Abstract
Bulk milk samples were collected from 256 dairy herds from 4 districts in Southern Norway: Gudbrandsdal (n = 35), Bergen (n = 15), Hedmark (n = 117) and Hardanger (n = 89).
A total of 6–8 samples were collected in each herd during the indoor season. Data concerning reproductive performance, milk production and nutrition were registered for a period of 15 months starting 7 months before the first milk sample was collected. The urea levels obtained during the sampling period were averaged generating a mean urea level of each herd. The mean urea levels were related to reproductive performance.
The urea levels within districts showed only minor variations during the sampling period. The mean urea level in Hardanger was significantly higher (p < 0.05) than in the other distrikts. This district also had the lowest fertility. Significant correlations between mean urea level and fertility were observed only in Hedmark. Fertility status (FS), an integrated index, and number of inseminations per animal inseminated were significantly affected by the interaction between mean urea level and district. Herds in Hardanger with cows treated for ovarian cysts had a significantly higher mean urea level (p = 0.02) than herds with non-treated cows.
The results appear to support the notion that a negative relationship may exist between bulk milk urea levels and reproductive performance. The great district variations observed indicate, however, that the practical value of such measurements is limited.
Keywords: dairy cows, health, milk production, nutrition, protein.
Sammendrag
Tankmelk-prøver ble samlet fra 256 besetninger fra 4 områder i Sør-Norge: Gudbrandsdal (n = 35), Bergen (n = 15), Hedmark (n = 117) og Hardanger (n = 89). Det ble tatt ut en prøve pr. måned i hver besetning fra oktober til mai. Opplysninger om fruktbarhet, helse, melkeproduksjon og fôring ble registrert fra sju måneder før første melképrøve ble samlet og i 15 måneder framover i hver besetning. Gjennomsnittsnivået for ureamålingene i hver besetning ble sammenholdt med fruktbarhets resultatene.
Det var lite variasjon i ureanivåene i prøveperioden. Hardanger hadde signifikant høyere ureanivå og dårligere fruktbarhetsresultater enn de andre distriktene. Signifikante korrelasjoner mellom ureanivå og fruktbarhet ble bare funnet i Hedmark. Det var en signifikant sammenheng mellom FS-tall og antall inseminasjoner pr. påbegynt ku på den ene siden og samspillet mellom ureanivå og distrikt på den andre. Besetninger i Hardanger hvor kyr var behandlet for cyster hadde høyere ureanivå (p = 0.02) enn besetninger uten cystebehandlede kyr.
Undersøkelsen indikerer at høye ureanivåer i tankmelk kan være forbundet med dårlig fruktbarhet. Store distriktsvise forskjeller bidrar imidlertid til å redusere den praktiske nytten av slike målinger.
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Acknowledgements
The authors wish to thank S. R. Eriksen, K. Sørensen and L.-W. Frederiksen for excellent analytical and technical assistance. Ø. Andresen, T. Lunaas and W. Farstad are gratefully acknowledged for their valuable comments to this manuscript.
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