Effect of Protein Supplementation of Forage Utilization by Cattle in Annual Grass-Dominated Rangelands in the Channeled Scablands of Eastern Washington

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Journal of Animal Science






American Society of Animal Science

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Medusahead [Taeniatherum caput-medusae (L.) Nevski] has become a major invasive plant on the annual grass–dominated rangelands within the Channeled Scablands of eastern Washington. Livestock typically avoid grazing medusahead, and forage alternatives are becoming limited in the region. Our hypothesis was that supplying a high-CP supplement would provide a nutritional context that complements the nutritional composition of medusahead and other annual grasses and thus aid cattle in utilizing this vegetation component, making grazing a more effective method of weed control. Cattle grazed annual grass–infested rangelands dominated with medusahead for 10-d periods during June, July, and August over 2 consecutive years. Eight separate pastures were grazed by cattle pairs during each of the 3 grazing periods. Cattle in 4 control pastures received no supplement and cattle in another 4 pastures received a supplement of canola meal that supplied 75% of the daily recommended CP requirement. Bite counts were used to determine diet composition. Forage categories consisted of annual grasses, perennial grasses, and forbs. Bites taken of annual grasses were similar between treatment groups during the first 5 d of the grazing period (P > 0.05), and then cattle supplemented with canola meal increased consumption of annual grasses, during d 6 to 10 of the grazing periods, over nonsupplemented animals (P < 0.05). Consumption of annual grasses was greater during the second year of the grazing study (P < 0.05), likely due to a decline in abundance of forage alternatives in the plant community. The percentage of medusahead in the annual grass forage class tended to decrease in grazed pastures over the 3 yr of the study (P = 0.056): 87 ± 4.2, 64 ± 3.6, and 50 ± 3.6%, respectively. The percentage of medusahead in the annual grasses was similar across years in nongrazed pastures (P > 0.05). Forb production was greatest the first year of grazing and declined the second year of grazing and continued to decline the following year with no grazing (P < 0.05). Perennial grass production was low throughout the study. The effects of grazing on medusahead abundance suggest cattle may be used to graze this weed after it has matured in an integrated management program with other forms of control to reduce infestation prior to seeding with desirable forage species.