Effect of heat stress during the dry period on mammary gland development

• Published in: Journal of dairy science Vol. 94; no. 12; pp. 5976 - 5986
• Main Authors: Tao, S., Bubolz, J.W., do Amaral, B.C., Thompson, I.M., Hayen, M.J., Johnson, S.E., Dahl, G.E.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.12.2011; Elsevier
• Subjects: Animal Feed; Animal productions; Animals; antigens; apoptosis; barns; Biological and medical sciences; Body Temperature - physiology; calving; Cattle; cell proliferation; cooling; cows; dairy protein; dry matter intake; dry period; epithelial cell; Female; Food industries; free stalls; Fundamental and applied biological sciences. Psychology; heat stress; Heat-Shock Response - physiology; Hot Temperature; Housing, Animal; lactation; Lactation - physiology; mammary gland; mammary glands; Mammary Glands, Animal - growth & development; Mammary Glands, Animal - physiology; metabolism; milk; Milk and cheese industries. Ice creams; milk equivalent; milk yield; respiratory rate; Seasons; somatic cells; sprinklers; temperature; Terrestrial animal productions; Vertebrates; heat stress; mammary gland; dry period; epithelial cell; Heat; Dairy industry; Development; Epithelial cell; Dry; Mammary gland; Stress
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2011-4329

Heat stress during the dry period negatively affects hepatic metabolism and cellular immune function during the transition period, and milk production in the subsequent lactation. However, the cellular mechanisms involved in the depressed mammary gland function remain unknown. The objective of the present study was to determine the effect of heat stress during the dry period on various indices of mammary gland development of multiparous cows. Cows were dried off approximately 46 d before expected calving and randomly assigned to 2 treatments, heat stress (HT, n=15) or cooling (CL, n=14), based on mature equivalent milk production. Cows in the CL treatment were provided with sprinklers and fans that came on when ambient temperatures reached 21.1°C, whereas HT cows were housed in the same barn without fans and sprinklers. After parturition, all cows were housed in a freestall barn with cooling. Rectal temperatures were measured twice daily (0730 and 1430h) and respiration rates recorded at 1500h on a Monday-Wednesday-Friday schedule from dry off to calving. Milk yield and composition were recorded daily up to 280 d in milk. Daily dry matter intake was measured from dry off to 42 d relative to calving. Mammary biopsies were collected at dry off, −20, 2, and 20 d relative to calving from a subset of cows (HT, n=7; CL, n=7). Labeling with Ki67 antigen and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling were used to evaluate mammary cell proliferation and apoptosis, respectively. The average temperature-humidity index during the dry period was 76.6 and not different between treatments. Heat-stressed cows had higher rectal temperatures in the morning (38.8 vs. 38.6°C) and afternoon (39.4 vs. 39.0°C), greater respiration rates (78.4 vs. 45.6 breath/min), and decreased dry matter intake (8.9 vs. 10.6kg/d) when dry compared with CL cows. Relative to HT cows, CL cows had greater milk production (28.9 vs. 33.9kg/d), lower milk protein concentration (3.01 vs. 2.87%), and tended to have lower somatic cell score (3.35 vs. 2.94) through 280 d in milk. Heat stress during the dry period decreased mammary cell proliferation rate (1.0 vs. 3.3%) at −20 d relative to calving compared with CL cows. Mammary cell apoptosis was not affected by prepartum heat stress. We conclude that heat stress during the dry period compromises mammary gland development before parturition, which decreases milk yield in the next lactation.