Carcass and Meat Quality

 

Carcass and Meat Quality Characteristics of Two Sheep and Two Goat Breeds Produced under Extensive Feeding Conditions.

P E Stydom (PhD) & P Tshabala

Animal Nutrition and Animal Products Institute, ARC, Private Bag X2, Irene, 0062 (This is an abridged version of the original article)

Materials and Methods

Twelve animals of two indigenous sheep breeds were purchased from commercial producers and slaughtered from extensive feeding conditions. Carcasses were processed into five wholesale cuts and these cuts were processed into subcutaneous fat, meat and bone. Meat is defined as muscle, intermuscular fat (seam fat or fat between muscles excluding fat on the carcass surface – subcutaneous fat) and intramuscular fat composition of the soft tissue of the carcass.

In the processing of the carcass, the meat of the one side was minced and frozen for meat quality evaluation and fatty acid profile. The meat of 10 of the 12 animals per breed was used for a sensory test. A 12 member trained sensory panel scored the samples on an eight point hedonic scale for overall flavour and aroma intensity, goaty flavour and aroma intensity, mutton flavour and aroma intensity, tenderness, juiciness and chewiness (amount of connective tissue after mastication).

Results and Discussion
Adjusted means of carcass characteristics of two goat and two sheep breeds are presented in Table 1. For the purpose of this report, only the results of the two sheep breeds will be discussed. The abbreviation, SCF will be used for subcutaneous fat.
The carcass weight of the Damara was 20% lower than that of the Dorper in this study. This is not necessarily a reflection of the typical carcass weight of the two breeds at this common fatness level (9.2% SCF), since final weight of the carcass is a function of a number of factors, including a feeding regime. However, it can be accepted that the Damara is an earlier maturing breed than the Dorper.

As expected, the Damara had a heavier tale than the Dorper. Dorper carcasses had a 4 percentage-age-units advantage for meat and bone yield over the Damara. This means that the Dorper carcass produces 1.2 units of meat per unit of bone more than the Damara in this trial. It has to be remembered that carcass development could highly depend on feeding regime, and although the two breeds came from the same are (habitat), different feeding practices (not exactly known in this trial) could partly have contributed to these differences. The kidney fat tended to be higher in Dorper carcasses than in the Damara carcasses. Significantly more (P<0.05) carcass weight was distributed in the shoulder, dorsal trunk and less in the ventral trunk of the Damara, compared to the Dorper. No significant differences were found for the neck and leg cuts and there were also no significant differences in distribution of meat and bone in the leg cuts of the two breeds.

Broadly speaking, more fat was distributed to the leg cut of the Damara carcass and less to the other cuts in comparison to the Dorper: a difference of about 9 percentage units. It is possible that this difference could be the result of the amount of fat trimmed off the leg cut of the Damara when the tail is removed. Since the workers were not specifically skilled in working with the fat-tailed carcass, it is possible that some fat from the tail was left on the carcass, accounting for some of the difference in fat distribution in the leg cut.

Table 1: Adjusted1 means (s.e) for carcass characteristics of two goat and two sheep breeds 
(n=12 animals per breed)

Trait Damara Dorper Boer Goat Indigenous Goat
Carcass weight (tail fat excluded; kg) 17.3*±0.69 21.5±0.72 13.4+±0.58 11.6±-0.47
Tail weight (kg) 1.2* 0.2 0.05* 0.03
Tail yield (% 6.2*±0.33 0.87±0.34 0.36*±0.04 0.22±0.03
Carcass Composition:
Meat (%) 70.7*±0.40 74.8±0.41 77.0*±0.54 73.9±-0.44
Bone(%) 20.0*±0.40 15.9±0.41 20.8*±0.54 23.9±0.44
Kidney fat (%) 1.9±0.33 2.6±0.34 1.5±0.23 1.5±0.18
Yields of different carcass cuts:
Neck (%) 9.8 ±0.28 10.1±0.29 9.8±0.44 10.6+-0.44
Shoulder (%) 16.6*±0.22 15.4±0.23 19.8±0.31 19.7±0.25
Dorsal cut (%) 24.0*±0.49 21.9±0.51 20.6*±0.45 17.0±0.37
Ventral cut (%) 16.7*±0.62 20.8±0.64 19.6*±0.45 21.4±0.36
Leg (%) 32.8±0.41 32.00±0.42 30.1*±0.34 31.3±0.27
Yields within the leg:
Meat (%) 33.0±0.12 32.7±0.09 30.7*±0.03 32.3±0.05
Bone (%) 31.5±0.34 32.3±0.23 29.5±0.16 29.2±0.21
Subcutaneous fat distribution
Neck (%) 8.4±1.10 10.1±1.14 3.0*±1.77 10.0±1.43
Shoulder (%) 11.0±0.42 11.2±1.03 23.4±4.59 24.3±3.71
Dorsal cut (%) 26.2±0.69 28.8±3.81 29.5±7.87 26.0±6.63
Ventral cut (%) 20.7±1.68 25.6±4.12 30.6±4.85 17.6±3.92
Leg (%) 33.7*±1.87 24.±-4.9 13.5±5.99 21.0±4.85

1 Means for sheep breeds and goat breeds adjusted to common subcutaneous fat levels of 9% and 2.3%, respectively, to compare breeds within each specie at a common fatness level Actual subcutaneous fat %: Damara = 10.3%, Dorper=8.0%, Boer goat=2.9%, Indigenous goat=1.6% 

2 Meat and bone yield expressed as % of carcass weight at a constant subcutaneous level (or carcass fat code). Weights of neck, shoulder, dorsal, ventral and leg cuts expressed relative to carcass weight.

