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Submitted to: Research Update for Fort Keogh Livestock and Range Research Laboratory
Publication Type: Popular Publication Publication Acceptance Date: 10/1/2002 Publication Date: 1/15/2003 Citation: GEARY, T.W. INITIATION AND SYNCHRONIZATION OF ESTROUS CYCLES IN COMMERCIAL BEEF HERDS FOR NATURAL SERVICE. RESEARCH UPDATE FOR FORT KEOGH LIVESTOCK AND RANGE RESEARCH LABORATORY. p. 41-42. 2003. Interpretive Summary: Most producers believe estrous synchronization is a tool used only for synchronization of estrus to facilitate use of artificial insemination (AI). However, synchronization of estrus is actually very applicable to natural service because it can often induce estrous cycles in anestrous cows or heifers and shorten the interval from calving to conception. It also gives cattle more opportunities to conceive during a defined breeding season, resulting in increased pregnancy rates, and earlier calving dates the following year, ultimately translating into older and heavier calves at weaning. Producers will likely only adopt an estrous synchronization protocol for natural service if it is cheap, easy to administer (generally requiring only one handling of cows), and effective on the majority of the cowherd. These studies make use of the facts that a single injection of prostaglandin (PGF) is only effective in cyclic cattle with a corpus luteum on their ovaries (approximately day 6 to 18 of the estrous cycle), that PGF is capable of terminating pregnancies, and that exposure of cows to bulls following calving shortens the interval to return to estrous cyclicity. The goal of these studies was to determine whether fertile bull exposure coupled with an injection of PGF could be used to synchronize the estrous cycles of cyclic and anestral cows and heifers. Cows that received PGF at approximately d 25, 30, or 35 of pregnancy returned to estrus within 6 days of PGF and had 68, 79, and 86% synchronized pregnancy rates, respectively. Control, non-pregnant cows receiving PFG during the futeal phase of their estrous cycle had a 69% synchronized pregnancy rate. These preliminary results are promising and will be followed with larger field traits. Technical Abstract: Most producers believe estrous synchronization is a tool used only for synchronization of estrus to facilitate use of artificial insemination (AI). However, synchronization of estrus is actually very applicable to natural service because it can often induce estrous cycles in anestrous cows or heifers and shorten the interval from calving to conception. It also gives cattle more opportunities to conceive during a defined breeding season, resulting in increased pregnancy rates, and earlier calving dates the following year, ultimately translating into older and heavier calves at weaning. Producers will likely only adopt an estrous synchronization protocol for natural service if it is cheap, easy to administer (generally requiring only one handling of cows), and effective on the majority of the cowherd. These studies make use of the facts that a single injection of prostaglandin (PGF) is only effective in cyclic cattle with a corpus luteum on their ovaries (approximately day 6 to 18 of the estrous cycle), that PGF is capable of terminating pregnancies, and that exposure of cows to bulls following calving shortens the interval to return to estrous cyclicity. The goal of these studies was to determine whether fertile bull exposure coupled with an injection of PGF could be used to synchronize the estrous cycles of cyclic and anestral cows and heifers. Cows that received PGF at approximately d 25, 30, or 35 of pregnancy returned to estrus within 6 days of PGF and had 68, 79, and 86% synchronized pregnancy rates, respectively. Control, non-pregnant cows receiving PFG during the futeal phase of their estrous cycle had a 69% synchronized pregnancy rate. These preliminary results are promising and will be followed with larger field traits. |
