Ask the Vet
Evaluate Factors To Calculate Hay Needs
READER: We had a rough hay year, and I am sure we will not have enough hay. We will need to buy hay while it is still available, but I don't know how much I will need. Is there a good way to estimate how much hay we need to buy?
DR. McMILLAN: This is tough because every operation is different even in the same area. Some farms have winter grasses that provide significant nutrition for some or most of the winter months. Others are almost totally dependent on hay and supplements. Cow sizes vary, and some cows are just more efficient than others. The stage of gestation and production will have a tremendous effect. Dry cows in the early third trimester have much lower nutritional requirements than a cow nursing a calf. And, the biggest variable is how long and how hard the winter is. Some winters come early, stay late and are colder and wetter than others. Cold, wet conditions can increase nutrient requirements 20% or more. Hay quality also varies greatly. Cows need to eat a lot less high-quality hay to get the same nutrient requirements as average quality hay, and cows may not be able to eat enough low-quality hay to meet their requirements even if they are in that early third trimester.
But, there are some rough guidelines. Let's assume your cows average 1,200 pounds. Traditionally, we have estimated cattle will consume about 2% of their body weight in hay, so that comes out to 24 pounds of hay on a dry matter basis. So that we are comparing apples to apples, feeds should always be converted to a dry matter basis. Let's assume the hay is 70% dry matter on an as-fed basis. The math is 24 pounds divided by 0.70 equals 34 pounds of hay per cow per day. For this exercise, let's assume a 25-head cow herd. Next, you need to estimate how many days you expect to feed hay. In the South, this number may be 100 to 120 days, and in the North, it may be 150 days or more.
For 100 days, the math is 100 days multiplied by 34 pounds multiplied by 25 head equals 85,000 pounds per ton divided by 2,000 pounds per ton equals 42.5 tons. But, what if your cows are 1,500 pounds, and you estimate 150 days feeding? These cattle will need almost 43 pounds, so the math is 150 days multiplied by 43 pounds multiplied by 25 head equals 161,250 pounds divided by 2,000 pounds per ton equals 80.6 tons. As you can see, this is a huge difference.
There is one additional factor that must be calculated, and that is hay loss from storage and feeding. Hay stored outside, uncovered, on the ground and not fed in rings or rolled out can have a loss of more than 50%. You must estimate your losses and adjust the amount above to account for this. More importantly, you need to start now to minimize hay loss.
READER: Our cows do not seem to be holding their body condition this winter as they have in the past, and it has been pretty mild so far. We calve in the spring and usually overwinter on hay and some stockpiled forages. What could be causing this?
DR. McMILLAN: There are many variables that could be in play, but I would first look at hay quality. I recommend that each hay cutting or any purchased hay have a forage analysis run on it so you know the quality you are feeding. This will help you compare hay from one year to the next and can help you know if cattle need supplemental feeding.
Hay quality can vary greatly based on rain and the stage that you harvest. One of the biggest factors affecting hay quality is the stage of maturity at harvest. Most grass hays should be harvested when the grass has reached the "late boot stage," which is when the seed head first emerges from the sheath.
Fall and winter is a great time to get a head start on next year's hay crop. Get soil samples as soon as possible. These should be done every two to three years and as often as annual on intensively managed hayfields. The soil test can be used in the spring to apply the correct blend of nutrients for optimal growth. Not only will getting your soil fertility right improve your forage yields and quality, desirable plants will be healthier and better able to compete with weeds, insects and drought conditions.
Always remember: We are grass farmers first. Take care of your grasses.
**
-- Please contact your veterinarian with questions pertaining to the health of your herd. Every operation is unique, and the information in this column does not pertain to all situations. This is not intended as medical advice but is purely for informational purposes.
-- These are only my thoughts and general guidelines. Please get with your veterinarian and together develop the best program for your herd.
-- Email Dr. Ken McMillan at vet@dtn.com
[PF_0125]
(c) Copyright 2025 DTN, LLC. All rights reserved.