INVESTIGATION OF THE HERITABILITY OF PHENOTYPES OF FERTILITY AND MILK PERFORMANCE OF SIMMENTAL CATTLE BREED IN SERBIA

Results of the effect of direct and indirect selection of quantitative traits of fertility and milk performance of first calving cows of Simmental breed in Serbia are presented. Investigation of genetic parameters of heritability (additive genetic variance in total phenotypic variability of quantitative traits) and analysis of milk traits was done in four breeding regions and several tenths of farms where 3980 daughters of 32 sires were housed and reared. Results of analysis were obtained by application of mathematical-statistical data analysis, using mixed models (Harvey, 1990). Mathematical-statistical analysis of data was done using linear methods, i.e. method of least squares (LS method). Based on obtained results it was established that bulls-sires and several paragenetic factors caused no significant variation of fertility traits in relation to general average (P<0.01). Quantitative milk traits of first calving cows, under the influence of breeding region, had significantly higher deviation from the general average (** P<0.01). Significant deviations (*P<0.05) were caused by year of calving on milk yield and yield of milk fat (4765.0 kg and milk fat 3.86%). Established heritability coefficients for reproductive traits were following: .102, .051 and .088, and milk traits .297, .207 and .197).


Introduction
The largest cattle population in Republic of Serbia is population of Simmental cattle (approx.500.000female breeding animals or over 80%).Cows of Simmental breed are reared in Republic of Serbia in semi-intensive conditions of housing, care and nutrition, i.e. on small farms with several heads of cattle, to farms with several tenths of female breeding animals in intensive system of housing, care and nutrition.Current programs all over the world which relate to same problem and which is target objective in our country, is increase of production performance of cattle in Serbia, which is now structurally different from situation ten or twenty years ago.If we consider current changes in regard to genetic improvement of cattle and huge progress in technologies of reproduction, it is obvious that present programs will have to be changed and improved.Since economical importance of reproduction and milk traits is high, knowledge of certain factors which influence the fertility and milk performance of cows, and are divided into genetic and para-genetic factors, is necessary.Success in improvement of fertility by genetic way is limited with low heritability values, which doesn't mean that genes have no effect on these traits, but that value of additive genetic variation is low.Heritability, i.e. study of additive genetic variance in total phenotypic variability of quantitative traits, represents the part of the most important researches from the aspect of creation of population of cattle of high genetic potentials and selection of parent couples for future generations.Values of the heritability coefficients for fertility traits are under the influence of different factors, such as: genotype, age, intensity of selection, breeding method, environment conditions, etc.
Breeding regions were: Šumadija (1), Pomoravlje (2), Rasina (3) and Braničevo (4).I season of calving included months of February, march and April, II season May, June and July, III season included months of August, September and October, and IV season November, December and January.Bulls -sires are also Simmental and are in exploitation by two Livestock-Veterinary Centres in Republic of Serbia.
All investigated cattle (cows) were housed tied and free on farms of private, individual producers (of 8 to 65 heads per farm) and were fed standard diets, differences were in quantity, ratio and quality of forage and concentrated feeds (breeding region).

Investigation of heritability of fertility and milk performance included following traits:
Reproductive and Productive traits: -Age at first fertilisation, days (AF) -Duration of pregnancy, days ( DP) -Duration of service period, days ( DSP) -Milk yield 305 days (MY305D) -Milk fat yield 305 days (MFY305D) -Percent of milk fat 305 days (%MF305D) Mathematical-statistical data analysis was done using mixed model of least squares with fixed and random effects (LS-Least Squares), applying the program of least squares (LSMLMW), Harvey, 1990.In analysis of effect of breeding region, year and season of calving, bulls-sires on fertility and milk performance phenotypes of cows in the first lactation the following model was used: where: Y ijklm -individual animal m, deriving from sire i, reared in j region, calved in k year, l season μ -general population average R i -fixed effect (region) of breeding region (1-4) Y j -fixed effect of year of calving (1-6) S k -fixed effect of season of calving (1-4) B l -random effect of bull-sire (1-32) b 1 -linear regression effect of age at calving e ijklm -other non-determined effects

Results and Discussion
Different number of individual animals in certain classes, as well as presence of multiple effects (region, year of calving, season of calving, bulls-sires) which influenced expressions of investigated traits, induced analysis where method of least squares was used.
Bulls-sires and series of para-genetic influences caused no significant variation of fertility traits in relation to general average (P>0.001).Similar data on variation of fertility traits were obtained by Petrović et al. (2001Petrović et al. ( , 2007) ) and Petrović et al. (2006).Phenotypes of milk yield and yield of milk fat obtained in our research were higher compared to results for the same breed determined by Kapš and Špehar (2004) in Croatian population of Simmental cows, and Panić and Vidović ( 2006), Petrović et al. (2006), and significantly higher compared to results obtained by Pantelić et al. (2008).
Quantitative milk traits of first calving cows under the influence of region had highly significant deviation from general average (** P<0.01).Significant deviations (*P<0.05)were caused by calving year on yield of milk and milk fat.Season of the beginning of lactation in cows included in our research showed significant deviations of milk yield and yield of milk fat from the general average (P<0.01).So, heifers calved in February, March and April had significantly more milk and milk fat in comparison to those which calved in other months of the year.Coefficients obtained in study of additive genetic in total phenotypic variability, i.e. parameters of heritability of fertility and milk traits, are presented in Table 3. Established heritability coefficients of reproduction traits obtained in our research had low values and were bellow level compared to those obtained by Petrović et al. (1998Petrović et al. ( , 2001Petrović et al. ( , 2006)).Results of heritability of milk traits obtained in our research were higher compared to coefficients for the same traits published by Panić and Vidović (2006), lower compared to research results of Petrović et al. (1999) and Kapš and Špehar (2004) and in accordance with heritability coefficients determined in Turkish population of Simmental cows by Ulek and Tekun (2006).

Conclusion
In this paper, results of the effect of direct and indirect selection of quantitative fertility and milk traits are presented, as well as share of additive genetic in total phenotypic variability (heritability) of first calving cows of Simmental breed in Serbia.Analysis included four regions -breeding regions in Serbia.Investigation included 3980 first calving cows of Simmental breed, daughters of 32 bulls-sires, calved in the six year period (2002)(2003)(2004)(2005)(2006)(2007).Results of the analysis were obtained using mathematical-statistical data analysis, mixed models (Harvey, 1990).Mathematical-statistical data analysis was done using linear methods, method of least squares (LS method).
Based on obtained results it was established that bulls-sires and series of para-genetic effects caused no significant variation of fertility traits compared to general average (P>0.01).Quantitative milk traits of first calving cows under the influence of breeding region had highly significant deviation from general average (** P<0.01).Significant deviations (*P<0.05)were caused by calving year on yield of milk and milk fat (4765.0kg and 3.86% of milk fat).Established heritability coefficients for reproductive traits were .102,.051and .088and of milk traits .297, .207 and .197).