A study on stress response and fertility parameters in phenotypically thermotolerant and thermosensitive dairy cows during summer heat stress

Abstract

It is well documented that heat stress (HS) causes subfertility in dairy cows. However, during the last ten years we have been observing that, under high temperature-humidity index (THI ≥ 75), despite the overall reduced fertility, some cows conceive at the first artificial insemination (AI). Here, we examined distinctive features of cows with conserved fertility under severe HS. From the databases of three herds, 167 lactating Holstein cows were selected; group TT cows (n = 57) conceived in the previous summer (THI ≥ 75) at the 1st AI, and group TS (n = 110) failed to conceive at the same period after at least 2 consecutive AIs. The animals calved in spring, and in August, blood samples were collected during a hot day (THI ≥ 81) for the determination of cortisol and HSP70 concentrations. In one farm, the validity of fertility data of the previous year was reexamined. In 28 cows from group TT and in 39 cows from group TS, the conception rate was examined during July and August. In 6 cows from each group (TT and TS) the oestrous cycles were synchronized, ovulation was induced with GnRH (THI = 80), and the concentration of the pre-ovulatory LH surge was determined in 9 blood samples. The progesterone concentration in the ensuing cycle was determined in blood samples collected every other day. Overall, cortisol and HSP70 were significantly lower in TT group compared to TS. More (p < .05) animals from group TT conceived at the first AI compared with those from group TS. The induced pre-ovulatory LH surge peaked at higher level (p < .002) in group TT than in group TS, while no difference was recorded among groups either in mean progesterone concentrations or in the duration of the ensuing oestrous cycle. These results are highly suggestive that thermotolerance in some dairy cows is an inherent characteristic, warranting further genetic investigation.

Ultrasonographic findings of the corpus luteum and the gravid uterus during heat stress in dairy cattle

“…In this study, we describe for the first time structural and haemodynamic differences in the gravid uterus and the CL of pregnancy that were associated with a long exposure of cows to elevated ambient temperatures. In a previous study, we have shown that despite the cooling methods used, cortisol and heat shock protein 70 (HSP70) concentrations are elevated during the hot months of the year (Nanas et al., 2020). In the present study, neither the dry matter intake was affected (results not shown) nor the body temperature exceeded the normal range of the breed, confirming our previous findings.…”

“…The determination of cortisol and progesterone concentrations were carried out by ELISA, according to the manufacturers’ recommendations as previously described (Nanas et al. 2020). The samples were analysed in duplicate; when differences exceeded 10%, the samples were re‐analysed.…”

“…HS affects not only general physiology, dry matter intake and milk yield (Collier et al., 2017; West, 2003) but also, and most importantly, fertility and reproductive efficiency. The effects of HS on reproduction include dramatic reduction in conception rates, increased early embryo death and abortion rates (Yaser M. Al‐Katanani et al., 1999; De Rensis & Scaramuzzi, 2003; Nanas et al., 2020).…”

Heat Shock Protein 70 Improves In Vitro Embryo Yield and Quality from Heat Stressed Bovine Oocytes

“…Depending on the experiment, the maturation medium was modified with the addition of 5 ng/mL HSP70. The HSP70 dose was selected on the basis of HSP70 concentration that we measured in the peripheral blood of 164 heat stressed dairy cows [ 29 ]. COCs ( n = 1933) were randomly allocated to 1 of 4 maturation protocols: 39 °C for 24 h without (group C39, n = 471) or with HSP70 (group H39, n = 353), for 6 h at 41 °C (from the 2nd to 8th hour of IVM) followed by 16 h at 39 °C in the presence (group H41, n = 704) or in the absence of HSP70 (group C41, n = 405).…”

Developmental competence of heat stressed oocytes from Holstein and Limousine cows matured in vitro

“…During summer months despite the overall suppression in conception rates, and the increased embryo losses, a proportion cows remain extremely fertile conceiving at the first A.I. (Nanas et al., 2020). We have examined the difference of some characteristics between summer and winter early pregnancies, and we found that during the summer, the pregnancy associated glycoproteins (PAGs) concentrations are higher than those of the winter (Nanas et al., 2021).…”