254 research outputs found
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
Unilateral twin pregnancy: a non-infectious factor required for the etiological diagnosis of abortion in dairy herds
Twin pregnancies are classified into bilateral (one fetus in each uterine horn: 44%) and unilateral (both fetuses in the same uterine horn, right or left: 56%). The incidence of abortion during mid- to late gestation is approximately 1% in cows carrying bilateral twins and more than 40% in cows carrying unilateral twins. In this period, abortion seems most commonly associated with infectious agents. However, although this imbalanced abortion rate may imply that unilateral twin pregnancy is a non-infectious abortion factor, few available data can describe the cause of abortions in twin pregnancies. The current findings suggest that unilateral twin pregnancy is a non-infectious factor required for the etiological diagnosis of abortion in dairy herds
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