Boar semen cryopreservation : studies on the influence of the semen donors, freezing protocols, insemination techniques and In vivo fertility

Abstract

EXP I and EXP II were conducted to evaluate factors affecting FT boar sperm quality. Three ejaculates from each of 15 purebred boars (5L, 5Y and 5D) were frozen using the lactose-egg yolk extender and 9% glycerol with or without 1.5% Equex STM Paste. The processed semen was loaded in 0.25- and 0.5-ml straws and frozen in a styrofoam box. The FT sperm quality was improved when adding Equex STM Paste into the freezing media (P<0.05) and was higher when loading into a 0.5-ml straw compared with a 0.25-ml straw (P<0.05). The breed of boar and the individual boars within the same breed significantly influenced most of the FT sperm quality and sperm of the Y boars seemed to be most sensitive to freezing-thawing process. Therefore, in the following experiments, boar semen were cryopreserved in the freezing extender containing Equex STM Paste and packaged in a 0.5-ml straw. EXP III and EXP IV were conducted to evaluate fertilization rate at 2 days (EXP III) and farrowing rate (FR) and number of total piglets born per litter (TB) (EXP IV) of sows after IUI (using 2x109 total sperm per dose) and DIUI (using 1x109 total sperm per dose) with FT boar semen. Ovulation was determined using real-time B-mode ultrasonography. In EXP III, weaned sows were divided into 2 groups, IUI (n=6) and DIUI (n=6). The sows were inseminated at 24 h after the detection of estrus and repeated every 12 h until ovulation. At 48 h after ovulation, numbers of fertilized and unfertilized oocytes flushed from the oviducts were counted. The results revealed that fertilization rates between the left and right oviducts did not differ significantly in both groups. However, the rate of fertilization was superior for IUI compared to DIUI (66% vs 31%, P<0.05). In EXP IV, weaned sows were inseminated twice at 24 and 36 h using IUI (n=9) or DIUI (n=9). There were no differences in both FR and TB between IUI and DIUI. Nonetheless, TB of the IUI group tended to be higher than the DIUI group (10.5±2.9 vs 7.7±3.0 piglets per litter, P>0.05). Based on the results of EXP III and IV, the IUI procedure was therefore used in further studies. EXP V Effectiveness of exogenous hormones, hCG and GnRH (buserelin), in controlling ovulation in sows was investigated. Weaned sows were randomly allocated to 3 groups: 1) the sows (n=10) were allowed to ovulate spontaneously; 2) the sows (n=10) were induced ovulation with 750 IU hCG; and 3) the sows (n=13) were controlled ovulation with 10 μg GnRH. The hormones were given at the standing estrus. Ovulation was determined using transrectal ultrasonography. The results indicated the efficacy of both hormones in controlling ovulation in sows. However, hCG seemed to be more effective than GnRH since, after administration, no incidence of ovarian cysts and less variation in the estrus-to-ovulation interval (EOI) among treated sows were observed. EXP VI and EXP VII Fertility of sows after IUI with FT semen studied under farm conditions was evaluated. Weaned sows were assigned to 2 groups for IUI with low numbers of FT spermatozoa. Group I, spontaneously ovulating sows were inseminated at 24 h after estrus detection and repeated every 12 h until ovulation. Group II, hCG induced ovulating sows were inseminated once at 41 h after estrus detection (EXP VI) and were inseminated at 36 and 42 and/or 48 h after estrus detection, until ovulation (EXP VII). It was shown that no significant differences were found for the fertility between group I and II in both experiments (P>0.05). However, in EXP VI, both FR and TB in the induced ovulating sows which were inseminated once tended to be lower than the spontaneously ovulating sows inseminated several times; and in EXP VII, number of insemination in group I was higher than group II (+0.5 time/estrus). The results of all trials indicated that semen cryopreservation and artificial insemination with FT boar semen could be successfully performed in Thailand. IUI seemed to be an appropriate insemination technique for FT boar semen and the number of insemination required for achieving acceptable fertility could be decreased when IUI was conducted in sows with induced ovulation