The aim of the present study was to compare the chemical composition and
fatty acid (FA) content of the muscle tissues of lambs and adult sheep bred
for meat production. Throughout the research period, the animals were
managed in a confinement indoor system under uniform environmental
conditions. After slaughter, meat samples collected from the musculus biceps femoris were used to
determine the basic chemical composition and fatty acid content in the
intramuscular fat. The analyses showed that, compared to lambs, meat from
adult animals exhibited a more beneficial ratio of n-6 to n-3 FAs, as well as
a favorable percentage of OFAs (dietary fatty acids having an
undesirable hypercholesterolemic effect on humans). The results of this
study support the inclusion of dietitian-recommended mutton into the human
diet and the promotion of the production of meat from adult animals as a
high-value product. The sheep industry could benefit economically,
particularly in countries where this meat type has not enjoyed a high
standing in consumer preferences.
Introduction
Diet-related diseases are considered one of the leading causes of mortality
in western European countries and the USA. These diseases are directly
linked to the advancing development of contemporary civilization, and, as
hazard scales indicate, they afflict approximately 50 %–60 % of the adult
population in these countries. Notably, diet-related diseases are generally
nonexistent or rare in hunter–gatherer societies, in which the nutritional
patterns differ markedly from those of westernized cultures (Cordain et al.,
2005). Increasing societal wealth is a major determinant of increased meat
consumption and associated meat production (Speedy, 2003). Kourlaba and
Panagiotakos (2009) thus suggest that research should focus on the
development of dietary guidelines centered on the primary prevention of
lifestyle-related diseases that can impose a substantial burden on
society.
One of the major factors associated with increased risk of lifestyle-related
diseases is a high intake of saturated fatty acids (SFAs), which can
increase levels of blood cholesterol and, as has been well established,
contribute to atherosclerotic growth. A report by the FAO/WHO concluded that
dietary replacement of SFAs with polyunsaturated fatty acids (PUFAs)
decreases the risk of coronary heart disease (FAO, 2010). According to the
recommendations of dietitians and physicians, meat can be considered a
healthy food if it is low in fat with an appropriate fatty acid (FA) profile. It is vital
that both n-3 and n-6 FAs are present in meat at sufficient levels.
However, research has shown that the n-6 / n-3 FA ratio is 15/1 to 16.7/1 in
the typical western diet, leading to increased incidences of a number of
lifestyle-related diseases. Importantly, a lower n-6 / n-3 FA ratio can reduce
the risk of these diseases (Simopoulos, 2008), particularly cardiovascular
disease (Nestel et al., 2015; Wen et al., 2014; Endo and Arita, 2016),
cancer, and respiratory diseases (Simopoulos, 2008; Gold et al., 2016;
Rovito et al., 2015; Wiggins et al., 2015). FAs play critical roles in
immune response development and the transport of fat-soluble vitamins such
as vitamins D, E, and K (Webb and O'Neill, 2008). Although the vast majority
of scientific papers published to date have focused on PUFAs, the role of
other FAs should not be neglected. Recent reports have highlighted the vital
function of stearic acid in lowering the low-density lipoprotein (LDL)
cholesterol level, whereas until very recently this FA was considered a
thrombosis-promoting agent (Li et al., 2005; Hunter, 2010).
As meat production and consumption, including that of sheep meat, is
projected to continue growing (Speedy, 2003; OECD, 2015), special attention
should be paid to livestock product quality. It is necessary to determine
the nutritive value of each type of meat and identify the factors affecting
its chemical composition and, consequently, the quality of the consumed
food. Sheep are widely recognized as a good source of valuable, high-quality
meat. Research has confirmed that sheep meat is rich in many vitamins,
minerals, and essential PUFAs (Ponnampalam et al., 2016b). Nevertheless, in
the case of sheep, mutton (meat of adult animals) is frequently underrated
as a culinary product because of stereotypes associated with it. Consumer
unwillingness to consume mutton is likely due to its excessive fattiness,
which is frequently associated with inferior sensory attributes. Pethick et
al. (2005) reported similar findings that confirmed the higher palatability
of lamb. However, they stated that the aversion of customers to so-called
“mutton flavor” is virtually insignificant if the content of back fat and
intramuscular fat (marbling) is reduced. According to the present authors,
this undervalued meat deserves far more attention, especially considering the
marked and significant reductions in animal fattiness in recent years and the
increasing importance of the production of sheep as meat sources. Obviously,
selective breeding of sheep for meat production has affected the chemical
composition of the obtained meat. Taking into account the fact that product
quality is rapidly becoming a chief consumer concern, comparative studies
are needed that focus on the chemical composition and profile of FA content in
the muscle tissues of lambs and adult sheep bred for meat production. The
research results can be helpful for promoting the consumption of meat from
adult animals as a high-value product, which should consequently improve the
profitability of sheep production.
