Managing Reproduction During Heat Stress in Dairy Cows

Abstract

Heat stress can compromise reproductive function of lactating dairy cows throughout much of the world. Among the key events associated with reduced reproductive function are reduced expression of estrus, disruptions in follicular and oocyte function, increased embryonic mortality, and reductions in fetal development. Reproductive function during heat stress can be improved by modifying animal housing to reduce the magnitude of heat stress. In addition, manipulation of physiological function can mitigate some deleterious effects of heat stress. Effects on estrus detection can be reduced by incorporation of estrus detection aids and eliminated by utilization of timed artifi cial insemination protocols. Effects on fertility can be reduced by use of embryo transfer. Other approaches, such as feeding antioxidants, offer some promise for improving fertility, whereas others, such as hormonal treatments, have not resulted in consistent improvements in fertility during heat stress. In the future, it may be possible to select cows for resistance to heat stress as genetic markers for thermotolerance at the physiological and cellular level are identifi ed.Heat stress adversely affects fertility of dairy cattle in most temperate regions of the world where dairy cattle are raised. The magnitude and duration of the reduction in fertility during seasonal heat stress is greater in Dairy Production Medicine, First Edition. Edited by Carlos A. Risco, Pedro Melendez Retamal.

Recent progress in bovine in vitro‐derived embryo cryotolerance: Impact of in vitro culture systems, advances in cryopreservation and future considerations

“…High straw cost dilution among multiple donors due to microenvironment fertilization (Blondin et al, 2009;Gordon, 2003a;Wheeler et al, 2006) More females (90%:10% vs. 50%:50%) with sexed semen (Johnson, Welch, & Rens, 1999) Transfer of female embryos into lactating cows to increase pregnancy rates especially under high temperature/heat stress conditions (Al-Katanani, Paula- Lopes, & Hansen, 2002;Ambrose et al, 1999;Block et al, 2010;Hansen, 2011;Jordan, 2003;Rensis & Scaramuzzi, 2003;Rutledge, 2001;Stewart et al, 2011) Secures replacement needs (Rath & Johnson, 2008;Wheeler et al, 2006) Facilitates the eradication of diseases from the farm because of a female surplus…”

External Progesterone Supplementation During the Ovsynch Protocol Reduces the Incomplete Luteolysis in Dairy Cows Under Heat Stress

“…The upper critical point of this range marks the onset of heat stress. Heat stress adversely affects fertility of dairy cattle and compromises their reproductive function through reduced expression of estrus, disruption of follicular and oocyte function, as well as increased embryonic mortality (1). In addition, cows chronically exposed to heat stress have a reduced progesterone (P4) concentration (2) leading to decreased fertility due to its importance on pregnancy maintenance.…”