Level of rumen undegradable protein (RUP) in high-grain diets fed to feedlot lambs

J.J. Reed, M.L. Bauer, G.P. Lardy, P.T. Berg.

Introduction

Rumen undegradable protein (RUP) is protein that bypasses the rumen. Rumen undegradable protein flows to the small intestine where digestion takes place. Rumen degradable protein (RDP) is protein that is broken down by ruminal microorganisms. Loe et al. (2000) evaluated the addition of RDP and RUP to corn-based lamb finishing diets. Treatments with added RUP contained 7.3% RUP. Lambs fed additional RUP had heavier final weights, gained more rapidly, and were more efficient compared with RDP fed lambs. Loe et al. (2001) conducted research to determine the optimum level of RDP in lamb finishing diets. Feeding levels between 6.1 and 11.0% RDP did not affect gain or feed efficiency. They concluded that the optimal level of RDP does not appear to be above 6.1% in lambs with the ability to gain at least 1.06 lb/day. Little research has been conducted on RUP in lamb finishing diets. The objective of this study was to determine the optimum level of RUP in lamb finishing diets.

Materials and Methods

Seventy-four crossbred ram lambs (85.4 .83 lb initial weight) were fed for 74 d days to determine the optimal level of RUP in corn-based finishing lamb diets. Lambs were housed at the NDSU Animal Research Center barns. The lambs were blocked by weight and allotted randomly to dietary treatments (5 pens/treatment). Each pen had access to an outdoor and indoor run and fresh water.

Diets consisted of corn, beet pulp pellets, molasses, soybean meal, urea, feathermeal, bloodmeal, and supplement (Table 1). Diets were offered ad libitum once daily. Treatments contained 6, 7, 8, or 9% RUP (dry matter basis). Rumen undegradable protein sources were feathermeal and bloodmeal combinations. Level of RDP was held constant at 6.9% in all treatments.

Three day weights were taken at the beginning and end of the trial to measure average daily gain. Unconsumed feed was removed from the bunks and weighed weekly to measure dry matter intake. Carcass data was collected at slaughter. Hot carcass weight, fat thickness, rib-eye area, bodywall thickness, marbling, flank streaking, leg score, and conformation score were taken.

Results

No treatment affects on performance occurred (Table 2). Rib-eye area increased linearly (P = 0.06) with increasing level of RUP. There were no other affects on carcass characteristics (Table 3) with respect to treatment.

Conclusions

Lack of treatment effects may indicate that lambs on finishing diets do not need more than 6% RUP. However, a previous study indicates improved performance with lambs fed 7.3% RUP versus 5.9%.

The lack of treatment effects in this study may be due to poor lamb performance. In this study, lambs gained only 0.66 lb/day. In a previous study (Loe et al., 2000), lambs fed RUP at 7.3% gained .87 lb/day. In another study (Loe et al., 2001), lambs fed 7.3% RUP with varying levels of RDP gained 1.07 lb/day.

Table 1. Formulated dietary treatments (%, DM Basis)

 

Level of rumen undegradable protein, (%, DM Basis)

Item

6

7

8

9

Corn

75.43

74.28

73.13

71.99

Beet pulp pellets

12.50

12.50

12.50

12.50

Molasses

5.00

5.00

5.00

5.00

SBM

1.99

1.33

0.66

0.00

Urea

0.22

0.15

0.07

0.00

Feathermeal

1.51

3.02

4.53

6.04

Bloodmeal

0.38

0.76

1.13

1.51

Supplement

2.97

2.97

2.97

2.97

Protein

 

 

 

 

Crude

12.90

13.90

14.90

15.90

Rumen degradable

6.90

6.90

6.90

6.90

Rumen undegradable

6.00

7.00

8.00

9.00

Metabolizable

7.66

8.47

9.28

10.08



Table 2. Effect of treatment on performance

 

Level of rumen undegradable protein, (%, DM Basis)

Item

6

7

8

9

Standard

Error

Weight, lb

 

 

 

 

 

Initial

85.3

84.7

86.1

85.5

0.8

Final

131.3

134.3

136.7

134.8

2.5

Dry Matter Intake

 

 

 

 

 

lb/day

3.01

3.08

3.30

3.19

0.10

% of body weight

2.80

2.82

2.99

2.90

0.08

Average daily gain, lb

 

 

 

 

 

live wt basis

0.62

0.67

0.68

0.67

0.04

carcass basisa

0.65

0.68

0.67

0.68

0.04

Gain: Feed

0.206

0.217

0.206

0.210

0.007

Feed: Gain

4.85

4.60

4.85

4.76

---

a Based on hot carcass weight and 50% dress


Table 3. Effect of treatment on carcass characteristics

 

Level of rumen undegradable protein, (DM Basis)

Item

6

7

8

9

Standard

Error

Hot carcass weight, lb

66.55

67.49

68.01

67.90

1.42

Fat thickness, in

0.17

0.17

0.17

0.19

0.02

Rib-eye area, in2a

2.35

2.49

2.49

2.53

0.06

Bodywall thickness, in

0.91

0.93

0.86

0.90

0.04

Marbling

375

389

377

359

17

Flank streaking

369

339

350

337

14

Yield grade

2.08

2.12

2.12

2.30

0.18

Leg score

11.12

11.20

11.50

11.22

0.21

Conformation score

11.07

11.20

11.25

11.22

0.22

a Linear response to treatment (P = 0.06)

b Marbling score of 300 = slight

c Score of 11 = low choice