I was recently driving west through the southern Prairies and saw a beef cow herd grazing late-autumn straw-coloured pasture. I suspected the calves were probably just weaned, which simply puts these dams at their lowest dietary requirements. I believe that these particular cows were getting plenty to eat, but they were probably not getting enough protein from this dried-out pasture. This quick drive-by was a good reminder that cattle producers should ensure all protein requirements of their gestating cow herd must be met as these animals approach the upcoming calving season.
A gestating cow herd facing an overwinter protein deficiency will have immediate problems. For example, mature cows desired to maintain or build body condition score to an optimum six out of 10 points will instead lose body fat (often dropping to a less than a five BCS), and be unable to cope with harsh winter conditions. As well, replacement heifers will not be prepared to deliver a healthy and strong first calf because they will fall short to put on their necessary growth and required bodyweight gain by calving time.
Unseen to our eyes, these protein-deficient cows/heifers do not supply enough essential protein metabolites (ammonia) to their forage-digesting ruminal bacteria. In turn, these bugs cannot maintain adequate growth rates, which leads to three nutritional-related outcomes: a reduction in overall forage digestibility, a slowdown in the rate of feed digestion and decreased forage intake by the entire cow herd. As a result, less dietary energy is derived from any forage consumed by these cows, which allows less available dietary energy (and protein) for good cattle body condition or growth in the first place
Lack of essential dietary nutrients affects good early and mid-gestation fetal development as well. Researchers at the University of Wyoming (2010) speculated low-quality (protein) pastures grazed by mid-gestation cows were responsible for a significant decrease in muscle-fibre formation in their fetuses, which led to lighter spring calves at weaning age.
Protein shortages for cows and heifers can largely be avoided as long as we provide them with about 2.0-2.5 lbs. of total crude protein per head, daily. Based upon a DMI (dry matter intake) of two per cent in mature beef cows (1,200 lbs.), it also calculates to about 8.5-10.5 per cent in their final diet. These vital protein requirements usually go hand-in-hand with an early- to mid-gestation energy requirement of about 50-52 per cent TDN, respectively.
Many of these early/mid-gestation beef cows are still out on pasture during the beginning of autumn until the first snowfall and still rely on pasture for most of their protein (energy) nutrition. Some producers purchase molasses lick-tubs to supplement dietary protein.
As a beef nutritionist, I make it a point to choose the type of molasses lick-tub to complement the quality of the pasture. For example, 30 per cent protein blocks should be placed on mature autumn pastures where grass protein is no more than seven per cent protein: a 1,200-lb. mature beef cow should consume roughly 24 lbs. of pasture grass (24 x 0.07 = 1.7 lb. of protein) + 1.0 lb. of a molasses block (1.0 x 0.30 = 0.30 lb. of protein) = 2.0 lbs. of total dietary protein.
As we get closer to the first snowfall, some cattle remain on the same pastures for the entire winter or are moved to other areas such as higher protein (11-12 per cent) swath-grazing acres, or low-protein stubble/corn and stover fields (six to eight per cent). Similar molasses lick-tubs of varying amounts of proteins might be switched over to complement these different types of forage. At the same time, many cows are moved back home to drylot where producers first feed harvested bales of low-quality forages for the first part of the winter. Then they feed better-quality forage a month or so before calving-time.
That’s what a friend who overwinters about 400 red Angus gestating cows plans to do. His mid-gestation diets use wheat and lentil straw as a forage base. Some grass hay is added and complemented with barley grain and a 32:16 beef protein supplement. He will feed this nine to 10 per cent protein diet from November to about mid-February. Afterwards, he plans to reduce the amount of straw and add back some fair-quality hay as his cows enter the last trimester of pregnancy to assure they are getting enough dietary protein.