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Somatotropin increases plasma ceramide concentrations in relation to enhanced milk yield in Holstein dairy cows.

A. N. Davis



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Somatotropin increases plasma ceramide concentrations in relation to enhanced milk yield in Holstein dairy cows.
A. N. Davis*1, W. A. Myers1, C. Chang1, B. N. Tate1, J. E. Rico1, M. Moniruzzaman2, N. J. Haughey2, J. W. McFadden1. 1Cornell University Ithaca, NY, 2Johns Hopkins University Baltimore, MD.

Recombinant bovine somatotropin (rbST) changes metabolism to spare glucose for milk synthesis in cows. Ceramide inhibits insulin responsiveness in bovine adipocytes, and the accumulation of ceramide in circulation and tissues is associated with insulin resistance and milk production in cows. The mechanisms by which rbST supports lactation may involve ceramide. Eight multiparous lactating Holstein cows were enrolled in a 2 � 2 replicated Latin square design with 14-d periods. Cows received a single rbST injection (Posilac; Elanco Animal Health, Indianapolis, IN; 0.062 mg/kg BW) or no injection. An epinephrine challenge, insulin tolerance test, and liver biopsy were performed. Plasma glucose and total fatty acids (FA) were measured using colorimetry. Plasma insulin concentrations were determined using radioimmunoassay. Plasma and liver ceramides were quantified using mass spec. Data were analyzed using a mixed model. Somatotropin increased yields fat-corrected milk and energy-corrected milk, and feed efficiency (energy-corrected milk/dry matter intake; P < 0.01). All cows started in positive energy balance; however, rbST-treated cows entered negative energy balance by d 3 (P < 0.05; not observed for control cows). Area-under-the-curves for FA in response to epinephrine and insulin were greater in rbST-treated cows (P < 0.05). In response to insulin, glucose concentrations (20 and 30 min post-challenge) and insulin area under the curve were higher with rbST treatment (P < 0.05, 0.10, and 0.01, respectively). Somatotropin tended to reduce glucose clearance rate at 20 min following the insulin challenge (P = 0.10). Treating cows with rbST increased plasma total and very-long-chain (C22:0-, C24:0-, and C26:0-) ceramide concentrations (P < 0.01). Liver C18:0-ceramide concentrations decreased; however, no other liver ceramides were altered with rbST treatment. Plasma ceramides were positively correlated with circulating FA (r = 0.57; P < 0.05) and milk yield (r = 0.63; P < 0.05). We conclude that rbST administration increases plasma ceramide concentrations in association with increased milk production in Holstein cows.

Keywords: ceramide, dairy cow, somatotropin.