SOURCES OF VARIABILITY OF GROWTH AND BODY DEVELOPMENT TRAITS OF SIMMENTAL BULLS IN PERFORMANCE TEST

: To test the variability of traits of Simmental bulls in performance test, data of the Livestock - Veterinary Centres for Reproduction and Artificial Insemination of Velika Plana and Krnjača were used. In the analysis, data on 113 performance tested bulls born from 2008 to 2009 were used. The analysis included two sets of characteristics: body development traits and growth traits. The average body mass of calves entering the test was 195.75 kg, while the body mass at the end of the test was 476.50 kg, average daily gain in the test was 1138.69 g. Average values of body development traits measured at the end of the test, with 12 months of age were: height at withers 127.13 cm, chest circumference 179.42 cm, the chest depth 61.19 cm and body length 151.34 cm. The influence of their sires, the year and the Centre on the variability of traits was studied. The effect of age is present at a high level of statistical significance (p<0.01) for all traits that are registered at the end of the test, while the effect of the Centre was present in the variability of body mass at the end of the test, the daily gain in the test and the length of the body. The bulls-sires' influence was demonstrated (p<0.05) on the variability in body mass of calves entering the test.


Introduction
Simmental cattle belong to the combined type, which means almost equal economic importance of milk and meat production. It belongs to the big breeds that have the genetic potential for intensive improvement of both components. Therefore, proper selection and selection of young bulls as future breeding bulls should ensure improvement of traits and improvement of production of milk and meat (Bogdanović, 2001).
In assessing the breeding value of performance test bulls is one of the main animal husbandry practices, which determines the genetic improvement of a certain group of properties. Selection based on the results of performance test, is of special importance for traits that are characterized by medium to high heritability values (Bogdanović, 2001).
Performance test is used for production traits which can be determined or measured in each individual animal. This process is known as direct test because its application covers control of production traits that are directly measured on animals still in development.
The performance test of Simmental bulls in Serbia officially started to be performed during 1982 in Test station at the Center for Artificial Insemination in Velika Plana. From the very beginning, the adopted test technique was in compliance with all recommendations of the European Zootechnical Federation (Bogdanović, 2001).
The study of of growth and body development traits of performance tested Simmental bulls, was topic of research of several researchers in Serbia. The variability of characteristics and influence of individual factors on the variation, values of heritability, phenotypic and genetic correlations of mentuioned traits are stated in the studies of Perković ), Romčević, (1999) and Bogdanović (1999, 2001, 2003, 2006, 2007.
Bearing in mind the importance of Simmental breed in cattle production of Serbia, as well as the lack of research associated with this breed, the aim of this study was to determine the average expression and variation of traits of growth and body development, and then to determine the influence of certain genetic and nongenetic factors on traits measured in performance test.

Material and methods
To test the variability of growth and body development traits of Simmental bulls in performance test, data of the Livestock Veterinary Centres for Reproduction and Artificial Insemination (SVC) from Velika Plana and Krnjača were used. Bulls included in the test are taken to the Centre based on the application of the owner or holder of the bull, from private and state farms. Before bringing the young bulls to the Centre, examination and evaluation are carried out to determine whether they meet the basic requirements to enter the test.
Selected male calves come into the station at the age of about three months, they are placed in quarantine and adjust to conditions of housing and nutrition for at least 30 days, in order to eliminate as much as possible pre-existing effects. After a preparatory period, at the age of 4 months, the test starts and lasts until the age of one year. Bulls in the test are held in adequate groups, not more than 5 animals in the group, formed in relation to age. Basic forage -alfalfa hay is given at will, while the amount of concentrate is limited by age. During the test, in regular one-month intervals, the body weight and the most important dimensions of the body (withers height, chest circumference, breast depth, width of round, pelvic width and length of the body) are measured. At the end of the test, the average daily gain in the test is calculated and it is a key feature on which the evaluation of bulls in the test is based.
Data The analysis included two sets of characteristics: body development traits and growth traits.
Body development traits are represented by the linear dimensions of the body measured at the end of the test, at 12 months of age: height at withers, chest circumference, chest depth and body length.
The following growth traits are included: body weight at the beginning of the test (with 4 months of age), body weight at the end of the test (with 12 months age), average daily gain during the test.
The most attention in the test is directed towards the average daily gain during because it fully reflects the capacity and intensity of the growth of the animal, and therefore its predisposition to a particular form of production.
Statistical analysis of data obtained during the performance test was divided into two parts.
The first part of the analysis included the determination of the basic variation-statistical parameters: • Arithmetic mean (X), • Variation range (Min-Max), • Standard deviation (SD), • Coefficient of variation (CV).
Descriptive statistics analysis was performed using the statistical program StatSoft. Inc (2004), Statistica for Windows version 7.
The second part of the data processing included the identification of various influences on traits variability in performance test. Analysis of the influence of non-genetic and genetic sources of variability was performed by the method of least squares LSMLMW. To analyse the influence of non-genetic sources of variability a fixed model with fixed effect of birth and centre is used. 1. Fixed model for analysing the impact of non-genetic sources of variability of traits in performance test: • Y ijk : studied trait, • µ: population average for said trait, • G i : fixed effect of i-th year of birth of the bull (i=1, 2), • C j : fixed effect of j-th centre (j=1, 2), • e ijk : random error with characteristics N (0,σ 2 ).
To analyse the influence of sires on the variability of traits in the performance test of the basic sample, a sub-sample of 66 bulls originating from 8 sires was formed. For this subsample all sires with 5 and more tested sons were selected. Distribution of tested bulls by fathers is shown in Graph 1.

