Abstract
Abstract. This study was conducted on a sample of 2237 Polish Holstein-Friesian cows. The aim was to estimate the effect of selected environmental factors on the level of urea in cow's milk and on its genetic parameters, i.e. the heritability coefficients, and genetic correlation with other selected traits of milk production. The present study has revealed the existence of a highly significant influence of herd, year of calving, parity, lactation phase, and milk performance level on the urea content in cow's milk. A high urea level in milk was detected in samples collected from older animals, both during the winter season and the middle phase of lactation (101–200 days). The heritability estimates were generally at a low level, particularly in terms of milk yield (0.183) and urea content (0.152–0.159), which may indicate the dominant role of the environment in shaping them. Relatively low values of genetic correlation (−0.097–0.140) between the urea content and other traits suggest that improvement of milk yield and its composition modify the urea level in milk only to a small degree.
Highlights
An appropriate cow feeding programme is a major factor in high milk production
It should be noted that, for accurate interpretation of the urea content, the feed factor and other factors should be taken into consideration
The aim of the present study was to evaluate the effect of the selected environmental factors on the level of urea in cow’s milk and its genetic parameters, i.e. the heritability coefficients and genetic correlation with other selected traits of milk production
Summary
An appropriate cow feeding programme is a major factor in high milk production. Many authors (Aguilar et al, 2012; Biswajit et al, 2011; Geerts et al, 2004; Hojman et al, 2004; Oltner et al, 1985) are of the opinion that, for dairy cows, the level of urea in cow’s milk (MU, milk urea) may be the indicator of whether the energy balance and protein ratio are proper. It should be noted that, for accurate interpretation of the urea content, the feed factor and other factors should be taken into consideration These factors include breed (Rodriguez et al, 1997), parity (Broderick and Clayton, 1997; Godden et al, 2001; Sawa et al, 2011), body weight (Kohn et al, 2002), milk yield (Godden et al, 2001), fat and protein content, days in milk (DIM), milking frequency (Godden et al, 2001; Kgole et al, 2012), and month of the year (Arunvipas et al, 2003; Biswajit et al, 2011; Borkowska et al, 2012; Frand et al, 2003; Hojman et al, 2004; Kgole et al, 2012; Oudah, 2009; Rafieei, 2011; Rzewuska and Strabel, 2013b). In Polish breeding programmes, urea content in cow milk has been monitored since 2000
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