The document attached has been archived with permission from the World Congress on Genetics Applied to Livestock Production.As far as most consumers are concerned, a good steak is a steak with visibly desirable colour (doneness), a large portion of muscle and a small amount of fat, especially the seam fat located between the muscles. During the intensive growth to commercial slaughter weights in feedlots, there is a distinct change in the composition of the body with the amount of fat increasing and the musculature remaining reasonably constant (Pitchford and Bottema, 2000). Cattle breeds deposit fat at different rates and in different locations (subcutaneous, intermuscular or intramuscular). For example, early maturing Jersey cattle deposit more fat intramuscularly than late maturing Limousin cattle (Pitchford and Bottema, 2000). These differences suggest that there is a genetic basis for fat distribution. The aim of this study was to investigate the genetic variation in seam fat distribution within loin muscles of Jersey and Limousin cross cattle, independent from carcass size and fatness

Bottema, C.

Deland, M.

Kruk, Z.

Pitchford, W.

Adelaide Research &amp; Scholarship

7th World Congress on Genetics Applied to Livestock Production, August 19-23, 2002, Montpellier, France GENETICS OF SEAM FAT IN CATTLE   Z.A. Kruk1, W.S. Pitchford1, M.P.B. Deland2 and C.D.K. Bottema1  1 Livestock Systems Alliance, Adelaide University, Roseworthy Campus, SA 5371 2 South Australian Research and Development Institute, Struan Research Centre, Naracoorte  SA 5271, Australia  INTRODUCTION As far as most consumers are concerned, a good steak is a steak with visibly desirable colour (doneness), a large portion of muscle and a small amount of fat, especially the seam fat located between the muscles. During the intensive growth to commercial slaughter weights in feedlots, there is a distinct change in the composition of the body with the amount of fat increasing and the musculature remaining reasonably constant (Pitchford and Bottema, 2000). Cattle breeds deposit fat at different rates and in different locations (subcutaneous, intermuscular or intramuscular). For example, early maturing Jersey cattle deposit more fat intramuscularly than late maturing Limousin cattle (Pitchford and Bottema, 2000). These differences suggest that there is a genetic basis for fat distribution. The aim of this study was to investigate the genetic variation in seam fat distribution within loin muscles of Jersey and Limousin cross cattle, independent from carcass size and fatness.  MATERIALS AND METHODS Animals and management. The animals used in this study were part of the Davies Cattle Gene Mapping Herd, ¾ Jersey (XJ) and ¾ Limousin (XL) (Kruk et al., 1997). They were born between April/May, 1997. The animals comprised 50 XJ and 31 XL steers, progeny of pure Jersey and Limousin dams crossed to the three F1 (Jersey/Limousin) sires (# 361, 368, 398). The steers were raised on pastures under the same management conditions, weaned at 250 days of age, fed a grain based ration for 170 days and then slaughtered.   Slaughter, measurements and data collection. All steers were slaughtered and after standard processing, the carcasses were stored in the chiller (0-4°C). Approximately 18 hours later, carcasses were quartered between 10th-11th rib and chiller assessment was performed by accredited AUS-MEAT and MSA graders. Parameters such as meat colour, fat colour, eye muscle area, loin temperature, ossification, pH and marbling score were assessed. Additionally, photographs of each eye muscle area cross-section were taken using a Pentax P30N camera. Every image contained a small ruler used for calibration.  Image processing and analysis. After the photographs were developed, a computer program (PV32) was used to measure the total (steak) area as trimmed according to retailer specifications (3-5 mm of fat). Also various muscle areas and fat depots between the muscles were measured. Each image was individually calibrated and the area of interest assessed manually. The following areas of the image were calculated: M. longissimus dorsi (M1), M. spinalis dorsi (M2), M. longissimus costarum (M3), M. trapezius thoracis (M4-not present on the diagram), M. multifidi dorsi (M5), Mm. intercostals externus and internus (M6), fat area F1 Session 11. Growth and meat quality Communication N° 11-35  7th World Congress on Genetics Applied to Livestock Production, August 19-23, 2002, Montpellier, France (between M1, M2, M5), fat area F2 (between M1, M3, M5, M6), and fat area F3 which was the remaining fat in the image (Figure 1).          