Abstract
Sperm samples used on fertilization strongly influence the in vitro production (IVP) rates. However, sperm traits behind this effect are not stated consistently until now. This study aimed to evaluate the isolated and combined effect of some sperm traits (MB: total motility before Percoll® gradient, MA: total motility after Percoll® gradient, AI: acrosome integrity, MI: membrane integrity, MP: mitochondrial membrane potential, and CR: chromatin resistance) on IVP rates. This is the first study focusing on the isolated effect of distinct traits. For this purpose, the experiment was divided in three steps. In first step, to study behavior of traits sperm samples (n = 63 batches) were analyzed and ranked based on each trait. In second step, samples ranked were selected from target ranks regions and allocated in groups of four to five batches, creating Higher and Lower groups, according to two different approaches. One aimed to form groups that differed to all sperm traits simultaneously (effect of combined traits). The other aimed to form groups that differed only to a single sperm trait while no differences were observed for the remaining traits (effect of each isolated trait). In third step, for each group successfully formed in step 2, sperm samples were individually and prospectively used for IVP. Cleavage, embryo development and blastocyst rates were recorded and compared between Higher and Lower of respective trait groups. Surprisingly, evaluation of isolated effects revealed that lower levels of MB, AI and MP resulted in higher embryo development and blastocyst rates (p<0.05), which was not observed on cleavage rate. We conclude that sperm traits strongly influence embryo development after in vitro fertilization (IVF), affecting the zygote competence to achieve blastocyst stage. Individually, levels of MB, AI or MP could be some of the key traits that may define IVP efficiency on current systems of embryo production.
Highlights
In vitro production (IVP) of bovine embryos has allowed the use of a waste biological resource from valuable females to increase their offspring in breeding programs, in Brazil [1,2]
In attempt to better understand the relation between sperm traits and IVP rates, we chose sperm traits previously suggested as possible predictor candidates for IVP performance: motility [9,14,16,17,19], status of acrosome [7,8,9,13,14,16,19], plasma membrane [9,13,14,16,19], chromatin [16,19,20,21] and mitochondria [9,21], and we evaluated their effect on IVP
The sperm traits selected for this study were total motility before Percoll1 Gradient (MB), total motility after Percoll1 Gradient (MA), acrosome integrity (AI), membrane integrity (MI), mitochondrial membrane potential (MP), and chromatin resistance (CR)
Summary
In vitro production (IVP) of bovine embryos has allowed the use of a waste biological resource from valuable females to increase their offspring in breeding programs, in Brazil [1,2]. In addition to IVF shortcomings, the bull effect has been generally related as a cause of variation on IVP rates, including differences between batches from same bull [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18] In this context, attempts to select sperm samples with improved in vitro performance based on sperm features would be an interesting tool to indicate, beforehand, IVP performance and improve embryo production yields [9]. This is probably due to the unknown importance of sperm traits analyzed and the disregards of possible confounding effects such as bull effect and interactions among traits
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