The Effect of Seasonal Variation and Fertilization on the Nutritional Content of C4 Grasses

Horses are an herbivorous species of mammal that evolved to consume grass and other forages for their nutritional needs. They quality of forage consumed is important to the health of the animal, and there can be an effect of season and fertilization seen in the nutritional content of the grass. Many studies have looked at the nutritional content of C3 grasses, but few have looked at C4 grasses common in Texas. Therefore, the focus of this research was to analyze the nutritional content of 3 varieties of warm season grasses in response to season, time of day, and fertilization. Plots were set up in a grid design to prevent cross-contamination. Half of the plots were fertilized at a rate of 260 kg/ha (FERT) and half were unfertilized (CON). Samples were collected at 6AM and 6PM on, or as close to the first of the month as possible, from June through September, which encompassed the entire growing season for these grasses. Samples were analyzed for NDF, ADF, crude protein, and the water-soluble sugars fructose, glucose, and sucrose using standard laboratory procedures. The fiber content of all three varieties of grass was lowest in June and highest in August and September. There was an average NDF content of 63.8 ± 0.5 %DM and an average ADF content of 34.0 ± 0.6 %DM in June, versus an average NDF content of 68.1 ± 0.5 %DM and an average ADF content of 40.2 ± 0.6 %DM in September. The crude protein in all three varieties of grass was higher in FERT samples than CON samples, with an average protein content of 10.5 ± 0.5 %DM in CON samples and an average protein content of 13.4 ± 0.5 %DM in FERT samples. There were no significant effects of time, treatment, or month in the sugars, or any effects of interactions. This indicates that C4 grasses grown in East Texas have a lower overall nutritional content than C3 grasses, especially in the sugar content. Therefore, horses that may be sensitive to rich pasture may be safely grazed throughout the growing season of these C4 grasses.