EFFECT OF UREA LEVEL IN PROTEIN SUPPLEMENTS ON PERFORMANCE BY BEEF COWS CONSUMING LOW-QUALITY, TALLGRASS-PRAIRIE FORAGE

One hundred thirty two Hereford × Angus cows grazing tallgrass-prairie range during winter were used to evaluate the effects of varying the amo unt of supplemental degradable intake protein (DIP) derived from urea on cow and calf performance. Treatment groups were: 0, 15, 30, and 45% of the supplemental DIP from urea. Supplements were formulated to contain 30% crude protein (CP), with approximatel y 70% of the CP being DIP. Palatability was not a s ignificant problem within the range of urea inclusion tested. In general, prepartum weight and condition losses were greater with increasing levels of urea, although the magnitude of condition loss was greater when urea comprised more than 30% of the DIP. Calf performance was not affected by treatment.


Introduction
Supplementin g cattle consuming lowquality, tallgrass-prairie forage with DIP has been shown to increase forage intake and digestio n and subsequently enhance animal performance .True proteins from feedstuffs such as the oilseed meals are rich in DIP and have been used frequently in formulating protein supplements.However, such feedstuffs are typically quite e xpensive.Previous research at Kansas State University has suggested that urea can replace at least 30% of the DIP in a natural-protein , dry supplement without adversely affecting forage intake and digestion.In contrast, trends have been e vident in previous research for a decline in per f ormance when urea exceeded that level.This study was conducted to evaluate supplement palatability and animal performanc e when urea accounted for up to 45% of the supplemental DIP in dry supplements fed to beef cows consuming lowquality, tallgrass-prairie forage.

Experimental Procedures
Our study was conducted to evaluate the influence of increasing the portion of DIP from urea in dry supplements on cow body weight and body condition changes, pregnancy rate, and calf performance when cows grazed dormant, tallgrass-prairie range.
The experimen t consisted of four supplement treatments furnishing 1) no urea, 0% of the supplemental DI P (0% of the supplemental CP) or the fo llowing amounts of urea 2) 15% of the supplementa l DIP (11% of the supplemental CP), 3) 30% of the supplementa l DIP (22% of the supplemental CP), and 4) 45% of the supplementa l DIP (34% of the supplemental CP).
One hundred thirty two Hereford × Angus cows (BW = 1175 lb, final 3 to 5 months of pregnancy ) were assigned randomly to supplement treatments and pastures.Three pasture s were used, and all supplements were represented within each pastu r e. Cows received approximatel y 4.95 lb per day of supplemental dry matter (DM).
Supplements were formulated with rolled sorghum grain, soybean meal; urea (15, 30, 45% treatments only); molasses; and minerals to contain 30% CP and a nitrogen to sulfur ratio of 10:1.Based on previous KSU research, the DIP s upplied by this amount of supplement should have been sufficien t to maximize the digestible forage intake.
Body weight and condition measurements were taken at approximately 5-wk intervals beginning on November 30 and continuing through calving, with additional measurements taken 48 hours after calving, before breeding (April 26), and at weaning (Octo-ber 1).After calving, all cows were handled as a group and received 10 lb per d a y of alfalfa hay (as-fed basis), (89.3% DM, 18.0% CP and 45.7% neutral detergent fiber (NDF) on DM basis) until adequate new grass growth had occurred (end of April).
Calf birth weights were recorded within 48 hours.Calf average daily gai n was calculated as weaning weight minus birth weight divided by the number of days from birth .Cows were bred by natural service after a single shot of PGF2 % was administered at the beginning of the breeding season.Body condition scale: 1 = extremely emaciated; 9 = extremely obese.Percent of the total supplemental N from urea is 0, 11, 22, and 34, respectively.

Results and Discussion
All supplements were consumed readily, which agrees with previous work at K-State suggestin g that palatability was not affected by providing up to 45% o f the DIP in a dry supplement from urea .Cumulative body weight loss before calving increased (linear; P=.06) with increasin g level of urea inclusion.This was primarily due to differences in response noted during the first 5-week period (cubic; P<.04).In contrast, body conditio n loss durin g the same time frame was greatest for those cattle receiving 45% of the supplemental DIP from ure a (quadratic; P=.04).By weaning, change s in body weight and condition were similar among treatments.Calf birth weight, ADG, and weaning weights were not affected ( P$.40) by the level of urea fed to their dams prior to calving (Table 2).Similarly, pregnanc y rate was not affected (P=.44) by treatment in this study and averaged 92%.Percent of the total supplemental N from urea is 0, 11, 22, and 34, respectively. c