Population genetic analysis of milk performance traits in German Improved White -: 1st communication:: Influence of systematic environmental effects

The objectives of this study were to analyse the influence of fixed effects on milk traits of German Improved White. The analysis was based on 12,766 test day records of 1,026 German Improved White with 1,713 lactation records. The milk records were sampled between 1988 and 2002 from 80 flocks in Lower Saxony, Saxony and Baden-Wuerttemberg. The average daily milk yield was 3.16 +/- 1.20 kg with a fat content of 3.03 +/- 0.66 % and a protein content of 3.12 +/- 0.69 %. Somatic cell count (SCC) was transformed into somatic cell score (SCS). Mean SCS was 5.37 +/- 1.75. The average lactation length was 233.8 +/- 63.8 days. The analysis of variance showed a significant influence of stage of lactation on all analysed milk production traits. Also litter size significantly influenced all milk production traits except fat content. Month of lambing and lactation number had a significant influence on milk, fat and protein yield and on fat content. Year of lambing significantly influenced all analysed milk production traits except fat yield and SCS. Furthermore, milk and fat yield and fat and protein content were significantly affected by region. The most striking differences between milk performance traits were observed for the different regions. Dairy goats of Baden-Wuerttemberg produced the lowest daily milk yields and fat content, but the highest protein content as compared with dairy goats from Lower Saxony and Saxony. Animals lambing in January and February had a significant higher milk yield, but a lower fat content than animals with lambings later in the year. In contrast to these findings the differences in milk performance traits between lactation numbers were small. The largest differences in milk yield were 0.7 kg, in fat content 0.04 %, in protein content 0.05 %, and in SCS 0.4 units.