Studies on Somatic Cell Counts in Milk from Swedish Dairy Cows

Abstract

A program has started in Sweden to screeen the udder health status of individual cows by bucket somatic cell counting. A study was undertaken to investigate the causes of variation in test-day somatic cell counts (SCC) in milk sampled at monthly intervals. The material included data from two breeds and totalled 87760 observations. The SCC were transformed to a log scale with base ten (LSCC). Large differences between breeds and between parities within breed were demonstrated for both overall means and variation as well as for the impact of different effects on cell count level. The variation in LSCC within breed and parity was shown to be affected by a number of factors, the most important one was the individual cow, which accounted for 38–46% of the total variation, while herd-effects, though highly significant, were of considerably lesser magnitude (5–14%). Stage of lactation, year-month of test and daily milk yield also exerted significant effects on LSCC in most parties. The within lactation repeatability ranged from 0.47 to 0.59. It is suggested that the effects of breed, herd, lactation number, year-month of test, daily milk yield and/or stage of lactation on LSCC-values, should be considered before LSCC-values are used for various evaluation purposes.

Key Words:

• Cell count
• bovine milk
• causes of variation