Estimating spotted knapweed intake of sheep using NIRS technology
Targeted grazing is proving to be effective in controling spotted knapweed infestations. Maximizing the potential of targeted grazing requires a method to determine the botanical composition of individual diets of grazing animals over time Fecal near infrared reflectance spectroscopy (NIRS) has been used to estimate the botanical composition of sheep consuming, leafy spurge, mountain big sage brush, and juniper, but has not been used to estimate dietary composition of sheep consuming spotted knapweed. Fecal NIRS spectra collected from three feeding trials were used to develop modified partial least squares regression equations to predict percent spotted knapweed in sheep diets. Independent validation of individualy developed equations resulted in R² values of .22 - .72. An equation developed by combining data from all three trials resulted in acceptable levels of precision (R²= .96) and was used to analyze data collected from range fecal sampling trials conducted in 2006. Two fecal sampling trials were conducted in 2006 to determine NIR's ability to detect differences in dietary composition of sheep grazing spotted knapweed infested range over time. Approximately 90 fecal samples were collected on July 13 and again on August 15 from a band of 900 ewes grazing spotted knapweed infested range to determine changes in diet over time. Fecal samples from five randomly selected ewes in the same band were collected weekly (June 22 - August 17) to detect variation in indiviudal intake over time On July 13, 55% of ewes from had 0-5% spotted knapweed in their diets while 44% had 5-20% spotted knapweed in their diets. On August 15, 1% of ewes, had <10% spotted knapweed in their diets and 44% had 20-25% spotted knapweed in their diets. With the exception of July 6, individual intake of spotted knapweed was similar (P > .05) from June 22, through July 20, but was greater (P > .05)from July 27 through August 17 than from June 22 through July 20. These results suggest that the appropriate time to apply grazing for spotted knapweed control is later in the growing season when sheep are including more of the target plant in their diet.