The author is a beef cattle specialist for Texas A&M AgriLife Extension based in Overton, Texas.
Performance of grazing animals is primarily affected by forage quality, the animal’s ability to select plant parts, and forage intake. Knowing these factors and implementing good grazing strategies can significantly improve animal performance and reduce supplementation needs.
Forage quality is affected by several factors, but three of the primary factors include forage species and cultivar, plant maturity, and temperature. Generally, cool-season forages will be higher in digestibility and total digestible nutrients (TDN) than warm-season forages. Annual forages will be higher in TDN than perennial forages, and forages grown in arid environments will be higher in TDN than forages grown in humid environments.
Beyond these general guidelines, also look at the expected animal performance of specific forage species. Table 1 provides the potential average daily gains (ADG) of growing animals, such as heifers and weaned calves, for some species under good to excellent grazing conditions; forages are grouped by type and potential animal performance.
Although performance differences are illustrated using growing animals, the same relative differences would be excepted for cows grazing these forages. With cows, the differences are seen as changes in cow body condition and improved milk production.
When comparing perennial native forages to perennial introduced forages, a large part of the difference is due to how these forages are grazed. Utilization goals of native perennial forages is to let cattle consume 25% of the forage produced. This compares to introduced warm-season perennials where target consumption is often above 65%. When target consumption is higher, cattle are not able to be as selective and, consequently, eat more of the lower quality portions of the plant.
Plant maturity is also a big factor affecting forage quality. As plants advance in maturity, the concentrations of plant structural components such as lignin and fiber rise and forage digestibility declines. This results in lower concentrations of TDN and crude protein.
Grazing cattle can select
Maturity and quality are not equal throughout the plant. Some leaves and stems may have been growing for weeks while others may have just recently started to grow. Because of this, the top third of the plant will be the highest quality, the middle third will be the next best quality, and the bottom third will be the lowest quality under most conditions. When hay is cut, all the plant is removed and eventually fed; however, under grazing conditions, cattle can be allowed to selectively graze the highest quality parts, which can greatly impact animal performance.
Lignin is one of the most important factors affecting forage digestibility. As temperatures rise, lignin deposition increases in most warm-season perennial forages. Consequently, forage grown in the spring and fall will typically have a higher TDN concentration than forage grown during the summer.
Stocking rates significantly influence both animal performance and total gain per acre. A two-year experiment conducted in East Texas with steers grazing a ryegrass and cereal rye mixture overseeded on bermudagrass provides an example of these impacts. Steers, weighing about 600 pounds at the start, were grazed from December to May, and pastures were fertilized with a total of 267 pounds of nitrogen.
Three stocking rates were compared: 1.6 steers per acre (low), 2.2 steers per acre (moderate), and 2.8 steers per acre (high). The average daily gains were 2.95 pounds for the low stocking rate, 2.12 pounds for the moderate stocking rate, and 0.96 pounds for the high stocking rate. Additionally, total animal gain per acre was 743 pounds, 740 pounds, and 436 pounds for the low, moderate, and high stocking rates, respectively.
Research at Oklahoma State University shows the importance of stocking rate with native perennial forages as well. Under both continuous and rotational grazing, animal performance was reduced significantly with higher stocking rates. Even though you may be limited to certain forage species, you can still improve grazing animal performance with appropriate stocking rates and good grazing management.
During hot weather, make sure cattle have access to shade to maximize performance. Cattle that are not able to cool off will not eat as much, which leads to lower performance.
Water availability and quality can also impact performance. If water intake is reduced, it will lead to both lower forage consumption and performance, so make sure cattle always have access to a good source of water.
This article appeared in the March 2022 issue of Hay & Forage Grower on page 9.
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