3 Yields of these tissues expressed relative to total weights of the specific tissue in the carcass (e.g. 33% of all the meat in the Damara carcass was distributed in the leg cut)

(*) Means for two breeds within the specie (goat or sheep) differ significantly (P<0.05). Means were not compared statistically between species (goat and sheep)

While there were relatively large differences in certain meat quality characteristics between the goat and sheep breeds, differences within the two sheep breeds were small and statistically non-significant. For most of the attributes, mutton had significantly more favourable scores than goat meat (i.e. if high intensity of goaty flavour is regarded as less favourable). As expected mutton aroma and flavour intensity scores were higher and goaty flavour and aroma intensity scores lower for sheep meat than for goat meat in general. In addition, overall tenderness, chewiness, juiciness and greasiness scored significantly lower for goat meat than for sheep meat. Differences in carcass fatness could have contributed to these differences. Regarding goat meat, Boer goat meat had significantly higher scores for overall aroma intensity than meat from both sheep breeds and the Indigenous goat and was also more greasy and had a higher flavour intensity than the Indigenous goat meat.

Table 2: Means and standard error of means (SEM) for sensory meat quality characteristics 
of two goat and two sheep breeds (n=10 animals per breed)

Trait Damara Dorper Boer Goat Indigenous Goat Sem
Overall aroma intensity 7.1b 6.9b 7.6a 7.0b 0.32
Goaty aroma intensity 1.3a 1.6a 6.4b 5.6b 0.26
Mutton aroma intensity 6.1a 5.7a 1.3b 1.3b 0.22
Overall tenderness 6.8c 6.5c 4.0b 3.3a 0.16
Chewiness 6.4a 6.0a 3.7b 2.7b 0.22
Juiciness 6.7c 6.4c 4.2b 3.7a 0.23
Greasiness 6.2c 5.8c 3.7b 2.6a 0.17
Overall flavour intensity 6.9c 6.8bc 6.5b 6.0a 0.10
Goaty flavour intensity 1.5a 1.5a 5.8b 5.2b 0.23
Mutton flavour intensity 5.9a 5.5a 1.3b 1.3b 0.22

abc Means on the same row with different superscripts differ significantly (P<0.05) Scores were between 1 and 8 where 1 indicates meat with an extremely low aroma and flavour intensity (also goat and mutton aroma), extremely low in tenderness, extremely dry, extremely abundant in connective tissue (chewiness), extremely low in perception of fat release in the mouth during mastication. A score of 8 indicates meat with an extremely high aroma and flavour intensity (also goat and mutton aroma), extremely high in tenderness, extremely juicy, devoid of residual connective tissue (chewiness), extremely high in perception of fat release in the mouth during mastication.

Although the fatty acid profile is incomplete, the saturated fatty acid content of all species is slightly higher than the unsaturated fatty acid content, which was expected of meat (Table 3). Recently, it has become clear that Western diets have an imbalance between n-6 and n-3 poly-unsaturated fatty acids (PUFA), with n-6:n-3 averaging around 10 instead of below 5. Grass fed ruminant meat has a beneficially low n-6:n-3 according to Sanudo et al. (2000). Damara meat had the highest level of unsaturated fatty acid (UFA) of all three species, which was also reflected in a higher C18: PUFA(n-3) content which is favourable. It has to be kept in mind that this is only a tendency, and it cannot be stated with certainty that this is to the advantage of the Damara because the n-6 fatty acids (C18:2) were not determined to confirm a favourable n-6/n-3 ratio. There was a slight difference in mutton flavour between the Dorper and the Damara, which coincide with the difference in n-3 fatty acids, but due to the magnitude of the differences, this relationship is inconclusive.

Table 3: Limited fatty acid profile of meat (muscle and fat combined) of two goat and two sheep breeds (n=12 animals per breed)

Trait Damara Dorper Boer Goat Indigenous Goat
C13:0 2.7 2.97 3.93 4.89
C14:0 7.48 8.38 6.34 5.96
C15:0 0.63 0.59 0.66 0.77
C16:0 22.95 24.31 21.22 19.66
C16.1 3.50 3.98 3.34 3.17
C17:0 2.15 2.09 2.24 2.34
C18:0 16.10 14.41 2.42 19.99
C18:1 38.55 37.55 36.57 37.75
C18.3 3.92 3.25 3.44 3.85
C20:1 2.04 2.24 1.85 1.67
SFA 51.94 52.82 54.80 53.59
UFA 48.06 47.18 45.20 46.41
MUFA 44.13 43.92 41.76 42.57
PUFA 3.93 3.26 3.44 3.85

SFA: Saturated fatty acid – C13:0, C14:0, C15:0, C16:0, C17:0, C18:O

MUFA: Monounsaturated fatty acids – C16:1, C18:1, C20:1

PUFA: Poly-unsaturated fatty acid – C18:3

Conclusion

Under the conditions of this trial and within the limitations of the protocol (i.e. feeding regime was not controlled although animals came from the same region), the two sheep breeds and the two goat breeds were very similar in carcass and meat quality, while differences between species were quite significant. Within both species the breeds with larger carcasses (Dorper and Boer goat) also had higher proportions of meat relative to bone. Statistically significant differences in carcass proportion were found between breeds (within species) although the magnitude of the differences may or may not have commercial impact depending on the processing of the carcass.