The aim of the study was to evaluate the growth, body and ultrasonic
measurements and some carcass traits of purebred Ramlıç, Texel and
crossbred (87.5 % Ramlıç and 12.5 % Texel) lambs in a marker-assisted introgression (MAI) project. The effects of some environmental
factors such as genotype, sex, birth type, dam age, weaning age, and birth
weight on growth, ultrasound measurements, and carcass traits were
significant (P<0.05). There were no significant differences
between pure Ramlıç and its myostatin carrier (+/-) and non-carrier
(-/-) second backcrosses (BC2) for birth weight, daily live weight
gain, and weaning weight. The BC2 genotype (+/-) was statistically
caught up with pure Ramlıç for wither height, body length, and rump
width. Differences in the longissimus muscle depth indicated that the
BC2 (+/-) genotypes tended to be better for both pure Ramlıç
and Texel lambs. Texel lambs were superior to Ramlıç in the aspect of
some carcass characteristics such as leg length, cold right-half carcass
weight, foreleg weight in the left-half carcass, and muscle weight in the
left leg. BC2 (+/-) lambs were in the middle of both breeds
for the traits. BC2 lambs carrying myostatin did not vary from Ramlıç morphologically. The new type of Ramlıç was also closer to Texel
in the aspect of carcass characteristics. In this connection, improvement of
indigenous breeds could be achieved by MAI without changing the essential
characteristics. For the summary, please visit http://www.mustafatekerli.com (last access: 14 June 2022).
Introduction
Türkiye, with a population of 45 million heads of sheep, is a leading country
in Europe. Increasing population and industrialization caused an intense
demand for meat production in the country. However, boosting the number of
sheep would not be sufficient for highly priced carcass parts and a
profitable income. Urbanization and diminishing pastures require the use of
technology in the sheep industry. In recent years, great activities on
crossbreeding including molecular techniques have been emphasized for more
production in livestock breeds. Marker-assisted introgression (MAI) may take
place in the sheep industry to develop the characteristics of meat. Texel is
one of the most known muscled sheep breeds. The single nucleotide
polymorphism (g+6723G > A) found in the 3′UTR region of GDF8
gene in Texel sheep which is known as myostatin was reported to cause
superior muscularity (Clop et al., 2006; Çelikeloğlu et al., 2021;
Grasset et al., 2009; Johnson et al., 2005; Yalçın et al., 1978;
Yayvan and Özkul, 2018). This mutation accelerates growth and increases
muscularity in Texel and does not have a negative effect on the eating
quality and intramuscular fat of the loin (Kijas et al., 2007). An
introgression project was initiated to give a new dimension to Ramlıç's meat quality and quantity through the integration of the Texel myostatin
mutation (g+6723G > A). The detailed introductory information
and F1 and first backcross (BC1)-related results were articulated
in our previous paper (Çelikeloğlu et al., 2022).
The study aims to evaluate the influence of myostatin mutation (g+6723G > A) on morphometric and post-slaughter characteristics of
BC2 genotype in comparison with Ramlıç and Texel pure lambs.
Materials and methods
The animals were used in compliance with the rules of experimental animals
ethical committee in Afyon Kocatepe University (decision no. 49533702-26). A
total of 103 pure Ramlıç ewes (-/-) were mated with 24 BC1
(+/-) ram lambs by flock mating to obtain more lambs carrying myostatin
mutation, and 118 BC2 (12.5 % Texel, 87.5 % Ramlıç) lambs
were produced. Ramlıç and Texel contemporary lambs whose parents were
checked for myostatin mutation were used for comparisons. All lambs were
weighed at birth with a 10 g precision weighbridge in the first 24 h.
The lambs were approximately weaned at 120 d of age and weighed with a 50 g precision on a platform scale. The wither height, body length, chest
circumference, and rump width were taken with a sheep-type measurement
stick, calliper, and tape (Hauptner and Herberholz, Germany) at the same
time. The depth and area of musculus longissimus dorsi (MLD) and backfat thickness were measured by
real-time ultrasound. The processes of introgression of myostatin mutation
from Texel to Ramlıç sheep and genotyping methods of second backcross
lambs (53 female and 61 male) were as described in the first paper of the
project (Çelikeloğlu et al., 2022).
