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Effect of heat stress during the dry period on estradiol and prolactin interactions in mammary gland gene expression of Holstein cows.

J. A. Negrao

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06-22-2020

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Abstract:

M80
Effect of heat stress during the dry period on estradiol and prolactin interactions in mammary gland gene expression of Holstein cows.
J. A. Negrao*1,2, V. Ouellet2, M. Marrero-Perez2, T. F. Fabris2, J. Laporta2, G. E. Dahl2. 1University of Sao Paulo Pirassununga, SP, Brazil, 2University of Florida Gainesville, FL.

The dry period, a 6 to 8-week nonlactating state between lactations, is essential for maximal mammary development and lactation in dairy cows. Although late-gestation heat stress decreases estrogen (E) and increases prolactin (PRL) concentrations in blood, those impacts on mammary development remain unclear. The objective of this study was to determine how late gestation heat stress-induced E and PRL alterations affect the expression of their receptors and signaling in the mammary gland at different stages of the dry period. Fourteen cows were either exposed to in vivo heat stress (HT, n = 7) or active cooling by fans and soakers (CL, n = 7) for the entire dry period (~45 d). Mammary gland biopsies were performed on d 3 (i.e., involution) and 35 (i.e., proliferation) relative to dry off and equally divided in 3 explants, that were incubated in vitro for 24h in 1 of the 3 mediums: 1- Basal (Bm no PRL or E); 2- CL mimic (Cm: basal + 20ng/mL PRL + 5.8ng/mL E; and 3- HT mimic (Hm: basal + 40 ng/mL PRL + 2.9ng/mL E). Gene expression of PRLR-SF, PRLR-LF, ESR1 and ESR2 were measured using Real Time qPCR. An ANOVA using the mixed procedure of SAS was performed to assess the impacts of in vivo (HT, CL), in vitro (Bm, Cm, Hm) treatments and their interaction on relative transcript expression. Dry cows subjected to HT had increased rectal temperature and respiration rate relative to cows subjected to CL (39.1 vs 38.8 � 0.01�C and 65.2 vs 55.4 � 1.2 breaths/min, respectively), which confirms cooling conditions are effective and necessary for the thermal equilibrium of the CL cows. In vivo HT increased the expression of PRLR-LF relative to CL. However, Hm in vitro treatment decreased the expression of PRLR-SF, ESR1 and ESR2 relative to Bm treatment. These results suggest that E and PRL alterations caused by heat stress exposure can modulate the expression of receptors in the mammary gland, with potential implications for normal mammary development during the dry period.

Keywords: heat stress, mammary explants, culture.