Downing, T.W., Tillamook County Extension, Oregon State University
French, P., Southern States Cooperative

ABSTRACT

Dairy nutritionists have known for years that forages with the exact same laboratory analysis could have significantly different performance in lactating cows. It has been speculated that the digestibility of neutral detergent fiber (NDFD) may explain much of this variation. The objectives of this study were to demonstrate digestibility variation between varieties and season and use this information as the basis of an extension education program. Eleven ryegrasses that were commonly grown in Oregon were selected and planted in September 2004 in Tillamook, OR. Plots were 5' x 20', replicated three times and all planted at the same time. Plots were fertilized in four separate applications of nitrogen annually of approximately 75 lbs/acre/year or 300 lbs N annually. For two years, the plots were mechanically harvested six times a year at approximately 28 day intervals beginning in March and continuing through August. Yield data was recorded and samples were dried in a 550C in a forced-air oven for 48 hour. Samples were ground and analyzed for neutral detergent fiber and NDFD. Fiber digestibility was determined using a Daisy II Incubator. Total dry matter produced ranged from 6.5 tons down to 5.8 tons of dry matter per acre. The fiber digestibility data indicated there was around a 10% difference between the highest variety Elgon and the lowest Flanker. When digestibility and total dry matter yield were combined, this analysis showed a 32% variation in digestible fiber per acre from the highest (Elgon) to the lowest (Tonga). It is estimated the amount of extra energy produced in the form of digestible fiber from our highest ryegrass over our lowest is enough to produce an extra 28 cwt of milk per acre per year. While there was some variation from year to year, most varieties were very consistent from one year to another. This project has been used as the basis of an extension educational program. This information has been used to change the way livestock rations are balanced and hopefully alter the types of grasses being developed in the future.
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