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The aim of this doctoral thesis was to investigate the effects of dry period length and type of diet through dry and transition periods on feed intake, lactation performance, health status and reproduction of high-yielding dairy cows. The experiment was conducted with 29 high-yielding dairy cows which were divided into two groups. The control group (C; n=14) was assigned to a traditional dry period of approximately 60 d (57 +- 5.9 d) and was fed a far-off dry cow ration from dry-off until 21 d prepartum. From d 21 until calving, the cows were switched to a pre-calving ration containing an additional 3 kg of concentrates. The cows of experimental group (S; n=15) were assigned to a shortened dry period (35 +- 6.3 d) and were continuously fed a late-lactation diet until calving. After calving, both groups were fed the same lactation diet corresponding to their lactation requirements. Dry matter intake of the cows assigned to a shortened dry period and fed a late-lactation diet (17.1 kg/cow/d) was approximately 4.11 kg per cow/d greater compared with the control group (13.0 kg/cow/d) through 60 d prepartum (P=0.0004). After calving, however, the average dry matter intake was approximately 0.71 kg per cow/d higher in the control group (21.48 kg/cow/d (C) vs. 20.77 kg/cow/d (S); P>0.05). Cows with a shortened dry period produced approximately 3.34 kg/d (8.3%) less milk and had flatter lactation curves during the first 100 d of lactation. Through standardized lactation (305 days) cows produced in the average 10 583 kg (C) and 9 638 kg (S) of milk. No differences were observed in live body weight, body condition score or back-fat thickness between the treatments. Shortening the dry period and feeding a late-lactation diet increased the concentrations of VFA and decreased the rumen pH (P<0.05). No differences were observed in basic parameters of blood and rumen fluid after calving. The insemination interval of the cows with shortened dry period was in the average about 34 days shorter compared with conventional dry period (S 64.67 d vs. C 99.11; P=0.007). Shortening the dry period did not affect the colostrum quality or birth weights of the calves.

Over the past 20 years the approach to fertilisation of most of the crops on agricultural land has changed considerably. Complex nutrition has unfortunately gradually changed into one-sided nitrogen fertilisation; to a very limited extent also applying phosphorus and potassium. Other macro-nutrients are usually used for fertilisation only very sporadically and on a long-term basis only more deepening the deficit of nutrients in the soil and decreasing the soil reaction (pH).

My thesis is focused on possible improvement of prediction of net energy lactation (NEL) and net energy fattening (NEV) concentrations by organic matter digestibility (OMD) which is determined by the laboratory method ELOS suitable for routine operations. This should improve current practice when the determination coefficients are taken from the stock-feeding tables. This method of OMD in vitro determination with ANKOM DaisyII Incubator allows serial digestion of more samples in one batch in the fermentation vessel en bloc which significantly decreases laboriousness of operation, filtration is not necessary anymore, and alternatively inoculum can be chosen according to the laboratory potential (rumen juice -- buffer, resp. clean cellulases). Prediction accuracy, when the cellulase preparations made in the Czech Republic with balanced cellulolytic and other activities were used in this experiment, proved to be sufficiently accurate and fully applicable for practical use within a wide range of grass samples. The accuracy of determination of OMD in vitro by ELOS method within values usual for grasses in technical maturity (grazing, conservation), i.e. 60 -- 80, demonstrates results which are practically identical (+-2.43 OMD units) to the Tilley, Terry (1963) method. Specific differences in growth rhythm of 7 tested grasses were stated (P 0.01), and the difference in heading of the earliest grasses (Fl - Hy 'Hykor', FA 'Kora' -- table 5) and late grass (LP 'Kentaur' -- table 5) was 3 weeks. The OMD value decrease is in the average of species, 7 dates of sample collection, two sites and two harvest years 4.44 units, decrease of NEL and NEV values by 0.42 MJ.kg-1 dry matter per week.