Effect of rumen-escape protein level on feedlot performance and Effect of rumen-escape protein level on feedlot performance and carcass traits of implanted vs nonimplanted yearling steers carcass traits of implanted vs nonimplanted yearling steers

One hundred eighty yearling steers (743 lb) were blocked by weight; implanted with Synovex® (S), Synovex plus Finaplix® (SF), or not implanted (C); and fed diets containing 11.75% (L), 13.0% (M), or 14.25% (H) crude protein with all supplemental protein above 11.75% being supplied by corn gluten meal and blood meal in a 50:50 ratio (crude protein basis). An addition al protein level fed to S and SF implanted cattle was H for the first 70 days on feed and L thereafter (H-L). Animals were reimplanted on day 70. Steers treated with SF gained faster and more efficiently than non-implanted cattle. Differences in protein level had no effect on fat deposition in control steers, but cattle receiving SF and consuming M had more back fat and kidney, pelvic, heart (KPH) fat than those fed either H or L and also had more marbling than those fed H. Also, no apparent differences occurred between cattle fed M throughout the trial and those switched from H to L at 70 days.


Summary
One hundred eighty yearling steers (743 lb) were blocked by weight; implanted with Synovex® (S), Synovex plus Finaplix® (SF), or not implanted (C); and fed diets containing 11.75% (L), 13.0% (M), or 14.25% (H) crude protein with all supplemental protein above 11.75% being supplied by corn gluten meal and blood meal in a 50:50 ratio (crude protein basis).An addition a l protein level fed to S and SF implanted cattle was H for the first 70 days on feed and L thereafter (H-L).Animals were reimplanted on day 70.Steers treated with SF gained faster and more efficiently than non-implanted cattle.Differences in protein level had no effect on fat deposition in control steers, but cattle receiving SF and consuming M had more back fat and kidney, pelvic, heart (KPH) fat than those fed either H or L and also had more marbling than those fed H. Also, no apparent differences occurred between cattle fed M throughout the trial and t hose switched from H to L at 70 days.

Introduction
Cattle receiving growth promotants, particularly trenbolone acetate (TBA), have greatly enhanced rates of lean deposition, which may increase their demand for metabolizable protein above traditional levels of supplementation.The amount of protein reaching the small intestin e can be increased by using high rumen-escape protein sources such as blood meal and corn gluten meal, while requirements for ruminally available nitrogen are met with urea.

Experimental Procedures
One-hundred eighty head of mixed crossbred yearling steers were received off North Texas summer grass in September, 1992.Cattle were dewormed, vaccinated, ear-tagged, and fed a 57% concentrate ration for 28 days on a receivin g study.The cattle were weighed (October 13 and 14, 1992; avg 743 lb); implanted with either Synovex-S (S), Synovex-S plus Finaplix (SF), or not implanted (C); and stepped up onto a 12% roughage finishing ration (Table 1).Cattle also were assigned to a diet containing either 11.75%, 13%, or 14.25% cr u de protein.The two higher protein levels were achieved with a 50:50 blend (crude protein basis) of blood meal and corn gluten meal (crude protein basis).An additional protein level assignment fed to S and SF implanted cattle was H for the first 70 days on feed and L thereafter (H-L).Cattle were reimplanted with their respective implants o n day 70 and weighed at 35-day intervals until finished.Final weights were the averages of weights on 2 consecutive days (March 30 and 31, 1993).Hot carcass weights were taken at slaughter, and 12th rib fat thickness, ribeye area, KPH estimation, and marbling measurements were taken after a 24-hour chill.

Results and Discussion
Rate of gain was slower than expected for this size and type of cattle, even though intake was near expected levels across all treatments, probably because of several periods of freezing rain.These low gains may have limited the response to bypass protein supplementation.
Final weights in this study were hot carcass weights adjusted to an average dressing percent of 61.1.Cattle implanted with SF gained faster (P<.05;Table 2) and more efficiently than nonimplanted steers.Steers implanted with SF also had heavier carcasses and greater ribeye areas (P<.05).
Interactions (P<.10) between implant and protein level affected dressing percent, fat thickness, KPH fat, and marbling.Steers receiving SF and consuming M had slightly lower dressing percentages, which may have been a function of slightly higher intake.Within the control group, no differences occurred in fat deposition, but within the SF treatment, steers consuming M had more back and KPH fat than those consuming either L or H (P<.10) and slightly more marbling than steers consuming H (P=.14).
Implants have been shown to be most effective in cattle with superior genetics for growth and in cattle on high energy intakes.Feedlot trials have shown benefits of escape protein supplementation, with the greatest advantages in fast gaining cattle.Although the SF-treated steers outperformed controls, faster gains across all treatments would be expected during milder weather.For this reason, further research is warranted on crude protein level and escape protein supplementation for implanted feedlot cattle.