Quantification of bull sperm traits as measured by CASA and the relationship to pregnancy rate following controlled breeding
Mphaphathi, Masindi Lottus
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The biological importance of a bull’s contribution through artificial insemination to reproductive efficiency is of great importance because the sperm represents half of the genetic composition of its progeny. Therefore, the main objectives of the current study were: (1) To characterise, compare and evaluate fresh (raw) and frozen-thawed semen of both Bonsmara and Nguni breeds using computer aided sperm analysis (CASA) technology, (2) to compare the oestrous synchronization response and conception rate of Bonsmara, Nguni and Nguni type cows following fixed timed artificial insemination (FTAI) with Bonsmara or Nguni semen, and (3) to find the relationship between cows conception rate (in vivo and in vitro fertilization) and bull sperm motility rate (sperm traits) assessed by CASA technology following insemination regardless of bull breed. Electro ejaculator method was used to collect semen from Bonsmara (n = 4) and Nguni bulls (n = 4). Collected semen samples were evaluated for both macroscopic and microscopic traits.Following semen evaluation, the semen samples were either loaded into 0.25 or 0.5 mL straws and frozen using a programmable freezer. The semen straw was thawed at 37° C and analyzed by a CASA technology. In addition, purchased (from commercial AI center) frozen semen straws of Nguni and Bonsmara breed were also thawed. Sperm characteristics examined included total motility (rapid, medium and slow) progressive and non-progressive motility. Velocity characteristics included curvilinear and straight-line velocity, average path velocity, linearity, straightness, wobble, amplitude of lateral head displacement, beat cross frequency and hyperactive. During in vivo sperm fertility test, 100 Bonsmara, 452 Nguni and 94 Nguni type cows were randomly selected and subjected to oestrous synchronization protocol and FTAI with frozen-thawed assessed semen by CASA before FTAI. Briefly at Day 0, cows were inserted with an intravaginal CIDR® and removed on Day 7. Prostaglandin was then administered on Day 08 and a heat mount detector was placed on the hind quarter of each cow. In vitro sperm fertility test, collected oocytes from slaughterhouse were in vitro matured (n = 360) and in vitro fertilized (1 x 106 sperm/mL) in 100 μL droplets (final volume) of BO-IVF medium per treatment bulls (Bonsmara or Nguni bull). The frozen/thawed semen straws of Bonsmara and Nguni bulls were randomly selected and were used under the same IVF conditions. The microscopic of thawed bulls sperm characteristics were examined by CASA prior to in vitro fertilization. Data was analyzed using ANOVA. Treatment means were compared using the Fisher's protected t-test least significant difference. The average ejaculated semen volume of Bonsmara and Nguni bulls was 4.5 mL and 3.7 mL, respectively. The Bonsmara semen pH was 7.2 to 7.8 and Nguni semen 6.9 to 7.2, with an average value of 7.4 and 7.1 semen pH recorded, respectively. Individual variation ejaculates (raw semen) of the Bonsmara and Nguni bull’s total sperm motility traits (ranged from 86.5 to 93.9 % and 89.5 to 95 %, respectively) were recorded. Sperm cell concentration differed significantly among individual Bonsmara bulls (48.8 × 109 sperm/mL). Most of the ejaculates with live and normal sperm were above 85.3 % and 90.1 % in the Bonsmara and Nguni bulls, respectively. There was a significant difference on oestrous response for the Bonsmara (83.0 %), Nguni (90.8 %) and Nguni type cows (84.0 %), respectively. The Nguni type cows recorded a significant higher pregnancy rate (65.7 %), compared to the Bonsmara (59.0 %) and Nguni (37.1 %) breeds (P < 0.05). The sperm traits (TM, PM and RAP) were found to be positively correlated to conception rate (r = 0.06, 0.03 and 0.08, respectively). There was a significant difference on the average frozen-thawed sperm TM rate of ARC-Bonsmara (92.9 %), ARC-Nguni (92.2 %), CO-Nguni (85.2 %) and CO-Bonsmara (87.7 %). There was a positive correlation (r = 0.52) between oestrous response and pregnancy rate, for both Bonsmara, Nguni and Nguni type cows. There was a minimal fertilization rate following IVF with Bonsmara and Nguni breed bulls sperm. There was significant relationship on sperm TM and fertilization rate for both Bonsmara and Nguni breed. In conclusion, Nguni cows had the highest oestrous response compared to Bonsmara cows; however, the pregnancy rate was lower in Nguni cows. The sperm traits from both Bonsmara and Nguni bulls were found to be related to in vivo conception and in vitro fertilization rate when sperm cells were assessed by CASA technology.