24th Int. Symp. “Animal Science Days”, Ptuj, Slovenia, Sept. 21st−23rd, 2016. Acta argiculturae Slovenica, Supplement 5, 89–93, Ljubljana 2016 COBISS: 1.08 Agris category code: L10 DOES THE SELECTION ON SS-CASEIN AFFECT THE TRAITS IMPORTANT FOR DAIRY PRODUCTION OF SLOVENIAN BROWN SWISS CATTLE? Klemen POTOČNIK 1, 2, Barbara LUŠTREK 3, Ana KAIĆ 4 Does the selection on ß-casein affect the traits important for dairy production of Slovenian Brown Swiss cattle? 1 University of Ljubljana, Biotechnical Faculty, Department of Animal Science, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia 2 Corresponding author, e-mail: Klemen.Potocnik@bf.uni-lj.si 3 Same address as 1, e-mail: barbara.lustrek@gmail.com 4 University of Zagreb, Faculty of Agriculture, Department of Animal Science and Technology, Svetošimunska 25, 10000 Zagreb, Croatia, e-mail: akaic@agr.hr ABSTRACT The purpose of this study was to determine the impact of genomic selection on A2A2 ß-casein genotype in Brown Swiss cattle on important dairy production traits – traits included in total merit index (TMI). A total of 190 Slovenian Brown Swiss cattle, 83 females and 107 males, with known direct genomic values (DGV) from InterGenomics project and known genotype for ß-casein were used for estimation of the genotype effect. The determined genotype frequen- cies in population were 2.63 % for A1A1, 35.26 % for A1A2 and 62.11 % for A2A2 genotype. For DGV data analysis a single–trait model was used, considering genotype for ß-casein as fixed effect. Analysis showed significant differences between genotypes for ß-casein for three dairy production traits –TMI for dual purpose, pasterns and rear teat position. Our research indicates that selection on A2A2 ß-casein genotype would not have implications for traits important for dairy production. Key words: genomic selection, ß-casein, Brown Swiss, dairy production, A2 1 INTRODUCTION Selection of Brown Swiss cattle in recent decades was based on the polygenic traits that are especially im- portant for dairy production. In the last few years the importance of genomic selection increased, which ena- bled faster genetic improvement for traits under selec- tion. Genotyping also provided information about mo- nogenic characteristics (traits and disorders) such as: genotype for ĸ- and ß-casein, ß-lactoglobulin, bovine polledness, etc. These monogenic characteristics can be associated with: processing and quality of dairy prod- ucts, influence on human health and heard manage- ment. Their importance is increasing in both livestock and processing industry. Nowadays bull catalogues of selection companies make the information about mo- nogenic traits available in their catalogues (Select Sires Inc., 2016; Inseme S.p.a., 2015). One of such traits is milk protein ß-casein, which is present in bovine milk in one of two genetic variants – A1 or A2. Form of this milk protein is determined by the genotype for ß-casein. In cattle it exists in three different variants: A1A1, A1A2 and A2A2. Primary form of ß-casein is recognized as A2, while its mu- tated form is recognized as A1 ß-casein (Jakob, 1994; Kamiński et al., 2007). Consumption of A1 ß-casein in dairy products is associated with negative impact on human health. Some reports suggest that A1 ß-casein is causing: formation of beta-casomorphin-7 (which is thought to induce immune response), worsened gastro- intestinal physiology and digestive discomfort symp- toms, type 1 diabetes mellitus, ischaemic heart disease, neurological disorders (schizophrenia, autism, postpar- tum psychosis) and even sudden infant death syndrome (Elitsur and Luk, 1991; Kamiński et al., 2007; Clarke and Trivedi, 2014; Jianqin et al., 2016). Acta agriculturae Slovenica, Supplement 5 – 201690 K. POTOČNIK et al. The frequency of the A1 allele varies in different cattle breeds. Several studies reported that Holstein Friesian breed has higher (~50 %) while Brown Swiss breed (and similar breeds) has lower A1 allele frequen- cy (~ 25 %) (Jann et al., 2002; Kamiński eta al., 2007). However, A2 allele prevails in Brown Swiss and this is an advantage compared to Holstein Friesian which is used as main breed for dairy production in Slovenia and Europe. For Slovenian Simmental breed, we do not have allele frequency information available. Several studies researching associations between genetic variations of ß-casein and main economically important traits for dairy production exists (milk, pro- tein and fat yield), most of them regarding Holstein cattle. Their general findings are confirming the asso- ciation between A2A2 genotype or A2 ß-casein variant and increased milk yield (Ng-Kwai-Hang et al., 1984; Ng-Kwai-Hang et al., 1990; Comin et al., 2008; Olenski et al., 2010), increased protein yield (Comin et al., 2008; Olenski et al., 2010) and decreased fat