The effect of altering the timing of GnRH administration and artificial insemination in a modified 5-d CO-Synch protocol using sex-sorted semen in dairy heifers

被引:5
|
作者
Macmillan, K. [1 ]
Gobikrushanth, M. [2 ]
Mapletoft, R. J. [2 ]
Colazo, M. G. [1 ]
机构
[1] Univ Alberta, Dept Agr Food & Nutr Sci, Edmonton, AB T6G 2P5, Canada
[2] Univ Saskatchewan, Dept Large Anim Clin Sci, Saskatoon, SK S7N 5B4, Canada
关键词
Split timed AI; Estrus response; Delayed AI; Pregnancy rate; GONADOTROPIN-RELEASING-HORMONE; DELAYED INSEMINATION; CONVENTIONAL SEMEN; ESTRUS DETECTION; INITIAL GNRH; BEEF HEIFERS; PREGNANCY; PROGESTERONE; AI; SYNCHRONIZATION;
D O I
10.1016/j.theriogenology.2020.10.016
中图分类号
Q [生物科学];
学科分类号
07 ; 0710 ; 09 ;
摘要
The objective was to optimize fertility in a modified 5-d CO-Synch protocol by altering the timing of GnRH administration and AI. Holstein heifers (14-16 mo) received a controlled internal drug releasing device (CIDR) on d 0 and on d 5, CIDR were removed, prostaglandin F2 alpha was administered and estrus detection patches were applied. Estrus was detected at 36, 48, 56 and 72 h after CIDR removal. In Experiment 1, control heifers (n = 195) received GnRH concurrent with timed-AI (TAI) 72 h after CIDR removal, regardless of expression of estrus. Treatment heifers expressing estrus at 36 or 48 h were AI at 56 h (n = 101) and the remaining heifers were randomly assigned to one of two groups: GnRH administration at 56 h and TAI at 72 h (GnRH56, n = 147) or GnRH administered concurrently with TAI at 72 h (GnRH72, n = 148). In Experiment 2, heifers expressing estrus at 36 or 48 h following CIDR removal were AI at 56 h (n = 118) and the remaining heifers were either TAI at 72 h (TAI72, n = 102) or 80 h (TAI80, n = 102), with only heifers not displaying estrus by TAI given GnRH concurrent with AI. All heifers were inseminated with sex-sorted semen and pregnancy diagnosis was performed at 28 d following TAI. In Experiment 1, estrus rate (P = 0.81) and pregnancy per AI (P/AI; P = 0.34) did not differ among control, GnRH56 and GnRH72 groups, so GnRH56 and GnRH72 groups were combined into one split-TAI (STAI) group. The P/AI was greater in heifers displaying estrus by 48 h compared to those not displaying estrus and receiving GnRH in both groups (69.5 vs. 31.3%; P < 0.01) and there was a tendency for P/AI to increase in STAI heifers displaying estrus compared to control heifers displaying estrus (73.3 vs. 62.1%; P = 0.10). In Experiment 2, the estrus rate was increased in TAI80 compared to TAI72 heifers (81.4 vs. 62.7%, P < 0.01); however, there was no difference in P/AI (P = 0.74). Heifers displaying estrus in the TAI72 group had a greater P/AI than heifers not displaying estrus in either group (P < 0.01) and tended to have a greater P/AI than heifers in estrus in the TAI80 group (87.5 vs. 69.9%, P = 0.07). Across both experiments, P/AI was increased in heifers that displayed estrus before AI compared with heifers that did not and performing a STAI tended to increase P/AI in heifers that displayed estrus before AI. Other attempts made to optimize P/AI in the modified 5-d CO-Synch protocol by altering the timing of GnRH administration and/or AI were unsuccessful. (C) 2020 Elsevier Inc. All rights reserved.
引用
收藏
页码:53 / 59
页数:7
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