Holstein × Montbéliarde-sired F1 generation crossbred female calves have an increased cellular immune response potential compared with purebred Holsteins.

It is well known that crossbreds show many advantages over purebreds in improving calf health traits, but the immunological factors responsible for this heterosis remain largely unclear. The objective of this study was to compare the cellular immune responses and antibodies of Holstein (HO) and Montbéliarde-sired × Holstein (MH) F1 generation female calves, and investigate the effects of crossbreeding on the immunity. Fifty three-month-old healthy female calves (25 HO, 25 MH) were selected meticulously in a farm with the same criteria. Subsequently, complete blood count, flow cytometric analysis of T cell subsets and intracellular IFN-γ production, as well as indirect ELISA analysis of antibodies were performed in order to determine the immune profiles of the two groups of calves. We found that MH calves had higher percentage and number of CD4⁺ and CD8⁺ T cells than HO calves in the peripheral blood (p < 0.05), with higher MFI of CD44 on CD4⁺ and CD8⁺ T cells (p < 0.05). When stimulated by PMA and Ionomycin, the CD4⁺ and CD8⁺ T cells from MH calves secreted more IFN-γ than that of HO calves (p < 0.01). These results suggested that some immunological traits have been improved in MH calves, which may be an important cause of heterosis in crossbred animals.