Effects of sex-sorting and sperm dosage on conception rates of Holstein heifers: is comparable fertility of sex-sorted and conventional semen plausible?

The conception rates of Holstein heifers after AI with 2.1 or 10 × 10(6) sperm dosages of sex-sorted or conventionally processed sperm were compared. Ejaculates collected by artificial vagina from 8 Holstein sires were cryopreserved at either 2.1 or 10 × 10(6) sperm per dose with or without sorting to 90% purity for X-chromosome-bearing spermatozoa using flow cytometry. All treatments were processed in an egg-yolk (20%), TRIS, glycerol (7%) extender and packaged in color-coded 0.25-mL French straws. Straws (n=350 straws/treatment per sire) were packaged and distributed in aliquots of 12 (3 straws of each treatment) to 51 herds of Holstein heifers. Straw color was recorded in the on-farm record keeping system at the time of AI and retrieved by electronic download. In total, 9,172 services were recovered, providing a mean sample size of 287±3.5 services/sperm dose per semen type within sire (range: 248 to 318). Conception rates were influenced by the main effects of herd, sire, semen type, sperm dosage, and service number. The herd by sperm dosage interaction was the only interaction determined to be significant and implies that some herds (technicians) are more proficient than others at maintaining high levels of conception with decreased sperm dosages. Across herds and sires, the conception rates of each semen type by sperm dosage combination were as follows: 2.1 × 10(6) sex-sorted, 38%, n=2,319; 10 × 10(6) sex-sorted, 44%, n=2,279; 2.1 × 10(6) conventional, 55%, n=2,282; and 10 × 10(6) conventional, 60%, n=2,292. The observation that conception rates of sex-sorted semen were improved by the 10 × 10(6) sperm dosage is encouraging toward the prospectus of development of a commercially available sex-sorted product with improved conception potential over existing technology. However, the failure of the 10 × 10(6) sex-sorted sperm dosage to achieve conception rates comparable to either dosage of conventional semen is somewhat discouraging toward the plausibility of comparable conception rates to conventional semen in the absence of major technological advances in efficiency of sperm sorting or cryopreservation.

Effects of 2.1 and 3.5x10(6) sex-sorted sperm dosages on conception rates of Holstein cows and heifers.

The objective was to compare conceptions rates of Holstein cows and heifers after artificial insemination (AI) with 2.1 or 3.5x10(6) sex-sorted sperm or 15x10(6) conventional sperm. Ejaculates collected from 7 Holstein sires were cryopreserved conventionally at 15x10(6) sperm per dose or sorted to 90% purity for X-chromosome-bearing spermatozoa using flow cytometry and cryopreserved at either 2.1 or 3.5x10(6) sperm per dose. All treatments were processed in an egg-yolk (20%), Tris, glycerol (7%) extender and packaged in color-coded 0.25-mL French straws. Straws (n=700 straws/dosage per sire) were packaged and distributed in aliquots of 12 (4 straws/sperm dosage) to 69 Holstein herds with an across-herd goal of achieving approximately 50% use in heifers and cows. Straw color was recorded in the on-farm recordkeeping system at the time of AI and retrieved by electronic download. Data for cows and heifers were analyzed separately. Among heifers, 6,268 services were retrieved from 45 herds (298+/-4.2 services/sperm dose per sire; range: 244 to 344). Conception rate of heifers was influenced by the sire by treatment interaction. Conception rate of the 2.1 and 3.5x10(6) sex-sorted sperm dosages were comparable in 6 of 7 sires. Conception rate of both sex-sorted dosages were less than those of conventional semen for 6 of 7 sires. Across sires, heifer conception rates for 2.1 and 3.5x10(6) sex-sorted sperm dosages and 15x10(6) conventional dosages were 44, 46, and 61%, respectively. Among cows, 5,466 services were retrieved from 52 herds (260+/-3.3 services/sperm dose per sire; range: 236 to 289). Conception rates of cows were influenced by herd, sire, and sperm dosage. Conception rates of the 2.1 and 3.5x10(6) sex-sorted sperm dosage were comparable for all 7 sires. Conception rates of 2.1x10(6) sex-sorted sperm dosage were less than those of conventional semen for 4 of 7 sires and conception rates of the 3.5x10(6) sex-sorted sperm dosage were less than those of conventional semen for 2 of 7 sires. Across sires, conception rates for 2.1 and 3.5x10(6) sex-sorted sperm dosages and 15x10(6) conventional dosages in cows were 23, 25, and 32%, respectively. In conclusion, these data could not confirm that a meaningful improvement in conception rates should be expected in cows or heifers from increasing sex-sorted sperm dosage from 2.1 to 3.5x10(6) sperm per dose.

Effect of sex-sorted sperm dosage on conception rates in Holstein heifers and lactating cows.

Ejaculates were collected by artificial vagina from 3 Holstein sires and sorted to 90% purity for X-chromosome-bearing spermatozoa (range 88 to 93%) using flow cytometry. Sorted sperm were diluted to 2.1, 3.5, or 5.0 x 10(6) sperm per dose in an egg yolk (20%), Tris, glycerol (7%) extender. Collections were repeated until >600 straws per sperm dose per sire were obtained. Each sperm dose was loaded into color-coded 0.25-mL French straws, with alternate colors used to define treatments across sires. Within sires, straws were packaged at 9 per cane (3 of each color) and strategically allocated to 75 Holstein herds with targets for 50% use in heifers and 50% in lactating cows. Straw color was recorded in the on-farm record-keeping system at the time of insemination. Data were analyzed separately for cows and heifers. Among heifers, a total of 2,125 usable records were retrieved from 51 herds (238 +/- 5.5 services/ sperm dose per sire, range: 218 to 263). Conception rates in heifers were influenced by the sire x sperm dosage interaction. Within sire A, conception rates of heifers were greater for the 5 x 10(6) (59.5%) than for the 2.1 x 10(6) (46.4%) sperm dose and intermediate for the 3.5 x 10(6) sperm dose (52.2%). However, across sires, sperm dosage had no effect on heifer conception rates (46.7, 51.2, and 52.5% for the 2.1, 3.5, and 5.0 x 10(6) sperm dosages, respectively). Among cows, a total of 2,369 services were retrieved from 56 herds (263 +/- 8.8 services/sperm dose per sire, range: 233 to 303). Conception rates of cows (29.4%) were not affected by sire or sperm dosage (27.0, 29.1, and 30.3% for the 2.1, 3.5, and 5.0 x 10(6) sperm dosages, respectively). In conclusion, these data indicate that an increased sperm dosage may enhance virgin heifer conception rates for some (but not all) sires, whereas neither sire nor sexed-sperm dosage affected conception rates of lactating cows. Additional studies of sexed-sperm dosage across a larger sampling of bulls are warranted to determine whether and how such a practice can be implemented cost effectively for the benefit of the dairy industry.