Fertility of frozen sex-sorted sperm at 4 × 10~6 sperm per dose in lactating dairy cows in seasonal-calving pasture-based herds

摘要

The objective was to evaluate the reproductive performanceof frozen sex-sorted sperm at 4 × 10~6 spermper dose (SexedULTRA 4M, Sexing Technologies, Navasota,TX) relative to frozen conventional sperm inseasonal-calving pasture-based dairy cows. Semen fromHolstein-Friesian (n = 8) and Jersey (n = 2) bulls wasused. Four of the Holstein bulls used were resident ator near a sex-sorting laboratory (Cogent, UK, or STBenelux, the Netherlands). The remaining 6 bulls werelocated at studs in Ireland. For these 6 bulls, ejaculateswere collected, diluted with transport medium, and courieredto Cogent in parcel shippers. Transit time fromejaculation to arrival at the sorting laboratory was 6 to7 h. For all bulls, ejaculates were split and processedto provide frozen conventional sperm (CONV) at 15 ×106 sperm per straw and frozen sex-sorted (SS) spermat 4 × 10~6 sperm per straw and used to inseminate lactatingdairy cows after spontaneous estrus. Pregnancydiagnosis was performed by ultrasound scanning (n =7,246 records available for analysis). Generalized linearmixed models were used to examine effects on pregnancyper AI (P/AI) at first artificial insemination,with sperm treatment (CONV vs. SS), bull (n = 10),and treatment × bull interaction as the fixed effects,and herd (n = 142) as a random effect. Overall, P/AI was greater for cows inseminated with CONV thanfor those inseminated with SS (59.9% vs. 45.5%; 76.0%relative to CONV). This study was not designed tocompare resident bulls vs. shipped ejaculates, but themagnitude of the difference between P/AI achieved byCONV and SS was apparently less for resident bulls(60.3% vs. 50.2%) than for shipped ejaculates (58.6%vs. 40.7%). We discovered a treatment × bull interactionfor shipped ejaculates (P/AI ranged from 45 to86% relative to CONV) but not for the resident bulls(P/AI ranged from 81 to 87% relative to CONV). RelativeP/AI of SS compared with CONV was greater incows with high or average fertility potential (76.1%and 78.3%, respectively) than in cows with low fertilitypotential (58.1%). In 33.1% of the enrolled herds, theP/AI achieved with SS was 90% or more of the P/AI achieved with CONV; this was mainly explainedby herds in which SS performed exceptionally well butCONV performed poorly. In conclusion, SS had loweroverall P/AI compared with CONV; however, P/AIachieved with SS was dependent on the bull, fertilitypotential of the cow, and herd. Strategies to improvethe P/AI with SS in seasonal-calving pasture-basedlactating dairy cows require further research.