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Review

Thermal Mechanisms Preventing or Favoring Multiple Ovulations in Dairy Cattle

1
Department of Veterinary-Medical Science, University of Parma, Str. dell’Università, 12, 43121 Parma, Italy
2
Department of Animal Science, University of Lleida, 25198 Lleida, Spain
3
Agrotecnio Centre, 25198 Lleida, Spain
4
Transfer in Bovine Reproduction SLu, 22300 Barbastro, Spain
*
Author to whom correspondence should be addressed.
Academic Editor: Raffaele Boni
Animals 2021, 11(2), 435; https://doi.org/10.3390/ani11020435
Received: 19 January 2021 / Revised: 4 February 2021 / Accepted: 6 February 2021 / Published: 8 February 2021
(This article belongs to the Special Issue Therapeutics of Twin Pregnancies in Dairy Cattle)
While cows are usually monovular, the incidence of dizygous twin births has recently increased considerably alongside increasing milk production. Genetic progress and improvements in nutrition and management practices have led to a continuous increase in milk yield and thus also to multiple ovulations and twin pregnancies. Twin pregnancies are undesirable as they seriously compromise the welfare of the cow and herd economy. A better understanding of the processes associated with multiple ovulations should help to reduce rates of twinning. During the stages of the sexual cycle, temperature gradients are established within the ovary and throughout the genital tract. Pre-ovulatory local cooling of the reproductive system favors male and female gamete maturation and subsequent fertilization. In fact, thermal mechanisms may prevent or favor multiple ovulations and thus twinning. The purpose of this review was to update this topic.
While cows are predominantly monovular, over the past 30 years the incidence of multiple ovulations and thus twinning has increased considerably alongside milk production. Multiple pregnancies are not desirable as they negatively affect the health of cows and the herd economy. Although causal mechanisms associated with multiple ovulations have been extensively revised, the process of multiple ovulations is not well understood. Recent studies on the thermal biology of the reproductive system have shown how thermal mechanisms may prevent or favor multiple ovulations. This review focuses on this relationship between thermal dynamics and multiple pregnancies. Cooling of the pre-ovulatory follicle is able to regulate ovulation. In effect, pre-ovulatory local cooling of the female reproductive system favors male and female gamete maturation and promotes fertilization. Thermal stress is proposed here as a model of stress. Periods of high ambient temperature affect the processes of pre-ovulatory follicular cooling and multiple ovulations. While the ratio between unilateral and bilateral multiple pregnancies is normally close to one, under heat stress conditions, this ratio may be 1.4 favoring unilateral multiple pregnancies. A ratio approaching unity is here proposed as an indicator of cow wellbeing. View Full-Text
Keywords: graafian follicle; ovarian physiology; ovulation failure; unilateral ovulations graafian follicle; ovarian physiology; ovulation failure; unilateral ovulations
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MDPI and ACS Style

De Rensis, F.; Morini, G.; Garcia-Ispierto, I.; López-Gatius, F. Thermal Mechanisms Preventing or Favoring Multiple Ovulations in Dairy Cattle. Animals 2021, 11, 435. https://doi.org/10.3390/ani11020435

AMA Style

De Rensis F, Morini G, Garcia-Ispierto I, López-Gatius F. Thermal Mechanisms Preventing or Favoring Multiple Ovulations in Dairy Cattle. Animals. 2021; 11(2):435. https://doi.org/10.3390/ani11020435

Chicago/Turabian Style

De Rensis, Fabio, Giorgio Morini, Irina Garcia-Ispierto, and Fernando López-Gatius. 2021. "Thermal Mechanisms Preventing or Favoring Multiple Ovulations in Dairy Cattle" Animals 11, no. 2: 435. https://doi.org/10.3390/ani11020435

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