ABSTRACT:The objective of this study was to determine how non-nutritional factors such as herd, parity, days in milk, milk production, and milk components affect the concentration of milk urea. A retrospective, observational study comprising analyses of individual cow records from monthly dairy herd improvement milk tests including milk urea tests was conducted. Six commercial Holstein dairy herds were involved in the investigation from October 2000 to September 2003. The data were evaluated using the mixed linear model with repeated measures, and parameters were estimated by the REML method. Significant differences in milk urea concentrations were observed between herds (P < 0.0001), with a significant variability between test dates within herds. Significant effects of parity (P = 0.0003), days in milk (P < 0.0001), and their interaction were also found. Higher concentrations of milk urea were determined in the cows on the first and second parity (5.63 and 5.62 mmol/l, respectively) compared to the groups of cows on the third and fourth parity (5.47 mmol/l). It was found that milk urea concentration increased with the square of milk yield (P < 0.0001), while a negative quadratic relationship was found between milk urea concentration and milk fat % (P < 0.0001). It was concluded that milk urea concentration should be evaluated in association with days in milk, milk yield, milk fat %, and milk protein %.

This study was conducted to evaluate the body weights and measurements of 86 Gascon calves and their dams. The effects of the course of parturition, parity of the dams, sex of the calves, and live- or stillborn calves were analysed. Phenotypic correlations between different measurements and calf birth weight as well as the course of parturition were calculated. Internal pelvic measurements were significantly associated with the occurrence of assisted calvings and stillborn calves. Primiparous cows had a smaller pelvic area, lower live weight, and more frequent difficulty in calving compared to older cows. A higher incidence of difficult calvings was observed in bull-calves due to their higher (<I>P</i> < 0.001) birth weight. High and significant correlation coefficients were determined between the birth weight and body measurements of the calves as well as between the calf birth weight and the course of parturition (<I>r</i> = 0.34; <I>P</i> < 0.01). Negative correlations (<I>r</i> = –0.21 to –0.30) were calculated between the internal pelvic measurements of the cows and the course of parturition score. It was concluded that the internal pelvic measurements of the dam and the size and shape of the calf were the factors influencing the course of parturition in this study to the largest extent.

Fertility related traits as cost reducing factors are of increasing concern to Holstein breeders. Dystocia and stillbirth represent important economic costs either direct (loss of calf, death of dam, veterinary assistance and labour) or long-term (culling rate, milk yield and fertility) ones (Meijering, 1984). In spite of low heritability (Kemp et al., 1988 (Meijering, 1984). Adjustments for such non-genetic factors are made in genetic evaluations (Berger, 1994;McGuirk et al., 1999;Fuerst and Egger-Danner, 2003).The incidence of dystocia and stillbirths tends to be population specific because of genetic factors and a range of non-genetic factors (Berry et al., 2007). The Czech Holstein population is specific in its development (conversion from the original Czech Fleckvieh cattle by upgrading crossing with Black and White and Holstein bulls) and in management conditions in herds. In the Czech Republic, data on the course of deliveries on farms have been recorded by breeders for more than ten years, but they have not been used for the genetic evaluation of calving traits yet. A model for the estimation of breeding value of calving difficulty in populations