Effect of Long-Term, Year-Long Grazing at Moderate and Heavy Rates of Stocking on Diet Selection and Forage Intake Dynamics

William E. Pinchak, Stephen K. Canon, Rodney K. Heitschmidt, Steven L. Dowher
1990 Journal of range management  
A 2-year experiment was conducted to determine the effect of 27 years of continuous grazing at moderate (7 ha/cow/yr) (MC) and heavy (5 ha/cow&) (HC) rates of stocking on seasonal diet selection and forage intake dynamics. Nine trials were conducted to determine differences between treatments in botanical composition and quality of diets and forage intake. Proportion of Texas wintergrass (St&a hcothricu Trin. and Rupr.) in diets was greater (P<.OS) in the MC than HC treatment whereas amounts of
more » ... warmseason short-and midgrasses were less. Differences between treatments in botanical composition of diets were related to differences in seasonal availability and live:dead tissue ratios of forages. However, such differences did not generally affect diet quality. Supplementation of HC cattle with 20% CP breeder cube either replaced forage organic matter intake (January 1986) or substituted for insufficient forage availability (February 1987). Supplementation never stimulated forage intake. Forage organic matter intake was restricted at forage standing crops below 700 kg/ha. able and bimodally distributed with peak rainfall occurring in May (9.2 cm) and September (10.6 cm) (Fig. 1) . Average annual precipitation is 68 cm. Average maximum daily temperatures range from a high of 36O C in July to a low of 1 lo C in January. 2 n I Livestock production from forage based systems is the integrated product of complex interactions among (1) quantity and quality of forage produced, (2) quantity and quality of forage consumed, and (3) the efficiency with which consumed nutrients are converted into animal biomass. The primary factor affecting these relationships is stocking rate (Hart 1978) . These relationships become increasingly complex in multi-species rangeland environments, because rate of stocking often alters species composition and biomass production (Jameson 1963 , Ellison 1960 as a result of the discretionary effects of varying levels of stocking rate on the frequency and severity of defoliation of individual plants ( Gammon and Roberts 1978, Briske and Stuth 1982). The effects of long-term grazing practices on seasonal profiles of diet selection and nutrient intake are not well known (Cook et al. 1962, Cook and Harris 1968). The objective of this study was to quantify the effects of 27 years of yearlong continuous grazing at 2 stocking rates on seasonal dynamics of the quantity and quality of forage consumed.
doi:10.2307/3898922 fatcat:e55v5lioyna2bnb4vsznnnqzba