Effect of rotational grazing strategies and prescribed burning on cattle diet quality

Abstract

An experiment is being conducted at the Waggoner Ranch near Vernon in North Texas to evaluate the responses of the rolling plains to a series of different managements. From this main experiment an offshoot study was conducted to evaluate the effect of three different grazing strategies (1:1, 4:1 and 8:1 systems) affected by four prescribed burning regimes (1996, 1997, 1998 and no burn) on the quality of the diet selected by cattle. The diet quality was analyzed by taking fresh fecal samples. The sampling dates followed a planned schedule to detect the peaks and valleys of a diet profile. The samples were analyzed by the NIRS technique for CP and DOM. These values were compared and used to develop multiple regression equations. All systems followed similar trends in dietary CP and DOM levels during the almost two years of the study. Diet quality was highest in spring and lowest in winter, regardless of grazing system or fire regime, and was highly affected by precipitation events. During winter, the large paddocks in the 4:1 systems allowed enough selectivity and more efficient forage utilization so as to maintain diet quality similar to that in the continuous systems. This phenomenon did not occur with smaller paddocks as in the 8:1 systems. However, during spring, the smaller paddocks used in the 8:1 system provided higher diet quality than the 1:1 and the 4:1 systems. Fire decreased diet quality levels in spring, but the high-cattle-density system (i.e. 8:1) overcame this detriment. In summer fire increased diet quality levels and during the dry year of 1998 fire represented an important tool to overcome drought effects. However, benefits did not last for more than two years after burning. Rotational grazing and prescribed burning made diet quality levels fluctuate more during the year, while continuous grazing - no burning always maintained stable quality levels year long. The 8:1 system with no-fire or old-fire treatment appeared to offer the highest diet quality in spring (lactating period) than any other treatment at any season. However the low genetic milk production potential from the Hereford breed does not appear to take advantage of this nutrient surplus.