Manchurian bean

Useful reference: 108

One of the world's most important oilseed crops and a staple food of the Orient. Indigenous to the Far East, it is now cultivated elsewhere, particularly in the United States.

A typical legume, the soybean seed has a smooth, often shiny, thick coat. The soybeans are cleaned, dried (if the moisture content is more than 13%) and fed into cracking rolls. Often the hulls are removed as they contain little oil, thereby increasing the effective capacity of the processing plant. Because of the rather low oil content of the seeds (below 20%), solvent extraction is the most common method. The cracked seeds are prepared for this process by passing them through a flaking machine. The extracted meal is ground in a hammer-mill. The cake or meal is usually classified for marketing by its crude protein content; 41% for undecorticated expeller or hydraulic-process cake; 44% for undecorticated solvent -process meal and 50% for decorticated solvent-process meal. The actual crude protein content is somewhat higher than the guaranteed figure.

TRYPSIN INHIBITOR. The nitrogenous constituents of the seed include some inhibitory and toxic factors. The most important of these is the soybean trypsin inhibitor, which blocks the activity of the digestive enzyme trypsin. As it is destroyed by heat and as soybeans are normally heated before or during processing, it is of no concern in the oilcake. Whole seeds, however, should be thoroughly heated before feeding to pigs or poultry. Too high or too prolonged heat will destroy essential amino acids. Soybean also contains urease, an enzyme that releases ammonia from urea, and therefore cannot be fed together with urea.

SEEDS. Soybeans are the richest in protein of all the common seeds used for animal feed. They should not be stored until thoroughly dry. At harvest the seeds often contain too much moisture for satisfactory storage and must therefore be dried to a moisture content of less than 15%. For feed they should preferably be cracked or ground (grinding is easier if the beans are mixed with grain). If they are fed in large quantities to cattle, the diet must also contain adequate amounts of vitamin A. Ground soybeans cannot be stored long in a hot climate. For cattle, soybeans are an excellent feed without processing or specific conditioning by heat; but for monogastric animals, especially young pigs and poultry, the beans have to be heated to destroy factors that lower their nutritive value. This can be done in a heated rotating drum; however, this method is unsatisfactory because some beans are charred and others not heated enough. A safer method is to pressure-cook the crushed beans at 115 C for ten minutes or at atmospheric pressure for two hours. The carcass will lack firmness and be too juicy if the level of whole beans in the diet exceeds 20- 25%. For poultry, up to 30% whole, heated soybeans can be included in the diet with no depressing effects.

SOYBEAN MEAL. Soybean meal or cake is one of the most valuable sources of vegetable protein. The amino-acid composition is comparable to that of milk protein. It is essential, however, to remember the shortcomings of soybean meal as a substitute for animal proteins in compound feeds. Some minerals are present only in small quantities in soybean meal, and although it is a good source of some vitamins, it lacks vitamin B12, which is found instead in animal protein supplements. This vitamin is probably the one most often lacking in practical poultry diets.

From the taste of the meal it is possible to judge whether it has been heated enough during processing to be safe for pigs and poultry. It should have a pleasant nut-like taste and a light brownish colour. If the meal has a "beany" raw taste, it should be used only for ruminants. Properly heated soybean meal is an excellent feed for all classes of animals with no restraints on its use; however, soybean oil meal extracted with trichloroethylene is toxic to some animals and should not be used for feeding.

HULLS. Also called soybean mill feed or mill run, the hulls are the by-product of decorticated soybean meal. Rich in fibre, they are used for ruminants. If mixed with low-fibre ingredients, such as maize and soybean meal, they can be included up to 40% in the concentrate portion of the diet without significantly reducing the milk yield.

					As % of dry matter
				DM	CP	CF	Ash	EE	NFE	Ca	P	Ref
Seeds with hulls,
Zimbabwe				91.2	26.4	19.0	7.2	11.0	36.4			499
Seeds without
hulls, Trinidad				95.8	42.9	4.9	5.2	20.4	26.6			117
Oil meal with hulls,
solvent extracted,
Israel				89.2	49.9	5.0	6.3	0.7	38.1	0.20	0.74	365
Oil meal without
hulls, solvent ext-
racted, USA				89.8	56.7	3.1	6.2	0.9	33.1	0.29	0.69	356
Oilcake with hulls,
mechanically extr-
acted, Israel				91.0	44.0	8.1	7.5	7.7	32.7	0.20	0.73	365
Oilcake with hulls,
mechanically extr-
acted, Malaysia				84.8	47.5	5.1	6.4	6.4	34.6	0.13	0.69	292
Hulls, Trinidad				89.8	7.8	44.0	7.0	0.8	40.4			117
Hulls, USA					16.2	31.7	4.4	1.8	45.9			464
							Digestibility (%)
					Animal		CP	CF	EE	NFE	ME	Ref
Seeds with hulls					Cattle		85.0	72.0	84.3	88.1	3.34	499
Oilcake, extracted					Sheep		92.0	87.0	47.0	94.0	3.46	365
Oilcake, expeller					Sheep		85.0	73.0	86.0	91.0	3.42	"
Hulls					Cattle		64.4	61.1	43.8	78.6	2.52	464
		Amino acid composition as % of crude protein
Meal											Ref	528
Arg	Cys	Gly	His	Ils	Leu	Lys	Met	Phe	Thr	Try	Tyr	Val
7.4	1.6	4.5	2.4	4.6	7.8	6.1	1.4	5.5	3.8	1.3	3.5	5.2