PROBLEM TO BE SOLVED: To prepare a frozen sperm straw which can efficiently and quickly separate sperms having good motility from many sperms having different motility and can realize good fertilization efficiency even when used after freezing and thawing. A possible method for producing a sperm solution for fertilization is provided. SOLUTION: This is a distribution diluent having a composition obtained by excluding the egg yolk or defatted milk from the composition of the primary diluent for cryopreservation of livestock semen containing egg yolk or defatted milk, and contains sperms containing a plurality of sperms having different motility. A step of diluting the liquid to prepare a diluted sperm liquid, a distribution step of forming a swirling flow having a velocity gradient in the axial direction in the diluted sperm liquid, and transferring and distributing the sperm according to the running property, and the distribution. It was decided to have a fractionation step of fractionating the diluted sperm solution that had undergone the step to obtain a fraction containing a sperm group having good motility. [Selection diagram] Fig. 2【課題】運動性の異なる多くの精子の中から運動性の良好な精子を効率良く迅速に分離でき、しかも、凍結融解後に使用した場合でも良好な受胎効率を実現できる凍結精子ストローの調製に利用可能な受精用精子液の製造方法を提供する。【解決手段】卵黄又は脱脂乳を含む家畜精液凍結保存用一次希釈液の組成から前記卵黄又は脱脂乳を除いた組成よりなる分配用希釈液で運動性の異なる複数の精子が含まれた精子含有液を希釈して希釈精子液を調製する工程と、軸線方向に速度勾配を有する旋回流を前記希釈精子液に形成し、前記精子を走流性に応じて移行分配させる分配工程と、前記分配工程を経た前記希釈精子液を分画し、運動性が良好な精子群を含む画分を得る分取工程と、を有することとした。【選択図】図２
