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