Review/Oorsig Volume 22, Issue 02 - Page 28

Oorsig/Review Seasons in the SCC Dr Alf Lategan and Dr Martin van der Leek All over the world, dairies experience an increase in somatic cell count (SCC) during summer and autumn. The extent to which climatological factors contribute to this increase in South Africa is unknown, although the weather is blamed anecdotally. Consequently, the value of heat abatement or other preventative intervention cannot be established. The relative effect of season and/or heat stress on milk production and SCC is likely to be unique to South African conditions OBJECTIVES This study had three main objectives: • • to study the summer rise in somatic cell count and the possible influence of seasonal factors, using transitional category (TC) as the measure of interest; to study the summer rise in somatic cell count as it may be influenced by temperature 28 • humidity index (THI), using the same measure; and to identify any farm-specific or regional differences in TCs.METHODS The investigation included individual milk recording data for almost 60 000 cows from January 2013 to July 2015. Using current and previous SCC recordings, cows with an SCC>200 x 103 cells/ml were classified as high (H), and cows with an SCC≤ 200 x 103 cells/ml as low (L). Transitional categories (TC) were defined by the change in udder health status from one milk-recording test to another, and included healthy cows (cows with two consecutive low recordings, or LL), recovering cows (cows that had transitioned from a high to a low SCC, or HL), new infections (cows that had transitioned from a low to a high SCC, or LH), and chronically infected cows (cows with two consecutive high