Title

I. The Hormonal Response of Presynchronization with Gnrh and/or Calf Removal Leading up to Breeding. Ii. Evaluation of Stress on Calves During Separation.

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ag Science and Natural Resources

Date of Award

Summer 2015

Abstract

Estrus synchronization is used in beef cattle herds to control the time of estrus or ovulation, minimize time and labor needed for artificial insemination (AI), and/or improve conception rates to fixed-timed AI. Previous studies demonstrated that there may exist a relationship between estrogen concentrations prior to ovulation and fertility. This experiment evaluated estrogen levels before ovulation in cows that have undergone a presynchronization prior to an estrous synchronization protocol. This study also compared the effects of completely removing the calf or removal of the suckling effect but not the calf from the dam has on calf stress and the cows estrogen concentrations leading up to ovulation and insemination. Twenty mature lactating cows from the Texas A&M University-Commerce Farm were chosen according to days (33-145) post-partum and sex of the calf and randomly assigned to 1 of 4 treatments. Beginning 7 days before the start (day -7) of the 7-Day Co-Synch + CIDR protocol, the cows assigned to the presynchronization treatment were administered gonadotropin releasing hormone (GnRH). The control cows followed a traditional 7-Day Co-Synch + CIDR. Seven days later (day 0), all cows received the 7-Day Co-Synch + CIDR protocol. On day 7, at the time of CIDR removal, calves of cows assigned to the REMOVAL treatment were taken to a different location, whereas calves of cows assigned to the PADDLE treatment received a QuietWean?? nose paddle and returned to their dam. Blood samples were collected seven days (Day -7) prior to the start of the estrus synchronization protocol and at the time of CIDR insertion (Day 0) to assess progesterone levels. Blood samples were taken at the time of CIDR removal (Day 7) and prior to breeding (Day 9) to measure progesterone and estrogen concentrations respectively. Heart rate monitors were put on the calves at Day 7 to help determine the level of stress induced by separation, or the absence of suckling. In addition, fecal samples of the calves were collected over the following 2 days to test cortisol levels. Calves were returned to their dams and calf paddles removed 50 hours after CIDR removal.

Advisor

Douglas Eborn

Subject Categories

Agriculture | Animal Sciences | Life Sciences

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