There are some basic rules of thumb to follow when determining the hay supplies you will need to sustain your cow herd over the winter and into next spring.

1. Determine your average mature cow size. This can be done by weighing your 4-7-year-old cows and calculating the average weight. From mature cow size, we can approximate the amount of forage dry matter cows will need to consume per year or per day. For example: a 1,000-pound cow will consume about 26 lbs. of forage dry matter per day. A 1,400-lb. cow will consume about 36.4 lbs. of forage dry matter per day.

2. Determine your cow inventory.

3. Estimate the amount of time you expect to be feeding cows.

From this information, you can calculate the total amount of hay needed. For example: 100 cows weighing 1,400 lbs. will consume about 3,640 lbs. of hay per day. We should take into account that a certain amount of the hay fed will be wasted and there will be a certain amount of spoilage of each bale fed that won’t be consumed. With this in mind, we will add another 10% to the daily total to bump it up to about 4,000 lbs. (two tons) per day.

Remember that the amount of hay wasted or spoiled could be higher. If we are feeding hay carried over from last year, expect a higher percentage spoiled in each bale.

If we are expecting to feed hay from mid-October to mid-May, that is approximately 200 days of hay feeding. Four thousand pounds of hay needed per day multiplied by 200 days equals a total of 800,000 lbs. (400 tons) of forage dry matter that cows will consume over this time. If we are feeding or buying large rounds with an average weight of 1,250 lbs., that equates to 640 (800,000 divided by 1,250) big bales needed to sustain the 100 cows.

If possible, purchase hay by the ton. It leads to less error in securing the amount of hay you will need to purchase or have on inventory. If buying hay by the bale is your only option, make sure to weigh enough of the bales to have an accurate representation of bale weight. Also, take into account the amount of spoilage of each bale. One of the upsides of hay baled this summer is less spoilage.

Other factors such as weather, stage of gestation or lactating versus dry cows will obviously impact nutritional requirements of cows from day to day. Many producers are fortunate to have more standing forage than normal as we evaluate pastures right now. This may reduce hay needs and move back the starting date of hay feeding this year.