Carcass quality traits of beef cattle with different DGAT1 genotypes

The paper presents the research results on carcass quality traits of beef cattle for different DGAT1 genotypes. The study aimed to detect the effect of SNP DGAT1-K232A on carcass and beef quality of Hereford and Limousine bull calves of different genotypes. The tasks were SNP genotyping of animals by DGAT1-K232A, detecting the impact of SNP on carcass quality and morphological composition, weight and yield of half carcasses, organoleptic properties of meat, as well as the chemical composition of beef. The method of a polymerase chain reaction with a subsequent restriction fragment length polymorphism analysis was used to genotype fattening bull calves of Hereford (91 heads) and Limousine (109 heads) breeds. The animals were raised until 20 months of age in conditions of a resource-saving indoor and pasture-based system. There was an apparent effect of SNP DGAT1-K232A (DGAT1KK>DGAT1AA, P◘0.05) on the interior raw fat weight and yield indicators, subcutaneous fat tissue thickness, fat content in the rib eye and a sample of minced meat. Thus, genotyping by SNP DGAT1-K232A can be used as an additional criterion to improve the quality traits of meat in beef cattle breeding.


Introduction
The production of high-quality beef from single-purpose beef cattle is a key focus of agricultural development. One of the important resources to make highly productive herds of beef cattle is the use of marker-assisted selection as an additional criterion for selecting and breeding superior animals. Using genes that control economic traits is an important element in determining the breeding value of animals [1][2][3][4].
In references, there are evidences of a positive correlation between the DGAT1 enzyme activity and the content of subcutaneous fat, as well as intramuscular fat in the rib eye and semitendinosus. Thus, DGAT1 KK genotype animals were found to have a greater fat yield and thicker subcutaneous tissue [5][6][7]. Sorensen B. M. et al. (2005) proved that animals with the desired DGAT1 KK genotype in Holstein-Friesian and Charolais breeds had 5 times greater diacylglycerol acyltransferase activity than DGAT1 AK and DGAT1 AA genotype animals [8]. The [5,[9][10][11] showed a significant increase of intramuscular fat in DGAT1 KK genotype animals. Anton I. et al. (2011) found high rates of intramuscular fat in the rib eye of AA/AA genotype animals [12].
The study aimed to detect the effect of SNP DGAT1-K232A on carcass and beef quality of Hereford and Limousine bull calves of different genotypes. The tasks were SNP genotyping of animals by DGAT1-K232A, detecting the impact of SNP on carcass quality and morphological composition, weight and yield of half carcasses, organoleptic properties of meat, as well as the chemical composition of beef.

Materials and methods
SNP DGAT1-K232A genotyping was performed on one month aged Hereford and Limousine bull calves. Ninety-one young Hereford bulls were descendants of animals imported to private farm "SAVA-Argo-Usen" from Australia in 2009. 114 Limousine bull calves were the offspring of animals, bred at "SAVA-Agro-Yapryk" farm by accumulation cross-breeding of Simmental cattle with servicing bulls of French selection. Both farms use a resource-saving indoor and pasture-based system for keeping beef cattle. These are breeding farms that maintain fattening animals. Bull calves were raised and fattened until 20 months of age [13].
Blood samples were collected from the jugular vein. DNA was isolated from whole blood stabilized with sodium citrate using a set of "DNA-Extran" ("Syntol"). Genotyping was performed by the PCR-RFLP method [14] using primers: F: 5'-gca-cca-tcc-tct-tcc-TCA-ag-3' and R: 5'-gga-agc-gctttc-tcc-gga-tg-3'. Amplifiers were cleaved by the CfrI endonuclease. The number and length of the obtained restriction fragments were determined electrophoretically in 7.5% PAGE in UV light after staining with ethidium bromide. Gel visualization was analyzed with the Gel Doc XR system and the attached Image Lab 2.0 "DNA-analyser" software. Sizes of restriction fragments: 411 KK; 411, 208, 203 KA and 208, 203 AA base pairs. Sample slaughter of animals and meat sampling was carried out in SAVA meat processing plant. Depending on the DGAT1 genotypes carcasses were divided into three groups: group I (n=20) -DGAT1 KK ; group II (n=20) -DGAT1 KA ; group III (n=10)-DGAT1 AA .
Statistical processing of the research results was carried out by standard methods using Microsoft Excel.

