Induction of Lymphopenia Causes Luteal Dysfunction in Cattle

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Abstract
Studies were conducted to determine the effects of lymphopenia on reproductive function in heifers. Ten normally cycling heifers were injected with antilymphocyte serum (ALS) or normal horse serum (NHS) once daily between Days 3-6 or 9-17 of the estrous cycle. The ALS caused a significant reduction in circulating lymphocytes without affecting other blood cells. Concentrations of plasma progesterone were reduced (P less than 0.05) in heifers treated with ALS compared to NHS-treated heifers. The concentrations of circulating luteinizing hormone (LH) were also reduced in ALS-treated heifers. LH determinations in frequently collected blood samples showed that the number of LH pulses in the ALS-treated animals (1.4 +/- 0.4) was significantly (P less than 0.05) lower than NHS-treated controls (3.2 +/- 0.2). These studies suggest that immunosuppression caused by induction of lymphopenia causes luteal dysfunction in cycling heifers as a result of decreased pituitary LH secretion.