By Blake Jackson
Winter beckons, and for beef cattle farmers, it heralds the approach of calving season. But preparation starts months earlier, with winter feeding becoming the critical factor in setting your cows up for success. The last trimester of pregnancy sees the fetus undergo a growth spurt, demanding increased nutritional support from the mother. Neglecting this crucial period can have ripple effects on calf health, colostrum quality, and even milking performance later.
So, what makes a good winter diet for your pregnant cows? Forage quality tops the list. Simply put, the cow needs to be able to eat enough of it to meet her nutrient needs. Lower quality forages will require supplementation with concentrates to bridge the gap. Additionally, mineral supplements are always necessary, as forage alone can't fulfill all mineral requirements.
Now, let's delve into the specifics of good forage quality. Protein content plays a key role: the National Research Council suggests a minimum of 8% crude protein in a cow's diet during pregnancy. But just looking at percentages isn't enough. The key is how much protein the cow consumes.
This is where things get a bit complicated. Cows aren't just eating numbers. They rely on rumen microbes to produce high-quality protein, and these microbes need their own fuel source in the form of digestible carbohydrates. The interaction between protein sources and fermentable carbohydrates determines how much usable protein the cow ultimately gets.
Older research from Idaho sheds light on this, suggesting a minimum of 2 pounds of crude protein intake for late-pregnant cows. Lower amounts were linked to a higher prevalence of weak calf syndrome. Pregnant heifers, still growing themselves, also have similar protein needs.
However, forage maturity throws another wrench into the equation. Higher levels of neutral detergent fiber (NDF) in mature forages limit intake because rumen microbes take longer to ferment plant cell walls. The NRC suggests a maximum NDF intake of 1% of body weight for beef cattle. For a 1,200-pound cow, that's 12 pounds of NDF.
Understanding these principles, I ran some calculations for a 1,200-pound pregnant cow on four different forages, varying their crude protein and NDF content. The results reveal a sobering truth: most "typical" grass forages struggle to meet the cow's protein needs in late pregnancy, solely based on their assumed maturity and NDF levels.
Even forages with 8% crude protein wouldn't reach the desired 2 pounds of intake unless their NDF content dipped below 50% of dry matter. Heifers, with their lower NDF intake capacity, would need even higher protein content forages or supplementation.
Beyond protein and NDF, other factors contribute to overall forage quality. Mature, stored forages often lack vitamins A and E, crucial for calf survival and health. Most forages also fall short in trace minerals like copper, selenium, and zinc. And finally, energy content can be marginal in mature forages, barely meeting the cow's basic needs.
Photo Credit: gettyimages-peopleimages
Categories: Pennsylvania, Livestock, Beef Cattle