Eighteen ram lambs with the Ramlıç, BC2 (+/-) and Texel
genotypes (six lambs each) were slaughtered in a commercial slaughterhouse
at the age of about 6 months and with no statistical difference between
pre-slaughter weights. Hot carcass, head, foot, skin, heart and lung, full
and empty gastrointestinal tract, liver, spleen, kidney, and kidney fat were
weighed, and then carcasses were chilled at +4 ∘C for 24 h.
The pH and color parameters (L*, a*, b*) of longissimus muscle were measured at the 1st
and 24th hours after slaughter using a pH meter (WTW Multi 3410) and
Chroma Meter (Konica Minolta CR-400).
Empty body weights (EBWs) of lambs were calculated after subtracting
gastrointestinal content from pre-slaughter weight (PSW). Commercial
dressing percentage (based on pre-slaughter live weight) and real dressing
percentage (based on empty body weight) were calculated. After carcass
splitting in two symmetric parts along the vertebra, cold half carcass
weights (CHCWs) were recorded, and the left-half side was jointed into seven
anatomical parts as described by Colomer Rocher et al. (1988): shoulder,
flank, leg, neck, anterior rib, loin ribs, and tail. Each joint was weighed.
The legs of lambs were dissected to divide muscle, fat, and bone and then
weighed. Internal carcass length (first rib to anterior symphysis pubis),
external carcass length (atlas to tail), chest depth (sternum to sixth
thoracic vertebrae), shoulder width (distance between tubercle of the
humerus), rump width (distance between tubercle of coxae), and leg lengths
(1, anterior symphysis pubis to art. tarsometatarsal; 2, perineum to art.
tarsometatarsal) were determined on the right-half carcass by using
a tape measure (Figs. 1, 2).
The linear models including fixed effects of genotype, sex, birth type,
month of birth, age of dam, weaning age, and weight were used to describe
the collected data for growth traits and carcass characteristics by general linear model (GLM)
procedure of MINITAB 18 software. All two- and three-way interactions were
excluded from the models due to insufficient data in subgroups. The Tukey
procedure was used for multiple comparisons.
Results
Table 1 shows the least-squares means and standard errors of growth and
pre-slaughter carcass traits. The effect of genotype was statistically
significant (P<0.001) for all the traits except the MLD area and
backfat thickness. The least-squares means and standard errors for
post-slaughter carcass traits, pH and color parameters, and carcass
measurements are presented in Tables 2 and 3. The commercial and real dressing
percentages, pH and a* in first hour, external and internal carcass
length, and leg lengths (1 and 2) were significantly (P<0.05)
affected by genotype. In addition, the influences of genotype were also
significant (P<0.05) on weights of half carcass and shoulder, bone
and muscle weight in leg, bone and muscle ratio in the leg, weights of foot,
tail, and liver.
Least-squares means and standard errors for growth traits and
pre-slaughter carcass traits at weaning in contemporary Ramlıç,
BC2 (-/-), BC2 (+/-) and Texel lambs.
‡: P<0.10; *: P<0.05; **: P<0.01;
***: P<0.001.
abc: means with different superscripts in each line are significantly
different (P<0.05).
Discussion
In this study, the effect of genotypes on birth weight was found to be
significant (P<0.001), and the birth weights of Ramlıç lambs
were in the range of 4.0 and 4.95 kg reported by different researchers
(Bromley et al., 2000; Ceyhan et al., 2010; Demir, 1995; Fıçıcı,
2015; Hultz et al., 1935; Kaymakçı et al., 1999; Omar et al., 1992;
Yalçın, 1982; Yalçın et al., 1978) in Ramlıç, Rambouillet
and crosses. BC2 (+/-) lambs tended to be heavier than the other
genotypes at birth in this study. The mean birth weight of this genotype was
higher than in the literature as well (Ceyhan et al., 2010; Demir, 1995; Fıçıcı, 2015; Yalçın, 1982; Yalçın et al., 1978). The
introgression of the new myostatin allele into the gene pool of the Ramlıç breed may have resulted in higher weights at birth. A similar
trend supporting our findings was observed by Han et al. (2010) and
Farhadian et al. (2012). The birth weight (4.085 kg) of Texel lambs in the
study was in the range of 3.70–5.00 kg reported for pure Texel and crosses
(Estevá and Picard, 1989; Khusro et al., 2005; Koritiaki et al., 2013;
Maxa et al., 2005; Wuliji et al., 1995). The birth weight of Texel lambs was
significantly (P<0.05) lower than the other genotypes in the
study.
