Survival of Sperm of Mpwapwa Bulls in Ambient-temperature Diluents in the Climatic Conditions of Tanzania

Abstract

This study was conducted at the TALIRI Mpwapwa research center in Dodoma, Tanzania. It investigated the viability of Mpwapwa breed bull sperm in ambient temperature diluents for potential use in a local artificial insemination (AI) program. Thirty-five bulls were selected from 53 after breeding soundness examinations. Semen was collected via electro-ejaculation and assessed for volume, density, motility, and morphology. Each ejaculate was divided into three aliquots and diluted (1:1) with coconut water, egg yolk-TRIS, or Optixcell at 32°C, then loaded into straws. A two-year study, including a pilot (Year 1, n=3 bulls) and main study (Year 2, n=35 bulls), assessed the proportion of sperm demonstrating progressive motility (surviving) at varying temperatures (Year 1: 20°C, 27°C, 33°C; and Year 2: 8°C, 17°C, 33°C) over 6, 24, 48, 72 and 120 hours of incubation. Progressive motility (survival) was assessed using CASA. Data analysis utilized a two-stage zero-inflated negative binomial model, incorporating repeated-measures binary logistic and negative binomial models. Year 1 showed better sperm survival at 20°C than 33°C, and better survival in Optixcell and Tris than coconut water. Year 2 demonstrated better survival at 8°C than 33°C, with significantly poorer survival in coconut water. Considering 50% survival as the AI threshold, Optixcell at 8°C or 17°C maintained this level at 48 hours, while Tris only achieved it at 8°C. The study concludes that while lower temperatures improve survival, sufficient sperm survived at 17°C in Optixcell for potential use in a local AI service using ambient temperature diluents.