The aim of the present study was to compare the chemical composition and
fatty acid content of the muscle tissues of lambs and adult sheep bred
for meat production.
Materials and methods
The study was conducted at Bezek research station, a part of the University
of Life Sciences in Lublin, located in southeastern Poland. The farm houses
550 ewes in an indoor pasture system. Lambing occurred in January, and the
lambs remained with their ewes in the sheep house throughout the rearing
period.
The experiment was carried out in such a way that normal daily activities on the
farm were not disturbed, but it was ensured that all the conditions for the
care of the animals were in line with the standards recommended in the Guide for
the Care and Use of Laboratory Animals, Directive 2010/63/EU and Directive
1998/58/EU. This study did not require ethical consent because all the
procedures were breeding procedures. The study was carried out when selling animals to the slaughterhouse, which is a standard procedure in animal breeding. Samples constituting the commercial product of a
commercial slaughterhouse were bought for chemical analysis. At the
same time, the authors declare that all animals kept in the herd were under the
constant control of the advisory team for animal welfare of the Faculty of
Animal Breeding and Bioeconomy of the University of Life Sciences in Lublin.
Animal material
The study involved 30 animals of the synthetic prolific meat line SCP (15 adult ewes and 15 lambs). The synthetic prolific meat line is composed of the
following sheep breeds: Polish Lowland, 37.5 %; Romanowska, 12.5 %;
Suffolk, 25.0 %; and Charolaise, 25.0 %. Throughout the research period,
the animals were managed in the confinement housing system (indoors) under
uniform environmental conditions. Both ewes and their progeny were housed in
the same flock and building from birth until slaughter. During the
experiment, the animals were fed feed available at the farm in the doses
presented in Table 1. All of the lambs included in the study came from twin
births and remained with the ewes over the entire study period.
Approximate feed ration used for ewes and offspring (kg).
January February March April EwesLambsEwesLambsEwesLambsEwesLambsMother's milkad libitumad libitumad libitumad libitumCrushed oats0.40.50.030.50.20.50.25Bran0.030.20.25Dried sugar-beet pulp0.020.050.05Rape seed meal extract0.050.050.050.05Soybean meal0.020.02Hay0.80.80.10.80.20.80.2Green silage2.52.52.50.82.50.8Evaluation of slaughtered animals
After the lamb rearing period, both ewes and their offspring were
slaughtered. The age at slaughter was similar in both groups (i.e., lambs
100±4 d and ewes 6 years; for the past 20 years, lambing occurred in
January at the research station, so the difference in ewe age was 24 d).
Animal slaughter was performed on the same day.
The resulting animal carcasses were evaluated according to the SEUROP scale
(S – 6, E – 5, U – 4, R – 3, O – 2, P – 1) and then chilled at 4 ∘C for 24 h.
Chemical analysis of muscle tissue
Meat samples collected from the musculus biceps femoris (MBF) were examined to determine the basic
chemical composition and FA profile of the intramuscular fat. All chemical
determinations were carried out in the approved laboratory.
Analysis of basic chemical composition of muscle and determination of
caloric value
Each sample (approximately 250 g in weight) was placed in a sterile, tightly
closed Ziplock-type bag and stored under the same cooling conditions. The
analysis of the basic chemical composition (water, dry matter, fat, and
collagen content) was performed using near-infrared (NIR) spectroscopy. The
meat specimens (200 g) were homogenized with a cutter mixer (model K 35;
DITO Electrolux) and transferred to a cuvette FoodScan™
analyzer operated in NIR transmission mode in the region of 850–1050 nm and
equipped with a calibration artificial neural network (model developed using
artificial neural networks) according to norm PN-A-82109:2010.
On the basis of the results obtained with norm PN-A-79011-6:1998, meat
caloric values were calculated using Atwater factors. Total ash content
was established using a gravimetric method according to norm PN-ISO 936:2000
including drying, charring, and final incineration at 550±25∘C. After cooling, the residue mass was determined.
