You Are What Your Mom Ate

Adriane Good, MSU Extension Pondera County

I’m sure everybody has heard the phrase “You are what you eat”. This phrase may or may not be accurate for some people, but for livestock a more accurate phrase would be “You are what your mom ate”. How you feed your cows in the fall and winter has a major impact on the calf growth both prior to and after weaning thanks to something known as fetal programming.

Most of the cows around here should be getting pretty close to the mid-point of gestation. Their energy requirements are decreasing due to declining lactation, but the requirements for their growing fetus is increasing. This is the time of year when their nutrient requirements are the lowest and it may be tempting to squirrel all your good feed away for winter and leave your girls on the drying-up pasture and hope for the best, but this might not always be the best idea.

During the mid-point of gestation, the fetal calf is undergoing muscle cell and fat tissue development.  A calf is born with only a certain number of muscle cells; as it grows these cells can get bigger but never increase in number. When the calf is developing, brain and organ development take priority over muscle and fat tissue development, meaning if nutrients are restricted too much during a cow’s pregnancy, the carcass traits of that calf won’t reach their full potential. Research has shown that calves that were born to nutrient-restricted mothers had a decreased growth rate, poorer carcasses, and poorer feed efficiency in the feedlot than those whose mothers received adequate nutrients throughout gestation. It has also been shown that the middle of gestation was most important for determining the tenderness and marbling of steaks from those calves. Meaning what your cows are eating now have a big impact on what the meat from those calves will taste like.

Timeline of fat and muscle development in utero

So what do your cows actually need during the midpoint in gestation to ensure their calves will be as delicious as possible? The protein requirement for a cow in the 2^nd trimester of pregnancy is about 7% and the TDN requirement is about 50% of their total diet. These requirements are increased slightly for replacement heifers depending on how much they have to grow. These requirements can also change based on the condition of the cows. It’s important to body condition score them to determine if they can handle a little less or if they need to be pushed a little harder. If they are at a body condition score below 5, they’ll need a little extra. If they’re well above a 5 they can probably handle some of the sub-par pasture that you might have. If you’re concerned about what the nutrient level of your pasture or your forages are, bring a sample into the office and we can get that analyzed for you! We can also help you formulate rations to make sure your cows are at peak performance at all times of the year.