Presynchronization of estrous cycles in dairy cows before ovsynch + CIDR and resynchronization of repeat estrus using the CIDR

Postpartum anestrus is one of the major limitations to achieving acceptable pregnancy rates. The Ovsynch protocol is an excellent tool to improve reproductive efficiency of dairy cows because it can induce estrous cycles in anestrous cows. In the first experiment, administering two PGF2" injections to lactating dairy cows 14 days apart with the second injection given 12 days before the Ovsynch protocol increased (P<0.05) pregnancy rate by 10 percentage points in cycling and noncycling cows. Inserting a progesterone-releasing insert (CIDR) for 7 days during the Ovsynch protocol did not further increase pregnancy rates. In a second experiment, a resynchronization treatment consisting of a used CIDR inserted for 7 days from days 13 to 20 after insemination increased (P<0.05) embryo survival from day 30 to 58 by 11 percentage points but failed to increase overall rate of return to estrus and conception rate at the second AI (first eligible estrus after first AI).; Dairy Day, 2001, Kansas State University, Manhattan, KS, 2001;

1 We than k Oh lde's D airy (L inn, KS ) and M eier's Dairy ( Palmer, KS) for use of their dairy cows and participating in these studies and we thank the Kans as D airy Commission for their financial support.

Summary
Postpartum anes trus is one of the major limitations to achieving acceptable pregnancy rates. The Ovsynch protocol is an excellent tool to improve reproductive efficiency of dairy cows because it can induce estrous cycles in anestrous cows. In the first experiment, administering two PGF 2" injections to lactating dairy cows 14 days apart with the second injectio n give n 12 days before the Ovsynch protocol increased (P<0.05) pregnancy rate by 10 percentage points in cycling and noncycling cows. Insert ing a progesterone-releasing insert (CIDR) for 7 days during the Ovsynch protocol did not further increase pregnancy rates. In a second experiment, a resynchronization treatment consisting of a used CIDR inserted for 7 days from days 13 t o 20 aft er insemination increased (P<0.05) embryo survival from day 30 to 58 by 11 percentage points but failed to increase overall rate of return to estrus and conception rate at t he second AI (first eligible estrus after first AI).

Introduction
Previous studies indicated that conception rates were increased when dairy cows began the Ovsynch protocol between days 5 and 12 of the estrous cycle. We showed that a single injection of PGF 2" given 12 days before the Ovsynch protocol improved pregnancy rates in multiple-lactation dairy cows but not in first-lactation cows. This also was confirmed by research in Florida herds where two PGF 2" injections given 14 days apart with the second injection given 12 days before the Ovsynch protocol increased pregnancy rate by 12 percentage points. The objectives of the first experiment were to determine if two Presynch injections of PGF 2" would increase preg nancy rat es in cows treated with the Ovsynch pro tocol and whether inserting a CIDR during the Ovsynch protocol would likewise improve fertility.
Several studies indicated that luteal inadequacy during the luteal phase predisposes a greater risk for lower conception rates at the subsequent estrus. We also found that progesterone supplementat ion by intravaginal progesterone insert (CIDR; EAZI-breed CIDR-B insert, InterAg, Hamilton, NZ) for 7 days during the ovulation synchronization (Ovsynch) protocol increased pregnancy rates at first service and embr yo sur vival from day 3 0 to day 58 of pregnancy. The objective of the second experiment was to resynchronize the first eligible estrus in previously inseminated cows of unkno wn preg nancy stat us and determine whether the used CIDR would influence AI resubmission rates, conception rate at the repeat estrus, prior established pregnancy rates, and embryo survival of previously established pregnancies.

