Influence of prebreeding progesterone plus prostaglandin F2-α on estrus and fertility in lactating dairy cows

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Influence of prebreeding progesterone plus prostaglandin F2-α on estrus and Influence of prebreeding progesterone plus prostaglandin F2-on estrus and fertility in lactating dairy cows fertility in lactating dairy cows Progesterone administered before breeding may increase estrous expression and subsequent fertility in lactating dairy cows. Holstein cows (n=302) were assigned randomly at calving to three groups. Cows received no treatment (controls), one injection of prostaglandin F 2-alpha (PGF), or progesterone plus one injection of PGF (PRID + PGF). The average interval to estrus was 5 days shorter in PRID + PGF cows compared to cows given only PGF. In addi tion, more cows were observed in estrus 2 to 5 days after treatment in the PRID + PGF group compared to the PGF group. Average days from calving to conception were reduced in PRlD + PGF cows by 15 to 20 days compared to control and PGF cows. We concluded that prebeeding progesterone in combination with PGF appears to enhance fertility.

Introduction
Sever'al studies have attempted to synchronize estrus to a])ow for convenient breeding of dairy cows at first service at approximately 60 days postpartum. Most of these studies have used prostaglandin F 2-alpha (PGF) and a few studies have incorporated progesterone plus PGF in estl'ous synchronization. A previous attempt at the KSU dairy to synchronize estrus failed to show any benefit of utilizing two injections of PGF given 11 days apart. Furthermore, there is little information on the effects of progesterone in estrous synchronization. It has been demonstrated that cows with increased progesterone levels in their blood during the estrous cycle before breeding have better conception rates than herdmates with lower progesterone levels prior to breeding. This suggests that progesterone may have a prebreeding role for increasing fertility. Therefore, the objectives of this study were: (l) to determine the feasibility of using one injection of PGF to regress the corpus luteum (CL) prior to first service and (2) to examine further the prebreeding role of progesterone prior to CL regression on estrous expression and SUbsequent fertility.

Procedures
This study utilized 302 lactating Holstein cows in the KSU dairy herd. Cows were assigned randomly at calving to three groups. Group 1 consisted of 112 control cows that were inseminated at the first observed estrus after 42 days postpartum. Group 2 consisted of 97 POP cows given one injection of POF (25 mg Lutalyse®) between 56 and 62 days postpartum. Ot'OUp 3 consisted of 93 PRW + PGF cows. Cows in this group had a progesterone-releasing intl'avaginal device or PRID inserted into the vagina at approximately 54 days postpm·tum. A PRID is a silastic coil impregnated with 1.13 grams of crystalline progesterone. The PRlDs remained in place for 7 days with an injection of PGF (25 mg Lutalyse®) given 24 hI' prior to PRID removal. Cows in Groups 2 and 3 were inseminated at the first observed estrus after Lutalyse®. This allowed for all treated cows to be inseminated for the first service around 60 days postpartum.
Blood was collected at 0, 24, and 48 hI' after PGF injection and analyzed for concentrations of progesterone in serum. This enabled us to monitor the success of CL regression. Blood also was collected at the time of PRlD insertion and removal.

Results and Discussion
As illustrated in Figure 1, more PRlD + PGF cows were observed in heat 2 to 5 days after PGF injection, resulting in a more synchronous estrus compared to PGf cows. This result suggests that PRlD + PGF synchronizes more heats than one injection of PGF. However, progesterone may be enhancing behavioral signs of heat. Missed heats and PGF failure may have contributed to the wide distribution of observed heats in the PGF group.

t-·
In addition, the average interval to estrus after PGF injection was reduced (P<.05) from 16 to 11 days in the PRlD + PGF group compared to the PGF group.
Results of the reproductive traits examined are illustrated in Table 1. The average interval to first breeding was 10 days longer in the PGF group compared to controls. Conception rates were similar in all groups; however, in the PRlD group, conception rates tended to be higher in those cows conceiving 2 to 5 days after treatment compared to those conceiving 6 or more days after PGF (53 vs 32%). The reasons for this finding are unknown, but it could be related to the stage of the estrous cycle when the PH-IDs were inserted and/or the failure of CL regression after PGF administration. Interestingly, this effect was not observed in the PGF treatment group, since conception rates were similar 2 to 5 days and after 6 or more days (44 vs 46%).
The PRlD + PGF group averaged 20 fewer days to conception than the PGF group and 15 days fewer than controls. In addition, fewer services per conception were required in the PRlD + PGF group compared to the other groups. Fewer days between first service and conception were observed in the PRlD + PGF group compared to the other groups. The results of this study are preliminary, with further studies needed to investigate the role of progesterone. Howevel', our data suggest that one injection of PGF results in reproductive performance si milar to that of untreated controls and, therefore, provides no economical benefit.
It appears that estrous synchronization and fertility can be enhanced by administel'ing progesterone before breeding in combination with PGF.