Analysis of FA content
The FA profile was established using the intramuscular fat. FA methyl esters
were determined according to the guidelines specified in PN-ISO 5509:1996,
whereas FA composition was determined by gas chromatography using a
Hewlett-Packard 6890 (Agilent Technologies) instrument equipped with a
flame ionization detector and a highly polarized BPX70 column. The column
used was 60 m × 0.25 mm i.d. ×0.25µm film
thickness. The BPX70 column oven program was as follows: 100 ∘C for 0.5 min,
temperature program at 20 ∘C min-1 to 130 ∘C, hold
isothermally for 2 min, temperature program at 1 ∘C min-1 to 150 ∘C, hold isothermally for 3 min, temperature program at 3 ∘C min-1 to 220 ∘C, and hold isothermally for 6 min.
FAs were identified by the comparison of retention times with those of the
standard mixture FAME (Supelco 37 Component FAME Mix and C18 FAME isomers;
Sigma-Aldrich Co.).
Statistical analysis
The results were analyzed statistically using the one-way multivariate analysis
of variance (ANOVA) and the Statistica data analysis software system version 13
(Dell Inc., 2016). The experimental factor analyzed was the type of meat (i.e., mutton, lamb).
Results
The assessment results of dressing percentage and lamb carcass conformation
and fatness using the SEUROP classification are important for potential
customers (Table 2). Dressing percentage of adult sheep was 3.69 percentage
points higher than that of lambs, whereas SEUROP classification showed a 0.2 point higher lamb score compared to adult carcasses. In the case of
fatness, the tendency was opposite. Carcasses of adult sheep obtained a
higher fatness rating by 0.06 points.
The chemical composition of food products significantly affects their
quality. The results from the analysis of the basic chemical composition of the meat of mature ewes and lambs are presented in Table 3. A higher fat content
in the MBF was noted in adult sheep. The intramuscular fat percentage
determined was 1.5 times higher in the mature animal muscle tissues
compared to lamb meat (P≤0.01). However, an inverse relationship was
observed for the percent of protein content in the analyzed muscle. The values
obtained for adult ewes were at 18.96 % versus 20.73 % for lamb
meat (P≤0.001). The analysis of meat caloric value did not show any
statistically significant difference between lamb meat and mutton.
Quality traits of ewe and lamb musculus biceps femoris meat.
The level of human dietary FA intake is considered critical; therefore, the
amount of each FA and their group (Tables 4 and 5) were determined using 100 g of meat (mg per 100 g of meat). In almost all cases, a higher FA content in the
MBF was noted in adult sheep. Exceptions were acids from C10:0 to
C14:0 and C20:3 n-6 (Table 4). It is worth
noting that the muscles of sheep mothers showed an approximately 1.4 times
higher content of C16:0 FA compared to their progeny (P≤0.001). The same significant difference was observed for C18:3 n-6
and C18:3 n-3 acids. In the case of C18:3 n-6 acids, the values
obtained for adult ewes were 9.98 mg per 100 g of meat versus 5.15 mg per 100 g of meat
for lambs. The C18:3 n-3 FA content was 40.3 mg per 100 g of meat and 15.5 mg per 100 g of meat in ewes and lambs, respectively.
Fatty acid selected content (mg per 100 g muscle) of ewe and lamb musculus biceps femoris meat.
The content of nearly all of the acid groups differed significantly between
ewes and their offspring with the lone exception being OFAs (dietary fatty acids having an
undesirable hypercholesterolemic effect on humans) (Table 5).
Fatty acid group content (mg per 100 g muscle) of ewe and lamb
musculus biceps femoris meat.
*≤0.05. **≤0.01. ***≤0.001. ns: not significant. SFA: sum of all saturated fatty acids; MUFA: sum of all monounsaturated
fatty acids; UFA = PUFA + MUFA; OFA: dietary fatty acids having an undesirable
hypercholesterolemic effect
on humans (C14:0+ C16:0); DFA: dietary fatty acids having a desirable
neutral
hypocholesterolemic effect on humans (UFA + C18:0).
The dietetic value of meat depends to a great extent on the ratio UFA / SFA (UFA: unsaturated fatty acid),
as well as that between n-6 FAs and n-3 FAs (Fig. 1). A higher UFA / SFA
ratio was observed in mutton compared to lamb, whereas the n-6 FA / n-3 FA
ratio was almost 2-fold higher in lambs. In both cases, the differences were
statistically significant (P≤0.001).
