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EFFECTS OF BREED AND SLAUGHTER ENDPOINT ON CARCASS COMPOSITION
AND BEEF QUALITY IN LIMOUSIN AND CHAROLAIS STEERS FED HIGH CONCENTRATE DIETS

I.B. Mandell1, E.A. Gullett2, J.W. Wilton1 and V.R. Osborne3
1Department of Animal & Poultry Science and 2Department of Food Science, University of Guelph
3Department of Animal & Poultry Science, Ridgetown College of Agricultural Technology

Introduction

Over the last 20 years, Canadian beef producers have used Continental breeds extensively in their cross-breeding programs to optimize productivity. The use of exotics have increased weaning weights, rates of gain, muscling, and leanness. However, at the same time, carcass weights have dramatically increased from 570 lbs in 1970-71 to over 750 lbs today. In addition, palatability problems have developed in Canadian beef such that 1 in 5 steaks or roasts are tough according to Canadian consumers.

Heavy carcass weights may be advantageous to producers in their production systems and to packers due to the efficiency of processing large cattle vs. small cattle. Heavy carcass weights are not desired by the hotel and restaurant trade nor by retailers as their requirements for portion size in rib and loin cuts cannot be satisfied from processing heavy carcasses. In addition, consumers do not want rib and loin cuts from heavy carcasses due to larger portions than they desire and high costs per package.

Backgrounding has been used with exotics to take advantage of inexpensive feed through use of forages and compensate for slow rates of fattening in exotics to achieve enough finish for Agriculture Canada's "A" finish. While backgrounding may be advantageous to producers, the practice may be affecting beef quality due to marketing of older cattle approaching 2 years of age.

High energy diets may be the answer to avoid excessive carcass weights in exotics. Enough finish will be achieved with these diets to grade Canada "A" and ensure desirable eating quality for consumers. The purpose of this study was to examine the use of high energy diets with 2 different slaughter endpoints to avoid excessive carcass weights yet produce optimal beef quality.

Materials and Methods

One hundred and eight head of cattle were purchased from producers in Ontario, Manitoba, and Saskatchewan who could provide cattle with the following requirements: 1) at least 7/8 Charolais or Limousin; 2) 8 half-sibs per sire; and 3) male calves born between March 1 and May 15, 1993.

Six Limousin and 6 Charolais sires were used in the trial to examine within breed and between breed differences in growth performance, carcass composition, and beef quality. Cattle were adjusted to 80% grain diets (barley or corn) fed with a 36% crude protein supplement. The trial was conducted at Ridgetown College using Calan gates to obtain feed intake data for individual steers.

Two slaughter endpoints were used in the trial - a market liveweight of 1250 lbs regardless of backfat, or an ultrasound backfat reading of 7 mm regardless of liveweight. A market weight of 1250 lbs was chosen to ensure carcass weights under 750 lbs, the current cut-off prior to weight discounts for carcasses. An ultrasound backfat measurement of 7 mm was chosen based on American data which stated that at least .3 inches (7.62 mm) of backfat was needed for optimal beef flavour. The endpoints were chosen with the realization that a certain percentage of cattle would not finish at their designated endpoints and would grade Canada "B1" due to lack of finish.

Cattle were allocated such that all sires and breeds were equally represented on each diet and endpoint combination.

All cattle were slaughtered at a commercial abattoir which employed high voltage electrical stimulation. Carcasses were federally graded and the left primal rib from each carcass delivered to Meat Wing, University of Guelph. Ribs 9 to 11 were dissected into lean, fat, and bone to determine body composition. Ribeye roasts from ribs 9 to 11 of each animal were aged for 7 days prior to being frozen. A ribeye steak from the 12th rib of each animal was saved for chemical analyses.

In addition to the test cattle, 12 primal ribs from each of Agriculture Canada's marbling classifications (Trace, Slight, Small) were purchased and processed identically to ribs from test cattle. These primal ribs were randomly chosen from carcasses with weights that would most likely reflect a high proportion of Continental breeding.

Ribeye roasts were evaluated by a 10 member trained taste panel under the direction of Dr. Gullett. The taste panel evaluated the roasts for: 1) softness, the force required by the molar teeth to compress the sample; 2) tenderness, the force required to chew the sample after the initial compression (determination of softness); 3) initial juiciness or the amount of moisture released from the meat; 4) chewiness, the force and time required to chew the sample to be prepared for swallowing; 5) juiciness, the amount of saliva absorbed during the mastication process; 6) rate of breakdown, the rate at which the sample breaks down into small particles for swallowing; and 7) beef flavour, the amount of full meaty flavour. Six roasts were evaluated each day by the trained taste panel.

Results and Discussion

Charolais steers averaged 239 days of age and 285 kg at start of the trial vs an average of 249 days of age and 246 kg for Limousin steers. The 80% grain diets were changed to 75% grain, 5% alfalfa silage due to the occurrence of digestive upsets early in the trial. The trial was terminated after 281 days regardless of whether cattle had achieved their targeted endpoint.

Charolais steers gained faster than Limousin (Table 1) while gains were similar between endpoints. Dressing percentage favoured the Limousin as at a lower average market weight, hot carcass weights were heavier than Charolais. Gradefat did not differ between treatments even though backfat cattle were supposed to be slaughtered at 7 mm ultrasound backfat. The absence of treatment differences in backfat was due to the difficulty of fattening exotic straightbreds even when feeding 75% grain diets for 281 days. The limited finish in these cattle is reflected in at least 21% of each breed-endpoint combination grading as Agriculture Canada "B1" carcasses due to inadequate finish.

