by Dave Sparks DVM, Oklahoma State University
The required energy levels are the most variable, followed by protein, mineral and vitamin. Energy is important for all biological systems. Maintenance, weight gain, reproduction and milk production are all a product of energy utilization in the beef cow. TDN (Total Digestible Nutrients) is the term used for the measurement of energy (calories) converted to pounds or percentage of the diet. Proteins provide for functions such as enzyme systems, muscles, nerves and soft tissues. Proteins are utilized by microorganisms in the rumen to reproduce and digest carbohydrates, which aid in supplying energy to the animal. The requirement for protein increases as cow size increases. Forages that are lush or vigorously growing typically will provide sufficient ruminant protein. However, as the forage matures or the onset of feeding hay occurs due to weather conditions, the protein content will decrease, causing the need for supplementation.
Minerals also play an important role in many bodily functions. Bone mass and many of the enzyme systems, such as immunity, digestion, reproduction and milk production, utilize minerals. Mineral supplementation is very precise and difficult to manage because of the different mineral interactions. Small mineral changes can cause deficiencies.
Many of the vitamins can be readily available in growing forage. Vitamin A can be stored in the liver with protection for up to two to four months. Depending on when availability of your growing forage was depleted and supplemented with hay and calving season begins, vitamin A could become deficient and require supplementation. Requirements for vitamin A are 1,250 IU/lb of dry feed for pregnant cows and 1,770 IU/lb of dry feed for lactating cows. Cows rarely need any vitamin D supplementation because it is synthesized by beef cows exposed to sunlight or fed suncured forages. Vitamin E requirements depend on concentration of antioxidants, sulfur-containing amino acids and selenium in the diet and can be quite difficult to determine. Vitamin E is not stored in the body in large concentrations. The vitamin E requirement is estimated to be between 7 and 27 IU/lb dry diet.
The table below lists some of the basic nutrient requirements. This is based on an 1,100-lb mature cow with a peak lactation of 20 lb at different intervals after parturition. These nutrients are the basis of efficient production and ultimately will affect profit/loss…
Table 1. Nutrient Requirements of Mature Beef Cows 1,100 lb Mature Weight, 20 lb Peak Milk
| Months Since Calving |
DMI (lb/day) |
TDN (lb) |
NEm (Mcal) |
CP (lb) |
Ca (lb) |
P (lb) |
| 1 | 2.4 | 15.0 | 25.1 | 2.62 | 2.62 | .051 |
| 2 | 26.4 | 15.9 | 26.7 | 2.88 | 2.88 | .055 |
| 3 | 26.9 | 15.6 | 26.1 | 2.73 | 2.73 | .051 |
| 4 | 26.0 | 14.7 | 24.7 | 2.45 | 2.45 | .046 |
| 5 | 25.0 | 13.8 | 23.0 | 2.17 | 2.17 | .042 |
| 6 | 24.2 | 13.0 | 21.8 | 1.95 | .053 | .037 |