TSA – total steak area (trimmed to 4 mm of fat) M6 M5 M3 2 M1  Statistical analysewell as a percentagusing Proc GLM (Sfixed effects of breexpressed in cm2 wanimal size, anothe(HSCW) and ruminteraction. Breed models. Residual 1989).  RESULTS  Breed effect on fdiffered significantwere 28% heavier,were 19% larger (largest influence oThe variation in muweight (HSCW) arespectively. The vwas observed withLimousin having la More variation wasno difference betwobserved with F2 amore F3%. F1% respectively). Theshad significantly hihigher in almost all Session 11. Growth andF M1÷M6 – muscle areas as describe in the text  F1, F2, F3 - fat areas as described in the text  TMA – total muscle area = Sum (M1÷M6)  TFA – total fat area = Sum (F1÷F3) All areas expressed in cm2 All symbols followed by “%” are expressed  as percentage  of TSA  Figure 1. Diagrammatic representation and description of areas measured  F1 M2 s. The measurement of areas was expressed in square centimeters (cm2) as e of the total steak area. Least squares analysis of variance was carried out AS 1989). The model for analysis of percentage areas (Model 1) included ed, sire and the interactions between breed and sire. To test that the fat areas ere purely due to the fat distribution and not due to the total fatness or r model (Model 2) was utilized that included hot standard carcass weight p (P8) fat depth fitted as covariates as well as breed, sire and their by sire interactions were not significant for all traits and removed from the correlations between variables were computed using Proc CORR (SAS, atness and muscularity. As expected, Jersey and Limousin cross cattle ly in most of the fat and musculature areas. Carcasses of Limousin crosses  had 7% more muscle in trimmed steak area and the steaks from this breed Table 1). M. longissimus dorsi (M1) and M. spinalis dorsi (M2) had the n total muscle area (42-48% of TMA and 14-15% of TMA, respectively). sculature traits was low and for total steak area (TSA), hot standard carcass nd total percentage of muscle within steaks (TMA%) was 11, 10 and 6, ariation for M1% was also low (8%). The highest variation of musculature  the area of M2% (16%). There was a breed by muscle interaction with rger M1 (48.0 vs 42.3%) and Jersey having larger M2 (15.7 vs. 14.4%).  observed with fatness traits. P8 fat depth had a CV of 31% and there was een Jersey and Limousin crosses. A similar amount of variation was nd F3 (39% and 35%, respectively) with Jersey crosses having significantly and total fat percentage (TFA%) had less variation (23% and 19%, e two areas were significantly different between the breeds. Limousin cattle gher values for the majority of musculature traits, while Jersey crosses were  fatness traits.  meat quality Communication N° 11-35  7th World Congress on Genetics Applied to Livestock Production, August 19-23, 2002, Montpellier, France Sire effect on size, fatness and muscularity. Sire influence was evident only in some fatness traits. A significant difference was observed for P8 fat, F1% and F2%. The progeny of sire 361 had the thickest subcutaneous fat layer (9.7 mm) and the largest proportion of fat in areas F1 and F2 (7.5% and 5.8%, respectively). The progeny of the remaining two sires did not differ except in F1% where the sire 398 had significantly less fat than sires 361 and 368 (Table 1).  Table 1. Least square means for carcass traits and meat and fat distribution  Trait XJ XL Sire 361 Sire 368 Sire 398 HSCW (kg) P8 fat (mm) TSA (cm2) M1% M2% TMA% F1% F2% F3% TFA% 310.9±4.8B 8.4±0.4 166.1±2.7 B 42.3±0.5 B 15.7±0.3 A 74.9±0.6 B 7.2±0.2 A 5.2±0.3 12.7±0.6 A 25.1±0.6 A 399.7±6.2 A 8.7±0.5 197.7±3.5 A 48.0±0.7 A 14.4±0.5 B 80.4±0.8 A 5.6±0.3 B 4.7±0.4 9.3±0.7 B 19.6±0.8 B 362.2±6.3 9.7±0.5 A 181.0±3.6 44.8±0.7 15.4±0.5 76.6±0.8 7.5±0.3 A 5.8±0.4 A 10.1±0.7 23.4±0.8 353.1±6.2 7.8±0.5 B 182.6±3.5 46.9±0.7 14.3±0.4 77.6±0.8 6.6±0.3 B 4.6±0.4 B 11.2±0.7 22.4±0.8 350.6±7.6 8.1±0.6 B 182.1±4.3 45.3±0.8 15.5±0.5 78.7±1.0 5.2±0.4 C 4.6±0.4 B 11.6±0.9 21.3±1.0 A-C within rows means of the same class followed by the same letter are not significantly different (P>0.05)  Table 2. Correlations between musculature and fatness traits   TSA M1 M2 TMA F1 F2 F3 TFA TSA M1 M2 TMA F1 F2 F3 TFA  *** *** *** * ns * ** 0.77  * *** ns ns ns ns 0.49 0.25  *** ns ns ns ns 0.85 