The average daily gain (ADG) of BC2 lambs was in the middle of Ramlıç and Texel (P<0.05). ADG in Ramlıç and crosses were
found within the limits of 0.127–0.360 kg determined by different
researchers (TAGEM, 2009; Bromley et al., 2000; Hultz et al., 1935;
Jackson et al., 1997; Omar and Glafiro, 1995). The finding of the current
study for Texel was just behind the 0.190–0.318 kg reported by different
researchers (Ali, 1999; de Vargas Junior et al., 2014; Maxa et al., 2005).
The differences may have resulted from the conditions of the farm operation,
weaning ages, and statistical model.
Least-squares means and standard errors for post-slaughter carcass
characteristics, pH and color parameters and carcass measurements of Ramlıç, BC2 (+/-) and Texel lambs.
‡: P<0.10; *: P<0.05; **: P<0.01;
***: P<0.001.
abc: Means with different superscripts in each line are significantly
different (P<0.05).
The mean weaning weights of Ramlıç and BC2 lambs were
significantly (P<0.05) higher than that of Texel lambs and not
significant from each other. The findings for Ramlıç and BC2
lambs were also higher than the results of the literature (Demir, 1995,
1989a; Fıçıcı, 2015; Yalçın, 1982; Yalçın et al.,
1978). It is also closely similar with the range of 32.7–36.4 kg reported
by Bromley et al. (2000) in Columbia, Polypay, Rambouillet, and Targhee
breeds. Some researchers (Khusro et al., 2005; McEwan et al., 1988;
McMillan et al., 1988; Wuliji et al., 1995) reported that the weaning
weights for pure Texel and its crosses were between 20.9 and 34.42 kg. The
mean weaning weight of 26.09 kg for Texel in the current study was in the
range of the above literature.
No scientific reports were published for body and ultrasound MLD
measurements of Ramlıç lambs at weaning. These are the first findings
in the breed so far. BC2 lambs attained the level of pure Ramlıç
lambs in all body measurements. Wolf and Jones (2007) have reported that the
body length, wither height, chest circumference, and rump width of British
Texel lambs aged 140 d were 58.0, 55.8, 80.9, and 24.6 cm, respectively.
These findings are closely similar to our results except for rump width. The
chest circumference of Texel crosses was found to be 61.6 cm by Koritiaki et
al. (2013), and this value was lower than that of our study. The results of
the current study showed that the longissimus muscle depth of BC2
(+/-) lambs was higher than the Ramlıç and Texel lambs. Likewise,
Kijas et al. (2007) and Masri et al. (2011) were found that myostatin
carrier lambs had deeper and larger longissimus than non-carriers. On the
other hand, the result of Johnson et al. (2009) for longissimus depth was
not in agreement with us and the above literature. Milerski et al. (2006)
and Štolc et al. (2014) reported that mean muscle depth was between
20.71 and 26.18 mm in Texel lambs at approximately 100 d of age. Wolf and
Jones (2007) found ultrasonic MLD depth of 27.5 mm at the age of 140 d in
British Texels. These results were consonant with the findings of the
current research.
The slaughter was carried out at the end of the research. The highest
commercial and real dressing percentages were observed in Texel lambs. The
differences between Ramlıç and BC2 (+/-) genotypes were not
significant in these traits. Johnson et al. (2009) and Masri et al. (2011)
reported similar nonsignificant differences in a single-copy myostatin
carrier and noncarrier lambs. Some non-carcass traits such as head, skin,
foot, and visceral organ weights remained higher in BC2 lambs. This can
be the reason for higher dressing percentages in Texel lambs. When the
ultimate (24 h) pH and meat color (L*, a*, and b*) parameters were examined,
there were no significant differences among the genotypes. Blasco et al. (2019) deduced that the same production and slaughterhouse conditions and
similar pH values might partially explain the lack of differences in the
color of meat. This is consistent with the findings of the current study.
