Estrous and Endocrine Responses of Lactating Holsteins to Forced Ventilation During Summer

¹ Department of Animal and Dairy Sciences, Mississippi State University, Mississippi State 39762

Fourteen lactating and cycling Holsteins in each of two summers were assigned randomly to pens in a free-stall barn either with or without overhead fans to study the effect of fan cooling on certain endocrine and behavioral responses during the estrous cycle. After an adjustment period of 8 d in the first summer and 21 d in the second summer, jugular cannulas were inserted, and 25 mg of PGF₂, were injected. After injection, blood samples were collected frequently for 84 h in the first summer and 88 h in the second summer, followed by collection three times weekly for 3 wk thereafter each summer. Rectal temperatures were lower in the group cooled by fans than in the control group each summer. Luteal progesterone secretion tended to be greater in the fan group each summer; area under the luteal phase curve was significantly higher than for controls during the second summer. There was tendency for more preovulatory surges of LH and higher estrous response rates in the fan group during the second summer. Thus, fan cooling of lactating dairy cows for several weeks before anticipated breeding provides potential for more efficient reproductive performance during the summer.

Key Words: summer • fans • estrous behavior • endocrine changes

Submitted on June 1, 1992
Accepted on September 21, 1992