Perturbed metabolism and hormonal profiles in calves infected with Sarcocystis cruzi

Plasma concentrations of growth hormone (GH), thyroid stimulating hormone (TSH), insulin (IN), thyroxine (T₄), and triiodothyronine (T₃) in addition to metabolic parameters N balance (NB), urinary 3-methylhistidine (TMH), urinary creatinine (CR), and urinary hydroxyproline (HP)] were measured in 4-mo-old Holstein steers divided equally among groups infected with Sarcocystis (I), noninfected ad libitum fed (C), and noninfected pair fed to I (PF) (7 steers per treatment). Effects of infection on these parameters beyond those attributable to altered dietary intake were determined using orthogonal contrasts (effect of intake, C vs I + PF; effect of infection, PF vs I). NB was higher in C than I and PF (P<.05) and lower in I than PF (P<.02). Hydroxyproline and CR were influenced by intake (P<.05) and HP excretion was reduced in association with infection (P<.05). Reduced intake was associated with lowered mean basal plasma concentrations of GH, IN, T₃ and T₄ (P<.05). Infection further reduced (P<.001) plasma T₃ concentration.

Triiodothyronine and T₄ responses following an intravenous bolus of thyrotropin releasing hormone (TRH) were measured. The magnitude of the responses in I and PF were lower than those observed in C (P<.05). Plasma T₃ responses were further reduced in association with infection (P<.05). Insulin responses to intravenous arginine infusion (ARG) were also low in association with reduced intake. Growth hormone responses to TRH or ARG were affected by the level of feed intake only. These data suggest that hormonal perturbations associated with the insult of infection further compromise metabolism and the direction of nutrient partitioning that would ordinarily be associated with developmental growth in young steers beyond those responses anticipated from solely the reduction of feed intake.