Acta Veterinaria Scandinavica 2009, 51:48 http://www.actavetscand.com/content/51/1/48 Ovsynch protocol has also been applied for beef cattle. Geary et al. [21] have reported a pregnancy rate of 52% in beef cows after the Ovsynch protocol. In the same study, they also modified the Ovsynch protocol by adding 48-h calf removal from the PGF2α administration to the second GnRH treatment. This calf removal tended to increase the pregnancy rate (from 52 to 61%). Geary et al. [1] earlier carried out a quite similar experiment where the Ovsynch protocol with 48-h calf removal led to a pregnancy rate of 54%, suggesting that the pregnancy rate without calf removal would be slightly below 50%. Two other studies have obtained similar results; pregnancy rates have varied from 47.7% to 53% after the Ovsynch protocol in beef cows [22,23]. These results are quite identical and accord well with the results of the present study. Several modifications for the Ovsynch protocol have been developed. For example a strategy known as Cosynch eliminates one cow handling period (the second GnRH and AI at the same time) and facilitates once-daily restraint of cows for administration of hormone injec- tions and timed AI. In Cosynch protocols, the time inter- val between the PGF2α administration and the second GnRH + AI has varied from 48 h to 72 h. Pregnancy rates after the use of the Cosynch method have been similar or slightly lower than those obtained in the Ovsynch [19,24]. Despite this the Cosynch method should be remembered as an alternative in beef herds, where the handling facilities may be poor. The fact that the concep- tion rate is affected by the stage of the oestrous cycle at the beginning of the protocol [15] has led to the development of presynchronisation methods preceding the Ovsynch and Cosynch protocols. The presynchronisation methods include either two PGF2α administrations before the first GnRH injection (Presynch) [25] or a progesterone releas- ing intravaginal device inserted for the first seven days of the program [26]. In beef cattle, presynchronisation with progesterone supplementation has been studied, but no additive effects were detected [27]. It should be kept in mind that all these handlings and treatments cause extra costs, and it is questionable whether these are cost-effec- tive. Interestingly, the fertility after fixed-time AIs seems to be better following shorter rather than longer intervals from parturition to start of the protocol. The low sample sizes among some of the cells (Table 2) limit the effective anal- ysis for interactions, but observed percentages of preg- nancy rates suggest that long interval from calving to the start of the program may be a risk factor, especially for the first parity cows. This finding disagrees with the well known fact obtained in dairy cattle that the conception rate to AI increases along an increasing interval from par- turition to at least 120 days [28,29]. Nevertheless, in line with our finding, Geary et al. [1] have obtained similar results in beef cows after the Ovsynch protocol. The preg- nancy rates were 74%, 51% and 52% when the cows entered the program <70, 70-90, and >90 days post par- tum, respectively. The fairly poor pregnancy results in the groups having a long interval from parturition to start of the protocol can partly be explained with a bias in the selection of animals into the groups. It is possible that the group of animals with a long interval might have included more animals that had had problems in reproductive functions. However, even a more interesting finding is that fertility was best in those animals having the shortest interval from the calving. In dairy cattle, fertility during the corresponding period is lowest, and a negative energy balance during the first weeks after the calving has been shown to be one of the most important reasons for the poor fertility [30,31]. In suckling beef cattle, the milk yield is clearly lower, and thus negative energy balance flatter than in dairy cattle, which could be one explanation for the excellent fertility fairly soon after calving. However, in beef cattle, suckling has been shown to be one of the major factors in determining the length of puerperal anoe- strus [32]. In our study, this did not seem to affect the fer- tility after 50 days after calving. The synchronisation program used in this study was slightly modified from the original Ovsynch protocol which principally does not include any clinical examina- tions of the animals entering the program. In the present study, ovaries of the involved animals were palpated per rectum, and those animals not having a functional CL were omitted from the program. One of the goals of the program was to optimize the number of offspring per AI dose, since the target was to import new and valuable genetic material into the herd rather than conceive all ani- mals per AI. Vasconcelos et al. [15] have reported that of cows having low progesterone concentrations at the time of the administration of PGF2α, 68% of them had a syn- chronized ovulation compared to an overall synchroniza- tion rate of 87% in all cows - keeping in mind that these cows were cyclic. In addition to the fact that cyclic cows having low progesterone concentrations at the time of the administration of PGF2α had a distinctly lower synchroni- sation rate, the pregnancy rates in anoestrous cows have been lower than in cyclic cows (48% vs. 62%) [21]. Simi- lar, although not significant, differences have been reported by Geary et al. [1]. The Ovsynch regimen does not seem to be as effective for synchronizing heifers as lactating dairy cows. Statistically, there was a lower percentage of heifers that responded to the first injection of GnRH, and this may have resulted in only 75% of heifers being synchronized compared to 100% of cows [10]. According to Pursley et al. [12], heifers have a lower pregnancy rate per AI after Ovsynch than after PGF2α and detected oestrus. They concluded that Page 4 of 6 (page number not for citation purposes)