Short-term feeding of melengestrol acetate plus GnRH and PGF2α to enhance reproductive efficiency of replacement dairy heifers

Abstract EN

Forty six pure Holstein heifers were assigned randomly to two synchronization treatments Select Synch (n = 21) and MGA 7-11 Synch (n = 25).

The MGA 7-11 Synch heifers were fed MGA (0.

5 mg/h/day) for 7 days concluded with PGF2α injection.

Four days later, both groups (Select Synch and MGA 7-11Synch) were administered GnRH followed with PGF2α on day 0.

Heifers were inseminated with frozen semen according to the AM/PM rule.

Within 24-48h peak response period after PGF2α injection more (81 %, 17 / 21) Select Synch heifers displayed estrus compared to MGA 7-11 Synch (68.

1%, 17 / 25).

However, overall percentages of heifers detected in estrus were not different between Select Synch (95.

2 %, 20 / 21) and MGA 7-11 Synch (84 %, 21 / 25) heifers.

Select Synch heifers had empirically improved (P = 0.

2) conception rate to first artificial insemination (AI, 75%, 15/20) compared to MGA 7-11 Synch heifers (57 %, 12 / 21), while overall pregnancy rates were 95.2 and 96%.

The total number of follicles (TNF) on both ovaries was not different between the Select Synch (2.

4 ± 0.

3) and MGA 7-11 Synch (2.

2 ± 0.

3) heifers.

Likewise, the overall diameters of largest follicles were not affected by treatments.

However, Select Synch heifers had larger (P < 0.

05) follicles (11.

4 ± 0.

9mm) than the MGA 7-11 Synch (9.

2 ± 0.

6 mm) heifers on day -7.

Percentages of induced CLs on days 0 (62 vs.

76 %) and 10 (76.

2 vs.

80 %) after PGF2α injection were not different between Select Synch and MGA 7-11 Synch heifers.

Similarly, diameters of induced CLs on days 0 (19.

3 + 2.

9 vs.

18.

3 + 2.

5 mm) and 10 (19 + 2 vs.

21.

3 + 1.

6 mm) were not different.

Progesterone concentrations were greater (P < 0.

01) on day -7 in the Select Synch (7.1 ± 1ng /ml) compared to the MGA 7-11 Synch (2.

5 ± 0.

7ng / ml).

Short-term feeding of MGA (MGA 7-11Synch) to dairy heifers produced acceptable overall pregnancy rates while Select synch treatment tightened the synchrony for estrus compared to MGA 7-11 Synch.

Further research is needed to improve estrual responses and synchrony after short-term of MGA feeding to dairy heifers.