Evaluation of a modified GnRH-based timed-AI protocol associated with estrus detection in beef heifers inseminated with sex-selected or conventional semen.

Autor: Colazo MG; Livestock Research Section, Alberta Agriculture and Forestry, Edmonton, T6H 5T6, Canada. Electronic address: marcos.colazo@gov.ab.ca., Whittaker P; The Farm Animal Hospital, Leduc, T9E 6Z9, Canada., Macmillan K; Livestock Research Section, Alberta Agriculture and Forestry, Edmonton, T6H 5T6, Canada., Bignell D; Livestock Research Section, Alberta Agriculture and Forestry, Edmonton, T6H 5T6, Canada., Boender G; The Farm Animal Hospital, Leduc, T9E 6Z9, Canada., de Carvalho Guimaraes R; Sao Paulo State University, Aracatuba, 16050-680, Brazil., Mapletoft RJ; Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, S7N 5B4, Canada.
Jazyk: angličtina
Zdroj: Theriogenology [Theriogenology] 2018 Sep 15; Vol. 118, pp. 90-95. Date of Electronic Publication: 2018 May 31.
DOI: 10.1016/j.theriogenology.2018.05.037
Abstrakt: The main objective was to compare pregnancy per AI (P/AI) between sex-selected and conventional semen in cyclic beef heifers subjected to a 5-day Co-synch plus CIDR protocol and evaluated the usefulness of an estrus detection (ED) aid to identify heifers that were most likely to conceive. This study also determined if the expression of estrus before timed-AI (TAI) would be associated with increased P/AI in acyclic heifers inseminated with conventional semen. Heifers (n = 1690; 320-523 kg of body weight, and 13-15 mo of age) at three locations over 2 years were scanned by ultrasonography to determine cyclicity (presence of luteal tissue) and reproductive tract normalcy. Cyclic heifers (n = 1331) received a progesterone releasing device (CIDR) on Day 0, CIDR removal and 500 μg of cloprostenol (PGF) on Day 5, and 100 μg of GnRH along with TAI on Day 8. Acyclic heifers (n = 275) received the same treatment with the addition of GnRH on Day 0. On Day 5, all heifers received ED patches (Estrotect™) that were scored from 0 to 3, based on color change between initial application and Day 8; 0 = unchanged, 1 = ≤ 50% color change, 2 = > 50% color change, 3 = missing. Estrus was defined to have occurred when an ED patch was scored 2 or 3. Cyclic heifers were inseminated with either frozen-thawed sex-selected or conventional semen from either of three sires available commercially (two per year). Acyclic heifers were inseminated with conventional semen. Pregnancy diagnosis was performed by transrectal ultrasonography 28 or 48 d after TAI, depending on management. The percentage of cyclic heifers was 83.9% and the average estrus response was 63.8%. P/AI was greater (P < 0.01) in cyclic compared to acyclic heifers (53.3 vs. 36.0%) and tended to be greater (P = 0.07) for conventional semen (52.3 vs. 47.6%), despite all acyclic heifers being inseminated with conventional semen. Heifers with an ED patch scored 2 (61.1%) or 3 (58.6%) had greater (P < 0.01) P/AI than those scored 0 (31.8%) or 1 (33.1%), regardless of semen type. Pregnancy per AI was greater (P < 0.01) for heifers detected in estrus (60.6 vs. 32.3%). In cyclic heifers that did not exhibit estrus, P/AI was lower (P < 0.01) in those inseminated with sex-selected semen (27.8 vs. 45.9%), while in heifers that exhibited estrus, P/AI only tended to be lower (P = 0.08; 56.7 vs. 65.5%). In summary, P/AI was greater in cyclic heifers, in those inseminated with conventional semen and in those exhibiting estrus before TAI. The ED patches were considered useful to identify animals for TAI with sex-selected semen and could be used to increase the adoption of this technology in beef herds.
(Copyright © 2018. Published by Elsevier Inc.)
Databáze: MEDLINE
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