During the summers of 2007-2009, Noble Research Institute interns conducted a grazing preference study using stocker-weight cattle on a series of warm-season perennial grasses that were established in 1998. The results were worthwhile and a bit surprising.
This study had two major objectives. First, we were interested in knowing the preference, for or against, Alamo switchgrass. Alamo switchgrass is a lowland switchgrass known for its biomass production and for its ability to grow into a massive plant. Due to its biomass, it is touted as a biofuel crop, but it was believed that cattle don't like it for forage because it is such a big, rough plant. If cattle were found to readily consume Alamo switchgrass, it could open the door to its use in monocultures as a dual purpose crop for both cattle grazing and biofuels. Our second objective was to determine the plant characteristics that influenced grazing preference.
To evaluate preference, 14 warm-season perennial grasses were randomized and placed into three replications. A six-day grazing period was started the first week of June each year using three stocker-weight steers. Steers would be turned into a replication each day and removed when they reached their fill in about three hours. Each replicate would be grazed twice in the six-day period. To determine preference, the number of bites per steer per day of each grass was recorded. At the end of the six-day grazing period, plots recovered for approximately 30 days, and then a second six-day grazing period was repeated the first week of July. At the conclusion of the study, 173,623 bites had been recorded. A summary of the 2007-2009 preference results are given in Figure 1.
In the study, Alamo switchgrass and Midland 99 bermudagrass were the most preferred grasses. The Alamo switchgrass came as a surprise and, there was a strong difference in preference between the two switchgrass entries, Alamo and Blackwell.
For our second objective, we collected data before and after the grazing periods. This included yield, quality, percent leaf, percent stem, leaf-to-stem ratio, grass height, greenness and grass reproductive stage. Correlations were then run to determine the relationship between each of these variables and the number of bites recorded. A summary is given in Table 1. A negative correlation means fewer bites and a positive correlation indicates an increase in bites. Across all grass entries, cattle preferred vegetative, low fiber (ADF, NDF), high energy (TDN) forage.
In general, we saw a 6-7 percent difference between leaf and stem crude protein and energy, although energy appears to vary more. Producers should keep this in mind when producing hay or grazing cattle on gain. Looking at the preference results, only one of the top four preferred grasses (Midland 99 bermudagrass) is a sod-former with strong rhizomes and stolons. Midland 99 can take heavy grazing pressure while the others cannot. Preference was measured for only a short period of time, so it would be expected to change through the course of the year as these grasses vary in maturity and growth rates. In data not shown here, cattle were beginning to transition in July from Alamo switchgrass and Selection 75 kleingrass toward Midland 99 bermudagrass.