Understanding the nutrient requirements of beef cows is essential to ensuring that requirements are being met and cow performance is optimized while utilizing available feeds in a cost-effective manner. All animals have requirements for protein, energy, minerals, vitamins, and water. If any of these nutrients are deficient or excessive to the point of being toxic in the diet, animal performance will suffer.
When determining a cow’s requirements, one of the first things to consider is what stage of production she is in. This is most typically identified as mid-gestation, late gestation, early lactation, or late lactation. To further describe these periods:
- Mid-gestation: From weaning until the last trimester of gestation begins.
- Late gestation: The last trimester (about 90 days) until calving.
- Early lactation: Approximately the first 90 days following calving
- Late lactation: From the end of early lactation until weaning.
Nutrient requirements of cows vary among each of these phases, with the highest requirements during early lactation and the lowest requirements during mid-gestation. Requirements are highest in early lactation because of the nutrients needed for peak milk production, and lowest in mid-gestation because the cow is not lactating and growth of the fetus is still relatively small.
Along these same lines, you must determine the average weight of the cows in the herd. If you do not have access to scales to weigh cows, the next-best option would be to use the sale weights of cull cows as a guideline. Next, what is the body condition score of the cows? Body condition score (thinness or fatness) and whether it has increased or decreased in the recent past is a great indicator of the nutritional status of cows. Changes in body condition score over time indicate whether nutrient requirements have been met and if cows are in a status where they need to lose, maintain, or gain body condition. Extensive research has indicated that adequate body condition is tremendously important to reproductive performance.
Another important factor is dry matter intake, i.e. how much feed the animal can consume. Dry matter intake will vary greatly depending on diet quality as well as stage of production. Lower-quality forages will result in lower dry matter intake, while higher-quality forages result in higher dry matter intake as a % of body weight. Typically cows in late gestation will have the lowest dry matter intake due to the fetus taking up space in the abdominal cavity, while cows in early lactation will have the highest dry matter intake due to the cow’s requirement to lactate. Other factors that can play a role in dry matter intake are cold and heat stress. Cold stress will increase dry matter intake, while heat decreases it. Due to all of these factors, it is difficult to accurately predict intake, but having an idea of intake is important to understanding overall performance.