Modification of a GnRH-based system to synchronise oestrus in Bos indicus cattle improves pregnancy rates to AI in heifers but not cows

Cavalieri, Jo, and Das, Sourav (2022) Modification of a GnRH-based system to synchronise oestrus in Bos indicus cattle improves pregnancy rates to AI in heifers but not cows. Australian Veterinary Journal, 100 (4). pp. 162-171.

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Abstract

Objective: To investigate if modification of a gonadotrophin-releasing hormone (GnRH) based protocol to synchronise oestrus in Bos indicus cattle will improve response rates to the first administration of GnRH and improve pregnancy rates to artificial insemination (AI).

Design: Randomised control study.

Methods: Bos indicus heifers, nonlactating and lactating cows allocated to a GnRH-18 treatment (n = 237) were treated with an intravaginal device (IVD) and cloprostenol (0.5 mg IM) on day −11 and on day 0 remaining animals in the GnRH-7 treatment (n = 222) were administered an IVD and every animal was treated with GnRH (100 μg IM). On day 7, equine chorionic gonadotrophin (400 IU IM) and cloprostenol were administered and IVD's were removed. Animals detected in oestrus on day 9 were artificially inseminated while those not detected in oestrus were administered GnRH (100 μg IM) at 1700 hours and inseminated on day 10. Bulls were inserted 2 weeks after completion of AI and remained until day 65.

Results: The GnRH-18 protocol increased the diameter of the largest follicle in the ovary on day 0, increased the percentage of new CL's induced after day 0 (46.3% vs 36.1%, for GnRH-18 and GnRH-7; P = 0.022), decreased circulating concentrations of progesterone on day 7 and increased odds of pregnancy to AI in heifers but not in nonlactating and lactating cows.

Conclusion: Treatment with the GnRH-18 compared to the GnRH-7 protocol increased pregnancy rates to AI in heifers but not in nonlactating or lactating cows.

Item ID: 71519
Item Type: Article (Research - C1)
ISSN: 1751-0813
Copyright Information: © 2022 The Authors.Australian Veterinary Journalpublished by John Wiley & Sons Australia, Ltd on behalf of Australian Veterinary Association. Australian Veterinary JournalThis is an open access article under the terms of theCreative Commons AttributionLicense, which permits use, distribution and reproduction in any medium, provided theoriginal work is properly cited.
Date Deposited: 11 Feb 2022 01:23
FoR Codes: 30 AGRICULTURAL, VETERINARY AND FOOD SCIENCES > 3003 Animal production > 300301 Animal growth and development @ 40%
30 AGRICULTURAL, VETERINARY AND FOOD SCIENCES > 3003 Animal production > 300305 Animal reproduction and breeding @ 40%
49 MATHEMATICAL SCIENCES > 4905 Statistics > 490502 Biostatistics @ 20%
SEO Codes: 10 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 1004 Livestock raising > 100401 Beef cattle @ 50%
10 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 1004 Livestock raising > 100402 Dairy cattle @ 50%
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