Record low spring and summer temperatures, severe drought in some parts, while other areas were soaked with continuous rains, and with the occasional snowstorm thrown in, describe this years’ growing season across the prairies.
Wishing for global warming hasn’t helped. Good quality forages particularly alfalfa and mixed grass hays are in short supply for feeding beef cows and other livestock this winter. For many producers, a stack of straw bales is their only alternative winter forage, but luckily it can pull most herds through with the proper nutrient supplementation. It’s also a good idea to include some feed and management strategies when feeding straw, so when the time comes, most of your cows are prepared for calving.
The best candidates for feeding straw as the main forage in winter rations are mature mid-gestation beef cows. They should be going into the winter in good body condition (2.5 –3.0; 1= thin, 5= obese) and be healthy. Such cows have the lowest nutrient requirements until about the last trimester; 50 –53 per cent TDN, seven to nine per cent protein, and 0.25 per cent calcium and 0.20 per cent phosphorus. Then their nutrient demands start to climb in the last three months before calving; 57 –58 per cent TDN, 10 –11 per cent protein, 0.30 per cent calcium and 0.25 per cent phosphorus. Trace mineral and vitamin requirements follow a similar pattern. Balanced straw-based rations should be able to maintain these modest nutrient demands as they change throughout the winter as well as assure any additional dietary needs are met; namely, an extra 150 –180 lbs. of fetus and fetal membranes weight, which is lost on the day the calf is born.
Fortunately, a large six-year-old pregnant cow can eat alot of straw to meet part of these dietary needs, but there are limits!
Straw’s largest limiting factor to good dry matter intake by beef cows is straw’s high fibre content that quickly fills up the cows’ rumen and is slowly digested by ruminal microbes. For example, cereal straws (re: barley, wheat and oats) contain about 70 –85 per cent NDF-fibre (44 –48 per cent TDN energy) and four to six per cent protein compared to fair quality mixed-grass hay of 55 –65 per cent NDF-fibre (52 –58 per cent TDN energy) and 11 –12 per cent protein.
The implication of feeding such low-energy and low-protein straw forage to beef cows weighed against finding better quality grass hay is two-fold: 1. a big beef cow is only able to consume about 25 –30 lbs. of straw (gut-fill), and 2. the resident rumen microbes can only digest 60 –65 per cent of that amount of straw per day.
As a result, fair-to-good quality grass hay will often meet most of the nutrient needs of gestating beef cows at the start of the winter, while plain straw fails to do so without the aid of grain, protein supplements, minerals and vitamins. Consequently, if cows are forced to rely on straw’s lowly nutritional merits alone in order to satisfy elevated dietary needs (more than the rumen microbes can digest), then cows are susceptible to deadly impaction. Grinding straw and mixing it with a bit of grain helps increase straw consumption, but this physical processing does not improve its limited digestibility.
Luckily, good straw-based diets for over-wintering beef cows are not that difficult to formulate if one secures the right feedstuffs. Let’s consider three well-balanced rations using barley, screening pellets and corn distillers’ grains for a target of 1,400 lb. mid-gestation cows and compare feed-costs:
18 lbs. barley straw @ $50/mt, 8 lbs. barley @ $125/mt, 1.5 lbs. 32 per cent beef supplement @ $375/ mt and 3 oz of commercial 2:1 mineral with salt @ 11c/head/d. = $1.23/head/day.
18 lbs. barley straw @ $50/mt, 10 lbs. 14 per cent cow screening pellets @ $160/mt and 3 oz. of commercial 2:1 mineral with salt @ 11c/head/d. = $1.24/head/day.
18 lbs. barley straw @ $50/mt, 8 lbs. corn distillers grains @ $200/ mt and 3 oz. of commercial mineral with salt @ 11c/head/d. = $1.24/head/day.
The actual feed ingredient prices of these diets may vary from farm-to-farm, but the point of this exercise largely illustrates what feeds are used in a complete mid-gestation beef cow diet as well as demonstrates many similarities in feeding costs.
As shown above, barley is the mainstream grain, used as a source of supplemental energy for many straw-based cow winter diets. Its quality is often based upon kernel plumpness, bushel-weight and the occasional laboratory protein analysis. When barley is fed in any beef cattle diet, the common recommendation is to grind it into coarse hammered kernels to improve its digestibility.
In the last few years, grain screening-pellets and corn distillers’ grains have been used as barley substitutes, particularly when barley prices are relatively high. In doing so, one should realize that not all grain screenings are created equal, because they are the portion of the cereal crop, which remains after the grain is cleaned in the elevator.
Many people buy screening-pellets that may consist of various levels of actual grain kernels, oilseeds (such as canola), weed seeds and also cereal stems, pods, chaff and dust. Fortunately, most of these ingredients that constitute screening pellets are ground up and go through a steam-conditioning process (weed seed viability is destroyed), before the feed is made into pellets. Corn distillers’ grains have many similar quality issues compared to grain screenings when used as a barley substitute in overwintering straw-based cow diets.
The composition of such well-balanced straw-based diets fed to mid-gestation beef cows is always important in meeting all of their nutrient requirements, but there are other feed-related recommendations to consider, so cows can survive overwinter and be in good shape for calving. Such strategies include:
Analyze different straw sources — the NDF-fibre content of most straw samples range from 70 –85 per cent and protein values of four to eight per cent. Such variation in nutrient content may make a difference in the magnitude of feed supplementation that the cows receive.
Segregate out the young replacement heifers and thin cows — feed them separately from the main cowherd. A sound recommendation is to feed mature cows a straw diet and these separated cows a better grass forage, if available.
When the weather gets very cold,
feed extra energy — feed an extra lb. per head, daily for every -5C drop in temperature below -20C during the day. If the daily temperature for the third week in January is forecasted to be -35C, feed an additional 3 lb. of grain, screening-pellets or distillers’ grains.
The natural energy and protein requirements (as well as minerals and vitamins) of pregnant cows increase at least 20 per cent in late gestation. Appropriate nutrient adjustments should be made to all cow diets to match these respective dietary requirements.
Provide clean fresh water at all times — a mature cow will consume 10 –15 gallons of water per day. If snow is the cows’ source of water, make sure enough clean snow is available to meet similar water requirements.
Feeding straw as the sole forage for beef cows takes more thought and homework than simply putting out a bunch of straw bales in front of the cows on a cold winter day. Rather, than hope for the best, straw can work as the sole overwinter beef cow forage, if the right type and amount of nutritious feedstuffs are added to the total beef cow diet, so all beef cow nutrient requirements are met; now and at the start of a successful calving season.
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]