Table 1.
Physiological and production measures of first-lactation heifers that were exposed to heat stress (IUHT, n = 17) or cooling (IUCL, n = 18) conditions through the intrauterine environment.
Fig 1.
Histological evaluation of the mammary gland from first-lactation heifers.
Heifers were born to dams actively cooled with fans and water soakers (in utero cooled, IUCL; n = 10) or heat stressed (no heat abatement, in utero heat stressed, IUHT; n = 9) during the last 46 d of gestation. Mammary biopsies were taken from heifers at 21 and 42 days in milk (DIM). (A) Hematoxylin and eosin (H&E) stained and Masson’s trichrome stained mammary tissue at 20X. Connective tissue is stained blue. (B) Luminal area of mammary alveoli was smaller for IUHT (red bars) compared to IUCL (blue bars) (P = 0.001). (C) IUHT had a higher percent connective tissue comprising the mammary gland at 21 DIM compared to IUCL (P = 0.03). Total tissue area at 20X is 574,497 μm2. Data presented as LSM ± SEM. Disparate letters indicate significant differences. AL = alveoli lumen.
Fig 2.
Correlation between luminal area of mammary alveoli and mammary epithelial cell number.
Data are from mammary tissue collected from lactating cows at 21 days in milk (DIM). Data presented as mean ± SEM for in utero heat and cooled cows combined, r = 0.90, P < 0.001.
Fig 3.
Immunohistochemistry of proliferating (Ki67) cells in the mammary gland of first-lactation heifers.
Heifers were born to dams actively cooled with fans and water soakers (in utero cooled, IUCL; n = 10) or heat stressed (no heat abatement, in utero heat stress, IUHT; n = 9) during the last 46 d of gestation. Mammary biopsies from heifers were collected at 21 and 42 days in milk (DIM). (A) Ki67 staining of cells in mammary tissue. (B) Percent of proliferating mammary epithelial cells (MEC), stromal cells, and total mammary cells. There was a tendency for IUHT heifers (red bars) to have a lower percent of proliferating mammary cells compared to IUCL heifers (blue bars) (P = 0.09). (C) Negative (14 DIM mammary tissue without primary antibody) and positive (jejunum tissue from a 2-day old calf) controls for the Ki67 assay. Data are presented as LSM ± SEM. Red arrows indicate proliferating cells (stained brown).
Fig 4.
Immunohistochemistry of apoptotic (TUNEL) cells in the mammary gland of first-lactation heifers.
Heifers were born to dams actively cooled with fans and water soakers (in utero cooled, IUCL; n = 10) or heat stressed (no heat abatement, in utero heat stress, IUHT; n = 9) during the last 46 d of gestation. Mammary biopsies were collected at 21 and 42 days in milk (DIM). (A) TUNEL staining of cells in mammary tissue. (B) Percent of mammary epithelial cells (MEC), stromal cells, and total mammary cells undergoing apoptosis. (C) Negative and positive controls for the TUNEL assay. The negative control was mammary tissue of a 14 DIM cow run with TdT enzyme diluted in stop/wash buffer instead of reaction buffer. The positive control was rat mammary gland 3–5 days post-weaning. Differences in the percent of apoptotic cells between IUHT (red bars) and IUCL (blue bars) heifers were not significant for any cell type (P > 0.05). Data are presented as LSM ± SEM. Red arrows denote cells undergoing apoptosis (stained brown).