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Influence of different factors on fertility of dairy cows submitted to fertility protocols for first insemination post- partum and for resynchronization
Baldor, A.F.A.
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Objectives: The use of “fertility protocols” for artificial insemination (AI) at fixed time adding improvements to Ovsynch®, as presynchronization, use of a progesterone device and two doses of prostaglandin F2α (PG), has showed increases of conception rate in comparison to the normal Ovsynch protocol or natural estrus. At commercial farms level, the length of the protocol is something important so it can be long for first insemination postpartum but should be as short as possible in the case of resynchronizing open cows in order to reduce the number of days open.
In this study we tried two protocols for first AI: the G6G protocol, modified to end as Cosynch (with the last GnRH dose at the same time of AI), with 6 handlings, that lasts for 18 days, and a 7 d Cosynch plus progesterone device, with 4 handlings, that lasts for 10 d. For resynchronizing open cows we used a Resynch protocol (modified for administering the last GnRH at the same time of AI) starting with a GnRH 7 d before pregnancy diagnosis, with 4 handlings, that lasts for 3 d from the diagnosis of open cow. We analyzed some factors that could affect these protocols to understand how they can be used to improve reproduction efficiency in comercial dairy farms
Materials and methods: The study was conducted during 2019 in 12 dairy farms located in León, Spain. A total of 994 synchronization protocols were performed and the cows were explored by a veterinarian at the moment of insemination to evaluate the size of the follicle and the signs of estrus at uterine and ovarian level to inseminate only cows with estrus signs.
The cows enrolled for first AI were treated as “Group G6G” (n=421): day 0 PG, day 2 GnRH, day 8 GnRH, day 15 PG, day 16 PG, and day 18 AI plus GnRH; “Group progesterone device” (n= 227): day 0 GnRH + insertion of progesterone device, day 7 PG and progesterone device removal, day 8 PG, day 10 AI plus GnRH. In a subgroup of cows in groups “Progesterone device” and “G6G”, blood samples were collected at the beginning of the Cosynch, at the moment of the first prostaglandin of the Cosynch and at the moment of AI. The cows that didn’t show return in estrus, were enrolled as “Group Resynch” (n=346) receiving GnRH 7 d before the examination and if diagnosed “open” the day of the pregnancy diagnosis, they were treated: day 0 PG, day 1 PG, day 3 AI plus GnRH.
Data were analyzed with Medicalc® and the different chi- square test were performed for every variable.
Results: The synchronization rate was evaluated as percentage of cows accepted for AI and was high for the three groups: “G6G” 84.03%, “Progesterone device” 88.33% and “Resynch” 94.02% (p=0,057) with progesterone concentration profiles corresponding with that findings: beginning of Cosynch 2,16 ng/ml, first PG 2,90 ng/ml and moment of AI 0,32 ng/ml. The conception rate was high in the three groups: “G6G” 44.89%, “Progesterone device” 40.53% and “Resynch” 49,42%, (p=0,11). The median days to AI were significantly different in inseminations with diagnosis “pregnant” or “open”: open 121.47 and pregnant 134.08. (p=0.007). The conception rate of different follicle sizes were 10 to 15: 40.43%, 16 to 20: 40.00% and > 20: 30.77 (p=0.45%). The conception rate of different parities were 1: 49.86%, 2: 44.73%, 3 : 39,13% and cows with 4 or more calvings 49.26%. (p=0.08).
Conclusions: The numerical differences in conception rate between protocols could have been influenced by the days in milk at AI so, taking into account the high synchronization rate and fertility of these fertility protocols, they can be implemented at farm level, the longer ones for first post-partum AI considering their easiness of compliance, and the shorter one for a fast resynchronization of open cows.
The decreasing conception rate by parity have been previously reported, but the high conception rate in cows with 4 or more calvings could be influenced by the retention of the most fertile cows, showing that the retention of some old fertile cows could extend the general longevity of farms.
Keywords: Fertility, protocol, post-partum, resynchronization, insemination.
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Affiliation of the authors at the time of publication
AFRIVEPA, SOC COOP, Santa María del Páramo, Spain
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