Most work on the c-ros knockout model showed that the angulated spermatozoa could not pass the utero-tubal junction and never reached the eggs in the oviduct[14] and that the angulation indicated an increased cell volume [15, 16]. Differences in the composition of cauda epididymidal fluid from these animals included higher fluid concentrations [17], higher pH [18] and lower phos-phate concentrations [19], and spermatozoa from the null males had lower than normal myo-inositol and glutamate contents [17]. In the presence of clear cells and normal vacuolar-ATPase expression, the raised pH is explicable by downregulated NHE2 and NHE3 cation exchangers in the caput and cauda epididymidis [18]. The reduced intracellular glutamate could be explained by the absence-dependent glutamate transporter EAAC1 in of the Na+the caput epididymidis [20], as a result of the failure of the initial segment to differentiate at puberty [21], were the secreted glutamate to be taken up by maturing spermatozoa. As these models have not been examined systematically, there are as yet no common characteristics,apart from the angulated sperm flagella upon release from the epididymis. Raised luminal fluid pH was also found in Foxi1 knockout mice, but in this model apical and clear cell V-ATPase proton pump activity was depleted [12] and phospholipid hyroperoxide glutathione peroxidase PHGPx (GPX4) activity of spermatozoa was knockout mice [10].