Concentrations of 17β-Estradiol in Holstein Whole Milk

摘要

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 17β-estradiol (E_2) in whole milk from dairy cows and to determine whether E_2 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 E_2. The homogenized whole milk (3 mL) was extracted twice with ethyl acetate and once with methanol. The extract was reconstituted in benzenermethanol (9:1, vol/vol) and run over a Sephadex LH-20 column to separate E_2 from cholesterol and estrone before quantification using radioimmuno-assay. 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 E_2 concentration in whole milk was 1.4 ± 0.2 pg/ mL and ranged from nondetectable to 22.9 pg/mL. Milk E_2 concentrations averaged 1.3, 0.9, and 3.0 pg/mL for NP, EP, and MP cows, respectively. Milk E_2 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 E_2 mass accumulated in the morning milk was 23.2 ± 3.4 ng/cow. Likewise, using the overall mean concentration for E_2 in milk, the mean E_2 mass in 237 mL (8 fluid ounces) of raw whole milk was 330 pg. The quantity of E_2 in whole milk, therefore, is low and is unlikely to pose a health risk for humans.