Results and discussion
SNP DGAT1-К232А genotyping proved that genotype distribution in cattle of both breeds is very similar. In bull calves of both breeds, the DGAT1 KK genotype is more common (51.65% and 50.46%), the DGAT1 AK genotype is in second place (35.16% and 38.53%), and the DGAT1 AA genotype is in third place (13.19% and 11.01%). Allele frequencies are the same in both breeds: DGAT1 K (0.64) and DGAT1 A (0.36). The results of the given studies are consistent with the data obtained by Aviles C. et al. (2015). Genotyping commercial beef breeds Charolais (n=98) and Limousine (n=99) distinguished between the following allele frequencies -DGAT1 K -0.82 and 0.84, DGAT1 A -0.18 and 0.17, respectively [5]. Genotype and allele frequencies depend on the cattle type and breed. Thus, other researchers found that the DGAT1 GC allele (encoding alanine) frequency is significantly higher than that of the DGAT1 AA allele (encoding lysine) when genotyping beef cattle [11,12]. The allele encoding alanine is found only in Bos taurus taurus cattle and is absent in Bos taurus indicus, Bos grunniens, and Bubalus bubalus animals [14].
Carcasses from DGAT1 KK genotype Hereford and Limousine bull calves significantly (P<0.05) exceeded carcasses from DGAT1 AA genotype animals in terms of the weight of internal raw fat by 4.34% and 2.86%, fat yield by 0.25% and 0.15%, and the thickness of subcutaneous fat by 11.05% and 11.67%, respectively. There is a trend to increase the slaughter indicators in the direction of DGAT1 KK →DGAT1 KA →D GAT1 AA . The data obtained are consistent with the results of Aviles C. et al.  [6]. This dependence was not found in other studies [9,15].
The morphological composition of carcasses is shown in table 1. The table shows that Hereford cattle carcasses contain more fat tissue -7.55-6.90% compared to 7.10-6.40% in Limousine animals. The fat tissue content in the carcasses of DGAT1 KK genotype bull calves was 7.55% and 7.10%, respectively, exceeding the same indicator in the carcasses of DGAT1 AA genotype animals by 0.65% and 0.70%. There is an increase in the carcass fleshing index of the Limousine cattle by genotype in the direction of DGAT1 KK →DGAT1 KA →D GAT1 AA . These data comply with the results of Casas E. et al. (2005). They observed no significant association between the DGAT1K232A polymorphism and morphological composition of carcasses in Brahman cattle [16].
The weight and yield of the natural anatomical parts of half-carcasses are shown in table 2. The table shows that half-carcasses of Hereford cattle with the DGAT1 AA genotype had higher weight indices of cuts compared to those of DGAT1 KA and DGAT1 KK . They were 0.4 kg (3.07%) and 0.3 kg (2.31%) for the neck-; 0.80 kg (2.72%) for the chuck; 1.20 kg (3.00%) and 1.10 kg (2.74%) for the rib; 0.1 kg (1.32%) for the brisket; 0.30 kg (2.5%) and 0.20 kg (1.67%) for the loin; 1.00 kg (2.07%) and 0.60 kg (1.24%) for the round.
The difference between the cut weights of the DGAT1 AA >DGAT1 KA and DGAT1 AA >DGAT1 KK genotype Limousine bull calves was 0.9 kg (2.93%) and 0.4 kg (1.30%) for the chuck; 0.90 kg (2.13%) and 1.90 kg (4.50%) for the rib; 0.40 kg (3.03%) and 0.20 kg (1.52%) for the loin , 1.40 kg (2.63%) and 1.10 kg (2.07%) for the round respectively. The results are consistent with the data of Karolyi D. Et al. (2012). They found that the DGAT1 AA genotype bull calves slightly exceeded DGAT1 KA animals by 2.09% in terms of carcass weight and the yield of the most valuable natural anatomical parts of the carcass: the chuck (4.6%), the loin (2.7%) and the round (5.8%) [17]. The organoleptic evaluation of meat for processing demonstrated no effect of gene polymorphism on the indicators of visual appearance, smell, taste, consistency and juiciness of meat. On average, the overall quality of meat is high being 8.49-8.51 points and 8.58-8.59 points for the broth.
The content of intramuscular fat in the rib eye of the DGAT1 KK genotype bull calves is significantly higher (P<0.05) by 0.18% and 0.29%, respectively, than that of the DGAT1 AA genotype animals. There was a significant increase in this indicator (P<0.001) in the general sample of minced meat from the DGAT1 KK genotype Hereford bull calves by 0.58%; Limousine animals by 0.18% (P<0.05). The content of tryptophan and protein quality indicator increases in the direction of DGAT1 KK →DGAT1 KA →DGAT1 AA . The received data correspond to the findings of Aviles C. et al. (2015). They confirmed that the intramuscular fat content in the DGAT1 AA genotype animals is significantly lower (P 0.01) by 2.38 % than in the DGAT1 AK genotype, and higher (P 0.05) by 6.28 % than in the DGAT1 KK genotype [5] contradicting the results of D. Karolyi, (2012). The latter established that the carcasses of the AA genotype animals have a higher intramuscular fat content by 2.75 g/kg [17].

Conclusion
Thus, studies on the quality of carcasses and beef in Hereford and Limousine bull calves of different DGAT1 gene genotypes showed a reliable influence of SNP DGAT1-K232A on the weight and yield of internal raw fat, subcutaneous fat thickness, the fat content in the rib eye and a sample of minced beef. Thus, genotyping by SNP DGAT1-K232A can be used as an additional criterion to improve the quality traits of meat in beef cattle breeding.