Hierarchy of Nutrient Use by Beef Cattle
Each class of beef cattle has defined nutritional needs and uses the total nutrients consumed each day in a certain order of priority. This hierarchy of nutrient use is illustrated below and includes all the tasks we usually ask beef cattle to perform. Beginning at the bottom and moving up the hierarchy, an animal will use its daily intake of nutrients in this order until depleted.
Performance stops at whatever level the nutrients run out. An animal will not perform the next higher task in the hierarchy unless and until it has adequate nutrition to do so. As managers, it is our responsibility to see that these needs are met at all times if an animal is to perform as expected. Specific nutrient requirements for beef cattle are available from your Livestock Specialist. The purpose of this article is simply to illustrate how a beef animal uses the nutrients available to it. (Chart 1)
Of all the nutrients an animal consumes, parasites get their share right off the top. This is why a parasite control program is so important. Nutrients left over after the parasites get their share will be used for maintenance. The amount needed for maintenance will depend primarily on the animal's size and the climatic conditions. These first two levels are common to all classes of livestock.
Parasites and maintenance, however, we ask different things of different classes of animals. To use this hierarchy, simply list those levels you are asking from an animal at a given point in time. At this time of year, the hierarchy is most critical to spring-calving cows and heifers and the bulls we are using to breed them. As an example, let's look at the hierarchy of an open, lactating, mature cow. Her hierarchy in Chart 2.
The task of milk production significantly increases her level of nutrient need. The amount needed depends on her genetic ability to produce milk, and she will probably not rebreed unless she has nutrients in excess of that amount. As a comparison, this is the hierarchy of an open, lactating first-calf heifer in Chart 3.
To re-breed for her second calf, she must have adequate nutrition to reach that level in her hierarchy (breeding). Besides feeding parasites, maintaining herself, and producing milk, she still has additional growth to take care of. She will not conceive her second calf unless her level of nutrient intake exceeds the requirements needed to meet those first four demands. That's why so many first-calf heifers turn up open at pregnancy checking time, and why it is so hard to add condition to them.
From the time we turn out a mature bull, he is going to focus on the task of breeding and ignore his nutrition status. His hierarchy looks like Chart 4.
Immediately, he will be in a deficit and will begin using stored nutrients (condition) to meet the first 3 levels. When his condition is gone, his capacity for breeding can be adversely affected or halted altogether. Periodic rest and rotating fresh bulls into the cow herd is a common way to address this problem. Just be aware of what you are asking of your cattle at all times. Hopefully, this hierarchy is a simple way to keep track of it.