Sodium caseinate improves longevity and fertility of frozen bull semen

This study aimed to evaluate the effect of sodium caseinate added into freezing extender on the sperm parameters of cryopreserved bull semen and in vitro and in vivo fertility. One ejaculate of 30 bulls was used and processed using Botu-Bov (Botupharma, Botucatu, Brazil) with the addition of 20% egg yolk (EY) or 15% egg yolk with 2% sodium caseinate (EY thorn SC), subsequently submitted to freezing. Semen from both groups were evaluated immediately after thawing (T0) and after thermic stress at 37 degrees C for 90 min (T90), for sperm kinetics, by CASA method, and plasma membrane integrity (PMI), superoxide (O-2) concentration and high mitochondrial potential (HMP) by flow cytometry. In vitro fertilization (IVF) was performed to assess embryo cleavage rate on day 3, and blastocyst rate on day 8. The in vivo fertility test was performed using fixed-time artificial insemination (FTAI). In sperm evaluation, trajectory velocity, linear velocity, curvilinear velocity, and lateral head movement were higher (P < 0.05) in EY thorn SC at T0. At T90, while rectilinearity and linearity did not differ between EY and EY thorn SC (P > 0.05), the other parameters evaluated were higher in EY thorn SC. Similarly, the integrity of the plasma and acrosomal membranes (iPAM) was higher (P < 0.05) at T90 in EY thorn SC, but did not differ (P > 0.05) between the groups at T0. For O-2(-) and HMP, the values were lower (P < 0.05) in EY thorn SC group in both moments; furthermore, EY thorn SC showed higher cleavage and blastocyst rates in IVF. Likewise, pregnancy rates by FTAI were higher (P < 0.05) in the EY thorn SC group. In conclusion, the addition of sodium caseinate into freezing extender improves sperm parameters of frozen-thawed bull semen and fertility rates on during in vitro and in vivo tests. (c) 2020 Elsevier Inc. All rights reserved.