Carcass and Lean Quality Characterization of the Autochthonous Goats in the Semi-arid Zone of North-western Nigeria
The experiment was conducted with the aim of investigating effects of breed and age on carcass and lean quality characteristics of goats in the study area. To achieve the aim, a total of 32 intact bucks, matching condition score 3 of the Australian Standard for Live Goat Evaluation were balanced for weight across 8 replicates of 2 breeds (Sokoto Red and Sahel) and 2 age treatments (Young and Mature). Animals were bled by slashing their throats to sever the jugular, the carotid, the trachea and the oesophagus. After bleeding, the animals were partially skinned lying on their backs on the floor. Thereafter, the animals were suspended by the hind legs on a 14 cm wide gambrel for further skinning. The head was removed at the atlanto-occipital joint and the fore and hind feet removed at the carpal and tarsal joints respectively. Breed had no effect (p>0.05) on any of the traits investigated. Also, feathering, flank streaking and marbling were not affected by age (p>0.05). However, mature goats recorded significantly higher values (1.438, 1.625, 1.750, 1.812 and 1.625) for flank firmness, kidney fat score, subcutaneous fat score, lean texture and lean firmness respectively. Corresponding figures for young animals were 1.062, 1.125, 1.062, 1.000 and 1.188. It was observed that goats in the study area have poor carcass fat deposition.
Received: April 20, 2013;
Accepted: May 24, 2013;
Published: October 29, 2013
The potential of meat from indigenous goats in promoting the socio-economic
development of developing countries has been acknowledged (Devendra,
1980; Von Maydel and Spatz, 1981; Wilson,
1982). This, according to Griffin et al. (1992)
is especially in the area of nutrition and internal trade. The growing popularity
of goat meat worldwide will add value to this potential. A full realization
of this potential will require a system of quality assurance, or at least, some
form of grading of the commodity. Unfortunately, however, quality standards
have not been established in developing counties despite their share of over
95% of the global goat population, according to FAO (2005).
Pieces of information on quality traits of indigenous goats in developing countries
are limited (Tshabalala et al., 2003). The situation
might even be worse in the Semi-arid zone of North-western Nigeria, the region
that, according to the Nigerian Federal Department of Livestock
and Pest Control Services (1992), holds the greatest proportion of the Nigerian
national goat herd. Here, there is a virtual absence of information on goat
meat quality. The few researches on goat meat were on aspects of yield. The
present study will attempt to fill this research gap by characterizing the Sokoto
Red and Sahel goats for carcass and lean quality traits. The objective of the
study was to determine and compare quality traits on the carcass and lean of
Sokoto Red and Sahel goats as affected by age at slaughter.
MATERIALS AND METHODS
Experimental animals and design: A total of 32 intact bucks, matching
condition score 3 of the Australian Standard for Live Goat Evaluation
(ESMGPA, 2005) were balanced for weight across 8 replicates
of 2 breeds (Sokoto Red and Sahel) and 2 age treatments (Young and Mature).
Young goats were those with only milk teeth, 7-8 months of age and weighed 11-15
kg; while mature ones had one pair of permanent incisors, were about 13-15 months
old and weighed 17.5-25.5 kg. The animals were rested for 24 h during which
they were maintained on an ad libitum diet of 2:1 w/w mix of cowpea husk
and wheat offal prior to slaughter. Free access to water and mineral lick was
Slaughter operations: Animals were bled by slashing their throats to
sever the jugular, the carotid, the trachea and the oesophagus. After bleeding,
the animals were partially skinned lying on their backs on the floor. Thereafter,
the animals were suspended by the hind legs on a 14 cm wide gambrel for further
skinning. The head was removed at the atlanto-occipital joint and the fore and
hind feet removed at the carpal and tarsal joints respectively. Quartering,
jointing and tissue separation were carried out according to the standard methods
and procedures for goat carcass evaluation outlined by Colomer-Rocher
et al. (1987).
Data collection: Flank streaking, marbling, feathering, fat over eye,
kidney fat and subcutaneous fat were scored on a three-point heuristic scale
of increasing intensity, recommended by Colomer-Rocher et
al. (1987) for rating kidney fat (1 = little, 2 = medium, 3 = excessive).
