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Effect Of Increasing Urea Level In Protein Supplements
On Intake And Digestion Of Low-Quality Tallgrass-Praire Forage By
Beef Steers
The Influence of Various Levels of Supplemental
Starch and Degradable Intake Protein on Prairie Hay Intake and Digestion
by Beef Steers
"Effect Of Increasing
Urea Level In Protein Supplements On Intake And Digestion Of Low-Quality
Tallgrass-Praire Forage By Beef Steers"
H.H. Koster, R.C. Cochran, E.C. Titgemeyer, E.S. Vanzant, and
G. St Jean
SUMMARY
Twelve ruminally fistulated steers were used to evaluate the effect
of changing the proportion of supplemental degradable intake protein
(DIP) derived from urea on forage intake and digestion. Steers had
ad libitum access to a low-quality tallgrass-praire hay. Supplemental
treatment groups were:1) 0% of the supplemental DIP from urea, 2)
20 % of the supplemental DIP from urea, and 3) 40 % of the supplemental
DIP from urea. Supplements were formulated to contain 30% CP and
were fed with prairie hay once daily. Results from this study indicated
that urea can replace up to 40% of the supplemental DIP without
affecting forage intake and digestion.
INTRODUCTION
Because true protein (e.g., soybean meal) is one of the most costly
components in winter range supplements, there has been a long-standing
interest in the potential of nonprotein nitrogen (NPN) to substitute
for true protein in supplements. Recent work at Kansas State University
suggests that, conservatively, up to 50% of the supplemental DIP
can be provided by urea without compromising forage intake and digestion.
However, in that study, the supplements were infused into the rumen,
so it is unclear how different levels of urea inclusion might affect
supplement palatability or livestock performance. Therefore, this
digestion study was conducted in conjunction with a performance
study to evaluate forage intake and digestion responses when urea
accounted for up to 40% of the supplemental DIP in supplements fed
to beef cattle consuming low quality, tallgrass-prairie forage.
EXPERIENCE
Twelve ruminally fistulated steers (average BW = 835 lb) were used
in a randomized complete block design to evaluate the effect of
changing the proportion of supplemental degradable intake protein
(DIP) derived from urea on forage intake, digestion, and ruminal
fermentation characteristics. Animals were housed in a partially
enclosed barn (one side open) in 6 ft X 18 ft individual pens and
had ad libitum access to water and low-quality, tallgrass-praire
hay (2.4% CP, 73.5% NDF). Steers were assigned randomly to one of
three supplemental treatment groups: 1) 0% of the supplemental DIP
from urea (0% supplemental CP from urea), 2) 20% of the supplemental
DIP from urea (15% supplemental CP form urea), and 3) 40% fo the
supplemental DIP from urea (30% supplemental CP from urea). Supplements
were formulated with soybeen meal, urea, sorghum grain, and molasses
to contain approximately 30% CP and a N:S ratio of 10:1. Steers
received 3.63 lb of supplement DM daily. Based on previous research,
the amount of DIP provieed by the supplements and forage should
have been sufficient to maximize digestible OM intake (DOMI) of
the low-quality forage fed. Supplements and forage were fed once
daily in the morning (8 AM) with the supplement offered just before
feeding the hay. Generally, all supplements were consumed within
45 minutes. The experimental period ocnsisted of a 14-day adaptation
followed by 7-day intake and 7-day total fecal samples obtained
during the 7-day fecal collection period (days 22 to 28) were used
to estimate OM, NDF, and N digestibility. Ruminal DM and fluid content
were determined by manually evacuating the rumen just before (0
hour) and 4 hours after feeding. Fluid dilution rate, pH, ammonia
N, and volatile fatty acid (VFA) concentrations were determined
on ruminal fluid samples collected at feeding (0 hours) and 3, 6,
9, 12, and 24 hours after feeding.
