Synchronization of ovulation (OVSYNCH) in high producing dairy cattle herds.

A method for synchronization of ovulation (OVSYNCH) was evaluated for its p ractical use in seven North German dairy cattle herds. The original procedu re of PURSLEY et at. (1995) was applied, i. e. cows were injected Gonadotro pin Releasing Hormone (GnRH) at a random stage of the estrous cycle, follow ed by an injection of a prostaglandin F-2 alpha (PGF(2 alpha))-analogon sev en days later and another injection of GnRH two days after PGF(2 alpha). Co ws were inseminated 24 h after the last injection by artificial inseminatio n. Control animals were assigned by corresponding lactation number and stag e of lactation (month of partus). Cows from the OVSYNCH group returned to t he conventional reproductive management after the OVSYNCH treatment, which was the same management as that for the control group. The average milk yie ld in 1997 and 1998 was 8128.6 +/- 637.0 kg and 8688.3 +/- 665.0 kg per yea r, respectively. First service conception rate (FSC) in the OVSYNCH group (n = 187) (39.77 % ) was lower than in the controls (n = 175) (54.34 %; P < 0.01). In 1997, FS C for the OVSYNCH group did not differ from controls (48.94 % vs. 55.45 %; P > 0.05), whereas in 1998, FSC for the OVSYNCH group (29.27 %) was signifi cantly lower than in the control group (29.27 % vs. 52.78 %) and the OVSYNC H group in 1997 (each time P < 0.01). First service conception rate of firs t lactation cows in the OVSYNCH group was significantly lower than in the c ontrol group (37.84 % vs. 71.05 %; P < 0.01), whereas no difference was fou nd for the other lactation groups. The mean interval calving to first servi ce was shortened in the OVSYNCH group by about 14 d as compared with the co ntrols (P < 0.01). However, mean days open only differed by 2.92 d (P > 0.0 5). Proportion of cows in each class of lactation number (1., 2. and > 2. l actation number) with days open less than or equal to 115 d in the OVSYNCH group were similar to controls (P > 0.05). There was a great influence of b ody condition on the success of OVSYNCH. Cows with a body condition score ( BCS) of 3.00 had a significant better FSC than cows with a BCS < 3.00 (P < 0.05). First service conception rate was lower for cows with a BCS > 3.25 a nd < 2.75 (cows in good and poor condition taken together) than for cows wi th a BCS of 3.00 (P < 0.05). A positive effect of OVSYNCH was found in acyc lic cows as determined by progesterone concentration in blood plasma. Nine out of eleven cows reacted with the resumption of ovarian activity. Two cow s became pregnant after first insemination.