Figure 1 on the next page shows the experimental design used in the research trial done by Souza et al. (2008) comparing two presynchronization strategies (Traditional Presynch x Double-Ovsynch).
This trial was performed by researchers on two commercial dairy farms in Wisconsin, and used only first postpartum breedings from multi-parous and primi-parous lactating cows. The results of this trial shows that cows treated with Double-Ovsynch had greater conception rates at first postpartum A.I. compared with the traditional Presynch with two PGF2α (Fig. 2).
Researchers found no treatment-by-farm interaction, which means that Double-Ovsynch was superior to traditional Presynch in both farms. Thus, Double-Ovsynch seems to yield consistently greater fertility when used in different herds (Figure 3), on next page.
Figure 4 shows some of the blood sampling results collected in a subset of cows treated with these two presynchronization strategies (traditional Presynch x Double-Ovsynch). The “X” axis is showing the circulating progesterone concentration at the beginning of the TAI-Ovsynch. It is clear that a greater proportion of cows had higher circulating progesterone following Double-Ovsynch compared to traditional Presynch. Thus, Double-Ovsynch induced more cows to cycle before the timed A.I. protocol.
Further ongoing trials are being performed by Dr. Wiltbank’s group at the University of Wisconsin to study the physiological underlying reasons for greater fertility following the Double-Ovsynch protocol (Dr. Wiltbank, personal communication). For instance, a recent study using two variations of Double-Ovsynch (Cunha et al., 2008), is in accordance with the hypothesis that greater circulating progesterone concentrations during the interval from the first GnRH to PGF2α of the Ovsynch protocol is needed for maximal fertility responses in cows receiving TAI (protocol with low progesterone = 33.2%, n = 259 vs protocol with high progesterone = 48.2%, n=255). Therefore, recent modifications in TAI procedures seem to improve conception rate in Ovsynch treated animals.
Although Double-Ovsynch seems to be a very consistent protocol for lactating cows, farmers must make sure that all hormonal treatments are being given at the correct times, to correct cows, with the correct doses. Therefore, the suggested weekly schedule presented on the next page, (Figure 5) should be precisely followed by producers in order to improve compliance while using Double-Ovsynch. Notice that pre-synchronization injections are highlighted in red, and TAI-Ovsynch treatments are highlighted in blue. According to this calendar, TAI is scheduled to be performed on Thursdays tarting at 8:00 am.