The differences in external and internal carcass lengths for genotypes were
found to be significant (P<0.05). External carcass length in pure
Ramlıç lambs was 1.410 and 6.800 cm longer than BC2 (+/-) and
Texel lambs. The same values were 0.023 and 2.886 cm for internal carcass
length. No significant differences were found between Ramlıç and
BC2 lambs, but there was a shortening tendency in carcasses. Johnson
et al. (2009) reported that this can be due to the partially recessive
effect of myostatin. The legs in the carcass of Ramlıç and BC2
lambs were longer and lighter than that reported by Demir (1989b). The
differences may have arisen from selection throughout the years and the
absence of the fattening phase in our study. Ramlıç and BC2 lambs
were also leggier than Texel lambs (P<0.05). It was observed that
the left-leg weight of BC2 (+/-) lambs tended to be higher than
Ramlıç lambs. The differences between genotypes in muscle weight and
ratio in the leg were found to be significant (P<0.05). Texel
lambs were higher than the other two genotypes in these traits, whereas
bone weight and ratio in Texel lambs were significantly (P<0.05)
lower than the others. Some desirable improvements were observed in BC2
lambs in carcass characteristics (Tables 2, 3). Myostatin mutation may be
one of the reasons for this fact. Consequently, different researchers (Clop
et al., 2006; Hadjipavlou et al., 2008; Han et al., 2010; Haynes et al.,
2013; Hickford et al., 2010; Hope et al., 2013; Johnson et al., 2009; Kijas
et al., 2007; Masri et al., 2011) reported that having a single or
double copy of myostatin mutation results in leaner or muscled carcasses.
Conclusions
Based on the results of the present study the effects of factors such as
genotype, sex, birth type, age of dam, weaning age, and birth weight on pre-
and post-weaning growth characteristics, body measurements, and ultrasonic
carcass traits are important. These factors should be taken into
consideration in selection programs. BC2 phase has been attained by
marker-assisted introgression. BC2 lambs were superior to Texel lambs
for growth traits, while no significant differences with the maternal line
(Ramlıç) were detected. So, myostatin mutation has been introgressed
into the Ramlıç gene pool without harmful effects on the breed
performance. The BC2 lambs with deep longissimus muscle were promising.
The carcass characteristics of these lambs tended to be superior to Ramlıç lambs. However, the mutation should be homozygous for commercial
breeders to make maximum profit and produce leaner lambs. Therefore,
selection for double-copy myostatin mutation must be carried out by a
special breeding program including molecular technics. It would be useful to
take into account the myostatin mutation (g+6723G > A) as a
marker for genetic progress in meat quality and quantity.
Data availability
Data will be made available upon reasonable request.
Ethical statement
The animals were used in compliance with the rules of
the experimental animals ethical committee at Afyon Kocatepe University
(decision no. 49533702-26).
Author contributions
All authors contributed to the study conception and
design. Material preparation, data collection and analysis were performed by
MT, ME, SK, KÇ, EY, ÖH, ZB, MD and SÇ. The first draft of the
manuscript was written by MT, ME, KÇ and SÇ, and all authors
commented on previous versions of the manuscript. All authors read and
approved the final manuscript.
Competing interests
The contact author has declared that neither they nor their co-authors have any competing interests.
Disclaimer
Publisher’s note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Acknowledgements
The study's authors are thankful to the Republic of Türkiye
Ministry of Agriculture and Forestry General Directorate of Agricultural
Research and Policies and
the staff of Afyonkarahisar Sheep Breeders Association for their assistance
and collaboration.
Financial support
This research has been supported by the Tarimsal Araştirmalar ve Politikalar Genel Müdürlüğü, Türkiye Cumhuriyeti Tarim Ve Orman Bakanliği (grant no. TAGEM/15/ARGE/23).
Review statement
This paper was edited by Steffen Maak and reviewed by Cigdem Takma, Bilal Akyüz, and one anonymous referee.
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