As the summer months progress, the forage quality for grazing cattle begins to change rapidly for much of the western U.S. Cattle performance is dependent on the consumption of digestible nutrients; thus, forage quality and availability are essential for grazing-based systems.
Forage quality is typically determined by the crude protein (CP) and fiber content (neutral detergent fiber, or NDF, and acid detergent fiber, or ADF) of the forage. Dietary intake of cattle is controlled by the energy content and fiber level of their feed. Under low-fiber, high-energy conditions, cattle will graze until they have met their physiological demand for energy. However, as the fiber content in the diet increases, cattle intakes are limited by physical rumen fill. As forage plants mature, protein content will decrease while the fiber content increases, reducing the overall digestibility of the forage. Therefore, as the forage base for grazing cattle hits maturity, cattle may not be able to meet nutrient requirements due to the limited amount of the forage they can consume. This means forage maturity has the greatest impact on overall forage quality. However, weather patterns, seasonal changes and environmental factors all influence plant growth and, therefore, the quality of forage available to grazing cattle.
Weather conditions during the growing season have a profound influence on the growth and quality of forage. Precipitation, temperature and sunlight are the primary determinants of forage quantity and nutritional content. The fluctuations of these factors throughout the forage growing season influence the timing of maturity, with implications for nutrient content and digestibility. For example, abundant precipitation coupled with high temperatures and extended periods of daylight promotes plant growth and development, typically resulting in high-moisture-content forage in early spring, followed by above-average biomass production. While high-moisture-content early spring forage seems to be of good quality, these forages can frequently be below 25% dry matter, making it hard for cattle to consume enough forage to meet their nutrient requirements. Thus, these high-moisture-content early spring forages are often called “washy.” However, these conditions have the forages primed for increased growth rates and biomass production as long as growing conditions remain ideal. Although increased biomass production at first glance appears like a good thing, it comes with an increase in fiber and decrease in protein content, resulting in lower-quality forage compared to average conditions.
Conversely, under low-precipitation and high-temperature events, or drought conditions, forage maturity is often delayed with well-below-average biomass production. There is a misconception that forage quality during a drought is poor; however, forage quality during a drought is usually greater than average. This is because of the delayed maturity of the forage under drought conditions, resulting in lower fiber and greater protein content than average growing conditions. Therefore, the challenges of grazing cattle under drought conditions are more related to finding enough forage availability for grazing rather than forage quality.
Once we hit the late summer months and get into fall and winter, most forages will hit maturity and go dormant until the next growing season. Dormant forage is high in fiber and deficient in protein. Grazing low-quality dormant forage will likely result in decreased cattle performance without supplementation. Providing supplements to grazing beef cattle during times of low forage quality can improve animal performance. Traditionally, concentrate feeds (cereal grains) were used to supplement energy on dormant forage diets; however, it has been found that grain-based supplements can have negative impacts on the digestibility and dietary consumption of low-quality forage. This is mainly because dormant forages are typically deficient in protein and high in fiber, which physically limits dietary consumption. Protein supplementation helps by stimulating the cattle’s protein-starved rumen microbial communities and thereby enhancing digestibility and increasing dietary consumption to meet nutritional requirements with high-fiber, low-quality forages.
Navigating meeting cattle nutrient requirements in a dynamic system of changing forage quality and availability necessitates an understanding of the interactions between seasonal changes and weather on forage conditions. With this understanding, cattle producers can be adaptable, fine-tuning management practices to optimize forage availability and nutritional value throughout the year. Developing a good supplementation plan to meet cattle requirements when forage quality is low can help maintain performance goals. However, it is important to keep in mind that when developing a supplementation program for grazing cattle, the number one objective is to balance for the deficient nutrients as efficiently and economically as possible.