Ratings of subcutaneous fat colour, (1 = white, 2 = cream, 3 = yellow) and colour
of Rectus abdominis (1 = pale, 2 = pink 3 = red) were also utilized from Colomer-Rocher
et al. (1987). Kidney fat was also excised and weighed. Flank firmness,
lean texture and lean firmness were scored on a three point scale of 1 = fine,
2 = medium, 3 = coarse for texture and 1 = soft, 2 = firm, 3 = very firm for
firmness. A nine banded colour chart using the HSL colour model of Microsoft
PowerPoint® (Microsoft Inc., 2007), was
developed to quantitatively assess lean colour. Hue and saturation were set
on the red band (255). The bands were labelled by sequential reduction of 20
luminosity units, starting at 220. Samples were scored for the luminosity of
the colour band that best match their colours and rated numerically.
The surface of the loin eye of the right halves of the carcass was used for the evaluation of all lean quality characteristics.
Data analyses: Data generated were analyzed as a Completely Randomized
Design with a factorial arrangement of treatments (breed, age) using the general
linear model programme of SPSS (IBM Corporation, 2007).
A fixed model involving the main effects of breed and age was utilized. Interactions
were excluded from the model as they were not found to be significant.
RESULTS AND DISCUSSION
Carcass quality indices: Carcass quality indices are presented in Table 1. Breed had no effect on any of the indices. On the other hand, age had significant effects but only on flank firmness, kidney fat score and subcutaneous fat score; with mature goats having higher values in all cases.
Feathering, marbling and flank streaking: Feathering, marbling and flank
streaking showed similar trends across breed and age. This was probably because
of the strong correlation among them (Forrest et al.,
Part of the explanation for this poor carcass fat development may be found
in the nature of goat management in the study area and the other part in the
nature of goats themselves. The goat management system in the study area is
predominately free ranging. This system is characterized by poor feed supplementation
and a higher degree of energy expenditure on the part of the animal, occasioned
by roaming about in search for food, conditions that will not allow for deposition
of carcass fat. Secondly, goats by nature deposit very little fat in the carcass
(Gaili et al., 1972; Naude
and Hofmeyr, 1981; Devendra, 1988a; Attwood,
2002). This or the combined effect of the two factors (management and species
peculiarity) might be responsible for the trends shown by these parameters.
Flank firmness: Differences in flank firmness rating due to breed were
not significant, but significant differences were observed between mature and
young goats (1.438 and 1.062, respectively). The absence of breed effect on
flank firmness has earlier been reported (Johnson et
Carcasses of mature goats had firmer flanks than those of young (p<0.05).
This may appear unexpected owing to the assertion of Forrest
et al. (1975) that fat is a major contributor to carcasses firmness,
considering that the amounts of dissectible fat in both the flank and carcass
were not significantly different between young and mature goats. It is the opinion
in the present study that; while solidified fat in chilled carcasses may contribute
a lot to flank firmness (Forrest et al., 1975),
carcass fat may not play such an important role if carcasses were evaluated
hot as was the case in this experiment. Therefore, another factor will have
to be considered and this other factor may likely be the size of the muscle
|| Means and standard errors for fat-related carcass quality
|Means bearing different superscripts along the same row within
a subclass differ (p<0.05)
A possible explanation for the firmer flanks of mature goats may therefore
be their thicker muscle fibres. It is well documented that older goats have
thicker muscle fibres than young ones (Gaili et al.,
1972; Forrest et al., 1975). This view is
lent credence to, by the significantly coarser lean texture of mature goats,
as would be seen subsequently in this study. Lean texture itself is a measure
of muscle fibre size.
Kidney-and subcutaneous fats scores: Sokoto Red and Sahel goats had
similar ratings of subcutaneous and kidney fats, both of which were low. Low
subcutan cover appears to be a species characteristic of goats (Morand-Fehr,
1981; Devendra, 1988b) and because of that, any
difference between individuals of different breeds evaluated at similar age
should not be expected to be significant. Similarity in management system may
be another factor responsible for the similarity. This is because feeding exerts
a significant role in the accretion of adipose tissue (Morand-Fehr,
1981; Attwood, 2002) and both breeds happened to
be autochthonous to the study area and maintained under similar management conditions
of poor nutrition.
