To what extent does photoperiod affect cattle reproduction? Clinical perspectives of melatonin administration

The seasonality of reproduction in most mammals is dictated by photoperiod, temperature and nutrition. Melatonin, mainly synthesized in the pineal gland, is generally accepted as the active mediator of photoperiod responses including reproduction. While non-pregnant heifers and cows show continuous sexual activity and are therefore not seasonal breeders, it has been suggested that photo-periodicity may influence the appearance of puberty in heifers and the onset of parturition. Further, the light/dark ratio may influence endocrine patterns of gestation and a shorter light period correlates with the incidence of twin pregnancies. This review considers specific aspects of the effects of photoperiod and melatonin on reproduction in dairy cattle and discusses the clinical applications of melatonin

L'estrès per calor influeix en la fertilitat de les vaques lleteres

Patir condicions de temperatura superiors a la zona de confort tèrmic -el que es coneix com estrès per calor- és un dels principals factors relacionats amb la pèrdua de fertilitat de les vaques lleteres, especialment en zones amb estius calorosos, com Catalunya. Així ho conclou un estudi dut a terme a granges de vaques lleteres de Lleida i Osca per un grup d'investigadors de la Universitat de Lleida i de la Universitat Autònoma de Barcelona. Els científics han analitzat les dades de 10.964 inseminacions artificials realitzades a 4 ramats en relació a diverses variables climàtiques registrades al llarg de 3 anys.Sufrir condiciones de temperatura superiores a la zona de confort térmico -lo que se conoce como estrés por calor- es uno de los principales factores relacionados con la pérdida de fertilidad de las vacas lecheras, especialmente en zonas con veranos calurosos, como Cataluña. Así lo concluye un estudio realizado en granjas de vacas lecheras de Lleida y Huesca por un grupo de investigadores de la Universitat de Lleida y de la Universitat Autònoma de Barcelona. Los científicos han analizado los datos de 10.964 inseminaciones artificiales realizadas a 4 rebaños en relación con diversas variables climáticas registradas a lo largo de 3 años.Summer heat stress is a main factor related to low conception rates in high producing dairy herds in warm areas worldwide. A research group of UAB Faculty of Veterinary Medicine has studied the impact of several climate variables on conception rates in high producing dairy cows in northeastern Spain by examining 10,964 inseminations

Clinical overview of luteal deficiency in dairy cattle

Luteal deficiency is defined as reduced progesterone (P4) steroidogenesis by the corpus luteum (CL), either in the amount or duration, or both. This work provides a clinical overview of the current understanding of luteal deficiency and its association with low fertility in dairy cows. Low plasma P4 concentrations during the luteal phase post-artificial insemination (AI) are associated with lower conception rates. Treatments post-AI with P4, gonadotropin-releasing hormone (GnRH) or human chorionic gonadotropin (hCG) improve fertility in some conditions. Sub-luteal function during the late embryonic period (at pregnancy diagnosis, i.e., 28–34 days post-AI), is just one factor among other factors associated with pregnancy loss. Treatment with P4 in cows with one CL favors pregnancy maintenance, while GnRH treatment does the same in cows carrying twins. The diagnosis of sub-luteal function can be made clinically on the basis of plasma or milk P4 concentrations. Automated in-line milk P4 analysis systems to diagnose luteal activity emerge as a very interesting tool in dairy herds. Monitoring plasma or milk P4 concentrations with the help of Doppler ultrasonography to assess the CL function would allow individualizing the luteal phase support