Factors Influencing the Quality of Frozen/Thawed Semen from Estonian Holstein AI Bulls, and Relationships between Semen Quality Parameters and in vivo Fertility

Abstract

At present, dairy farming is definitely the most profitable sector of Estonia’s cattle industry. The effectiveness of milk production is dependent not only on the availability of high-quality genetic material but also on several other factors, including the quality of frozen bull semen. The purpose of this research was to assess the effect of different factors such as age, the proportion of Holstein genes, and season of the year on the quality of semen collected from breeding bulls. The studies were also aimed at determining the methods and parameters most suitable for routine semen analysis performed at artificial insemination (AI) stations, predicting pregnancy rates, and developing a relevant mathematical prediction model. Analysis of the experimental data revealed that the above factors affect sperm motility, mitochondrial activity, and the stability and integrity of plasma membranes. A positive correlation was found between pregnancy rates and sperm quality assessed by flow cytometry and the results of conventional laboratory tests used at AI stations. A combination of conventional laboratory tests and flow cytometric analysis of membrane stability and mitochondrial activity of frozen-thawed spermatozoa allowed better prediction of the potential fertility of bull semen in comparison to the conventional laboratory tests alone. Knowledge of these relationships and implementation of the research findings into practice enables AI stations to produce top-quality semen straws the use of which ensures higher pregnancy rates in cows. Based on the findings of the study, the semen collection and processing procedures were modified at the Kehtna AI station to take into accout age-specific and other particular features of each individual bull. Furthermore, collection of ejaculates and production of semen straws were rescheduled mostly for the autumn-winter period. Thanks to the improvements made to the semen collection and processing procedures, the number of semen straws per ejaculate has increased by about 15 percent at the Kehtna AI station. Over the last seven years, an increase in pregnancy rates by about 3 percent has been achieved, as a result of which dairy farmers have saved nearly 300,000 euros on their AI costs.

Tänapäeval on Eesti veisekasvatuses kõige tulusam pidada piimakarja. Piimatootmise tõhusus ei sõltu ainult väärtusliku geneetilise materjali olemasolust, vaid ka paljudest teistest teguritest, mille hulgas on tähtsal kohal sügavkülmutatud pullisperma kvaliteet. Uurimistöö eesmärk oli välja selgitada, kuidas mõjutavad sperma kvaliteeti pulli vanus, holsteini veresus ja sperma kogumise aastaaeg ning leida sperma kvaliteeti määravate meetodite seast sellised, mida saaks rakendada seemendusjaama tööprotsessis ja mis sobiksid samas ka emasloomade tiinestumise prognoosimiseks nii üksiktestina kui ka matemaatilise mudeli komponendina. Uuringust selgus, et sugupulli vanus, sperma varumise aastaaeg ja pulli holsteini veresus avaldavad mõju spermide liikuvusele, mitokondrite aktiivsusele, membraanide stabiilsusele ja terviklikkusele. Kehtna kunstliku seemendusjaama tootmisprotsessis arvestatakse pulli ealisi iseärasusi ja individuaalset omapära ning enamik seemendusdoose toodetakse sügistalvisel perioodil. Seemendusjaamas spermide hindamiseks kasutatavate testide ja voolutsütomeetriga määratud spermide kvaliteedi ja emasloomade tiinestumise vahel leiti positiivne korrelatsioon. Kõige parem mudel spermide viljastamisvõime hindamiseks moodustus kombinatsioonist, mis hõlmas nii seemendusjaamas kasutatavaid teste kui ka voolutsütomeetriga määratud spermide omadusi. Tänu selliste seoste väljaselgitamisele on võimalik garanteerida toodetud seemendusdooside tippkvaliteet, mis on vajalik emasloomade õigeaegseks tiinestumiseks. Uuringutest saadud teadmiste ja kogemuste rakendamine seemendusjaama tehnoloogilises protsessis on suurendanud ühest ejakulaadist toodetavate seemendusdooside arvu ~15% võrra. Viimase seitsme aasta jooksul on veiste kunstliku seemenduse tulemuslikkus Eestis tõusnud ~3% võrra ning seeläbi on põllumajandustootjad samal perioodil säästnud ~300 000 € seemendustele tehtavate kulutuste arvelt.