Seasonal heat load is more potent than the degree of body weight loss in dysregulating immune function by reducing white blood cell populations and increasing inflammation in Holstein dairy cows

摘要

We investigated the effects of seasonal heat stressand the degree of body weight (BW) loss postpartum(PP) on immune and inflammatory markers in transitiondairy cows. Blood sampled twice weekly duringthe transition period (3 wk prepartum to 3 wk PP)from 12 peripartum Holstein cows in summer and 12in winter was analyzed for plasma nonesterified fattyacids, the oxidative stress marker malondialdehyde(MDA), haptoglobin, and tumor necrosis factor-α(TNF-α). Complete blood counts and white blood cell(WBC) subpopulations (CD4, CD8, CD25, WC1, andCD335) were examined weekly during the transitionperiod. Adipose tissue biopsies were taken at 7 d PPfrom summer-calving cows. In cows calving duringseasonal heat stress, plasma TNF-α concentrationswere 4.9-fold higher prepartum and 5.1-fold higherPP, and MDA concentrations were higher prepartumand PP than in winter. Hematocrit was lower prepartumand tended to be lower PP in summer comparedwith winter, and after adjusting to hematocrit valuesfewer WBC prepartum (−17%) and PP (−22%), lowermonocytes prepartum (−37%) and PP (−49%), andfewer neutrophils (−25%) PP were found in summercompared with winter-calving cows. The percentages ofcytotoxic T cells (CD8) and natural killer cells (CD335)were lower, as well as prepartum gamma delta-T cells(WC1) in summer compared with winter-calving cows.Moreover, lower red blood cell counts prepartum andmean platelet volume and red blood cell distributionwidth prepartum and PP, as well as higher hemoglobinprepartum and PP, were found in summer than winter-calving cows. In summer, cows that lost moreBW PP had higher plasma MDA and TNF-α concentrations,fewer basophil numbers prepartum, a decreasein the percentage of cells expressing the IL-2 receptor(CD25), increased ratio of T helper cells (CD4):CD8,and a tendency for increased WC1 percentages inblood prepartum, as well as a higher percentage ofWC1 PP and higher abundance of TNF-α and lowerlipopolysaccharide-binding protein in adipose tissuecompared with cows that lost less BW PP. In conclusion,seasonal heat stress during the peripartum periodwas associated with lower WBC counts coupled withincreased levels of subacute inflammation, indicatingdysregulation of immune function, whereas the degreeof BW loss had minor effects. This suggests that heatload is a more potent stressor associated with immunefunction than the variation in the degree of BW loss PPin high-yielding peripartum dairy cows.