Reference Library

FATTY ACID AND CHOLESTEROL CONTENT OF BEEF FROM
LONGHORN AND BRITISH CATTLE AND THEIR CROSSES
by F. M. BYERS, G. T. SCHELLING, H. R. CROSS,
D. K. LUNT, & L. W. GREENE
Department of Animal Science, Texas A&M University, College Station 77843

Summary

Sixty-one Hereford (British; n = 12), Longhorn x Hereford (British cross; n = 24) or Longhorn (n = 25) steers were fed at the Texas Agricultural Experiment Station, McGregor, TX to provide carcasses of all cattle types differing in fatness and in quality grade. The Longhorn cattle were a random sample, and the Hereford and Longhorn x Hereford crosses were obtained from one ranch. The Herefords were selected to reflect typical British beef cattle, and not to represent any specific breed. Following slaughter at the TAMU Meat Science and Technology Center, College Station, carcasses were graded, fat content was measured via carcass density, and a 9-10-11 rib section was removed for physical dissection and to provide steaks for sensory, shear, lean, fat, fatty acid and cholesterol analyses.

The British, Longhorn x British and Longhorn cattle initally averaged 326 (718.1 lb), 279 (614.5 lb) and 212 kg (467.0 lb) body weight, and were fed toward targeted fatness endpoints in feeding periods ranging from 93 to 210 days. Longhorn and Longhorn x British crosses reached an average Select quality grade with less outside trim fat and more desirable yield grades than British cattle. Both subcutaneous and intermuscular physically separated fat were lower for Longhorns than for British and British crosses. Fat content of the longissimus muscle paralleled other responses with Longhorns having less fat (3.7%) than British crosses or British cattle which were similar (5.7 and 5.4%, respectively). Cholesterol content of the longissimus muscle was similar across cattle types and slaughter endpoints.

A category of "favorable" fatty acids, "monounsaturated', comprised over one third of longissimus muscle fat in all cattle. Muscle fat from Longhorn cattle was less saturated (41.8%) than from British crosses or British cattle due primarily to greater levels of polyunsaturated fatty acids with a smaller difference in monounsaturated fatty acids. At a similar marbling endpoint, Longhorn cattle had less longissimus muscle fat and it was less saturated. Sensory ratings were similar across cattle types and all groups produced acceptable beef based on ratings for sensory traits.

Overall carcass composition indicated that all cattle had reached a similar percentage carcass fatness endpoint, and differences in rib section (subcutaneous, longissimus) fatness reflect differences in priorities for fat distribution to different locations. Longhorn cattle preferentially deposited fat in internal non-muscle (i.e., kidney-pelvic) areas while British cattle placed a greater priority on subcutaneous and intramuscular fat and British crosses tended to be intermediate. As with other breed types, acceptable lean beef with less fat and a desirable fatty acid profile can be produced from Longhorn cattle.

Introduction

Of the many challenges that the cattle industry must address in the coming years, none is more fundamental than maintaining consumer demand for beef. The industry could increase total demand by reducing trimmable fat on retail cuts of beef. While this can be accomplished by trimming fat from the carcass, the resulting product will reflect the cost of producing and trimming that fat and the product may still have more seam fat that is more saturated than desired.

While extensive trimming of beef fat occurs from slaughter through the consumer and results in a reasonably lean beef product being consumed, only preventing this excessive fat deposition where it occurs will correct the image of beef as a fat, high-calorie product. While leaner beef products will assist in reducing caloric intake, it is also consistent with overall cattle industry objectives to reduce the wasteful production of excessive carcass fat.

Consumers are interested in reducing fat consumption, especially saturated fat, and are concerned about cholesterol levels - both dietary and circulating. Recent consumer pressure for leaner beef has encouraged consideration of many new cattle breeds not formerly a part of the US beef cattle industry. The Texas Longhorn has again surfaced as a breed with a potential contribution to make to the beef cattle industry. Longhorn cattle, especially as crosses, have received attention in recent years as a potential component in some beef production systems. While some information exists relative to growth and efficiency in feedlot situations, no information is available on the nature of the fat deposited or the cholesterol content of lean tissue in beef from Longhorn cattle and this project was designed to address these issues.

Experimental Procedures

Sixty-one Hereford (n = 12), Longhorn x Hereford (n = 24) or Longhorn (n = 25) steers were used in this project. The Hereford (British) and Longhorn X Hereford (British cross) calves were obtained from one ranch in Nebraska while the Longhorn cattle were collected from many locations in Texas. The Longhorn cattle were a random sample and were contrasted to the Herefords from one ranch to reflect typical British beef cattle. They were fed at the Texas Agricultural Experiment Station, McGregor, TX to provide carcasses of all cattle types ranging in fatness and in quality grade from Select to Choice. Cattle were fed in three groups by cattle type and half of the steers in each group were initially allotted to each slaughter group. Cattle were weighed and backfat was measured at 28-d intervals via real-time ultrasound.

