Back to Basics: Biological Use of Nutrients
By Amy E. Radunz, UW Extension Beef Cattle Specialist
In the second post of this series, we are going to discuss the biological use of nutrients or in other words how cattle prioritize the use of nutrients for use within the animal. This is an important concept to remember when trying to trouble shoot problems associated with nutrition on the farm. Regardless of the type of nutrient certain organs or systems within the animal are higher on this list of use of nutrients than others.
The hierarchy of nutrient use is as follows:
Now it is important that when we discuss nutrients this does not just mean the energy content of the diet, this would also include water, protein, vitamin, and minerals. The most important nutrient is the one missing, therefore need all these nutrients are needed to perform these functions.
One of the most challenging stages in the production cycle for the cow herd is post-calving to breeding. At this time the cow has the demands of lactation, recovering from calving, and gearing up for breeding. If cows do not have enough intake of nutrients and/or body reserves (i.e. fat), then first reproduction will fail and second, the milk production be reduced. If cows are gaining or maintaining body condition during this period, then you are most likely adequately supplying enough nutrients.
In first-calf heifers this presents an even greater challenge, because she has to add growth to her list of demands for nutrients. And growth will take priority over lactation and reproduction. This segment of the cow-herd is typically the most challenging to manage. The stress of calving and becoming a new mother also adds to the energy demands. Therefore, we typically see the lowest pregnancy rates in this age of females in the cow herd as well as these females end up calving later in the calving season next year. Therefore, giving heifers more time to recover to breed by calving them 30 days earlier and ensuring proper body condition score at calving (5-6), you will increase not only the success this year, but this will pay off in following calving seasons.
In fattening or finishing cattle, it also important to remember this principle of growth and development. In order for cattle deposit external fat as well as internal fat (i.e. marbling), the animal must be on high enough plane of nutrition. In the case of backgrounding or stocker cattle, the goal would be to provide enough energy for the animal to grow bone and muscle, but not to deposit fat, thus allowing the animal to reach a heavier finishing weight. In the finishing period, when animals have reached maximum muscle growth, the animal will start to deposit more fat. It also important to remember at this period that it is more efficient to growth muscle than fat and thus at this stage the animal are less efficient. In grass-based finishing systems, in order for cattle to finish it is important to provide enough energy during the summer slump of grazing and especially during the winter in order to keep cattle ‘on track’ by continuing to add muscle as well as deposit fat.
Keep this list in mind when developing nutrition and management strategies in any segment of the industry, because these decisions not only impact the expenses of the feed to the animal but also the productivity of the animal. When feed costs are high, taking a closer look to match nutrition to the needs of the animal becomes even more important to the bottom line.