Sexually dimorphic innate immunological responses of pre-pubertal Brahman cattle following an intravenous lipopolysaccharide challenge.

This study was designed to characterize potential sexually dimorphic immunological responses following a lipopolysaccharide (LPS) challenge in beef cattle. Six female (heifers) and five male (bulls) Brahman calves (average age = 253 ± 19.9 and 288 ± 47.9 days; average body weight = 194 ± 11 kg and 247 ± 19 kg for heifers and bulls, respectively) were challenged with LPS (0.25 μg LPS/kg body weight). Following administration of LPS, all cattle displayed increased sickness behavior beginning at 0.5 h, with heifers on average displaying less sickness behavior than bulls. A febrile response was observed in all animals following LPS administration, with a maximum response observed from 4 to 5.5 h. The average rectal temperature response was greater in heifers than bulls. In all cattle there were elevated serum concentrations of cortisol from 0.5 to 8 h, TNF-α from 1 to 2.5 h, IL-6 from 2 to 8 h, and IFN-γ from 2.5 to 7 h after LPS challenge. Additionally, serum concentrations of TNF-α were greater in heifers than bulls from 1.5 to 2 h after the LPS challenge. Concentrations of IFN-γ were also greater on average in bulls than heifers. Leukopenia occurred from 1 to 8 h, with a decreased neutrophil to lymphocyte ratio for the first 5 h among all calves. These data demonstrate the existence of a sexually dimorphic acute-phase response in pre-pubertal Brahman calves. Specifically, heifers may have a more robust acute response to LPS challenge, even though bulls display more signs of sickness.