The thesis goal was to evaluate the effect of selected breeding methods in Simmental cattle herd on chosen indicators calf birth weight, weight in the age of 120 and 210 days. The thesis deals with the evaluation of differences between sex and the comparison of calving seasons 2014 and 2015 and also shortly focus on the comparison of chosen sires and the evaluation of its effect on selected indicators. Proposal of measures in specific breeding based collected and statistically evaluated data in part of this thesis. As the first, using a linear model, analysed the effect of individual factors which can affect observed indicators was analysed. Afterwards the evaluation of difference between each factors category was done. Within first observed factor which was breeding method was found, that the best results are reached by embryotransfered calves with birth weight 46.81 kg, weight at 120 days 201.11 kg and weight at 210 days 318 kg. The weight at 210 days within artificial insemination group was only 304.33 kg and within natural breeding group 297.68 kg. Furthermore it was found that bulls reach better results in all observed indicators in comparison with heifers. In the light of birth difficultness is important birth weight which was 46.66 kg within group of bulls and 43.45 kg within group of heifers. Weight at 210 days was 321.59 kg, respectively 294.21 kg in case of heifers. It was also found that in 2015 the studied group of calves reached better results than in year 2014 in all observed indicators. Live weight in 210 days was 326 kg and 295.63 kg respectively. The evaluation of observed indicators according to sires showed that a sire significantly affects birth weight; however the effect was not significant on weight at 210 days. The best of compared sires was ZSI 478, birth weight of calves was 48.8 kg.

Lactation and weaning weight relationships were studied in 37 cows grazing Southern Utah irrigated pastures during the summer of 1979. The herd included 23 Hereford cows ranging in age from 2 to 12 years and 14 Simmental-Hereford half-blood cows aged 3 to 9 years. The suckling calves were sired by Hereford bulls. The average daily milk yield of 6.16 kg was affected by the cow breed. Simmental-Hereford cows produced 7.11 kg of milk per day, while the Herefords produced 5.21 kg per day. Milk production declined with increased days in lactation. The decline was linear in the Simmental- Hereford cows and quadratic in the Herefords. Milk production was also affected by the sex of the suckling calf. Heifer calves received 6.44 kg per day compared t o 5.80 kg per day for bull calves. Calf birth weight and test day weight influenced milk yield as cows nursing heavier calves produced more milk. Cow breed affected milk composition. Simmental-Hereford cows had higher percent solids-not-fat, while Herefords were higher for percent protein. Calf weights were affected by sex of calf. Bull calves weighed 33 .89 kg at birth, while heifers weighed 32.14 kg. At weaning, bulls weighed 188.63 kg, while heifers weighed 177.14 kg. While no breed difference was evident for birth weight, calves from Simmental-Hereford dams weighed more over the duration of the study than calves from Hereford dams. The difference between the mean 205-day adjusted weights for the calves from the Simmental-Hereford and Hereford cows was 24.96 kg (230.50 kg and 205.54 kg, respectively). Milk yield was highly correlated to calf gain (r 0. 71). The breed of dam influence upon weaning weight was largely a result of differences .in quantity of milk produced.

Variation among sires in daughters' reproductive performance was analyzed using data on 4,360 cows from nine herds obtained from the American Simmental Association. Cows were required to have at least 50% Simmental breeding, to have calved first at 2 yr of age and to have been born and subsequently calved in the same herd and season. Traits analyzed included first and second calving dates, first calving interval and the percentage of cows that returned to calve in the same season as 3-yr-olds. Data were adjusted for effects of percentage Simmental and first-calf calving ease score. At second calving, purebred Simmentals calved 1.7 ± 1.2 d later than 75% Simmental cattle and 5.1 ± 1.4 d later than 50% Simmental cattle. When compared to cows that calved without assistance at first calving, cows experiencing easy pulls were 1.7 ± 1.4% less likely to calve as 3-yr-olds and had 4.9 ± 1.0 d longer calving intervals. Cows with hard pulls were 9.0 ± 2.1% less likely to return and had 6.5 ± 1.6 d longer calving intervals. Cows requiring Cesarean section were 23.1± 2.5% less likely to return and had 19.6 ± 2.4 d longer calving intervals. Heritability estimates were .17 ± .04 for first calving date, .07 ± .06 for second calving date, .04:105 for calving interval and .11 ± .04 for percent return. Calving interval does not appear to be a useful selection criterion to improve reproduction. Phenotypic and genetic correlations of first calving date with calving interval were -.58 and -.83 ± .37, respectively. The genetic correlation between first and second calving dates was .66 ± .41. Given current data recording procedures, calving date appears to be the most useful potential selection criterion to improve reproductive fitness. / Master of Science

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