The gap in fertility between conventional and sex-sorted bovine sperm, known to be on the order of 10 percentage points, has never been bridged, even by increasing the number of sex-sorted sperm per inseminate. A concerted effort in the last few years has resulted in substantial changes in all stages of the sex-sorting process to develop an improved sex-sorted product called SexedULTRA™ (Sexing Technologies, Navasota, TX, USA). In vitro tests show that SexedULTRA™ maintained sperm integrity better than the previous XY method, and field trials were conducted to determine if this translated into improved bovine field fertility. The initial field trial was performed using ejaculates from 8 Holstein bulls located at Select Sires in Plain City (OH, USA). Each ejaculate was split in 2 aliquots that were then processed following the 2 methods (XY method or SexedULTRA™). A total of 6,930 Holstein heifers were inseminated across 41 commercial herds in the United States. Conception rate data were analysed using mixed model ANOVA (JMP 10.0.0; SAS Institute Inc., Cary, NC) with fixed effects of treatment, bull, bull by treatment interaction, and the random effect of herd. Sex-sorted bull sperm following the SexedULTRA™ method resulted in a greater (P < 0.001) conception rate compared with the XY method sperm (45.7 ± 1.7 v. 41.2 ± 1.6%). This is the first report of an improvement in conception rates using sex-sorted bovine semen in a decade since it became commercially available. A second field trial to investigate dose rate effects and compare against conventional semen was performed using 5 dairy bulls located at German Genetics International GmbH in Cloppenburg (Germany). Each ejaculate was split 4 ways, sex-sorted, and frozen in 0.25-mL straws as follows: XY 2.1 million/straw, SexedULTRA™ 2.1 million/straw, SexedULTRA™ 3.0 million/straw, and SexedULTRA™ 4.0 million/straw. A total of 7,855 heifers were inseminated with these sex-sorted straws, whereas 62,398 heifers were inseminated with conventional straws (15 million/straw) produced using contemporary ejaculates from the same bulls. The 56-day nonreturn rate was calculated by sire and treatment combination, and assigned a weight based on the total number of AI for each combination thereof. Table 1 contains the nonreturn rate weighted means and the relative fertility compared to conventional sperm. Data were analysed using a mixed model ANOVA (JMP 10.0.0; SAS Institute Inc.) with treatment and bull as fixed effects. SexedULTRA™ 4.0 sperm presented the greatest (P < 0.001) 56-day nonreturn rate followed by conventional 15.0 (66.73 v. 65.66%); XY 2.1 presented the lowest (P < 0.001) nonreturn rate. This is the first time a dose response effect with sex-sorted bovine sperm and parity in conception rates with conventional semen has been demonstrated. Table 1. Field trial results for number of inseminations, 56-day nonreturn rate (NRR) weighted means, and relative fertility1 compared with conventional sperm
In prepubertal bulls and heifers of dairy and beef breeds, puberty can be induced to occur earlier than typical with targeted high-energy diets due to precocious activation of the endocrine mechanisms that regulate puberty. Precocious activation of puberty in bulls intended for use in the AI industry has the potential to hasten and perhaps increase sperm production. It was hypothesized that feeding bulls a high-energy diet beginning at 8 wk of age would advance the prepubertal rise in LH and lead to advanced testicular maturation and age at puberty. From 58 to 230 ± 0.3 d of age, Holstein bulls received either a high-energy diet (HE;n = 9; targeted ADG 1.5 kg/d) or a control diet (CONT;n = 10; targeted ADG 0.75 kg/d). Thereafter, all bulls were fed a similar diet. The HE treatment increased LH secretion at 125 d of age, testosterone concentrations from 181 to 210 d, and scrotal circumference (SC) from 146 to 360 d of age relative to the CONT treatment. Beginning at 241 ± 5 d of age, semen collection (artificial vagina) was attempted every 14 d in bulls from the HE (n = 8) and CONT (n = 7) treatment until each bull attained puberty (ejaculate containing 50 × 10 spermatozoa with 10% motility). To assess semen production as mature bulls, semen was collected thrice weekly beginning at 541 ± 5 d of age until slaughter at 569 ± 5 d of age. After slaughter, epididymal and testicular measurements were collected and testicular tissue was fixed to determine seminiferous tubule diameter. Age at puberty did not differ between treatments (310 ± 35 d). Although testis and epididymal weight and testis volume were greater (P < 0.05) in the HE than the CONT treatment, sperm production of mature bulls did not differ between treatments. Diameter of seminiferous tubules also did not differ between treatments. We conclude that the HE advanced aspects of sexual maturation and increased testes size, but this was not reflected in hastened puberty or sperm production in the present experiment.
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