Conception and pregnancy rates in dairy cows after various Conception and pregnancy rates in dairy cows after various programmed breeding systems programmed breeding systems

Two experiments were conducted to measure conception and pregnancy rates in lactating dairy Follicular development must be controlled cows after various treatments followed by artifiand synchronized with the regression of the cial insemination (AI) after detected estrus or at corpus luteum after PGF in order to reduce one fixed time. In Experiment 1, Holstein cows variation in the intervals to estrus. Precise conin one herd were assigned randomly to four trol of follicular development with the regression treatments every 3 wk (27, 3-wk cluster groups): of the corpus luteum should allow improved 1) Ovsynch33, 2) GnRH+PGF , 3) 2×PGF , conception rates associated with one fixed-time 2" 2" and 4) 2×PGF +GnRH. In Experiment 2, Holinsemination. Such a synchronized ovulation 2" stein cows in one herd were assigned randomly protocol (OvSynch) has been tested. A first to two treatments every 3 wk (14, 3-wk cluster injection of GnRH is administered 7 days before groups): 1) Ovsynch48 and 2) GnRH+PGF . In PGF , and a second injection of GnRH is given 2" both experiments, frozen-thawed semen from 36 to 48 hr after PGF to ovulate the dominant multiple sires was used, one technician perfollicle via GnRH-induced release of luteinizing formed >95% of all inseminations, and preghormone (LH). The objective of these experinancy was diagnosed by palpation per rectum ments was to compare conception and pregnancy between 38 and 52 d after first insemination. rates in lactating dairy cows after various proAlthough actual conception rates resulting from grammed breeding systems used to synchronize inseminations after detected estrus were consisestrus before first postpartum inseminations. tently greater, pregnancy rates of cows were Specifically, we wished to determine the: 1) superior after fixed-time inseminations because effect of incorporating GnRH in a two PGF of poor rates of detected estrus in treatments that injection scheme (administration of GnRH after relied solely on observation of sexual behavior. the second PGF injection), 2) actual pregnancy


Summary
lactating dairy cows demonstrated that concep-Two experiments were conducted to measure conception and pregnancy rates in lactating dairy Follicular development must be controlled cows after various treatments followed by artifi-and synchronized with the regression of the cial insemination (AI) after detected estrus or at corpus luteum after PGF in order to reduce one fixed time.In Experiment 1, Holstein cows variation in the intervals to estrus.Precise conin one herd were assigned randomly to four trol of follicular development with the regression treatments every 3 wk (27, 3-wk cluster groups): of the corpus luteum should allow improved 1) Ovsynch33, 2) GnRH+PGF , 3) 2×PGF , conception rates associated with one fixed-time 2" 2" and 4) 2×PGF +GnRH.In Experiment 2, Hol-insemination.Such a synchronized ovulation 2" stein cows in one herd were assigned randomly protocol (OvSynch) has been tested.A first to two treatments every 3 wk (14, 3-wk cluster injection of GnRH is administered 7 days before groups): 1) Ovsynch48 and 2) GnRH+PGF .In PGF , and a second injection of GnRH is given 2" both experiments, frozen-thawed semen from 36 to 48 hr after PGF to ovulate the dominant multiple sires was used, one technician per-follicle via GnRH-induced release of luteinizing formed >95% of all inseminations, and preg-hormone (LH).The objective of these experinancy was diagnosed by palpation per rectum ments was to compare conception and pregnancy between 38 and 52 d after first insemination.
rates in lactating dairy cows after various pro-Although actual conception rates resulting from grammed breeding systems used to synchronize inseminations after detected estrus were consis-estrus before first postpartum inseminations.tently greater, pregnancy rates of cows were Specifically, we wished to determine the: 1) superior after fixed-time inseminations because effect of incorporating GnRH in a two PGF of poor rates of detected estrus in treatments that injection scheme (administration of GnRH after relied solely on observation of sexual behavior.

