Intra-follicular temperature acts to regulate mammalian ovulation

Negative photoperiod induces an increase in the number of ovulations in dairy cattle

This study sought to examine the impact of negative photoperiod on the incidence of multiple ovulations and pregnancies in dairy cattle. The study population consisted of 5,373 pregnant cows in their third or greater lactation that experienced their first post-partum pregnancy after spontaneous estrus. The positive photoperiod (increasing day-length) extends from December 22 to June 21, whereas the negative photoperiod (decreasing day-length) extends from June 22 to December 21. The odds ratios (ORs) for multiple ovulations and pregnancies in cows that became pregnant during the negative photoperiod and the remaining cows that became pregnant during the positive photoperiod were 1.4 and 1.3 (P < 0.0001), respectively. The ORs for cows that became pregnant ≥ 90 days in milk and the remaining cows that became pregnant < 90 days in milk were 4.3 and 4.1 (P < 0.0001), respectively. No significant differences were detected in the monthly rates of multiple ovulations or pregnancies during positive and negative photoperiods. Thus, the present study demonstrates that the ovarian function in cows is related to changes in day-length, with decreasing day-length being associated with greater multiple ovulation and pregnancy rates. The present study also shows that positive and negative photoperiods exhibit different trends. The results of this study are consistent with a growing body of work demonstrating the effects of photoperiod patterns on the reproductive physiology of cows, with clear implications for twin pregnancy prevention.

Cervix-rectum temperature differential at the time of insemination is correlated with the potential for pregnancy in dairy cows

This study sought to establish whether temperature gradients between the cervix, vagina, and rectum at and 7 days post-artificial insemination (AI) were associated with the incidence of pregnancy in lactating dairy cows (Experiment I; n = 90 ovulating cows) and to evaluate temperature gradient dynamics from the time of insemination to 7 days post-AI under heat stress conditions (Experiment II; n = 16 ovulating and 4 non-ovulating cows). In Experiment I, 39 cows (43.3%) became pregnant. The odds ratio for pregnancy was 2.5 for each one-tenth of a degree drop in cervical temperature with reference to the control rectal temperature at the time of AI (P = 0.01), whereas the same decrease in the cervix–rectum temperature differential 7 days post-AI resulted in an odds ratio of 0.44 (P = 0.02). In Experiment II, 5 of the ovulating cows (31.3%) became pregnant. The mean values of the vagina–rectum, vagina–cervix, and cervix–rectum temperature differentials at AI (day 0), 8 h, 24 h, and 7 days post-AI changed significantly from day 0 to day 7 (within-subject effect; P < 0.02) in ovulating cows but not in non-ovulating cows. Temperature differentials on days 0 and 7 were similar between ovulating cows and cows of Experiment I. Overall, our findings support the notion that a temperature differential between the caudal cervical canal and rectum at AI may be an indicator of the likelihood of pregnancy. Possible prospects of confirming estrus at the herd-level are also suggested.

Thermal Mechanisms Preventing or Favoring Multiple Ovulations in Dairy Cattle

Simple Summary

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.

Abstract

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.

Twin Pregnancies in Dairy Cattle: Observations in a Large Herd of Holstein-Friesian Dairy Cows

Simple Summary

Cows have two ovaries, two uterine horns, two oviducts, and a uterine body. Although they are commonly monovular, they can sustain twin or other multiple pregnancies to term. In cows with a single pregnancy, the embryo implants in the uterine horn that is on the side of ovulation where a corpus luteum develops. Multiple pregnancies are classified into bilateral (one or more embryos in each uterine horn) and unilateral (all embryos in the same uterine horn, right or left) and, in both cases, embryos occur on the side of their corresponding corpus luteum or corpora lutea. Multiple pregnancies are undesirable in dairy herds as they compromise the reproductive performance and productive lifespan of cows. The present study sought to: (a) gain information on the incidence of twin pregnancies, (b) assess and expand information on the relative incidence of bilateral twins compared to unilateral twins, (c) confirm corresponding laterality between embryos and corpora lutea, (d) tabulate the frequency of triplets or quadruplets, and (e) evaluate possible effects of environmental heat stress conditions on the incidence of multiple pregnancies. The data for this study were derived from the ultrasonographic examination of 1130 cows carrying twins, triplets, or quadruplets, and 3160 cows carrying singletons.

Abstract

Multiple pregnancies have devastating consequences on the herd economy of dairy cattle. This observational study examines incidence patterns based on data from the ultrasonographic examination of 1130 multiple pregnancies in cows in their third lactation or more carrying twins (98.8%), triplets (1.1%), or quadruplets (0.08%), and 3160 of their peers carrying singletons. Cows became pregnant following a spontaneous estrus with no previous hormone treatments. Irrespective of a significant decrease (p < 0.0001) in the conception rate (28–34 days post-insemination) during the warm period of the year, the multiple pregnancy rate was similar for both warm (26.5%) and cool (26.3%) periods. The incidence of unilateral multiple pregnancies (all embryos in the same uterine horn) was higher than that of bilateral pregnancies (at least one embryo in each uterine horn): 54.4% versus 45.6% (p < 0.0001). This difference rose to 17% during the warm season (p = 0.03). Pregnancy was monitored in unilateral multiple pregnancies until abortion or parturition (n = 615). In the warm period, the parturition rate was 43% compared to 61% recorded in the cool period (p < 0.0001). Thus, a warm climate is the main factor compromising the fate of multiple pregnancies. Some clinical suggestions are provided.

Temperature gradients in the mammalian ovary and genital tract: A clinical perspective

Temperature within mammalian reproductive tissues is noted to be a key component of fertility, and significant gradients in temperature can be demonstrated deep within the abdomen shortly before ovulation. Indeed, in the absence of such gradients in the ovary and genital tract, the processes of ovulation and fertilisation are severely compromised. This review aims to assess literature produced during the last five decades regarding temperature gradients in the mammalian ovary and genital tract. A large body of observations derived from rabbits, women, pigs and cattle is summarised in tabular form, ovarian follicular values being as much as 2.5 °C or more cooler than neighbouring ovarian tissues or deep rectal temperature. We highlight recent works demonstrating a positive correlation between pre-ovulatory follicular cooling and pregnancy. Understanding the significance of follicular cooling should help us (a) explain why so many potential pregnancies fail in vivo as in vitro and (b) inspire ways for improving the processes of fertilisation and establishment of a full-term pregnancy. Based on our findings in domestic animals, and most recently in cows whose Graafian follicles are comparable in size and timing of response to the LH peak with human follicles, we wish to encourage IVF and fertility preservation clinics to take advantage of this work. By so doing, the incidence of full-term pregnancies in women should be improved.

Evolutionary sequences in mammalian reproductive biology

Broad biological aspects and accepted evolutionary sequences may offer useful guidance towards a comprehensive explanation of the function of mammalian ovaries and oviducts and their vital contribution to the events of fertilization. Cooling of the preovulatory follicles before ovulation may well have its roots in the primitive stages of external fertilization in which aggregates of oocytes are shed into freshwater.