The effect of Presynch-Ovsynch protocol with or without estrus detection on reproductive performance by parity, and the long-term effect of these different management strategies on milk production, reproduction, health and survivability of dairy cows

- Genetic selection has focused primarily on milk production and components, which resulted in a decline in fertility.
- To overcome this problem, dairy herds have adopted management strategies such as ovulation synchronization protocols.
- The primary objective of this study was to evaluate the effect of two different strategies on reproductive outcomes.
- The secondary objective was to evaluate the long term impact of these two strategies.

During the Presynch-Ovsynch protocol, at least half of the cows enrolled display signs of estrus, which can present as an opportunity for cows to be inseminated before the completion of the protocol. The primary objective of this study is to compare two management strategies for first service using the Presynch-Ovsynch protocol: insemination at completion of the Presynch-Ovsynch program (TAIonly) or insemination after estrus detection during the Presynch-Ovsynch protocol, with the remainder of cows being inseminated at timed artificial insemination (ED + TAI). Cows inseminated at completion of the protocol have a longer voluntary waiting period, which could potentially extend their lactation length, allowing them to recover BCS at the end of their lactation and ultimately impacting their subsequent lactation. Therefore, this study has a secondary objective to evaluate the long term impact of these two strategies on reproductive outcomes, culling, milk production and health during the subsequent lactation. A total randomized field trial study design was used, and a total of 3489 cows were randomly enrolled to one of the treatment groups: ED + TAI or TAIonly. Cows enrolled in the TAIonly started the Presynch protocol receiving two injections of PGF2α at 55 ± 3 and 69 ± 3 DIM. They were subsequently submitted to the Ovsynch protocol: GnRH at 81 ± 3 DIM, PGF2α at 88 ± 3 DIM, and GnRH at 90 ± 3 DIM, and then inseminated at fixed time at 91 ± 3 DIM. Cows enrolled in the ED + TAI were submitted to the same synchronization protocol, but they were eligible to be inseminated at any time after the beginning of the synchronization protocol, if detected in estrous. During the experimental lactation, the effect of treatment on first service conception rate (FSCR) was conditional to parity: no difference among primiparous cows, but for multiparous cows, the FSCR was 41.2% and 35.3% for TAIonly and ED + TAI, respectively. Although TAIonly strategy increased the lactation length for primiparous and multiparous, no differences were observed on lactation and reproductive performances. The rate at which cows conceived, and the calving to conception interval during the subsequent lactation was not affected by management strategy. Additionally, no differences were observed in milk production during the experimental and subsequent lactations. The effect of management strategy on survivability was conditional to parity: no differences were observed for multiparous cows, while primiparous ED + TAI cows tended to be less likely to be culled than TAIonly counterparts. Additionally, no differences in health outcomes during the subsequent lactation were observed.