Abstract. The aim of this study was to analyse the effect of the temperament of cows on their lifetime production efficiency. Data on milk performance, longevity and culling reasons of 11 629 Polish Holstein-Friesian cows were extracted from the SYMLEK database. Using the methodology of the Polish Federation of Cattle Breeders and Dairy Farmers, cow temperament was assessed as follows: 1 – calm; 2 – normal; and 3 – excitable or aggressive. Most cows showed a normal temperament (89.52 %). Over successive years of the evaluation, there were increases in the proportion of cows with a calm (from 2.98 to 6.85 %) and excitable temperament (from 7.50 to 8.27 %). Temperament was found to have a highly significant effect on first lactation milk yield, first lactation daily milk yield, milk yield per day of age, and milk yield per day of productive life. In cows with a calm temperament, first lactation milk yield was 621 kg higher than in cows with a normal temperament and 329 kg higher compared to excitable (aggressive) cows.

Material for the study was collected from the SYMLEK database and provided information on 148385 parturitions of Polish Black-and-White Holstein-Friesian cows representing the active population (part of the performance evaluation) in the Pomorze and Kujawy regions. The animals first calved in 2006 and were used or culled by the end of 2012. GLM and chi-square procedures of the SAS package were used for the statistical calculations. The number and sex of calves born had an effect (P≤0.01) on the parturition process and on the level of perinatal mortality. As the number of foetuses increased, the proportion of difficult parturitions increased from 4.3 to 28.6%. A decrease in calving ease was also related to the fact that the calf was of male sex. The risk of perinatal mortality increased after multiple pregnancy and when a bull calf was born (among single calves perinatal mortality was over 3 times as frequent in bull calves compared to heifers; among samesex twins perinatal mortality was around twice as frequent when two bull calves compared to two heifers were born; for births of opposite-sex twins, perinatal mortality was more frequent among bull calves). It was also found that perinatal mortality of calves increased with increasing level of calving difficulty. For very difficult parturitions, the risk of perinatal mortality among calves, regardless of sex, increased 10-fold in relation to unassisted parturition.

An analysis of the effect of milk urea and protein levels in four consecutive lactations on fertility indices of Blackand-White Polish Holstein-Friesian cows, milk recorded in the Kujawsko-Pomorskie province has been made. Poorer fertility indices were found in first-calf heifers and second lactation cows receiving energy-deficient diets and in older (third and fourth lactation) cows receiving excess dietary protein and energy. Best fertility was found in young cows fed excess protein (>3.60%) regardless of milk urea levels, and in older cows having lower and optimum levels regardless of protein levels. Cow fertility is differentiated more by milk protein levels than by urea content. Fertility parameters were poorer in first and second lactation cows than in older cows. The coefficients of correlation between milk urea and protein levels and fertility indices were very low, with the only significant differences between protein content vs. calving interval and reproductive rest period.Key words: cows, urea, protein, fertility STRESZCZENIEAnalizowano wpływ poziomu mocznika i białka w mleku w czterech kolejnych laktacjach na wskaźniki płodności krów rasy polskiej holsztyńsko-fryzyjskiej odmiany czarno-białej, będących pod oceną użytkowości mlecznej w województwie kujawsko-pomorskim. Gorsze wskaźniki płodności występowały u krów pierwiastek i w II laktacji przy niedoborze energii w dawce pokarmowej, natomiast u krów starszych w III i IV laktacji zarówno przy nadmiarze białka jak i energii. Krowy młode wykazywały najlepszą płodność niezależnie od poziomu mocznika w mleku, przy nadmiarze białka >3,60%, natomiast krowy starsze niezależnie od poziomu białka przy niższej i optymalnej zawartości mocznika. Poziom białka w mleku bardziej różnicuje płodność krów niż zawartość mocznika. Parametry płodności były gorsze u krów w I i II laktacji niż u krów starszych. Współczynniki korelacji pomiędzy poziomem mocznika i białka w mleku a wskaźnikami płodności były bardzo niskie i tylko w przypadku zawartości białka a OMW i OSR istotne statystycznie Słowa kluczowe: krowy / mocznik / białko / płodność 476

The aim of the study was to analyse the effect of the housing system (tie-stall vs free-stall) on cow cleanliness, and the effect of the degree of cow dirtiness on the milk somatic cell count. Over 33% of the cows were found to be clean, with more of them in the free-stall barn. Analysis of the cleanliness of body parts showed that the highest hygiene level was characteristic of the udders and underbelly (scores of 1 for 47% and 56% of the cows, respectively). In the free-stall barn, there were over twice as many cows with clean udders (58%) and almost twice as few cows with very dirty udders. Regardless of the housing system, the degree of udder dirtiness created differences (P ≤ 0.01) in the natural log somatic cell count. The natural log somatic cell count increased from 11.54 to 12.37 on average with increased dirtiness of the udder. Greater differences in the cytological quality of milk were found in cows housed in the free-stall system. When analysing the effect of overall dirtiness of the cows and the body parts on the percentage of SCC classes, it was found that highest quality milk