Discussion
Diet is known to have a significant impact on human health. One current
concern relating to proper nutrition is the rise in the prevalence of
obesity as a consequence of excess caloric intake coupled with a lack of
caloric expenditure. The decline in caloric expenditure is the result of
decreased physical activity due to the widespread use of vehicles for
transportation, work automation, and a sedentary lifestyle (Behzad et al.,
2013). Considering the development of dietetic guidelines for different
population groups, one should keep in mind that fat also plays a major role
in proper nutrition, and FAs largely determine the health-promoting
properties of meat (Fisher et al., 2000). It is also worth noting that the
content of linolenic acid (LA) and alpha-linolenic acid (ALA) is a factor that limits its nutritive value
because, as discussed previously, humans lacks the enzymatic capacity to
synthesize LA n-6 FA and ALA n-3. In humans, LA and
ALA compete with each other for metabolism by the same enzyme,
delta-6 desaturase. It is important for human health as an LA intake that is too high decreases the amount of delta-6 desaturase available for ALA metabolism,
which increases the risk of cardiovascular diseases and especially
atherosclerosis.
UFA / SFA and n-6 / n-3 FA ratios of ewe and lamb musculus biceps femoris meat (mean ± SD). The asterisks indicate significance values ≤0.001.
A lower n-6 / n-3 FA ratio is desirable as a means of reducing the risk of a
number of chronic diseases of high prevalence in both western societies and
developing countries. As the present research has clearly demonstrated, the
n-6 / n-3 FA ratio is markedly more beneficial in the meat of mature sheep as
it was almost 2-fold higher compared to lamb's meat. Simopoulos (2008)
reported that an elevated n-3 FA level has a suppressive effect on many
diseases (e.g., a ratio of 4/1 is associated with a 70 % decrease in total
mortality due to cardiovascular diseases, whereas a ratio of 2.5/1 reduces
rectal cell proliferation in patients with colorectal cancer). Similarly, a
lower dietary n-6 / n-3 ratio has been linked to a decreased risk of breast
cancer in women. Notably, the ratio of these FAs determined in mutton was
in compliance with dietary guidelines recommended by dietitians. Therefore,
it is advisable to prioritize this information while promoting and marketing
this type of meat. Benefits of a good n-6 / n-3 FA ratio in sheep fat were
highlighted by Peng et al. (2010), who determined the FA content in back
fat, perineal, and tail-fat tissues. Although they obtained lower ratios,
this result could be attributed to the nutritional strategy applied. The
n-6 / n-3 FA ratio established in the meat from adult animals in the present
study was slightly lower than that determined for wild animal meat.
Importantly, the meat from free-range animals is frequently recommended by
doctors and dietitians with regard to a beneficial FA content. While
analyzing the research results obtained in the present study, it should be
noted that similar findings pertaining to the ratio of n-6 to n-3 FAs were
reported for the meat of roe deer hunted in Germany. Like mutton, the FA ratio
was more favorable in older animals and ranged between 2.4 and 2.6 versus
2.4 to 4.3 in juveniles (Dannenberger et al., 2013). Research indicates that
the ratio of n6 to n3 FAs depends mainly on nutrition. Several studies have
reported ratios in the range of 1.85 to 11.4 (Santos-Silva et al., 2002;
Jerónimo et al., 2009; Ponnampalam et al., 2009; Abuelfatah et al.,
2014). The reason for the higher ratio in lambs in this experiment is the
use of soybean meal in feeding. Mele et al. (2007) reported that soybean
meal has a significant impact on the n-6 / n-3 ratio. In farmed roe deer, in contrast, the n-6 / n-3 ratio is very close to that determined in the present
research on sheep meat (Phillip et al., 2007).
Another argument in favor of promoting the consumption of meat from adult
animals as a health-promoting food is the beneficial profile of OFAs
(C14:0+ C16:0). Admittedly, the analysis of OFA content
(mg per 100 g meat) in the present study revealed higher levels in the MBF of adult ewes, but the calculated differences were not significant. Therefore,
a lower fat content in the muscle tissue should help improve the values
discussed. It is worth noting that mutton was found to have both a higher
stearic acid (C18:0) profile and muscle content, which seems
beneficial in light of studies confirming the role of this acid in reducing
LDL cholesterol levels and decreasing coagulation factor VII activity (Li et
al., 2005; Hunter, 2010).
