Expression of estrus before fixed-time AI affects conception rates and factors that impact expression of estrus and the repeatability of expression of estrus in sequential breeding seasons

Richardson, Brittany N.; Hill, Scott L.; Stevenson, J. S.; Djira, Gemechis D.; Perry, George A.

doi:10.1016/j.anireprosci.2016.01.013

Cited by 91 publications

(67 citation statements)

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“…The current study and previous research indicates that more than 50% of cows in a split TAI program displayed estrus by 60 to 65 h (Thomas et al, 2014b;Hill et al, 2016). In previous research (Hill et al, 2016), time to the first assessment of estrus was 60 h after CIDR insert removal, resulting in 46.3% of cows in estrus compared with 61.3% of cows detected by 65 h in the current study. Furthermore, for cows not detected in estrus by 60 h in the latter study, administration of GnRH at either 60 h (15 h before AI) or 75 h (concurrent with AI) produced a similar PR.…”

Section: Discussionsupporting

confidence: 39%

“…In contrast, previous estrus cycle status of the sampled subpopulation of cows in the present study did not influence the proportion of cycling and noncycling cows detected in estrus by 65 h after PGF 2α . Cows with a lesser BCS, however, are less likely to display estrus than cows with a greater BCS (Richardson et al, 2016). Stage of the estrous cycle at the initiation of the synchronization program for cycling heifers can alter the timing of estrus (Atkins et al, 2008).…”

Section: Discussionmentioning

confidence: 99%

“…Inseminating cows after they have expressed estrus increases pregnancy risk (pR) compared with cows that do not display estrus in a timed AI (TaI) program (Richardson et al, 2016). Identification of estrus status can be facilitated by using estrus-detection patches.…”

Section: Introductionmentioning

confidence: 99%

“…Identification of estrus status can be facilitated by using estrus-detection patches. Varying AI timing according to estrus status has increased PR in some (Markwood et al, 2014;Thomas et al, 2014a;Hill et al, 2016) but not Gonadotropin-releasing hormone increased pregnancy risk in suckled beef cows not detected in estrus and subjected to a split-time artificial insemination program 1,2 all studies (Thomas et al, 2014b). Reducing the number of injections in a TAI program decreases labor requirements, stress on cows, and overall cost of the program.…”

Section: Introductionmentioning

confidence: 99%

“…A split-time AI program decreases the time between estrus expression and insemination compared with a single fixed-time AI when the first AI occurs before the recommended standard 60-to 66-h fixed time (Johnson et al, 2011). Delaying AI results in approximately 50% more cows displaying estrus when compared with a single insemination time (Hill et al, 2016). Eliminating the GnRH injection at AI for cows displaying estrus in a split TAI program can reduce the number of GnRH injections required and the program cost.…”

Section: Introductionmentioning

confidence: 99%

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Gonadotropin-releasing hormone increased pregnancy risk in suckled beef cows not detected in estrus and subjected to a split-time artificial insemination program12

Hill

Grieger

Olson

et al. 2016

Journal of Animal Science

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We hypothesized that GnRH would increase pregnancy risk (PR) in a split-time AI program for cows in which estrus was not detected. A total of 1,236 suckled beef cows at 12 locations in 3 states (Colorado, Kansas, and North Dakota) were enrolled. Before applying the fixed-time AI program, BCS was assessed. Cows were treated on d −7 with a progesterone insert concurrent with 100 μg GnRH and on d 0 with 25 mg PGF 2α plus removal of the insert. Estrus-detection patches were affixed to cows at insert removal. Estrus was defined to have occurred when an estrus-detection patch was >50% colored (activated). Cows in estrus by 65 h (n = 758; 61.3% of all cows) were randomly allocated to 2 treatments: 1) 100 μg GnRH and early + GnRH (E+G; n = 373) or 2) AI only at 65 h (early -no GnRH [E-G]; n = 385). The remaining cows were randomly allocated to 2 treatments: 1) 5(L+G; n = 252) or 2) AI only at 84 h (late no GnRH [L-G]; n = 226). Pregnancy was determined 35 d after AI via transrectal ultrasound. Pregnancy risk did not differ (P = 0.68) between E+G and E-G cows (61.9 vs. 60.4%, respectively). Conversely, for cows inseminated at 84 h, PR was greater (P = 0.01) in cows that received GnRH (L+G) compared with their herd mates not receiving GnRH (L-G; 41.7 vs. 30.8%, respectively). Of those cows not detected in estrus by 65 h, 42.1% were detected by 84 h, for a total expression of estrus by all cows of 77.6%. Administration of GnRH increased (P < 0.01) PR in cows not detected in estrus by 84 h (+GnRH = 33.4% [n = 146] vs. no GnRH = 15.0% [n = 128]) but had no effect in cows expressing estrus by 84 h (+GnRH = 65.3% [n = 103] vs. no GnRH = 61.7% [n = 97]). Neither estrus expression by 65 or 84 h nor PR was influenced by BCS, parity, or days postpartum at AI. Cows had greater PR when they had been detected in estrus before AI, and PR was improved by administration of GnRH at 65 h after insert removal in cows that were not detected in estrus and inseminated at 84 h.

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Section: Discussionsupporting

confidence: 39%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%