Steers were fed in small fenced lots with feed and water available at all times. The experiment was begun February 10, 1986 and the last group was slaughtered on September 8, 1986. Feeding periods ranged from 93 to 210 d for respective cattle groups. All cattle were started on a high roughage starter ration, switched to an intermediate ration and then placed on a high grain finishing ration from mid-March to slaughter.

Respective groups were transported 90 miles to the Texas A&M University Meat Science and Technology Center, College Station, TX, as targeted fatness endpoint of the group was reached. Following slaughter, all carcasses were weighed and graded following a 48-h chill in a 2 C cooler. Fat content was measured on each carcass via carcass density (specific gravity, 3). A 9-10-11 rib section was removed from the right side of each carcass to provide steaks for sensory, shear, lean, fat, fatty acid and cholesterol analyses. Separable rib tissue was measured by physical dissection of the 9-10-11 rib section.

Steaks were taken from the loin of each side for cooking loss, Warner-Bratzler shear and for sensory panel evaluation. Total fat content of the longissimus muscle was determined by extraction with chloroform:methanol (2:1). An aliquot of the extract was evaporated under a stream of nitrogen, saponified with alcoholic potassium hydroxide, separated with pyrogallol, acidified and prepared for spectrophotometric cholesterol analyses. A second aliquot of the chloroform:methanol extract was esterified for fatty acid analyses and chromotographed on a gas chromatograph with a capillary column.

All data were analysed using the SAS general linear models procedure (6) with main effects of cattle type, endpoint and the interaction evaluated. Treatment means for significant main effects were separated via Fishers Protected LSD.

Results and Discussion

The British, British cross and Longhorn cattle used in this project averaged 326, 279 and 212 kg body weight at initiation of the feeding period. Cattle were fed toward targeted fatness endpoints, and as a result, feeding periods varied and ranged from 93 to 210 days.

A summary of data collected at slaughter is presented in Table 1. Target fatness (backfat) endpoints were the basis for slaughter and, based on earlier research (1,4), lower outside fat endpoints were planned for Longhorns with greater fat for crosses and greatest fat for British cattle at each carcass target. As is evident from Table 1, this objective was met with lower backfat for Longhorns than for crosses or for British cattle at each slaughter endpoint (1 or 2).

Cattle averaged low to average Select quality grade at time one and average Select to low Choice marbling at the second slaughter endpoint. It is of interest that while quality grade of Longhorns was similar to British cattle at time one, actual back fat was approximately one half that of British cattle. Internal fat (kidney, pelvic and heart fat; KPH) was greatest for Longhorns and least for British cattle, reflecting a difference in distribution of fat. British crosses at the second slaughter point had similar or greater marbling scores than British cattle while actual backfat was only two thirds that of the British cattle.

Yield grade was similar for all breed groups at the first endpoint and was less desirable (greater fat) for British cattle (4.5) than for crosses (3.6) or Longhorns (3.0) at the second slaughter endpoint.

Overall, while all breed groups averaged Average-Select in quality grade and Average-Slight in marbling (348, 360, and 357 for British, British crosses and Longhorn), Longhorns and British crosses had less backfat and better yield grades than British cattle. In general, these data indicate that Longhorn and British crosses reached average Select quality grade with less outside trim fat and more desirable yield grades than British cattle. This reflects the lower priority for outside fat deposition in Longhorns and their crosses.

These results are consistent with responses noted in two earlier studies. At similar carcass weights, (1) Longhorn cattle had only one-third as much backfat (5.1 vs 16.5 and 18.5 mm) as Hereford and Angus (British) cattle. Yield grade, reflecting carcass leanness, was a full grade better for Longhorn than Hereford or Angus cattle (2.4 vs 3.4 and 3.8). In another study (4), Longhorn-cross cattle, while somewhat lighter in carcass wieght, (321 vs 341 lb), had more desirable marbling but had less external fat (.23 vs .36 cm) and a more desirable yield grade (3.2 vs 4.1) than Hereford cattle.

Collectively, these studies indicate the tendency for Longhorn cattle to produce leaner carcasses at similar endpoints to typical British cattle. It is interesting to note that in all studies, although Longhorn cattle had less backfat than typical beef breeds, they actually had similar or more marbling in all three studies.