“Cows will pick and choose what they eat from the straw, chaff, weed seeds in the stubble, slough hay from the low areas and mature hay growing along the fences and headlands,” says Barry Yaremcio, beef and forage specialist at the Alberta Ag-Info Centre.
“Quality of what they eat can be variable depending on the type of crop grown, fertility program and stage of maturity when the crop was cut or harvested. The combine setting – the amount of light grain and weed seeds thrown out onto the ground – will also impact what the cows eat.”
Straw, chaff and over-mature grass hays are typically low in protein, energy, calcium and magnesium, but relatively high in phosphorus. These feeds are also high in neutral detergent fibre, which can reduce total feed intake, and relatively high in phosphorus. Grains and weed seeds are also high in phosphorus and have higher energy and protein content than the grasses, straw and chaff.
He notes that cow-calf pairs turned onto stubble fields have different mineral supplementation needs than when they were on a mixed alfalfa-grass pasture. The lack of calcium and magnesium in the straw and forages can cause two problems.
“A diet that is low in calcium and higher in phosphorus can reduce phosphorus absorption,” explains Yaremcio. “Phosphorus is the driver of all metabolic functions. When it is not absorbed, feed intake is reduced. That in turn reduces milk production and weight gain on the calves. Cows can also start to lose weight. A continuous imbalance can impair reproductive performance, with cows taking longer to cycle and conceive a calf next year.”
“A calcium or magnesium deficiency can cause cows to go down. Winter tetany and milk fever can also occur. It generally requires a veterinarian to treat animals in this situation,” he adds.
A mineral supplementation program should contain additional calcium and magnesium, but Yaremcio says that a 2:1 mineral does not provide enough calcium to remedy the situation. He adds that a feedlot mineral with a 3:1 or 4:1 calcium to phosphorus ratio is preferred.
“If a 1:1 or 2:1 mineral is left over from the summer, mix 1 bag of limestone – 38% calcium – with 1 bag of mineral and 1 bag of fortified trace mineral salt – with selenium. One hundred cow-calf pairs should consume this mixture, weighing roughly 165 lb, in 5 to 6 days. If consumption is too low, add 8 to 10 lb of dried molasses to the entire mix and adjust to get the proper intake.”
He adds that if feeding a straight mineral, magnesium content should be 3 to 5% when the recommended intake is between 70 to 100 g per day.
“The added magnesium along with the calcium reduces the risk of downer cows. Magnesium can be purchased as an individual product if it is not present in the mineral.”
Feeds that are over-mature or crop aftermath are usually low in protein. A lactating cow needs a minimum on a dry basis 11% protein to maintain feed intake and milk production. Dry cows can manage on 8% protein.
Yaremcio says that supplementing protein on pasture can be troublesome, but protein tubs or blocks will help solve the problem as long as mineral and vitamin supplementation continues as described.
Other options include feeding 3 to 4 lb of grain every third day along with a protein supplement or putting dry cows onto these fields to reduce protein requirements.
He adds that when the cow energy and protein requirements are not met, milk production is reduced, cow weight loss is possible and calf gains will decline.
“To offset the loss of calf performance, creep feeding the calves with a ration that is between 14 and 16% protein will improve average daily gains. If feeding straight oats, which has 10 to 11% protein on average, the calves will put down fat rather than lean growth. They may not frame out properly, resulting in a calf that could be discounted at auction. A mixture of 1/3 peas and 2/3 oats or barley by weight will provide a creep ration that meets protein and energy requirements. With lower grain prices and high calf prices creep feeding will pay very well in the long run.”