0.91 0.56  ns ns ns * 0.24 -0.01 0.14 0.0  * ns *** 0.06 -0.20 0.12 -0.15 0.23  ns *** 0.26 -0.15 -0.21 -0.19 0.05 0.09  *** 0.32 -0.21 -0.08 -0.22 0.45 0.39 0.83  ns = not significant (P>0.05), *** = P<0.001, ** = P<0.01, * = P<0.05  Fatness and muscularity based on the statistical model 2. Model 2 was designed to test the significance of measured steak areas (expressed in cm2) which would not be affected by animal size (HSCW) or fatness (P8). With HSCW and P8 fat as covariates, all breed differences in musculature traits were no longer statistically significant except the size of M1 (data not presented). In terms of fatness, however, TFA and F1 were influenced by breed and sire as in model 1. Although F2% was affected by sire in the model 1, its counterpart F2 (area) was less significant in the model 2 (P=0.08). F3%, previously affected by breed in model 1, was not significant when expressed as area (F3).  Correlations between fatness and muscularity. The total area of steak was highly correlated with total muscle area, as well as with the area of the two major muscles, M1 and M2 (Table 2). The correlations between musculature and fat areas were low and not significant. Between Session 11. Growth and meat quality Communication N° 11-35  7th World Congress on Genetics Applied to Livestock Production, August 19-23, 2002, Montpellier, France different fat areas, there was a moderate correlation between F1 and F2. Total fat area was highly correlated with F3 and moderately correlated with F2 and F1. Total fat was also correlated with total meat area and the correlation was negative. The total area of steaks was highly associated with total meat area and moderately with total fat area.   DISCUSSION A proverb “size does not matter” may not apply to the size of a steak on a consumer’s plate as larger steaks are always more appreciated if purchased for a reasonable price. The size of a steak and its composition (muscle and fat content and distribution) can be influenced by the breed of cattle, size of the animal and feeding regime (Ewers et al., 1999). This was evident in the Jersey and Limousin crossbred steers, which differed significantly in body size and consequently, had larger steak areas. When HSCW and P8 fat were fitted as covariates, the breed effect was no longer significant, demonstrating that all variation related to the steak area was due to the carcass size.  However, the composition of steaks (muscling) was breed specific and, even after accounting for carcass size and fatness, was still significant. Thus, there could be breed specificity in the shape and size of muscles at a particular point of quartering. Rutley et al. (2002) did not find breed differences in the size of eye muscle between different quartering sites. However, other muscles were not measured in that study and these greatly contribute to the total steak area and possess a larger variation. Moreover, total steak area is more correlated with total muscle area than with M1 alone.  Fat distribution within steaks was also breed dependent and remained so in most cases, even when P8 fat was fitted as the covariate. The breed influence on total fat percentage and F1 was highly significant. F1 is important from a retailer perspective because if F1 and M2 are trimmed, then ~20% of the total steak area is lost. The F1 and F2 as well as P8 fat depth differed between sires. Sire 361 produced fatter progeny with more fat deposited within steaks. These results clearly demonstrate that fat deposition within the muscles of loin in cattle has a genetic basis.   REFERENCES Ewers, A.L., Deland, M.P.B., Pitchford, W.S., Rutley, D.L. and Ponzoni, R.W. (1999) Proc. Ass. Adv. Anim. Breed. Genet. 13 : 393-396. Kruk, Z.A., Malau-Aduli, A.E.O., Thomson, A.M., Siebert, B.D., Pitchford, W.S. and Bottema, C.D.K. (1997) Proc. Aust. Assoc. Anim. Breed. Genet.  12 : 278-282. Pitchford, W.S. and Bottema, C.D.K. (2000) Asian-Aus. J. Anim. Sci Suppl A : 485-488. Rutley, D., Deland, M.P.B. and Pitchford, W.S. (2002) 24th Proc. Aust. Soc. Anim. Pr. (in press). SAS Institute, Inc. (1989) "SAS user's guide: Statistics", Ver. 5.04, SAS Institute, Inc., NC. Session 11. Growth and meat quality Communication N° 11-35  

Genetics of seam fat in cattle

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Genetics of seam fat in cattle

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Genetics of seam fat in cattle

Abstract

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