Proceedings available at: http://www.extension.org/67720 The effects of ractopamine hydrochloride (RAC) and a steroidal implant (IMP), on whole body N metabolism were evaluated in 24 Hereford x Angus steers (BW 554.4 ± 26.8 kg). The experimental design was a completely randomized block design with a 2 x 2 factorial arrangement of treatments. Factors included: 1) RAC (0.0 or 400 mg×steer-1×d-1) and 2) IMP (0.0 or 200 mg trenbolone acetate and 28 mg of estradiol benzoate). Steers were housed in individual pens and allowed ad libitum access to feed and water throughout the experiment. Once cattle had been implanted for 48 d and had received RAC for 21 d, a nutrient balance study was conducted for 6 d.

1. MANAGEMENT TECHNIQUES
TO REDUCE NITROGEN
LOSSES FROM FEEDLOT
CATTLE
S. L. Archibeque, J. Ham, H. Han and M. M.
Kappen
Colorado State University, Fort Collins, CO

2. Purpose of Study
 Participants in the initiative include the Colorado Department of Public
Health and Environment Air Pollution Control Division, U.S. EPA Region
8 Air Program, the Air Resources Division of the National Park Service
and the U.S. Forest Service

3. USDA Awards National Food and
Agriculture Grant
 Alternatives producers have to decrease
nitrogenous excretions:
 Feed less protein (can be problematic)
 This study aimed to utilize approved technologies
that improve muscle accretion without hindering
productivity
 Hypothesis:
 Ractopamine, with or without steroidal implants, may
lessen nitrogenous excretions in yearling feedlot
cattle by stimulating a shift of body accretion to lean
tissue rather than adipose

4. Objective
 To determine if Ractopamine HCl with and
without Trenbolone acetate/estradiol benzoate
implants lessens nitrogenous excretions from
yearling crossbred feedlot cattle

5. Study Design
 Balance Trial
 Completely randomized block design
 24 Hereford x Angus cross steers were put into 4
treatment groups with 2 replications:
Optaflexx (ractopamine
Control hydrochloride) 430 mg/hd/day
for last 42 days feeding period
2 x 2 factorial topdressed
arrangement of
treatments
Synovex-Plus Implanted (200 Combination of Optaflexx
mg of trenbolone acetate and and Synovex-Plus
28 mg of estradiol benzoate) Implant

6. Materials and Methods
 Agriculture Research, Development and Education
Center (AREDEC)
 Wellington, Colorado
 36 Hereford x Angus crossbred steers
 Initial BW: 235 kg
 204 days on feed
 Initially housed in large drylot pens; 6 head per pen to
facilitate halter breaking
 Transitioned through 5 step-up rations

7. Materials and Methods
 Steers trained to balance trial procedures
 Day 137 steers were randomly selected from the
trained group of cattle and blocked into heavy and
light group classifications
 Within each group, steers were stratified by weight to
achieve equal weights within treatment groups

8. Materials and Methods
 Implanted 48 days prior to start of balance trial
 Implant used: Synovex-Plus (IMP) (200 mg
trenbolone acetate and 28mg of estradiol
benzoate, Fort Dodge Animal Health)
 Heavy Group:
 Implanted on day 137
 Light Group:
 Implanted on day 144

9. Materials and Methods
 Steers were individually fed
 RAC treatment groups received premix with 400 mg x hd-
1x d-1 of Optaflexx (Elanco Animal Health) in 449.6 g
ground corn and controls received 449.6 g ground corn
 Heavy Group:
 RAC topdress began on day 164
 Light Group:
 RAC topdress began on day 171

10. Methods: Data Collection
 Balance Trial
 Animals were weighed upon entry
and exit of metabolism barn
 Heavy group entered metabolism
barn on day 185
 Light group entered metabolism
barn on day 192
 Collections occurred over a 6 day period
 Total
urine, fecal excretions, feed offered and
refusals were collected, weighed and 10%
subsample was retained for analysis

11. Methods: Sample Analysis
 Dry Matter (DM)
 Fecaland feed samples: 60˚C until 2
consecutive dry weights were
obtained
 Nitrogen (N)
 LECO
 Urine Urea Nitrogen (UUN)
 Stanbio Laboratory BUN Enzymatic Endpoint

12. Methods: Statistical Analysis
 PROC MIXED in SAS
 Completely randomized block design with a 2x2
factorial arrangement of treatments.
 Fixed effects: IMP, RAC, IMPxRAC,
 Random effects: Block
 Steer was experimental unit

13. Results
 Implanted steers fed Ractopamine tended to
have lower DMI compared to other treatments
(IMPxRAC; P< 0.09)
 N intake (P>0.11) and fecal N (P>0.18) were
not different due to treatment, yet numerically
reflected the trend noted for DMI

14. Results
 Urinary N excretion was decreased by feeding
Ractopamine (P<0.01)
 Implanted steers receiving Ractopamine tended
(IMPXRAC; P<0.08) to excrete less urinary N than
steers receiving Ractopamine only (20 g vs 5 g
reduction/d)
 Steers fed Ractopamine had a decreased urine urea
N excretion (P<0.02) (12.5 g/d, )
 N retention was not affected by treatment (P>0.14)

15. Summary
 Results indicate that urinary N excretion can
be reduced by incorporating Ractopamine
according to labeled usage during the final
phase of the finishing period
 This effect may be enhanced by implant status
of the feedlot steers
 More studies will be required to elucidate the
potential interactions of beta-agonists with
implant status, timing of implantation, and
types of implants

16. Implications
 Based on the results of the study, use of beta-
agonists during the finishing period would
result in a 650 kg reduction in urinary N
excretion during each day from a 50K head
feedlot.
 Urinary N is the primary source of ammonia
emissions from feedlots.

17. Other methods of managing N
 Phase feeding
 Adjusting N provision with stage of growth
 Providing less N as cattle mature and shift growth
from lean tissue to adipose deposition
 Oscillating protein
 Creates a gradient of protein in the digestive tract
 Stimulates “urea recycling
 Problems
 Ration adverse feedlot systems

18. Potential for future mitigation
 Methodology must be relatively cheap and not
impair performance
 Most effective methods should be either
capable of continual use or rapid adaptation to
meet a specific temporal concern
 Linkages with early warning systems
 “Spot” reductions in N emissions
 Aggressive use of implants during Spring?
New labeling for beta-agonists?

19. Questions?