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The main aim of this thesis was to analyse growth abilities of hybrids (?Nb x ?Kal) in comparison with original parental population. Further were evaluated reproductive properties of parental breeds of rabbits New Zealand White and Californian and their combination (?Nb x ?Kal). Enter data were gathered in total from 27 litters. Obtained data were summarized and statistically treated in MS Excel programme and STATISTICA version 9. To assess the development of live weight, the rabbits were weighed at 7-day intervals from birth until the end of fattening, it is to the age of 126 days. For the analysis of reproductive abilities was in single females litters observed the number of all born offspring, from that the number of live-born and still-born offspring and the number of weaned offspring. Further, the length of gravidity, the length of season and age at weaning, milkiness and total mortality were observed. The assessment of growth and reproductive abilities was made in dependence on sequence of litter and on the observed calendar year. The results showed higher increases in 60th, 90th and 120th days of age hybrid offspring than a breeds pattern book by paternal population requires. The achievement of high weight gains confirms the suitability of using these hybrids for intensive production of quality dietetic rabbit meat. It was also achieved excellent results in milkiness females in the observed breeding. Its average value was 3965 g, which is comparable with milkiness of broiler breeds in large breedings. Total results confirmed the suitability of using Californian rabbit breeds in a maternal position and the New Zealand White in a paternal position to create commercial hybrids intended for fattening. Their hybrid offspring reach better growth ability than original parental population. Results of this study can be specific recommendation especially for small breeders of meat-type rabbits when choosing a suitable combination of breeds for fattening.

Urėja – vienas svarbiausių baltymų apykaitos produktų. Jį sintezuoja kepenys, o atrajotojams jis taip pat sintetinamas didžiojo prieskrandžio sienelėje iš amoniako, amino rūgščių ir amidų. Urėjos molekulė, maža ir neutrali, gali lengvai prasiskverbti į daugelį audinių. Ji laisvai praeina pro ląstelių membraną ir patenka į tarpląstelinį skystį, o iš ten – į kraujo plazmą ir laisvai filtruojasi šlapime. Palankiausia tyrimams terpė yra pienas, nes jis dažniausiai naudojamas įvairiems laboratoriniams tyrimams. Pieno urėja pradėta tirti ir duomenys apie šį rodiklį pradėti kaupti nuo 2002 m. sausio 1 d. Iki darbo pradžios 2006 m. jau buvo sukaupta daug tyrimo rezultatų. Analizei panaudoti patys naujausi 2006–2008 m. duomenys. Tai pirmas Lietuvoje atliktas visapusiškas urėjos rodiklio tyrimas, veisiamų karvių populiacijoje, panaudojant didelę duomenų imtį (5,4 mln. įrašų). Ir pirmą kartą Lietuvoje šiuolaikiniais tyrimų bei matematiniais ir genetiniais duomenų apdorojimo metodais įvertintos urėjos rodiklio kitimo priežastys, bei jos panaudojimo galimybės. Gautais rezultatais nustatyta urėjos kiekio įtaka reprodukcinėms karvių savybėms, aplinkos veiksnių įtaka urėjos kiekio kitimui, urėjos priklausomybė nuo karvių fiziologinės būklės, genetinė gyvulio įtaka urėjos kiekiui piene, urėjos koreliacija su kitais pieno sudėties ir kokybės rodikliais, urėjos kiekio paveldimumo koeficientas bei ištirta nevisaverčio ir subalansuoto racionų įtaka urėjos koncentracijai piene ir somatinių... [toliau žr. visą tekstą] / The Aim of the Research: To analyze the investigation of urea concentration and the dependence of its concentration in milk on various factors in the population of cows bred in Lithuania. To prepare proposals about the use of the research data about urea concentration for solution of ration balancing and cows healthiness problems. Main Objectives: 1. To evaluate the effect of non genetic factors on urea concentration in milk of the cows, bred in Lithuania. 2. To define the effect of congenerous copulation and heredity coefficient of milk urea. 3. To define the correlation of the heredity coefficients of milk urea and genetic correlation coefficients with milk production, composition and somatic cell count. 4. To define the relation between reproductive properties of cows and somatic cell count in milk and milk urea concentration. 5. To evaluate clinical importance of urea concentration for the prediction of cows’ healthiness and culling. 6. To study the effect of inadequate and balanced rations on urea concentration in milk and changes of somatic cell count during the experiment and at the level of the whole herd. Highly effective system for milk composition and quality evaluation is introduced in Lithuania. According to planned order and frequency milk composition and quality investigations are carried out for each controlled cow and each milk producer. Great number of milk investigation results and other additional data about dairy cows are collected in the database of the... [to full text]