Success of several programed AI-breeding protocols including ovsynch

In Experiment 1, four programmed AIbreeding treatments were tested. The so-called OvSynch program, which requires no heat detection before a fixed-time insemination, decreased conception rates compared with a similar treatment in which inseminations occurred after detected estrus (30 vs 51%). The traditional two-injection prostaglandin program produced greater conception rate for cattle inseminated after a detected estrus (53%) than after one fixed-time insemination was given in the absence of estrus (31%). A similar protocol of two prostaglandin injections plus an injection of gonadotropin-releasing hormone (GnRH or Cystorelin®) before one fixed-time insemination produced lower conception rates (33%) than when cattle were inseminated after detected estrus (53%). In Experiment 2, the OvSynch program was retested with the interval between the PGF and the second GnRH 2a injection being 48 hr (36 hr in Experiment 1). Conception in 27 cows on the OvSynch48 program with timed insemination (37%) was comparable with 43% in 21 cows on a similar program without the second GnRH injection but inseminated at estrus.; Dairy Day, 1996, Kansas State University, Manhattan, KS, 1996;


Success of several programed AI-breeding protocols including ovsynch Success of several programed AI-breeding protocols including ovsynch Abstract Abstract
In Experiment 1, four programmed AIbreeding treatments were tested. The so-called OvSynch program, which requires no heat detection before a fixed-time insemination, decreased conception rates compared with a similar treatment in which inseminations occurred after detected estrus (30 vs 51%). The traditional two-injection prostaglandin program produced greater conception rate for cattle inseminated after a detected estrus (53%) than after one fixed-time insemination was given in the absence of estrus (31%). A similar protocol of two prostaglandin injections plus an injection of gonadotropin-releasing hormone (GnRH or Cystorelin®) before one fixed-time insemination produced lower conception rates (33%) than when cattle were inseminated after detected estrus (53%). In Experiment 2, the OvSynch program was retested with the interval between the PGF and the second GnRH 2a injection being 48 hr (36 hr in Experiment 1). Conception in 27 cows on the OvSynch48 program with timed insemination (37%) was comparable with 43% in 21 cows on a similar program without the second GnRH injection but inseminated at estrus.; Dairy Day, 1996, Kansas State University, Manhattan, KS, 1996

Summary
In Experiment 1, four programmed AIbreeding treatments were tested. The so-called OvSynch program, which requires no heat detection before a fixed-time insemination, decreased conception rates compared with a similar treatment in which inseminations occurred after detected estrus (30 vs 51%). The traditional two-injection prostaglandin program produced greater conception rate for cattle inseminated after a detected estrus (53%) than after one fixed-time insemination was given in the absence of estrus (31%). A similar protocol of two prostaglandin injections plus an injection of gonadotropin-releasing hormone (GnRH or Cystorelin®) before one fixed-time insemination produced lower conception rates (33%) than when cattle were inseminated after detected estrus (53%). In Experiment 2, the OvSynch program was retested with the interval between the PGF and the second GnRH 2α injection being 48 hr (36 hr in Experiment 1). Conception in 27 cows on the OvSynch48 program with timed insemination (37%) was comparable with 43% in 21 cows on a similar program without the second GnRH injection but inseminated at estrus.

Introduction
Since prostaglandin F (PGF ) was 2α 2α demonstrated to be effective in controlling the estrous cycle for programmed breeding, attempts to develop estrus-synchronization systems for lactating dairy cows and dairy heifers to accommodate fixed-time inseminations have met with limited success. Conception rates following PGF usually produced 2α the best results when inseminations were performed after observed signs of heat. Our early attempts to use fixed-time inseminations at first services in lactating dairy cows demonstrated that conception rates were less than desirable.
Follicular development must be controlled and synchronized with the regression of the corpus luteum after PGF in order to reduce 2α variation in the intervals to estrus. Precise control of follicular development with the regression of the corpus luteum should allow improved conception rates associated with one fixed-time insemination. Such a synchronized ovulation protocol (OvSynch) has been tested. A first injection of GnRH is administered 7 days before PGF , and a second injection of 2α GnRH is given 36 to 48 hr after PGF to cause 2α ovulation of the dominant follicle via GnRHinduced release of luteinizing hormone (LH). The objective of this study was to compare conception rates achieved in heifers and lactating cows using two versions of the OvSynch AI-breeding protocol with a standard twoinjection, prostaglandin protocol commonly used on dairy farms.

Procedures
Experiment 1. Four treatments were used (Figure 1). Treatments A and B were similar. One injection of GnRH (100 µg of Cystorelin®) was given 7 days before one injection of PGF (25 mg of Lutalyse®). In 2α treatment A, cattle received a second injection of GnRH 36 hr after PGF and then received 2α one fixed-time insemination 18 hr later, whereas cattle in treatment B were inseminated according to the AM-PM rule at the detected estrus after PGF . 2α Treatments C and D were similar. All cattle received two injections of PGF 14 days 2α apart. In treatment C, cattle received one injection of GnRH 36 hr after the second injection of PGF and received one fixed-time 2α insemination 18 hr later. In the last treatment, cattle were inseminated at the detected estrus after PGF according to the AM-PM rule, or in 2α the absence of detected estrus, one fixed-time insemination was given at 72 (heifers) or 80 hr (cows) after the second PGF injection. 2α Treatments were applied randomly to replacement heifers (minimum body weight of 800 lb and 12 months of age) and to lactating cows (minimum of 60 days in milk) before first services. Cow and heifers were grouped in 3wk breeding clusters beginning in July, 1994, and the experiment continued until February, 1996. Conception rates were determined by palpation of the uterus and its contents between 38 and 52 days after insemination. Experiment 2. Treatments A and B were repeated in lactating cows except that the second injection of GnRH was administered 48 hr after PGF (Figure 2). Lactating cows 2α (minimum of 60 days in milk) before first services were grouped in 3-wk breeding clusters beginning in March, 1996, and the experiment is ongoing. Conception rates were determined by palpation of the uterus and its contents between 38 and 52 days after insemination.

Results and Discussion
Experiment 1. Conception rates achieved in each of four treatments are summarized in Table 1. Conception rate after OvSynch36 + timed insemination was less (P=.01) than that after insemination at estrus (treatments A vs B). Conception rate after two injections of PGF was greater (P<.01) when inseminations 2α were performed at estrus (treatment D) than after one fixed-time insemination in which ovulation was induced by GnRH after the second PGF injection (treatment C) or after 2α one fixed-time insemination at 72 or 80 hr in the absence of detected estrus (treatment D).

Experiment 2.
Although conception rates in lactating cows after OvSynch48 + timed insemination seem to be similar to those after a similar treatment + inseminations at estrus (Table 2), only a limited number of cows have been tested. Of 29 cows in the latter treatment, only 21 were detected in estrus during 5 days after PGF (72% heat detection rate). Concep-2α tion rate of the remaining 8 cows inseminated at estrus induced by another PGF injection 2α given 14 days was 37%. One advantage of the OvSynch protocol + timed insemination is that its success is independent of heat detection rate.

Conclusions
Recommended use of the OvSynch protocol is to administer GnRH on Monday, followed by PGF on the following Monday at 2α milking time (5 PM); the second GnRH injection at 5 PM on Wednesday (48 hr later); and inseminate cows on the next morning (Thursday) between 8 and 10 AM (Figure 2). If you do not want to use the timed insemination, give GnRH (Monday) and follow it with PGF in 7 2α days (Monday) and watch for heat. For inseminations with this system, follow the AM-PM rule when heat is detected. Do not use this protocol in replacement heifers, because results are inferior to what can be achieved with a PGF protocol.