Abstract
The current study aimed to determine the effects of the preovulatory follicular fluid (FF) of normal heifer (NH) and repeat breeder cows with subclinical endometritis (SCE) or without (nSCE) on oocyte maturation (Experiment 1) and fertilization rates (Experiment 2). Moreover, the pattern of gene expression of cumulus oocyte-complexes was evaluated in Experiment 1. In Experiment 1, nuclear maturation in the nSCE group was higher, compared to that in the SCE group (P = 0.05). In addition, the oocyte nuclear maturation in the normal heifer was significantly higher, in comparison to that of SCE groups (P < 0.05). Furthermore, the mean percentage of normal oocyte fertilization was higher in the nSCE group, compared to that in the SCE group (P < 0.05). The expressions of growth differentiation factor, GDF9; steroidogenic acute regulatory, StAR and follicle-stimulating hormone receptor, FSHr in the NH group were significantly higher, compared to those in SCE and nSCE groups (P < 0.05). Moreover, the expressions of all genes in the nSCE group were not significant, in comparison to those in the SCE group (P > 0.05). The supplementation of oocyte maturation medium with FF from pre-ovulatory follicles of repeat breeder cows resulted in less oocyte maturation and cumulus cell expansion. In conclusion, the lower fertility in RB cows could be ascribed to the lower oocyte maturation rate and less expression of GDF9, StAR, and FSHr in the cumulus-oocyte complexes.
Highlights
Repeat breeder (RB) cows are described as subfertile cows that do not become pregnant at least after three consecutive services
Percentage of Cumulus Expansion and Oocyte Nuclear Maturation The mean (±SD) percentage of cumulus-oocyte complexes (COCs) demonstrated that fully expanded cumulus cells were significantly lower in subclinical endometritis (SCE) group than the control, nSCE and normal heifer (NH) groups (30.4 ± 8.3 vs. 65.7 ± 12.1, 46.0 ± 12.9, and 48.8 ± 11.9, respectively; P < 0.05)
The results of the present study showed a significant reduction in follicle-stimulating hormone receptor (FSHr) mRNA expression of the matured COCs in SCE group in comparison with that of the NH group
Summary
Repeat breeder (RB) cows are described as subfertile cows that do not become pregnant at least after three consecutive services. Different factors, including uterine infections, hormonal imbalances, mismanagement in the artificial insemination, nutritional factors, and genetic disorders may result in the occurrence of RB syndrome in dairy cows [1]. A related study reported subclinical endometritis (SCE) in 52.7% of RB cows [2]. Researchers denoted that SCE is a major risk factor for reproductive failure resulting in lower reproductively of dairy cows [3, 4]. It was found that SCE is not the cause of RB syndrome in dairy cows [5]. Follicular Fluid Function in Repeat Breeder Cows
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