Document Type

Thesis - University Access Only

Award Date

2008

Degree Name

Master of Science (MS)

Department / School

Animal Science

Abstract

Progesterone is essential for the establishment and maintenance of pregnancy, and one proposed method to increase progesterone is by injecting GnRI I at insemination. However, there have been conflicting results with this method. Therefore, three experiments were conducted to evaluate the effects of an injection of GnRI I at insemination on LH pulses and subsequent progesterone. In Experiments I and 2, cows were synchronized with the Select Synch + Controlled Internal Drug Releasing device (CIDR) protocol: (d -7 100 ~tg GnRH and CIDR; d O 25 mg PGF2u and CIDR removal). In experiment 1, cows were allotted into two treatments: 1) GnRH (100 μg) given approximately 12 h after initiation of estrus (n = 5) and 2) control (n ccc 5). Blood samples were collected at 15-min intervals for 6 h at 12 h (bleed 1 ), 26 h (bleed 2), 40 h (bleed 3), 54 h (bleed 4), and 68 h (bleed 5) after onset of estrus. Daily blood samples were collected for 17 d. In experiment 2, cows were allotted into two treatments: GnRI I injected IO to 11 h (n = 10) or 14 to 15 h (n = I 0) after the onset of estrus. Daily blood samples were collected for 17 d. In Experiment 3. cows were synchronized with the COSynch protocol (d -9 100 μg GnRH; d -2 25 mg PGF211; d O 100 μg GnRH). and cows were allotted into two treatments 1) initiated estrus (n = 5) or 2) did not initiate estrus (n = 5) before d 0. Blood samples were collected at 15-min intervals from Oto 6 h (bleed 1). 12 to 20 h (bleed 2). 26 to 34 h (bleed 3 ), and 40 to 48 h (bleed 4) after GnRH. Daily blood samples were collected for 17 d. Cows treated with GnRH after onset of estrus tended (PS 0.075) to have greater LH release during bleed I, tended (P = 0.095) to have fewer pulses during bleed 2, had greater (P = 0.05) progesterone. and had an earlier (P =0.05) rise in progesterone than control cows. Cows treated with GnRH 10 to 11 h after onset of estrus had greater (P = 0.01) progesterone and a faster (P = 0.04) rise in progesterone than cows treated 14 to 15 h after onset of estrus. Initiation of estrus before the GnRH injection did not have an effect on LH release (P:.:: 0.22.) or the rise in progesterone (P = 0.28); however, cows detected in estrus had increased (P - 0.002) progesterone compared to cows not in estrus. In conclusion, timing of a GnRH injection following the onset of estrus influenced LH pulses and subsequent concentrations of progesterone.

Library of Congress Subject Headings

Cattle -- Reproduction

Luteinizing hormone releasing hormone

Estrus

Progesterone

Format

application/pdf

Number of Pages

108

Publisher

South Dakota State University

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