Mature goats rated higher in both kidney (1.625 against 1.125) and subcutaneous
(1.750 against 1.062) fat scores (p<0.05). This perhaps may be due to the
accumulation of fat in all depots occasioned by advancing age, as reported by
Gaili et al. (1972) and Morand-Fehr
Colours of subcutaneous fat and Rectus abdominis muscle: Across all
the sub-classes, mean rating for subcutaneous fat colour was 1.41, a figure
less than 2 indicting that the colour of subcutaneous fat was white. This finding
is in line with Ibarra (1988), who made a general observation
that fat colour in goat meat is chalk white. This generalization justifies the
absence of significant differences in subcutaneous fat colour rating between
and within the subclasses of the experimental animals.
There was also no variation in the colour rating of Rectus abdominis muscles
of the experimental animals for the simple reason that they all had the same
score (3) on the Colomer-Rocher et al. (1987)
scale. The score 3 signified the darkest red which tallies with the observation
of Ibarra (1988), that the colour of goat meat is brick
Lean quality indices: Table 2 represents the effects of breed and age on the lean quality indices of texture, firmness and colour. The effects of age on lean texture and lean firmness were significant. These apart, all other subclass-quality index combinations remain non-significant.
Lean texture: Lean texture, being a measure of muscle fibre size (Forrest
et al., 1975), expectedly rated higher (p<0.05) in mature than
in young goats (1.812 against 1.000), for the simple reason that growth in goats
and indeed in all animals, entails increases in thickness of muscle fibres (Gaili
et al., 1972; Forrest et al., 1975).
|| Means and standard errors for lean quality indices ratings
|Means bearing different superscripts along the same row within
a subclass differ (p<0.05)
This phenomenon allows for the muscles of mature animals to be coarser and
hence have a higher rating for lean texture than young animals.
Lean firmness: The absence of breed effect on lean firmness has been
reported by Johnson et al. (1995). The superiority
of mature goats in lean firmness (1.625 against 1.188) may be ascribed to their
possession of larger muscle fibres than young goats.
Lean colour: Mean lean colour did not differ within any of the subclasses
of breed and age (p>0.05). This phenomenon appears to be related to the apparent
species specificity of lean colour (Forrest et al.,
1975; Ibarra, 1988; Aduku and
Olukosi, 1991) which makes within species differences in colour hard to
detect, especially when appraisal is done visually as was the case in the present
The grand mean (124.38) obtained for the colour rating of lean represents HSL 255-255-124.38 which approximates the colour usually attributed to goat meat. Variations in mean colour rating within the age subclass are greater than that within breed. This shows that mature goats had (at least numerically) darker lean colour than young which is in line with the generally accepted trend of increasing darkening of lean with advancing age.
Carcasses of mature goats had firmer flanks and ranked higher for kidney and subcutaneous fat scores than carcasses of young goats. Meat from mature goats was also found to be firmer and of coarser texture than that from young animals.
The major findings of the study are as follows:
||Age is a more important factor determining quality of meat
from goats than breed. This was suggested by the greater number of variables
that were influenced by age
||Goat carcasses are poor in fat deposition as could be seen from the very
low rating and in some instances complete absence of some fat- related traits
||Fat needs not to feature as major consideration in goat carcass quality
||Goat meat could be of significant value as a source of healthy meat for
fat conscious individuals and communities
||The new meat colour evaluation technique developed in the course of this
study was found to be more sensitive and more responsive than the standard
method developed for the European Union by Colomer-Rocher
et al. (1987). The innovation could be improved by better scaling
Recommendation: Breed evaluation of goats for quality traits needs to be extended to cover the West African Dwarf goat which is not common in the study area, but together with the Sokoto Red and Sahel represent the dominant breeds of goats in Nigeria. Older animals which are not commonly slaughtered in the study area, need be investigated as well.
We sincerely thank Profs. W. Akin. Hassan, S. A. Maigandi and J. B. Adeyanju for supervising the project and Usmanu Danfodiyo University, Sokoto, Nigeria for partly funding the project.
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