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Concentrations of 17ß-Estradiol in Holstein Whole Milk

Department of Dairy and Animal Science, The Pennsylvania State University, University Park 16802

¹ Corresponding author: rsk7{at}psu.edu

Some individuals have expressed concern about estrogens in food because of their potential to promote growth of estrogen-sensitive human cancer cells. Researchers have reported concentrations of estrogen in milk but few whole milk samples have been analyzed. Because estrogen associates with the fat phase of milk, the analysis of whole milk is an important consideration. The objectives of this study, therefore, were to quantify 17ß-estradiol (E₂) in whole milk from dairy cows and to determine whether E₂ concentrations in milk from cows in the second half of pregnancy were greater than that in milk from cows in the first half of pregnancy or in nonpregnant cows. Milk samples and weights were collected during a single morning milking from 206 Holstein cows. Triplicate samples were collected and 2 samples were analyzed for fat, protein, lactose, and somatic cell counts (SCC); 1 sample was homogenized and analyzed for E₂. The homogenized whole milk (3 mL) was extracted twice with ethyl acetate and once with methanol. The extract was reconstituted in benzene:methanol (9:1, vol/vol) and run over a Sephadex LH-20 column to separate E₂ from cholesterol and estrone before quantification using radioimmunoassay. Cows were classified as not pregnant (NP, n = 138), early pregnant (EP, 1 to 140 d pregnant, n = 47), or midpregnant (MP, 141 to 210 d pregnant, n = 21) at the time of milk sampling based on herd health records. Mean E₂ concentration in whole milk was 1.4 ± 0.2 pg/mL and ranged from nondetectable to 22.9 pg/mL. Milk E₂ concentrations averaged 1.3, 0.9, and 3.0 pg/mL for NP, EP, and MP cows, respectively. Milk E₂ concentrations for MP cows were greater and differed from those of NP and EP cows. Milk composition was normal for a Holstein herd in that log SCC values and percentages of fat, protein, and lactose averaged 4.9, 3.5, 3.1, and 4.8, respectively. Estradiol concentration was significantly correlated (r = 0.20) with percentage fat in milk. Mean milk yield was 18.9 ± 0.6 kg for the morning milking. The mean E₂ mass accumulated in the morning milk was 23.2 ± 3.4 ng/cow. Likewise, using the overall mean concentration for E₂ in milk, the mean E₂ mass in 237 mL (8 fluid ounces) of raw whole milk was 330 pg. The quantity of E₂ in whole milk, therefore, is low and is unlikely to pose a health risk for humans.

Key Words: 17ß-estradiol • whole milk • pregnancy

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