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The Dairy Corner: Soybeans have excellent fit in dairy diets

Sometimes more expensive, but they can put more milk in the tank

I am fortunate to travel across wide stretches of Manitoba and have observed the explosive growth of soybean acres over the last decade. From 2005, only about 100,000 acres were planted and this acreage has steadily increased to about 1.3 million acres, today. Recently, I asked many dairy/soybean producers, why they grew this crop. Most tell me that shorter season varieties that became available in the last few years, less expensive inputs than other oilseeds, strong soybean prices and favorable on-the-farm crop rotations made soybeans attractive to grow.

In the light of this soy revolution, I have always been a big fan of adding soybean-derived ingredients into dairy lactation diets. Soybeans are a good source of dietary protein, and few people realize it is a high energy feed. Its ruminal degradable and un-degradable protein fractions compliment much of the total protein requirements of high milk producing dairy cows.

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High in protein

Whole soybeans are about 42 per cent crude protein and about 19 to 20 per cent fat. The rumen un-degradable portion of its protein (RUP) is about 26 per cent. When soybeans are crushed and the oil is removed, the resulting meal has a protein content of either 44 or 48 per cent crude protein depending on the level of fibrous hull allowed to remain after processing. Then its RUP feature also rises to 35 per cent bypass protein.

Although, soybean processing removes most of its fat, soybean meal (one per cent crude fat) still yields a high Nel value measured at 1.90 Mcal/kg compared to 2.0 Mcal/kg for barley or corn. I believe this energy partially comes from a modest amount of starch (six per cent) retained after processing.

On a personal note, sometimes, this energy comes in handy when I make 1:1 ingredient substitutions in dairy diets such as replacing one kilo of barley with one kilo of soybean meal in order to increase protein of the diet without tampering dietary energy value. Other oilseed meals such as canola and sunflower meals don’t have this advantage.

Despite this unique energy feature, many dairy nutritionists and I still like soybeans/soymeal in dairy rations as a primary protein supplement. The initial ruminal degradable protein (RDP) in soybean meal can supply some energy, necessary ammonia, amino acids and protein peptides for maximum microbial growth. Soybean meal’s RUP has the best amino acid profile of any oilseed, which can supply essential lysine in the small intestine. What amino acids that it may lack can be supplied by other complimentary protein ingredients.

Another reason that I like soybeans for dairy cows is that it lends itself to industrial processes such as roasting of raw whole soybeans, which causes favorable changes to its internal protein structure. As a result, this makes cooked soybean protein more unavailable to the microorganisms in the rumen, but allows more of it to travel to the small intestine where it can supply more essential amino acids required for greater milk production. Digestibility trials with cannulated dairy steers (re: experimental cows with surgically placed holes in their sides) have demonstrated that raw soybeans and regular soybean meal have a RUP of 25 and 35 per cent, compared to roasted soybeans valued at 55 to 60 per cent RUP.

Means more milk

There is no shortage of American and international dairy studies that frequently report up to a 1.5 kg milk yield increase when roasted beans replace either raw soybeans or soybean meal (energy adjusted) in early lactation diets, where protein and energy demands are the greatest. Typical positive milk responses tend to be more visible in these early diets where alfalfa-based diets are fed.

Such field evidence demonstrates soybeans and its derivatives can be a good protein source for good milk production, but actual roasted soybeans and soybean meal usage in dairy diets compared to other protein sources such as canola meal and corn dried distillers’ grains is still determined by inherent economic advantage. Sometime soybeans are not the cheapest protein sources in dairy diets.

A practical comparison for these common feedstuffs upon a protein and by-pass protein basis is as follows (commodity prices quoted are for demonstration purposes only):

  •  Soybean ml protein (48 per cent CP) = $580 mt/.48 = $ 1,208 mt vs Canola ml (36 per cent CP) = $370/.36 = $ 1028 mt
  •  Soybean ml protein (48 per cent CP) = $580 mt/.48 = $ 1,208 mt vs Distiller’s grain (28 per cent CP) = $260/.28 = $928 mt
  •  Roasted Soybeans RUP (41 per cent of CP) = $650 mt/.41/.50 = $ 3,170/mt vs Distiller’s grain RUP (60 per cent of CP) = $260/.28/ .60 = $ 1,548/mt

Just because their competitive economics for soybean meal and roasted beans doesn’t seem to work out in this example, doesn’t mean that I would pull them out or not add them to existing dairy diets. With no explanation, I have seen well managed high milking dairy herds could not achieve substantial milk peaks due to supplemental canola meal, which was alleviated with a simple and equal substitution of soybean meal. On other farms, I have also seen combinations of canola meal and dried distillers grains fail in the milk tank, only to have milk production boosted by roasted soybeans.

I believe soybeans, whether used as soybean meal or processed roasted bean can form a solid winning foundation in dairy diets. They offer a lot of good essential nutrients to support optimum milk production in dairy cattle. With the growth of soybean acres in Manitoba, and I hear another 300,000 acres were planted this year in Saskatchewan, the advocacy of using soybeans in dairy diets will most likely continue to grow.

About the author

Columnist

Peter Vitti is an independent livestock nutritionist and consultant based in Winnipeg. To reach him call 204-254-7497 or by email at [email protected]

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