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Influence of Estrus of Dairy Goats on Somatic Cell Count, Milk Traits, and Sex Steroid Receptors in the Mammary Gland

P. Moroni^*,1, G. Pisoni, G. Savoini, E. van Lier, S. Acuña^#, J. P. Damián^# and A. Meikle^#

^* Department of Veterinary Pathology, Hygiene and Public Health, and
Department of Veterinary Sciences and Technologies for Food Safety, University of Milan, via Celoria 10, 20133 Milan, Italy
Animal and Forage Sciences Department, Faculty of Agriculture, and
^# Department of Molecular and Cellular Biology, Veterinary Faculty, University of Uruguay, Montevideo, Uruguay

¹ Corresponding author: paolo.moroni{at}unimi.it

Two experiments were conducted to study the effect of the stage of a spontaneous estrus cycle on milk yield and constituents [somatic cell count (SCC), fat, protein, caseins, lactose, and urea content] and on estrogen receptor- (ER ) and progesterone receptor (PR) immunostaining in the mammary gland. In experiment I, the major components of milk and SCC were monitored weekly in 80 lactating Saanen goats for 6 wk, whereas detection of estrus was daily. In experiment II, milk samples were collected daily for SCC determination during 1 spontaneous estrus (d 0) until the second spontaneous estrus in 14 Saanen goats. The day of the estrous cycle was confirmed by plasma progesterone and 17ß-estradiol levels. Immunoreactivity of ER and PR was analyzed in mammary gland samples of 8 Saanen goats (d 0, n = 4; d 10, n = 4) and the number of positive nuclei and intensity of the staining were evaluated in 1,000 cells. In experiment I, milk casein and protein percentages were significantly affected by the stage of estrous cycle; during proestrus and estrus, these variables were higher (3.32 ± 0.06 and 4.44 ± 0.08) than during metestrus (3.03 ± 0.07 and 4.07 ± 0.10), but not higher than during diestrus (3.23 ± 0.06 and 4.35 ± 0.09, respectively). In experiment II, daily measurement of SCC revealed higher levels at estrus (7,195 ± 672 x 10³ cells/mL) and a decline toward the luteal phase (1,694 ± 672 ± 10³ cells/mL). Estrogen receptor- and PR immunostaining were exclusively detected on epithelial cells. The percentage of positive nuclei to ER was higher on d 0 than on d 10 (75.4 ± 8.8 vs. 68.3 ± 8.8%), but no change was observed for PR (4.0 ± 0.3 vs. 3.5 ± 0.4%). The average immunostaining intensity for both receptors was greater on d 0 than on d 10 (ER : 1.44 ± 0.02 vs. 1.35 ± 0.02; PR: 0.079 ± 0.008 vs. 0.057 ± 0.008). The high SCC at estrus in experiment II was associated with high plasma estradiol and low progesterone, suggesting that the increased SCC could be brought about by the estrogen-induced proliferation and exfoliation of epithelial cells. In addition, this action may be supported by the higher sensitivity to estrogens (ER content) found at d 0.

Key Words: estrus • sex steroid receptor • somatic cell count • dairy goat

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