THE EFFECT OF RUMEN DEGRADABLE AND UNDEGRADABLE PROTEIN SUPPLEMENTATION IN BARLEY-BASED HIGH-GRAIN FINISHING DIETS ON FEEDLOT

The Effect of Rumen Degradable and Undegradable Protein Supplementation in Barley-Based High-Grain Finishing Diets on Feedlot Performance and Carcass Traits of Beef Steers

Benjamin Pamp, Marc Bauer, Greg Lardy

NDSU Department of Animal and Range Sciences

Objectives were to evaluate the use of increased ruminally degradable (RDP) and ruminally undegradable protein (RUP) source on performance and carcass traits of finishing steer calves. Because of the high degradability of barley protein, the addition of RDP to the diet did not have a significant effect on performance or carcass traits. However, both performance and carcass traits were improved by the inclusion of RUP.

One hundred and forty-one crossbred steers (972 ± 16 lbs. initial BW) were allotted randomly to one of four dietary treatments (6 pens/treatment) in a completely randomized design and fed for 89 days. Initial weights were determined by a 3-day average during which steers were fed a common diet at 2 percent of BW. Dietary treatments and diet formulations were arranged in a 2 x 2 factorial. Factors were RDP (+/-) and RUP (+/-). Diets were formulated such that +RDP added 1 percent CP from urea and +RUP added 1% CP from the feather meal/blood meal combination. The basal diet was formulated to contain (DM basis) 83 percent barley, 5 percent alfalfa hay, 5 percent corn silage, 5 percent desugared molasses, 2 percent supplement, 25 g/ton monensin, and 10 g/ton tylosin, and was formulated to contain a minimum of 12.5 percent CP, 0.7 percent Ca, 0.3 percent P, and 0.7 percent K. Steers were fed once daily and weighed at 28-day intervals. Final weight was not affected by dietary treatment (P = 0.18); however, ADG tended (P = 0.08) to increase with RUP supplementation. The dietary treatments had no affect on DMI (P = 0.74), gain efficiency (P = 0.15), or hot carcass weight (P = 0.18). There was an RDP x RUP interaction (P = 0.02) for ribeye area which increased with RUP supplementation when RDP was not supplemented (13.6 vs. 12.1 + 0.2 in²); however, when RDP was supplemented RUP supplementation did not effect REA (13.6 vs. 12.7 + 0.2 in²). Supplemental RUP also decreased (P = 0.01) calculated yield grade (2.13 vs. 2.44 + 0.05). Supplemental RDP did not improve performance or carcass characteristics (P > 0.35). It appears that RDP may be adequate in barley-based finishing diets; however, supplemental RUP may improve performance in steers fed barley-based high grain diets.

Introduction

Protein consumed by ruminants is divided into RDP (ruminally degraded protein) and RUP (ruminally undegraded protein). Degradable protein is used by ruminal microbes, to convert feed nutrients to microbial protein, rather than by the animal itself. Ruminally degraded protein can come in the form of NPN (non-protein nitrogen) and true protein, which supplies the rumen microbes with amino acids and peptides. These nutrients are used by the microbes to support microbial fermentation. A deficiency in RDP would result in reduced carbohydrate digestion, VFA and microbial protein production. This would decrease animal performance.

A study was conducted to determine RDP requirement of finishing steers fed steam-flaked corn (Cooper et al., 2002). Cooper et al.(2002) found that as dietary RDP increased feed/gain and average daily gain responded quadratically. Dry matter intake also increased quadratically in response to increased RDP. Little research has been done with supplementation of RDP in barley-based finishing diets. Barley is higher in total protein than corn and has a much higher portion of total protein being degradable in the rumen than corn. The non-structural carbohydrates contained in barley are more quickly and completely fermented than those in corn, perhaps increasing the need for RDP. This raises the question as to whether RDP and/or RUP supplementation are needed in barley-based finishing.

Procedures

One hundred and forty-one crossbred steers (972.4 " 0.4 lb. initial BW) were allotted randomly to one of four dietary treatments (6 pens/treatment). Initial weights were determined by a 3-day average during which steers were fed a common diet at 2 percent of BW. The control diet (without added RDP and RUP) was formulated to contain a minimum of 12.5 percent CP, 0.7 percent calcium, 0.3 percent phosphorus, 0.7 percent potassium, and .25 percent salt. Diets containing added RDP (0.37% urea) added one percentage point more CP and diets containing added RUP (1.39% feather meal and 0.35% blood meal) added one percentage point more CP (Table 1). Protein sources replaced barley.

Steers were fed once daily for 89 days and weighed at 28 day intervals; final weights were calculated from hot carcass weight at 62 percent yield. Intakes were recorded daily. Diet samples were collected, weighed, and sampled for DM weekly.

Results

Final weight was not affected by dietary treatment (P = 0.18); however, although not significant, final weight tended to be slightly higher on average for the RUP treatment than for other treatments with supplemental protein and almost 37 lbs. higher than the control group.

Average daily gain increased (P = 0.08) with RUP supplementation. The dietary treatments had no affect on DMI (P = 0.74). Feed efficiency tended to increase (P = 0.15) with RUP supplementation both with and without the addition of RDP. Hot carcass weight (HCW) also was not affected by treatment (P $ 0.18).

There was an RDP x RUP interaction (P = 0.02) for ribeye area which increased with RUP supplementation when RDP was not supplemented (13.6 vs. 12.1 ± 0.2 in²); however, when RDP was supplemented RUP supplementation did not effect REA (13.6 vs. 12.7 ± 0.2 in²).

Supplemental RUP also decreased (P = 0.01) calculated yield grade (2.13 vs. 2.44 ± 0.05). Supplemental RDP did not improve performance or carcass characteristics (P > 0.35).

Note: This study is part of a collaborative research project that includes Animal and Range Sciences Department and the Carrington Research Extension Center.