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FORAGE & GRAZING LANDS

Effects of Spontaneous Heating on Estimates of Ruminal Nitrogen Degradation in Bermudagrass Hays from Two Harvests

Dep. of Animal Science, Univ. of Arkansas, Fayetteville, AR 72701

* Corresponding author (coblentz{at}comp.uark.edu)

Estimates of rumen degradable or escape N are an important component of current nutritional models for feeding livestock, but attempts to estimate these fractions for bermudagrass [Cynodon dactylon (L.) Pers.] have been limited, and the relationship between concentrations of these fractions and spontaneous heating during bale storage has not been evaluated. The objectives of this study were to (i) assess the relationship between rumen escape or degradable N and spontaneous heating in bermudagrass hays harvested from the same site during 1998 and 1999 and (ii) correlate estimates of rumen escape and degradable N with other measures of forage nutritive value that are evaluated commonly. A preparation of Streptomyces griseus protease was utilized in an in vitro laboratory procedure to quantify rumen degradable N in hays that heated spontaneously during storage in small haystacks. Maximum temperatures in these bales ranged from 37.1 to 69.8°C over 2 yr. Rumen escape N for 40 hays ranged from 407 to 613 g kg^-1 N and increased linearly (P < 0.05) with all indices of spontaneous heating in both 1998 and 1999; however, r² statistics were highest for bales made in 1998 (r² 0.588). Similar results were observed when ruminal escape N was expressed as a proportion of plant DM. Rumen degradable N expressed as a proportion of plant DM was related to indices of heating (P < 0.0001) when harvest years were evaluated together, but the slopes were not significant (P > 0.05) for specific harvest years.

Abbreviations: ADF, acid detergent fiber • ADIN, acid detergent insoluble N • DM, dry matter • HDD, heating degree days >35°C • NDF, neutral detergent fiber • NDIN, neutral detergent insoluble N • NDSN, neutral detergent soluble N

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