Somatic cell count (SCC) in sheep milk is analysed as a variable to be genetically improved. SCC in healthy animals was considered as a variable of milk composition, whereas SCC from infected udders was considered as indicative of mastitis.
SCC may be considered as a variable suitable to be used as a selection objective. It is easy to determine through automatic methods and it does not change after the addition of preservatives or after a few storage days either at room temperature or refrigerated. It is influenced by the infectious status of the udder and thus it shows large variability. A logarithmic transformation is needed in order to obtain a normal distribution.
Regarding SCC genetic characteristics, its heritability is nearly zero in healthy udders (0.03 ± 0.02) and low when it is considered as a mastitis indicator. In the latter case heritability shows a higher value (0.12 ± 0.03), when it is used as a lactational measure than when the estimation is obtained from test day measures (0.09 ± 0.02). Genetic correlations are negative (−0.10) with milk yield and near zero (0.03) with protein percentage. Significant effects on SCC are estimated both for herd and lactation, whereas type of birth does not show significant differences.
From a practical point of view, selection against high SCC might cause positive moderate responses. However is does not seem advisable in the present situation of sheep in Castille and León since quicker responses may be obtained through the improvement of the infectious status of herds.