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Effects of Spontaneous Heating on Estimates of Ruminal Nitrogen Degradation in
Bermudagrass Hays from Two Harvests
W. K. Coblentz, J. E. Turner, D. A. Scarbrough, K. P. Coffey,
D. W. Kellogg, and L. J. McBeth 1
Story in Brief
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 objective of this study was to assess the relationship between rumen escape N and spontaneous heating
in bermudagrass hays harvested from the same site during 1998 and 1999. 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 98.8 to 157.6°F over 2 years.
Rumen escape N for 40 hays ranged from 40.7 to 61.3% of N and increased linearly (P < 0.05) with spontaneous heating
in both 1998 and 1999; however, r 2 statistics were highest for bales made in 1998 (r 2 ≥ 0.597). Similar results were
observed when ruminal escape N was expressed as a proportion of plant DM. Based on this research, spontaneous heating
in bermudagrass hay appears to increase linearly the estimated proportion of plant N escaping the rumen intact.
Introduction
Many current nutritional models for ruminants require
knowledge of the rumen degradable or escape N content in
forages (NRC, 2000; Sniffen et al., 1992). This approach is
utilized to separate N requirements into the needs of the
microorganisms within the rumen and the needs of the animal,
and is based on the premise than the protein requirements
of ruminants are met by both undegraded intake protein
and microbial protein (NRC, 2000). Bermudagrass has
been described for more than a century as one of the most
important grasses grown in the southeastern U.S. This warmseason
grass is used widely by beef and dairy producers for
both grazing and hay production throughout this region.
However, efforts to assess rumen degradability of N in perennial
warm-season forages grown in the southeastern U.S.
have been very limited, and responses to spontaneous heating
during hay storage have not been evaluated. This creates a
clear void of needed information for nutritionists serving
clients in southern states and clearly complicates the development
of supplementation strategies for all livestock classes
consuming these forages. Our objective was to utilize a
preparation of Streptomyces griseus protease to assess the
relationship between rumen escape N and spontaneous heating
in bermudagrass hays harvested from the same site during
1998 and 1999.
Materials and Methods
Generation of Sample Sets. An approximately 15-yrold
stand of 'Greenfield' bermudagrass was harvested for hay
on June 15, 1998 and July 12, 1999 at the University of
Arkansas Forage Research Area in Fayetteville, AR. The hay
baled in 1998 was the initial harvest of the season, while the
hay harvested in 1999 was regrowth following an initial harvest
on June 6, 1999. The bermudagrass was mowed with a
John Deere Model 1219 (John Deere Corp., Moline, IL)
mower-conditioner equipped with metal conditioning rollers
in 1998 and a New Holland Model 465 disc mower without
conditioning rollers (Ford New Holland, Inc., New Holland,
PA) in 1999. The forage was not tedded either year. Prior to
baling, two swaths were raked together with a New Holland
Model 258 side-delivery rake. A New Holland Model 320
baler with hydraulic density control was used to produce the
conventional rectangular bales (average size = 19-in. x 15-in.
x 39-in.) both years. A description of the characteristics and
variability of bales produced by this baler has been reported
previously (Coblentz et al., 2000). Bales were stacked flat
(strings up) and stored on wooden pallets in small stacks that
were two layers high; treatment bales were insulated with
nonheating bales of either cured hay or straw in both years to
limit the effects of fluctuating ambient air temperature on
characteristics of spontaneous heating. For this study, bales
were made over a wide range of moisture concentrations,
1 All authors are associated with the Department of Animal Science, Fayetteville.
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