engleski

Comparison of two protocols for synchronization of ovulation on dairy farm in Croatia

Fertility is the main factor of the successful dairy industry. High-producing dairy cows are more or less subfertile thanks to many reasons, some of them being life conditions, high producing demands, stress, nutrition. During peripartal period, due to negative energy balans, cows are not able to create enough of energy and proteins, which results in metabolic disturbances with negative effect on hormonal status and fertility. The goal of controlled reproduction is to improve fertility. Today's knowledge of factors and driving mechanisms of folliculogenesis and luteogenesis has resulted in development of controlled reproduction protocols with timed artificial insemination, resynchronization of cows that have not concieved, including strategies for better embryo survival, factors for enhancing fertility and economical success. This is achieved with pharmacological methods of induction of folliculogenesis, luteogenesis and luteolysis, with well-timed resinchronization, in order to improve fertility and prevent subfertility. Protocols for synchronization of ovulation are routine procedures for induction of reproduction and resynchronization, used for improvement of conception rates and shortening the period between two successive inseminations in cows that have not concieved. The best way to obtain good conception rates, which are achieved when controlled reproduction protocol starts in the middle of estrous cycle, is to use presynchronization protocols, i.e. protocols which precede Ovsynch, and result in better synchronization of cycle, thanks to repeated use of hormons. The aim of presynchronization is to adjust cycle phases for use of Ovsynch, i.e. to synchronize the middle of cycle. The best effect is achieved when there is a dominant follicle present on ovary in the time of first GnRH application, but it has a stimulative effect even in anovulating cows. It is neccessary to determine cows not concieving to TAI as soon as possible, and to submit them to resynchronization protocols. In this way, period between two subsequent inseminations is shortened and herd's overall conception rates are increased. Sixty cows were randomly selected on one dairy farm in Croatia, and divided in two gropus of 30. Group A was presynchronized using GnRH synthetic analogue 9days, and PGF2α synthetic analogue two days before start of Ovsynch. Group B was synchronized with Ovsynch protocol (application of GnRH 7days before and two days after the application of PGF2α, with timed artificial insemination: first time with application of second GnRH and second time 18h later). Seven days before ultrasound pregnancy diagnosis, all cows recieved GnRH. Those negative on gravidity diagnosis continued once more with Ovsynch with timed AI, as described earlier. Collected data were analised using statistical program SAS, and PROC GLINMIX was used, with variables protocol, number of lactation, season in which cows were inseminated, milk yield in 100 and 305 days. The obtained results indicated no statistical difference in first conception rate between protocols (37.72% in group A vs. 47.67% in group B), while there was significant difference among groups for second conception rate (29.11% in group A vs. 71.57% in group B, p=0.0189). Other variables included in procedure showed no significant effect on conception rates among groups.

dairy cow; synchronization of ovulation; Ovsynch; presynchronization; resynchronization

nije evidentirano