Posted  28 Oct, 2019 
In: Articles

Originally published in the October 15 edition of Agri-News

Some nutritional concerns to consider when feeding a straw-grain ration to pregnant cows.

“With hay and silage in varying supply and quality across Alberta for this winter, feeding a straw-grain or low quality hay-grain ration to pregnant cows will be a viable alternative for some producers,” explains Barry Yaremcio, beef and forage specialist at the Alberta Ag-Info Centre.

To determine the quality of feeds available to use this winter, he says that testing is the first step.

“Balancing the rations is the next step, which includes portioning of limited feed supplies to different classes of livestock on the farm. Determining the number of animals that can be fed over the winter is part of the decision making process.”

Once the basics of how many animals can be fed are established, the next step is to determine what type of supplements or mineral product is needed.

“It is often a point of consternation when choosing what to use because each company ‘has the best’ product to use. Convenience, effectiveness of the product and cost are things to consider before making the purchase,” he adds.

When considering a straw-grain ration for pregnant cows, Yaremcio says some nutritional concerns need to be addressed.

Straw-grain ration

Straw typically is high in fibre, but low in energy, protein, calcium and magnesium.

“Straw should not be fed at levels more than 1.5% of body weight,” he says. “To be safe, and depending on the type and age of the straw, intakes could be only 1.25% of body weight. Using a 1,400 lb animal, straw intake can be anywhere from 17 to 21 lb per day on a dry basis. This example may be applicable for many operations this winter that are feeding pregnant cows.”

He adds that along with the straw, roughly 10 lb of barley or 11 lb of oats needs to be included to meet energy requirements.

Protein requirements

“The above mentioned straw-grain ration supplies roughly 6.5% protein on a dry basis. A cow in mid-pregnancy requires 7%. Late pregnancy protein requirements increase to 9% to reflect the larger needs of the growing calf, to produce colostrum, and to prepare for calving and milk production.”

Producers have several options to increase protein content in the ration, including adding 2 lb of peas in mid-pregnancy and 5 lb in late pregnancy to meet protein requirements.

He says that 1 lb of canola meal in mid-pregnancy and 3 lb in late pregnancy will also work.

“Cost per bushel of peas is 10.3 cents per pound, and canola meal 14.2 cents per pound. A 32% supplement is designed to be fed at 1 lb per head per day and is roughly 25 cents per lb. One pound per of 32% is not adequate to meet protein requirements for a late pregnancy cow, so a combination of supplement and peas or canola meal will be required.”

Yaremcio says to calculate the cost per pound of protein supplied to minimize cost.

“For example, peas contain 24% protein, which supplies 240 kg (528 lb) of protein from a tonne of peas. At a price of $230 per tonne, the cost of this protein is $1.06 per kg or 43 cents per pound. Canola meal contains 38% protein, which supplies 380 kg (837 lb) of protein per tonne. At a price of $306 per tonne, the cost of this protein is $0.88 per kg, or 36 cents per pound. Use this technique to minimize protein costs in the ration.”

Macro minerals, trace minerals and vitamins

To calculate the amount of macro minerals, trace minerals and vitamins supplied by a product, Yaremcio says to consider two factors.

“First, consider the expected intake of the mineral or supplement that is listed on the tag or label. Second, know the concentration of the nutrient being evaluated.”

The nutrient concentrations on the tag or label are listed as a percentage for the macro minerals – calcium, phosphorus, salt, magnesium and potassium. The trace minerals – copper, manganese, zinc, selenium, iodine and cobalt – are listed as mg per kg. Vitamins – A, D and E – are listed as international units (IU) per kg.

“For the macro minerals,” he says, “multiply the inclusion rate of the product in grams by the concentration of the nutrient. For example, if the product is fed at 100 grams per day and contains 16% calcium, multiply 100 g by 0.16 to determine that the product will supply 16 g of calcium. For the straw grain ration mentioned above, a high calcium product such as a 24:3 mineral, or even limestone is needed. A 1:1 and 2:1 mineral is not adequate to meet animals’ requirements.”

Yaremcio says for the trace minerals and vitamins, multiply the inclusion rate of the product in kg by the concentration of the nutrient.

“For example, if the same product is fed at 100 g and the copper has a concentration of 3000 mg per kg, multiply by the intake in kg (100 g = 0.1 kg) by 3000 to determine the product will supply 300 mg of copper. For vitamins, the process is the same but values will be in IU instead of mg.”

“When comparing what mineral to use, knowing what is needed to balance the ration and hand calculations can be time consuming,” he adds. “The use of a ration balancing program such as CowBytes can compute what is needed in short order, and the contribution of nutrients from different feeds, how to put the blend together, and what purchased product to use is made much easier than doing it by hand.”

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