Muscling favoured Limousins over Charolais as shown by larger ribeye areas. Intramuscular fat deposition was limited, ranging from 1.66 to 2.57% and was lower than the minimum requirement of 3% intramuscular fat cited in American studies to ensure optimal palatability. Limited intramuscular fat deposition was also reflected by only 7 carcasses achieving slight (AA) marbling vs 61 carcasses achieving trace (A) marbling.

Primal ribs from trace (A), slight (AA), and small (AAA) marbled beef were purchased to enable comparison of beef from test cattle against beef with the range of marbling found in Canada "A" beef. Carcass weights of the purchased ribs reflects Continental breeding as does the large ribeyes. While mm gradefat and intramuscular fat content in purchased ribs exceeded corresponding values in test cattle, the trained taste panel found no differences in softness, tenderness, chewiness, or rate of breakdown between beef from the test cattle vs. highly marbled beef (slight and small marbled purchased ribs) (Table 2). This is surprising since at least 21% of each breeds-endpoint combination graded as B1 carcasses. This absence of differences in softness, tenderness, chewiness, and breakdown rate between test cattle and slight and small marbled beef was probably due to the age of the test cattle prior to slaughter which averaged from 442 days (15 months) to 502 days (17 months) across treatments. In addition, all roasts were aged 7 days prior to freezing. While initial juiciness favoured slight and small marbled beef over the test cattle, the taste panel found juiciness to be greater in the test cattle. Beef flavour in slight and small marbled ribs exceeded the test cattle and is probably due to lower concentrations of intramuscular fat in the test cattle. The taste panel found no differences in palatability attributes among breeds and slaughter endpoints. This may be due to similar ages at slaughter, degrees of finish, and intramuscular fat content.

Significance to the Industry

This work demonstrates the difficulties in finishing exotic straightbreds especially when targeting carcass weights desired by retailers and consumers. While the authors acknowledge that exotics are usually included in a crossbreeding program with British breeds, this data is important as large numbers of exotic straightbreds with little or no British Blood are being produced. This data demonstrates that youthfulness of cattle is important regarding tenderness even when finish is lacking. Beef from these cattle could be targeted to "health" conscious consumers by marketing a lean product with limited concentrations of intramuscular fat but aged 7 days to produce tender beef.

Acknowledgements

The authors are grateful for financial support from OMAFRA Red Meat II and from the Ontario Cattlemen's Association to support this work. The authors are indebted to Chris Haworth and his staff and to Sue Buttenham for their technical expertise in carcass evaluation, physical dissections, and conduct of the trained taste panel. The assistance of the staff at the Ridgetown Beef Centre is also greatly appreciated.

Table 1. Effects of breed and slaughter endpoint on average daily gain and carcass composition in Limousin and Charolais steers fed to 1250 lbs liveweight or 7 mm backfat finish.

 

Purchased cattle fed at Ridgetown College to either 1250 lb market weight or 7 mm backfat

Primal ribs purchased from commercial

packing plant

Trait

Charolais Market Wt.

Charolais

Backfat

Limousin

Market Wt.

Limousin

Backfat

Trace

Marbling

Slight

Marbling

Small

Marbling

Average daily gain, kg/d

1.55

1.48

1.44

1.35

N/A

N/A

N/A

Final weight, kg

584

641

570

568

N/A

N/A

N/A

Hot carcass weight, lbs

701

790

741

731

794

801

832

Gradefat, mm

4.7

5.4

5.0

4.9

6.7

6.5

9.1

Ribeye area, sq cm

83.7

86.3

101.2

95.0

96.4

93.9

89.0

Intramuscular fat, %

1.99

2.57

1.66

1.87

2.71

3.56

4.97

% "B" carcasses

35

22

25

21

N/A

N/A

N/A

Table 2. Effects of breed and slaughter endpoint on palatability traits in Limousin and Charolais steers fed to 1250 lbs liveweight or 7 mm backfat finish1.

 

Purchased cattle fed at Ridgetown College to either 1250 lb market weight or 7 mm backfat

Primal ribs purchased from commercial

packing plant

Trait

Charolais Market Wt.

Charolais

Backfat

Limousin

Market Wt.

Limousin

Backfat

Trace

Marbling

Slight

Marbling

Small

Marbling

Softness

5.68

6.04

6.02

5.81

5.44

5.78

4.97

Tenderness

5.55

6.00

5.95

5.77

5.37

5.82

4.96

Initial juiciness

5.28

5.22

4.97

5.55

5.12

5.74

5.61

Chewiness

5.65

6.01

5.85

5.72

5.36

5.83

5.01

Juiciness

5.04

4.96

5.43

4.79

5.26

4.42

4.65

Rate of breakdown

5.67

6.07

5.87

5.77

5.35

5.91

5.06

Beef flavour

5.20

4.98

5.26

5.25

5.37

5.53

5.62

1 Palatability traits scored on a scale from 0 to 10. Traits include: Softness = 0 (very firm) to 10 (very soft); tenderness = 0 (very tough) to 10 (very tender); initial juiciness = 0 (very little) to 10 (very much); chewiness = 0 (very chewy) to 10 (not chewy); juiciness = 0 (very little) to 10 (very much); rate of breakdown = 0 (very slow) to 10 (very rapid); beef flavour = 0 (very weak) to 10 (very intense).