The present study found significant differences between the profiles and
contents of particular FAs in the meat from adult ewes and lambs. These
differences appear to be markedly affected by animal age and dietary
factors, which, despite the fact that the animals were housed under the same
conditions, must have exerted a substantial influence as the lambs were
nursed by the ewes until 100 d of age. The influence of the
aforementioned factors on FA profile and content has been confirmed in many
other studies (Watkins et al., 2010; D'Alessandro et al., 2015; Ponnampalam
et al., 2016a).
One of the objectives of the present research was to determine the dietetic
value of sheep meat. It should be noted that in contrast to the meat from
mature sheep, the dietetic value of lamb meat has received substantial
attention in the research literature and in studies conducted recently (Sun
et al., 2015; Janiszewski et al., 2016; Oliveira et al., 2016). Contrary to
lamb meat, only a few scientific studies examining the meat from adult sheep
have been published, and, according to the authors of those studies, this
meat is of high dietetic and culinary value. In a number of countries, the
meat from adult sheep is regarded as being fully equal to any other meat and is used
widely (Peng et al., 2010; Ponnampalam et al., 2016a).
The present research found a higher fat content in ewe meat compared
to lamb meat. The crucial finding of this study is the lack of
statistically significant differences between the caloric content of the meat of
mature sheep and lambs. The higher caloric value of mutton resulted
primarily from the higher fat level in the MBF. The lack of confirmed
significant differences along with the calculated standard deviations
indicate the differentiation of this trait between the two groups.
Noteworthy are the results of the SEUROP assessment, which indicate moderate
carcass fat content assessed during the SEUROP classification in both lambs
and adult sheep. This is especially relevant for adult sheep whose
excessive fattiness is likely to be the primary reason for consumers' unwillingness to consume it (Johansen et al., 2006). It is of
primary importance in the ongoing promotion of lamb meat especially since, as
Bock and Connely (2008) report, consumers will willingly pay more for
higher-quality premium products.
Meat market preferences for adult animal meat may be linked to price, which
is usually lower compared to the meat of younger animals. As Font-i-Furnols
et al. (2011) reported, consumers consider meat price the major factor
affecting purchase decision-making and not, as might be expected, the
feeding and housing system used. Interestingly, meat price has a greater
effect when considering the buying behavior of men versus women. The
desirable dietetic qualities of mutton confirmed in the present study,
coupled with reasonable mutton price (which is lower than that of lamb),
could contribute to a change in consumer perception (in Europe) of mutton as
a meat of inferior quality.
Conclusions
The meat from adult animals exhibits a more beneficial ratio of n-6 FA to
n-3 FAs compared to lamb meat, as well as a favorable percentage of
OFAs (dietary fatty acids with undesirable hypercholesterolemic effects on
humans). The results reported here should serve as the basis for the
inclusion of dietitian-recommended mutton in the human diet and consequently should
promote the consumption of meat from adult animals as a high-value product.
Finally, the economics of the sheep industry could improve, particularly in
countries where this meat type has not enjoyed a high standing in consumer
preferences.
Data availability
The original data are available upon request to the
corresponding author.
Author contributions
AJ designed the concept and research, analyzed and interpreted the data, and wrote the article. PN designed the concept and research, collected, analyzed, and interpreted the data and wrote the article. MM collected, analyzed, and interpreted the data and did a critical review of the article. PB collected data and approved the final version of the article. KB collected data and approved the final version of the article.
Competing interests
The authors declare that they have no conflict of interest.
Acknowledgements
The paper was supported by the project “The uses and the conservation of farm animal genetic resources under sustainable development” co-financed by the National Centre for Research and Development within the framework of the strategic R&D program “Environment, agriculture and forestry” – BIOSTRATEG, contract
number BIOSTRATEG2/297267/14/NCBR/2016.
We thank David Robinette Ph.D. from ScienceDocs Inc. for language editing.
Financial support
This research has been supported by the “The uses and the conservation of farm animal genetic resources under sustainable development” co-financed by the National Centre for Research and Development within the framework of the strategic R&D program “Environment, agriculture and forestry” (grant no. BIOSTRATEG2/297267/14/NCBR/2016).
Review statement
This paper was edited by Steffen Maak and reviewed by two anonymous referees.
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