Procedures
In the first experiment , 630 lactat ing dairy cows from two cooperating herds were used. Cows were less than 40 days in milk at the start of treatments and were milked 3× daily. Cows were then assigned randomly to four treatments based on days in milk and lactation number. Estr ous cycle s in Groups 1 and 2 were presynchronized with two injections (25 mg) of PGF 2" 14 days apart (Presynch) with the second injection given 12 days before the start of the Ovsynch pro to col. Est rous cycles in Groups 3 and 4 were not presynchronized (No Presynch). All groups of cows were t reat ed with t he Ovsynch protocol consisting of two injections of the gonadotr opin-releasing hor mone (GnRH; 100 µg) with a PGF 2" injection given 7 days after the first GnRH injection and 48 hr before the second GnRH injection. Cows were inseminated 16-20 hr after the second GnRH injection (timed TAI; TAI). During the Ovsynch protocol, Groups 1 and 3 were fitted with an intravaginal progesterone insert (CIDR; EAZI-breed CIDR-B insert, InterAg, Hamilton, NZ) at the time of first GnRH injectio n and remove d 7 d ays later. Groups 2 and 4 received no further treatment (No CIDR).
In the second experiment, all cows of unknown pre gnancy st atus in t he first e xper iment were assigned randomly to two treatments. A used CIDR was insert ed in the first group on day 13 a fter TAI for 7 da ys (Resynch). The second group received no further treatment (control). Cows were observed for signs of estrus for 5 days upon used CIDR removal (day 20).
Blood samples were collected prior to each hormone treatment for later determination of progesterone concentrations. Pregnancy was diagnosed by ultrasonography of uter ine contents (viable embryo) at day 30 and 58 a fter the first insemination (TAI). Pregnancy also was c onfirmed by the herd veterinary practictioner.

Results and Discussion
Based on concentr ations of pro gesterone measured in three blood samples collected prior the onset o f the Ovsynch protocol, over 85% of the cows were cycling. In the first experiment, the proportion of cows with elevated progesterone concentrations ($1 ng/mL) in their blood at the t ime of PGF2" injection, indicative of a functional corpus luteum, was high (91%) in the Presynch groups despite the CIDR treatment. Presynchronization with tw o injections of PGF 2" 14 days apart and 12 days before the Ovsynch protocol increased (P<0.05) pregnancy rates at day 30 after TAI by 10 percentage points in both cyclic and anestrous cows compared to the no Presynch cows (Table 1). Thus, a high percent age of the Presynch cows were likely in an early stage of the estrous cycle at the time of initiating the Ovsynch protocol. Treatment with CIDR for 7 days during the Ovsynch protocol decreased pregnancy rates by 5 percentage points in anestrous cows and by 9 percentage points in cyclic cows (Table 1).
In the second experiment, the Resynch treatment failed to increase both overall rate of return to estrus and conception rate at second AI (Table 2). In fact, conception rates of cows inseminated between 20 and 25 days after the TAI ( 0 and 5 d ays after removal of the used CIDR) were reduced (P<0.05) compared to controls. The used CIDR treatment did not have a detrimental effect on the pregnancies established after the TAI because pregnancy rates at day 30 after TAI were not different. In contrast, the Resynch treat ment (us ed CIDR in place from day 13 to 20 after TAI) increased (P<0.05) embryo survival to day 58 in pregnant cows by 11 percentage points ( Table 2). The increase in embryo survival to day 58 resulting from progesterone supplementation provided on days 13 to 20 might have had p ositive effects on t he develop ing embryo or t he uterus.
In conclusion, using two injections of PGF 2" 14 days apart and 12 days before the Ovsynch protocol improved pregnancy rates of bot h cyclic and anes trous co ws. This protocol pro vides dair y producers with an excellent alternative to increase reproduction performance over what can be achieved with the traditional Ovsynch proto col alone. The CIDR treatment is not warranted under these experimental conditions. The Resynch protocol with a used CIDR for 7 days inserted on day 13 after TAI improved embryo survival in pregnant cows but did not improve AIresubmission rate at first eligible estrus following TAI for nonpregnant cows and had a detrimental effect on conception rates of cows inseminated within 5 days after removal of the CIDR.   (255) 48 (246) Anestrus 41 a ( 56) 31 ( 67) 33 ( 55) 38 ( 68) a Different (P<0.05) from no Presynch within cycling status.