yield (Ng-Kwai- Hang et al., 1990; Olenski et al., 2010). The aim of this study was to investigate the exist- ence of association between selection on the A2 ß-ca- sein and traits important for dairy production (traits in- cluded in total merit index (TMI)) of Slovenian Brown Swiss due to the changes in the individual polygenic traits. N Mean SD Min Max Rump height 190 118.8 13.0 82.0 148.0 Rear legs-side view 190 97.6 14.7 44.1 149.8 Pasterns 190 110.9 16.1 64.5 166.3 Hoof height 190 111.6 18.9 67.2 170.9 TMI milk 190 111.3 7.5 90.9 130.8 TMI dual purpose 190 108.1 8.4 84.2 129.0 Teat length 190 88.3 13.4 43.3 122.7 Rump angle 190 99.3 13.6 53.2 139.4 Rear udder height 190 117.2 16.0 59.4 149.3 Rear udder width 190 117.2 13.8 75.9 148.3 Udder depth 190 110.5 14.6 71.0 153.5 Milking speed 190 104.9 16.2 54.9 150.6 Chest width 190 98.9 13.4 58.0 133.4 Front teat position 190 113.0 14.8 71.5 146.4 Rear teat position 190 112.1 13.7 70.6 144.8 Somatic cell score 190 104.0 6.3 92.3 126.6 Milk yield 190 113.4 9.0 84.6 137.1 Fat yield 190 113.9 9.5 87.0 142.6 Protein yield 190 115.5 9.5 87.3 144.4 Longevity 190 113.2 19.1 54.0 158.0 Body depth 190 109.7 18.9 55.8 159.6 Structural width 190 116.5 15.0 71.5 151.8 Fore udder attachment 190 114.6 17.3 65.4 170.5 Udder cleft 190 112.7 16.3 65.5 155.6 Legs overall 190 114.4 23.5 59.6 182.3 Udder overall 190 119.1 17.9 71.6 161.6 Exterior overall 190 120.4 21.3 62.9 171.6 Fat and protein index 190 115.2 9.4 87.2 143.4 Table 1: Descriptive statistics for direct genetic values of economically important traits N – number of animals; SD – standard deviation; Min – minimum value; Max – maximum value; TMI – total merit index Acta agriculturae Slovenica, Supplement 5 – 2016 91 DOES THE SELECTION ON SS-CASEIN AFFECT THE TRAITS IMPORTANT FOR DAIRY ... OF SLOVENIAN BROWN SWISS CATTLE? 2 MATERIAL AND METHODS The data set consisted of 190 genotyped Slovenian Brown Swiss cattle (83 females and 107 males) with di- rect genomic values (DGVs) for economically important traits. DNA was isolated either from animal hair samples or bull semen. The allelic variants for ß-casein were ob- tained from genotypes using a routine procedure. Chi- square test was used to determine if population was in Hardy-Weinberg equilibrium. The effect of different vari- ant of ß-casein genotype (A1A1, A1A2, A2A2) on DGVs was analysed by GLM procedure of statistical package SAS/STAT (SAS 9.2., 2008), considering genotype for ß-casein as fixed effect (Model 1). DGVs are expressed on standardised scale where mean is 100 and standard deviation is 12 points. yij = μ + Gi + eij Model 1 where yij – DGV; Gi – ß-casein genotype; i = 1, 2, 3; eij – residual; j = 1,…190 3 RESULTS AND DISCUSSION The observed genotype frequencies were 2.63 %, 35.26 % and 62.11 % for A1A1, A1A2 and A2A2 gen- otypes, respectively. We are not aware of results from other Brown Swiss populations being available. How- ever, in studied populations of Slovak Spotted cattle (Miluchová et al., 2013) and Romanian Spotted cat- tle (Grădinaru et al., 2015) which included a similar number of animals as our study, A2A2 genotype was also prevalent. In studies of Romanian and Polish Hol- stein Friesian cattle with numerically similar or bigger animal populations, the prevalent genotype was A1A2 (Grădinaru et al., 2015; Olenski et al., 2010). Sex ratio (female : male) by genotype frequency was 40 : 60 for A1A1 genotype, 47.8 : 52.2 for A1A2 genotype and 41.5 : 58.5 for A2A2 genotype. Allele fre- quencies were 20.3 % for allele A1 and 79.7 % for allele A2. The ß-casein genotypes in population were distrib- uted according to Hardy-Weinberg equilibrium. The frequency of allele A2 in observed Brown Swiss popula- tion was four times higher than frequency of allele A1. These results are in agreement with prior findings of similar study where 40 animals from Slovenian Brown Swiss population were observed (Potočnik, 2015). Mean DGV (Table 1) for TMI for dairy produc- tion was 111.3 which is almost one standard deviation (SD) higher than the average of Slovenian Brown Swiss population. For most of individual traits average DGVs were around one SD above population average. That was somehow expected because genotyped animals were preselected on parent average. For rear legs – side view, teat length, rump angle and chest width average DGVs were close to Slovenian Brown Swiss population’s average. The average value for pasterns was 110.9 while the minimum and maximum values ranged from 64.5 to 166.3. The average of investigated populations is very close to the optimum value (109 points). The average pasterns are just a little bit steeper than the optimal ones. The average for rear teat position was 112.1 while the minimum and maximum values ranged from 70.6 to 144.8. Optimum value for rear teat position is 100, while