Seasonal variation in non-specific immunity in relation to management and feeding practices in a semi-extensive dairy sheep farm in Greece

Non-specific immune function of dairy sheep was studied from January to August 2002 in Greece. Eight ewes from a commercial semi-extensive farm unit of 95 ewes were randomly selected and blood samples were obtained monthly where monocyte/macrophages and neutrophils were isolated. The following parameters were measured: total cell-associated urokinase-plasminogen activator (u-PA), membrane-bound u-PA and superoxide anion production by activated macrophages and neutrophils, as well as free unoccupied u-PA binding sites of activated and resting (non-activated) macrophages and neutrophils. Results indicate seasonal variation (P < 0.001) in non-specific immunity. More specifically, a significant decline in total cell-associated u-PA, membrane-bound u-PA and superoxide anion production by activated macrophages and neutrophils was recorded in March. Free, unoccupied u-PA binding sites of resting and activated macrophages and neutrophils reached their lowest values in March and remained low in April. All immune parameters (total cell-associated u-PA, membrane-bound u-PA, free unoccupied u-PA binding sites and superoxide anion production) measured, during the subsequent summer period (May–August) reached the same or even higher values than those of the winter months (January, February). It is unlikely that poor nutrition was responsible for the decline in non-specific immune function during March and no apparent correlation between non-specific immunity and the hours the animals spent grazing daily was observed. However, restricted pasturing for a week due to adverse weather conditions, immediately before the March sampling period, appears responsible for this decline. In conclusion, it can be said that dairy sheep, under local Greek farming management practices, should have aminimal daily access to pasture for proper immune (non-specific) function. © 2003 Elsevier B.V. All rights reserved