Abstract. Decreased conception rate of dairy cows in the summer is mainly associated with the deleterious effects of environmental thermal stress on the female reproductive tract. Here, we suggest that decreased reproductive performance might be partially due to inferior-quality semen. Semen from five representative bulls was collected in summer (August to September) and winter (December to January) and evaluated with a computerized sperm-quality analyzer for bulls (SQA-Vb). No seasonal effect was found in fresh ejaculate, but sperm examined post-thawing showed lower velocity, motility and progressive motility (P<0.04) in summer vs. winter samples. Element concentrations in the seminal plasma, determined by inductively coupled plasma-atomic emission spectrometry, differed between seasons, with higher (P<0.01) concentration values of K, Mg, Na and S elements in winter vs. summer samples. Therefore, season-induced alterations in seminal plasma element concentration should be taken into account when using an extender for cryopreservation. Acrosome integrity was assessed by a triple-fluorescence test using Hoechst 33342, fluorescein isothiocyanate-conjugated Pisum sativum agglutinin (FITC-PSA) and propidium iodide. Acrosome reaction was examined by a one-step staining method using FITC-PSA. The proportion of sperm cells with a damaged acrosome post-thawing tended to be higher (P<0.07) in semen collected during the summer vs. winter. Such alterations suggest that seasonal reductions in sperm function might also be involved in the decreased conception rate of dairy cows in summer. Decreased fertility of dairy cows during the summer is mainly associated with the deleterious effects of environmental thermal stress on the female reproductive tract. However, the effects of heat stress on semen quality may also contribute to the phenomenon [1, 2].Mature mammalian spermatozoa are quiescent in the male reproductive tract. Upon ejaculation, they undergo capacitation, develop hyperactive motility and acquire acrosomal ability to react [3]. These events involve sperm membrane hyperpolarization, activation of plasma-membrane ion channels and changes in intracellular Ca 2+ concentration, [Ca 2+ ] i [4,5]. Thus, season-induced alterations in one of these events might compromise spermatozoon fertilization competence.In bovines, the sperm flagellum contains cyclic nucleotidegated (CNG) channels-nonselective cation channels that regulate Na + , Mg 2+ and Ca 2+ influx under cGMP and cAMP control [4][5][6]. CNGA3 (formerly CNGα3) ion channels are expressed along the entire sperm flagellum, whereas CNGB1 (formerly CNGβ1) channels are localized to its principal part [4,7,8]. Activation of CNG channels leads to depolarization of the membrane voltage and a concomitant increase in cytosolic cation concentrations [9]. In addition, calcium flux through sperm inositol 1,4,5-trisphosphate (IP 3 ) receptors (IP 3 Rs) located in the sperm's head and connecting piece plays a pivotal role in acrosomal exocytosis, as binding of IP 3 to IP 3 Rs trig...

The decrease in dairy cow fertility during the summer is mainly associated with the deleterious effects of heat stress on the female reproductive tract. The present study suggests that the decreased reproductive performance is, in part, a result of using semen of inferior quality. Evaluated parameters included (1) ionic concentrations in the seminal fluid of bull semen, including [Ca2+], [K+], and [Na+]; (2) expression of ion channels CNGB1, CNGA3, and IP3R; (3) parameters of semen quality such as volume, concentration, motility, and progressive motility; and (4) acrosome integrity. Semen was collected from 5 representative bulls throughout the summer (August and September) and winter (December and January), and was evaluated according to a computerized sperm quality analyzer for bulls (SQA-Vb, Medical Electronic Systems, Caesarea, Israel). [Ca2+], [K+], and [Na+] in the seminal fluid were determined by inductively coupled plasma-atomic emission spectrometry. A semiquantitative PCR and the computer program Scion Image (Scion Corporation, Frederick, MD) were used to determine RNA expression of ion channels CNGB1, CNGA3, and IP3R. Acrosome integrity was assessed by a triple-fluorescence test, which included Hoechst 33342 (h33342), fluorescein isothiocyanate-conjugated Pisum sativum agglutinin (FITC-PSA), and propidium iodide (PI) staining. Data were presented as mean ± SD and analyzed by t-test (JMP-in 5.1). Findings revealed seasonal differences in [K+], [Na+] (P < 0.01), and [Ca2+] (P < 0.08) in the seminal fluid. These were associated with differences in RNA expression for ion channels CNGB1, CNGA3 (P < 0.01), and IP3R (P < 0.09), which are known to be involved in acrosome reactions. Although no differences were found in fresh semen, a progressive decrease in motility was noted for post-thaw semen collected in the summer (P < 0.05). Furthermore, the proportion of sperm cells with damaged acrosomes was higher in post-thaw semen collected in the summer than in its counterpart collected in winter (54.2 ± 3.5% v. 51.4 ± 1.9%, respectively; P < 0.08). The results suggest that semen collected during the summer is less able to survive cryopreservation, as reflected by its inferior vitality post-thawing. Further examination is required to determine whether such alterations are involved in the low summer fertility of dairy cows. The authors thank the Israeli Artificial Insemination Center, Sion, for semen and Medical Electronic Systems (Caesarea, Israel) for providing the SQA-Vb sperm quality analyzer.