the average value of the studied population is one SD higher meaning that rear teats are placed closer to the central ligament than it is desired. The average DGV within gender for pasterns and rear teat position was higher for females (112.8 and 113.7) than males (109.4 and 110.9, respectively). Presented results refer only to the traits with sta- tistically significant differences among genotypes for ß-casein (Table 2). Significant differences between genotypes for ß-casein were recorded at two type traits (pasterns and rear teat position) and TMI for dual pur- pose (Table 3). Animals with A2A2 genotype had significantly steeper pasterns (113.4 ± 1.5 points,) and higher TMI for dual purpose (109.2 ± 0.8) than animals with A1A2 genotype (106.9 ± 1.9 and 106.1 ± 1.02, respectively). The rear teat position significantly differ between A1A1 and A2A2 genotypes – animals with A1A1 genotype Pasterns TMI for dual purpose Rear teat position LSM SE LSM SE LSM SE A1A1 104.5ab 7.08 108.4ab 3.7 126.7b 6.06 A1A2 106.9b 1.9 106.1b 1.02 112.4ab 1.7 A2A2 113.4a 1.5 109.2a 0.8 111.3a 1.2 Table 2: Leas square means (LSM) and standard errors (SE) of direct genomic values (DGV) for pasterns, total merit index (TMI) for dual purpose and rear teat position by ß-casein genotype a, b – Means within a row with different superscripts differ (p < 0.05) Acta agriculturae Slovenica, Supplement 5 – 201692 K. POTOČNIK et al. had rear teats placed closer to the centre of the udder quarter (126.7 ± 6.06) which is not desirable. Since the use of mechanical milking (robot) is increasing, close rear teat position indicates issues relating to the ease of milking unit attachment. Braunschweig et al. (2000) found no significant effect for parental casein haplotypes on dairy produc- tion traits (milk yield, fat percentage) for Brown Swiss cattle. In comparison with our results this could in- dicate that genotype for ß-casein is not closely linked to the expression of main polygenic traits for dairy production, considering that TMI for dual purpose includes higher economical weights for meat produc- tion traits than dairy production traits. However, in contrast to the results of Braunschweig et al. (2000), Boettcher et al. (2004) found statistically signifi- cant associations between casein gene haplotypes for milk yield and protein and fat percentages in Italian Brown Swiss population. They also came to indication that the same haplotypes were having similar effects in both Italian Brown Swiss and Holstein cattle with greater magnitude for the Brown Swiss cattle. Regard- ing both Slovenian Brown Swiss and Czech Fleckvieh being dual purpose breed, we can also consider the re- sults of Kučerová et al., (2006) who found significant differences among genotypes of ß-casein gene locus in breeding values for milk, protein and fat yield, and fat content. Their results show tendency of allele A2 to in- fluence milk content parameters while allele A1 tends to increase milk yield. 4 CONCLUSIONS The analysis did not show statistically significant differences between ß-casein genotypes for traits in- cluded in TMI. Inventive producers and suppliers of milk and dairy products have now an opportunity for a new niche market, which is with increasing usage of genomic selection already slowly expanding and occu- pying its own space in the market. Results in literature are contradictory. Our results indicate that selection on A2A2 ß-casein genotype would not lead to the loss of variability and would not cause any major genetic changes of the most important poly- genic traits in the next generations of Brown Swiss animals. There is indica- tion of changes for three traits (TMI for dual purpose, pasterns and rear teat position) but the trend is in favour of the desired ß-casein genotype. How- p-values A1A1 – A1A2 A1A1 – A2A2 A1A2 – A2A2 Pasterns 1.0000 0.6570 0.0219 TMI for dual purpose 1.0000 1.0000 0.0467 Rear teat position 0.0711 0.0412 1.0000 Table 3: P-values of traits with estimated significant differences between ß-casein genotypes ever, for more explicit results and better comparison it would be necessary to make more advanced studies regarding Brown Swiss cattle and to use larger number of animals with known genotype for ß-casein and esti- mated breeding values. 5 REFERENCES Boettcher, P.J., Caroli, A., Stella, A., Chessa, S., Budelli, E., Ca- navesi, F., Ghiroldi, S., Pagnacco, G. (2004). Effects of casein haplotypes on milk production traits in Italian Holstein and Brown Swiss cattle. Journal of dairy science, 87, 4311–4317. Braunschweig, M., Hagger, C., Stranzinger, G., Puhan, Z. (2000). Associations between casein haplotypes and milk production traits of Swiss Brown cattle. Journal of dairy sci- ence, 83, 1387–1395. Clarke, A., Trivedi, M. (2014). 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