The Infertility of Repeat-Breeder Cows During Summer Is Associated with Decreased Mitochondrial DNA and Increased Expression of Mitochondrial and Apoptotic Genes in Oocytes1

Abstract

Oocyte quality is known to be a major cause of infertility in repeat-breeder (RB) and heat-stressed dairy cows. However, the mechanisms by which RB oocytes become less capable of supporting embryo development remain largely unknown. Thus, the aim of this study was to investigate whether the decreased oocyte competence of RB cows (RBs) during summer is associated with an altered gene expression profile and a decrease in mitochondrial DNA (mtDNA) copy number. Therefore, oocytes collected from heifers, non-RBs in peak lactation (PLs), and RBs were used to evaluate mtDNA amounts as well as the expression levels of genes associated with the mitochondria (MT-CO1, NRF1, POLG, POLG2, PPARGC1A, and TFAM), apoptosis (BAX, BCL2, and ITM2B), and oocyte maturation (BMP15, FGF8, FGF10, FGF16, FGF17, and GDF9). The oocytes retrieved from RBs during winter contained over eight times more mtDNA than those retrieved from RBs during summer. They also contained significantly less mtDNA than oocytes retrieved from heifers and PLs during summer. Moreover, the expression of mitochondria- (NRF1, POLG, POLG2, PPARGC1A, and TFAM) and apoptosis-related (BAX and ITM2B) genes, as well as of GDF9, in RB oocytes collected during summer was significantly greater than that in oocytes collected from heifers and PLs during the same season. In oocytes from heifers and PLs, the expression levels of these genes were lower in those collected during summer compared with winter, but this difference was not observed in oocytes collected from RBs. Altogether, these data provide evidence of altered gene expression and reduced mtDNA copy number in the oocytes collected from RBs during summer. This indicates a loss of fertility in RBs during summer, which might be caused by a possible mitochondrial dysfunction associated with a greater chance of oocytes to undergo apoptosis.

Effect of BMP15 and/or AMH during in vitro maturation of oocytes from involuntarily culled dairy cows

“…Oocyte quality is known to be a major cause of infertility in repeat‐breeder and heat‐stressed dairy cattle. R. M. Ferreira et al () reported the lower expression of genes associated with mitochondria (NRF1, POLG, POLG2, PPARGC1A, and TFAM), apoptosis (BAX and ITM2B), and oocyte maturation (FGF16, BMP15, and GDF9) due to heat stress and peak lactation. Besides, Saini et al () reported the lower expression of gene BMP15 and GDF9 in low‐quality oocytes recovered from living donors.…”

Factors that interfere with oocyte quality for in vitro production of cattle embryos: effects of different developmental & reproductive stages

“…Evidently, several factors appear to be critical to oocyte quality including follicle size (Lonergan et al, 1994;Seneda et al, 2001), environment factors such as heat-stress (Torres-Júnior et al, 2008;Ferreira et al, 2011;Ferreira et al, 2016), genetic background Sales et al, 2015), age (Batista et al, 2016a) and lactation status of donor animals , all having a remarkable influence on the results of IVP. Additionally, there is a growing body of scientific literature demonstrating the direct role of hormonal milieu during follicle development on oocyte quality.…”

“…As a result, excessive increase in insulin concentration in blood, mainly in dairy cows later in lactation, are negatively associated with oocyte quality (reviewed by Baruselli et al, 2016). Exposure to heat stress is widely known to be deleterious to oocyte competence in Bos taurus cattle (Ferreira et al, 2011;Ferreira et al, 2016). Surprisingly, Bos indicus donors although more resistant to environmental heat stress conditions, are also affected by heat stress and may require nearly four months to recover oocyte quality to pre-heat stress levels, even after a short period of heat exposure (Torres-Júnior et al, 2008).…”

Genetic market in cattle (Bull, AI, FTAI, MOET and IVP): financial payback based on reproductive efficiency in beef and dairy herds in Brazil

“…Besides to faster genetic progress, ET also has the potential to increase fertility in dairy cows experiencing heat stress (Putney et al, 1989;Ambrose et al, 1999;Baruselli et al, 2010;Rodrigues et al, 2004Rodrigues et al, , 2007Rodrigues et al, , 2011 and those diagnosed as repeatbreeders (Dochi et al, 2008;Rodrigues et al, 2011), because it bypasses problems associated with fertilization failure and disruption of the oocyte quality in dairy cows (Ferreira et al, , 2016. For example, Baruselli et al 2011, utilizing data from a large commercial herd in Brazil, showed that conception results can be increased in about ~8% (cooler months) to 20% (warmer months) percentage points with the use of ET when compared to AI (Fig.…”