Introduction
Attempts to develop estrus-synchronization systems for lactating dairy cows and accommo-Experiment 1.Four treatments were used date a fixed-time insemination have met with (Figure 1).Treatments A and B were similar.limited success since prostaglandin F (PGF ) One injection of GnRH (100 µg of Cystorelin®) 2" 2" was demonstrated to be effective in controlling was given 7 days before one injection of PGF the estrous cycle for programmed breeding.
(25 mg of Lutalyse®).In treatment A, cows Conception rates following PGF usually were received a second injection of GnRH 33 hr after 2" best when inseminations were performed after PGF and then one fixed-time insemination 18 observed signs of heat.Our early attempts to use hr later, whereas cows in treatment B were fixed-time inseminations at first services in tion rates were less than desirable.
rates among systems that require or do not PGF in the OvSynch system.inseminated according to the AM-PM rule at the became pregnant) were not significantly differdetected estrus after PGF .ent among treatments; however, conception rates 2" Treatments C and D were similar.All cows D) in which AI was administered after detected received two injections of PGF 14 days apart.
estrus.In treatment B, cows not detected in 2" In treatment C, cows received one injection of estrus after the initial synchronization were GnRH 33 hr after PGF and one fixed-time inseminated at their next nonsynchronized estrus, 2" insemination 18 hr later.In the last treatment, and 8 of 22 (36.4%)conceived.In treatment D, cows were inseminated at the detected estrus 24 of 46 (52.2%) cows inseminated at estrus after PGF according to the AM-PM rule or in conceived, and 8 of 55 (14.6%) conceived in the 2" the absence of detected estrus, one fixed-time absence of detected estrus when inseminated at insemination was given at 80 hr (cows) after the 80 hr after the second of two PGF injections.second PGF injection.

2"
Treatments were applied randomly to lactat-signed to treatment that became pregnant) were ing cows (minimum of 62 days in milk) before more uniform among treatments.The similar first services.Cow were grouped in 3-wk breed-pregnancy rates, despite lower actual conception ing clusters beginning in June, 1994, and the after fixed-time inseminations, resulted from experiment continued until December, 1995.
rather poor heat-detection rates in treatment B. Conception rates were determined by palpation Treatment D, similar to the Targeted Breeding® of the uterus and its contents between 38 and 52 system, produced the greatest pregnancy rates.days after insemination.

Experiment 2. Treatments A and B of
and pregnancy rates in Experiment 2 are illus-Experiment 1 were repeated in lactating cows, trated in Table 2. Heat-detection rates were less except that the second injection of GnRH was (P<.01) in the Ovsynch48 treatment compared to administered 48 hr after PGF (Figure 2).treatment B in which a second GnRH injection 2" Lactating cows (minimum of 58 days in milk) was not administered after PGF .These rates before first services were grouped in 3-wk breed-were quite similar to those observed in Experiing clusters beginning in December, 1995 and ment 1. Conception rates tended to be lower in ending in March, 1997.Conception rates were the Ovsynch treatment, but the reverse was true determined by palpation of the uterus and its for pregnancy rates.This reversal was due to the contents between 38 and 52 days after insemina-rather poor heat response in treatment B. tion.

Results and Discussion
after various programmed-breeding treatments, Experiment 1. Estrus-detection, concep-achieved per unit of time) always will be supetion, and pregnancy rates achieved in each of rior with a treatment that utilizes a fixed-time four treatments are summarized in Table 1.The insemination.Treatment D in Experiment 1 and proportion of cows detected in heat during 96 hr Ovsynch48 in Experiment 2 produced the most after PGF was less (P<.01) in treatments A and pregnancies per unit of time.

2"
C in which GnRH was administered after PGF 2" to induce ovulation of the follicle.This GnRH injection caused estrogen secretion by the preovulatory follicle to cease and, therefore, prevented further mounting and standing activity in most cows.Conception rates (proportion of cows detected in estrus and inseminated that tended to be greater in those treatments (B and 2" Pregnancy rates (proportion of cows as-Experiment 2. Heat-detection, conception, 2" As long as poor heat-detection rates occur pregnancy rates (the number of pregnancies

Recommendations
Actual conception rates tended to be less after fixed-timed inseminations, whereas conception rates tended to be greatest when inseminations occurred after detected estrus.Pregnancy rates tended to be less when programmed breeding systems depended partly or wholly on detection of behavioral estrus, whereas they were greatest after fixed-time inseminations.Conception (pregnancy) rates are probably maximized after OvSynch when the second GnRH injection is given closer to 48 h after PGF 2 .Fixed-time inseminations with a two-injection PGF 2 system may achieve acceptable conception (pregnancy) rates if GnRH is given closer to 48 h after the second PGF 2 injection (before fixed-time insemination), but this needs to be tested.
The recommended use of the OvSynch protocol is to administer GnRH on Monday, followed by PGF 2 on the following Monday at milking time (5 PM), administer the second GnRH injection at 5 PM on Wednesday (48 hr later), and inseminate cows the next morning (Thursday) between 8 and 10 AM (Figure 2).If you do not want to use the timed insemination, give GnRH (Monday), follow it with PGF 2 in 7 days (Monday), and watch for heat.For inseminations with this system, follow the AM-PM rule when heat is detected.Do not use the Ovsynch protocol in replacement heifers, because results are inferior to what can be achieved with a PGF 2 protocol.  Cows inseminated at estrus = 24/46 (52.2%).Cows inseminated at 80 h = 8/55 (14.6%) a,b,c (P<.O1).