RESULTS AND DISCUSSION
Increased proportions of supplements DIP from urea did not change
(P .38) forage OM intake, total OM intake, or DOMI in this study
(Table 1). Similarly, total tract OM and NDF digestibilities did
not respond (P .37) to increasing urea level.
"The Influence of
Various Levels of Supplemental Starch and Degradable Intake Protein
on Prairie Hay Intake and Digestion by Beef Steers"
T.J. Jones, R.C. Cochran, K.C. Olson, E.S. Vanzant, and E.C. Titgemeyer
Summary
A study was conducted to determine the effect of varying the amount of supplemental degradable intake protein (DIP) and starch on prairie hay intake and digestibility. In general, DIP increased forage intake, whereas starch decreased intake. Diet digestibility also improved with increasing DIP; however, the effect of starch on digestion depended on the level of feeding. Digestible dry matter intake (which estimates total energy input) responded dramatically to DIP but not to starch. These results illustrate the positive effect of DIP on forage intake and digestibility; however, supplying additional starch with a DIP level appeared to have minimal effect on altering total energy supply.
Introduction
Supplements with high crude protein concentrations increase the forage intake and digestibility of forages containing less the 7% crude protein. However, because protein is expensive, it is important to quantify how much is needed to achieve a given level of response. Recent studies at KSU have determined the amount of degradable intake protein (DIP; i.e., ruminally available protein) required to maximize the use of low-quality, tallgrass-praire forage. However, it is unclear how the addition of energy in the form of starch will affect the response to DIP supplementation. This study was designed to evaluate the interaction between supplemental starch and DIP with regard to their effect on prairie-hay intake and digestibility.
Experimental Procedures
Thirteen Angus x Hereford steers (average initial body weight = 570 lb.) were used in a four-period, 13-treatment, incomplete, Latin square. The treatments were arranged in a 3 x 4 factorial arrangement with a negative control. Within the supplementation treatments, there were three levels of supplemental starch (cornstarch grits; 0, .15, and .30% BW) and four levels of supplemental DIP (casein; .031, .062, .092, and .123% BW). Supplements were placed in the rumen of each steer prior to feeding prairie hay (5% CP) at 115% of the previous 5- day average intake. Each period consisted of a 14 - day adaptation followed by a 9 - day sampling period. Digestibility was determined via total fecal collection.
Results and Discussion
Forage intake generally responded positively to increasing DIP supplementation. In contrast, addition of supplemental starch within a DIP level typically resulted in reduced forage intake. Previous KSU research determined that forage intake would by maximized when approximately 11% of the digestible material in the total diet was present as DIP. In our study, this level was approximated at the highest level of DIP supplementation. Thus, we would predict maximum forage intake for the group receiving the highest level of DIP and no supplemental starch.
As noted for forage intake, the effect of increasing DIP on diet digestion was generally positive. However, response to increasing starch was somewhat variable. This probably was due to conflicting effects of starch on fiber digestion versus total diet digestion. The starch added to the rumen was more highly digestible than the forage material. If the addition of starch within a DIP level had no effect on forage digestion, we would expect the total diet digestion to increase slightly. This occurred in some instances, particularly at the intermediate levels of DIP supplementation. In contrast, if the starch addition depressed forage digestion sufficiently, the total diet digestion should decrease, compared to forage alone. This appeared to be the case for the high level of starch addition when DIP supplementation was low.
Total digestible dry matter intake (DDMI) is the product of intake and digestion and roughly represents the total energy supply. Because of the positive effects of DIP supplementation on forage intake and digestion, the DDMI generally increased with increasing DIP supplementation. However, because of the variable and, at times, conflicting effects of starch on intake and digestion, total DDMI remained relatively constant with increasing starch addition. As a result, little improvement in total energy supply would be expected with starch addition within a DIP level. These results suggest that ruminally available protein is more limiting to the utilization of low-quality forage than is ruminally available energy. Therefore, supplementation program for livestock consuming low-quality forage should give first consideration to providing adequate DIP.
