Estimates of forage production for long-term ungrazed, lightly, moderately, and heavily grazed treatments (0,20,40,60% removal of annual forage production) established in 1939 in shortgrass steppe communities were subjected to multiple regression analyses to assess long-term temporal trends resulting from grazing and short-term sensitivities to abiotic factors. Average production based upon alI data from 1939-1990 was 75,71,68, and 57 g mm2yrm1 for ungrazed, lightly, moderately, and heavily grazed treatments, respectively. Variability in forage production was explained mostly by cool-season precipitation, and magnitude of forage production was more sensitive to annual fluctuations in precipitation than to long-term grazing treatments. Production per unit increase of precipitation was greater for cool-season than warm-season precipitation, but only when cool-season precipitation was above average. This was attributed to differences in evaporative demand of the atmosphere resulting in different utilization-efficiencies of small and large rainfall events in the 2 seasons. Based upon a regression model constructed using data from 1939 through 1962, forage production was not effected by grazing to 20 to 35% removal. For pastures of average relative productivity, grazing at 60% level of consumption for 25 years resulted in a 3% decrease in forage production in wet years and a 12% decrease in dry years. Estimates of productivity after 50 years of heavy compared to light grazing treatment were -5 and -18% for wet and average years of precipitation, respectively.

This study was initiated to determine the effects of defoliation frequency (based on amount of growth present), intensity, and length of grazing season on quantity and quality of big bluestem (Andropogon gerordi Vitman) in the Southern corn belt and to provide further data regarding the reasons for rapid quality decline of warm-season grasses. Three clipping frequencies (when plants reached heights of 30,41,51 cm) at 2 intensities (stubble heights of 10 and 20 cm) were imposed on established plots of pure big bluestem (cv. Kaw). Harvest season length was studied by terminating clipping on 15 August and 15 September as 2 separate treatments. Two years of data indicated that big bluestem regrows insufficiently after 15 August to warrant additional harvests under the imposed managements. Prolonged regrowth and leaving a short stubble of 10 cm resulted in greatest yield. Short stubble led to greater reductions in nonstructural carbohydrates, but did not damage the stand compared to pre-study measurements. Nonstructural carbohydrate levels and stand composition improved with taller stubble. In vitro dry matter digestibility and crude protein were higher on treatments clipped to leave a lO-cm stubble. The greatest proportion of leaves resulted from treatments where a 20-cm stubble remahred. These results agree with studies indicating that leaf maturity is more responsible for lower quality forage than is the amount of stem material present in the stand. Our results indicate heavy use can be more safely accomplished in the Southern corn belt than for areas to the west because big bluestem can be more intensively defoliated In the Southern corn belt (IO-cm) than that recommended for other areas (20 to 40 cm).

One hundred eighty yearling Holstein steers and heifers grazed a series of 2‐acre tall fescue (Festuca arundinacea Schreb.) pastures over a three‐year period. Pastures were infected with Acremonium coenophialum at levels from 3 to 83%. A significant overall relationship between endophyte infection frequency (EIF) and average daily gain (ADG) was described by the equation: ADG (lb/d) = 1.46 − 0.01 × EIF(%). Seasonal variation existed whereby spring‐summer gains were reduced 0.15 lb/head/d for each 10% increase in EIF, while no relationship existed for fall grazing. Although the relationships between EIF and ADG were significant, low R2 values suggest other factors are involved. Still, the general relationship may be useful for estimating animal performance on tall fescue when EIF is known and for making economic decisions regarding management and renovation of infected tall fescue stands.

Spring application of a plant growth regulator, mefluidide, to tall fescue (Festuca arundinacea Schreb.) pastures grazed from May to September reduced (P less than .05) available DM and digestible OM per hectare by 51 and 41%, respectively, compared to untreated pastures. However, seasonal averages for N, Ca and P content and in vitro OM disappearance (OMD) were greater (P less than .05) and NDF was lower (P less than .05) in tall fescue from mefluidide-treated pastures than in untreated pastures. Compared to hand-clipped samples, esophageal extrusa of tall fescue was 63% higher (P less than .05) in N (2.7 vs 1.7%) and 26% lower (P less than .05) in NDF (52.6 vs 69.9%) than hand-clipped tall fescue samples, regardless of treatment. Extrusa and hand-clipped herbage samples were similar (P greater than .10) in OMD during May and September, but OMD of extrusa was greater (P less than .05) during June, July and August compared to clipped samples. As a consequence of preventing stem elongation and seedhead formation earlier in the growing season, mefluidide treatment of tall fescue maintained forage quality at a higher level during midsummer.

Two studies were conducted to assess the effects of topically applying a prepared cellulase solution (PCS) as a forage pretreatment to increase digestibility of tall fescue (Festuca arundinacea Schreb.). Fall regrowth and stockpiled tall fescue were harvested from the field (Mexico silt loam: fine montmorillonitic mesic Udollic Ochraqualf) and studied in laboratory Exp. 1 and 2, respectively. Experiment 1 involved topical application of 40 mL of PCS to 100 g (on a dry‐matter basis) dried and fresh leaf material that had either been chopped or remained whole. Further treatments involved 1‐, 6‐, or 12‐h drying times post‐application and freezing to curtail enzymatic activity or no freezing. Experiment 2 involved whole and chopped fresh leaf material with a surfactant treatment added and post‐application drying times altered to 1,12, 24, and 48 h. In vitro dry matter digestibility (IVDMD) of tall fescue was significantly increased (28 g kg−1) by topical application of PCS in both experiments. Allowing longer exposure time of herbage to PCS was not an advantage. Addition of a surfactant to PCS decreased IVDMD (36 g kg−1) but increased IVDMD (14 g kg−1) when PCS was not applied. Allowing the PCS to dry on herbage for 1‐, 12‐, and 24‐h post‐application resulted in significant IVDMD increases compared to no PCS (22,27, and 31 g kg−1, respectively) while PCS application most benefited IVDMD for 24 h. Scanning electron micrographs revealed cuticular disruption on leaf blades which may be at least partially responsible for increased IVDMD of PCS‐treated samples. These studies indicated that topical PCS treatment can extend existing forage supplies. Further studies under field conditions and animal trials are needed.