Graph 1. Distribution of tested bulls by sires
In this part of the analysis the mixed model with random influence of the sire was applied.
In countries with developed cattle breeding, performance test is practically no longer performed in the test stations but in the production conditions of the population or is replaced by other methods of selection. Although the number of bulls tested at the centres decreases each year, in Serbia it is still justified given that the progeny test on slaughter traits is not performed.   Table 4 shows the influence of non-genetic sources of variability of traits in the performance test of Simmental bulls.

Results and Discussion
The average body mass of calves entering the test was 195.75 kg, which is consistent with the findings of Bogdanović (2006). Body mass of young bulls at the beginning of the test is characterized by a wide range of variation. Perković et al (1999) state that the average body mass of calves entering the test in Krnjača was 233 kg.
The year and centre showed no statistically significant influence (p>0.05) on the variability of body mass at the start of the test which leads to the conclusion that the body mass of young bulls is more influenced by the farm of their origin. Due to the different climatic conditions in which farms are located, feeding and housing that are designated as farm management, body mass at the beginning of the test is more influenced by pre-test factors. The body mass of calves entering the test is heavily influenced by maternal effects and housing/rearing system prior to weaning.
The average body mass of bulls at the end of the test was 476.50 kg, while slightly higher values (515.86 kg) for Simmental bulls tested in the LVC Velika Plana are reported by Bogdanović (2006). Perković et al (1999) found that the bulls in Krnjača ended the test with a body mass of 509 kg. Body mass at the end of the test varied less in relation to initial body mass of calves entering the test as a consequence of standardized conditions for feeding, housing, etc. Year and centre statistically significantly (p<0.01) influenced variation of body mass at the end of the test.
Average daily gain in the test was 1138.69 g with a coefficient of variation of 20.34, which is consistent with the results obtained by Perković et al (1999). The high variability (p<0.01) was statistically significantly influenced by the year and centre. The height of withers and depth of chest at the end of the test were not under significant (p>0.05) effect of centre, but the influence of year was significant source of variability (p<0.01). The average height to withers at the end of the test was 127.13 cm with a coefficient of variation of 2.60, the average depth of the chest was 61.19 cm with a coefficient of variation of 6.88, which is in line with the results presented in the paper by Bogdanović (2007). An average height at the withers of 127.1 cm is reported by Perković et al. (1999).
The variability of chest circumference and body length were under statistically significant (p <0.01) of the year, while the variability in the length of the body also included the effect of the centre. The average chest cir4cumference (girth) of Simmental bulls at the end of the performance test was 179.42 cm and the average body length 151.34 cm. Comparing the results of this study with the results obtained by Perković et al. (1999), the bulls at the end of the test had smaller chest size but greater body length compared to bulls tested in Krnjača in the period from 1992 to 1997.
By perceiving the traits of body development and growth in the monitored performance test much lower variability of body development traits can be observed. Given that both sets of characteristics are under the influence of same abiotic factors, it can be concluded that the body development of young bulls is under greater genetic influence.
The effect of the year is present at a high level of statistical significance (p<0.01) for all traits that are registered at the end of the test. The impact of the year includes the climatic factors, the schedule and amount of precipitation which is reflected in the quantity and quality of available food.
Although the performance test technique is the same, the influence of centre was statistically significant (p <0.01) on the variability of growth traits measured at the end of the test and the body length. The effect of the centre is reflected in the geographical environment of the station, food quality, conditions in the test, management of the animals, etc.  Table 5 shows the influence of sires on the variability of the traits in the performance test of Simmental bulls.
The effect of the bull sires (p <0.05) was present in regard to the variability in body mass of calves entering the test, while their impact on the variability of traits measured at the end of the test was not significant. The reason is very different conditions on farms of origin of bulls entering the performance test. Lack of influence of sires on the variability of traits measured at the end of the test is explained by the effect of compensatory growth with a standardized feeding conditions, housing and care in the performance test will enable the young bulls, future breeding males, to fully exert additive genetic value, on which the estimates of breeding values are based.

Conclusion
Standardizing of conditions for feeding, housing and care in performance test provides the young bulls, future breeding males, to fully exert additive genetic value, on which the estimates of breeding values are based. In the variability of the monitored traits in the performance test, the effect of year was present at a high level of statistical significance (p<0.01) for all traits that are registered at the end of the test, while the AI Centre showed statistically significant (p <0.01) influence on the variability of growth traits measured at the end of the test and the variability of body length. The effect of the bull sires (p<0.05), was present on the variability of body mass of calves entering the test, while their impact on the variability of trait measured at the end of the test, showed no statistical significance.
Properties covered by the performance test are characterized by medium to high heritability values indicating that they are hereditary enough to exert selection on them. The results obtained indicate that the traits of growth and body development contained sufficient variability for the successful selection and improvement of the traits of domestic Simmental cattle.