ABSTRACT
In vitro embryo production is one of the main reproductive techniques used in dairy Gyr cattle. In addition, linear type measures are well characterized and have been used in dairy Gyr breed selection for the last 4 decades. The estimation of genetic parameters for the number of aspirated oocytes and in vitro-produced embryos associated with the linear type measures would support genetic progress for animal breeding programs toward embryo production. This study aimed to estimate genetic parameters for aspirated oocytes, embryo in vitro production, and linear type traits, exploring the association between them. The repeatability model was applied to 14,251 ovum pick-up events from 1,916 Gyr donors. A subset of 604 donors from the same group had their body measurements taken. Single- and 2-trait analyses were carried out using the BLUPF90 family programs. Heritability estimates of 0.38, 0.34, and 0.20 were obtained for total oocytes, viable oocytes, and embryos, respectively,-and the heritability of the linear type traits ranged from 0.22 to 0.40. High genetic correlations between total oocytes and viable oocytes (0.99), and between oocytes (total and viable) and embryos (0.83) were obtained. Low to high genetic (-0.07 to 0.92) and phenotypic (0.32 to 0.86) correlations were obtained between the linear type traits. Moreover, low phenotypic correlations (0.01 to 0.13) were observed for oocytes (total and viable) and embryos with the linear type traits, whereas low to moderate genetic correlations (0.07 to 0.42) were observed between the same traits, especially for ilium width (0.42), rump area (0.38), and hip height (0.33). Thus, selection for in vitro production is achievable in Gyr dairy cattle, and superior genetic progress is associated with the selection of oocytes (total and viable). Furthermore, the moderate genetic association between oocytes and embryos with linear type traits, especially ilium width suggests that progress on in vitro embryo production may be achieved by accessing these measurements.
ABSTRACT
Breeding soundness evaluation (BSE) is the best methodology to estimate the fertility potential of future bulls and performing indirect selection for their fertility. However, the outcome of the BSE is influenced by several factors, including genetics, environment, and BSE guidelines. Herein, in this retrospective study, our first aim was to characterize the reasons for failure in 46,566 BSE from 2-year-old beef Bos indicus bulls (Nellore) born from 1997 to 2018. Our second aim was to determine whether or not BSE was associated with reproductive potential improvement of the bulls over the years. Due to changes in the BSE criteria, we used the same dataset, but only bulls born from 2002 to 2018 were included resulting in 35,856 BSE. For the second aim, the effect of the year and farm were included in the model of the multivariate logistic regression. We also determined if the main reasons for BSE failure decreased over time. Bulls were classified as approved (satisfactory potential breeders and qualified for natural breeding service) and not approved (deferred and unsatisfactory potential breeders). The reasons for BSE failure in Nellore bulls were poor semen quality (53.1 %) and physical defects (46.9 %), with the main physical defect being testis abnormalities (19.7 %). The overall percentage of bulls approved each year was 87.1 %, with no improvement over the years of study. However, the percentage of approved bulls at the first BSE increased over the years (P < 0.05). This increase was evident by a reduction in the difference between the overall percentage of the bulls approved vs the percentage of bulls approved at the first BSE. Furthermore, there was an increase in the percentage of bulls classified as satisfactory potential breeders in the BSE and an evident decrease in the percentage of bulls qualified only for natural breeding service (P < 0.05). In addition, an increase of the scrotal circumference (SC) of the herd was found (P < 0.05). These results indicate the overall quality of the bulls improved over the years. To associate and identify the main sperm abnormalities, 3461 not approved bulls were clustered. The most frequent defects were strongly coiled tail spermatozoa, proximal droplets, and acrosomal defects. Overall, there was no change in the frequency of bulls not approved by the sperm morphology nor the frequency of the main sperm abnormalities over the years. Nevertheless, the frequency of the defects remained very low, implying they were controlled. Additionally, abnormalities in the testis decreased over the years and was associated with the increase in the SC of the herd and a decrease of culled bulls due to low SC. In conclusion, this study demonstrates that there is an association between implementation and use of BSE with improvements in the reproductive quality of future generation bulls.
Subject(s)
Breeding , Semen Analysis , Animals , Cattle/physiology , Male , Semen Analysis/veterinary , Retrospective Studies , Fertility , Reproduction/physiologyABSTRACT
Anti-Müllerian hormone (AMH) concentration and number of recovered oocytes (ROOC) are phenotypic parameters associated with in vitro embryo production (IVEP). More recently, anogenital distance (AGD) has been proposed as a proxy for fertility in dairy cattle that is easy to collect at a low cost. The aim of this study was to characterize the AGD and its phenotypic and genetic associations with AMH and IVEP in Bos indicus Gyr dairy cattle. The hypothesis was that the number of ROOC, in vitro-produced embryos, and AMH concentration would increase as the AGD decreases. From July to December 2021, a single morphometrical measurement of AGD was collected in 552 donors from 6 herds in Brazil. A subset of donors had AMH assayed on the same day. Only ovum pick-up events that occurred up to 12 mo preceding and 7 mo succeeding the AGD measurement were used to assess the association between AGD, AMH, and IVEP. Thus, 472 donors (1,551 ovum pick-up events and 140 donors with AMH) were considered in the analysis. A raw average was calculated for each individual donor's ROOC, viable oocytes, total produced embryos, viability rate, and embryo rate (defined as total produced embryos/viable oocytes). Comparisons were conducted within the age categories of 3 to <6 yr or 6 to <10 yr. Phenotypic associations were performed in SAS software (SAS Institute Inc., Cary, NC). Genetic correlations were estimated using the BLUPF90 family of programs. The AGD (128.7 mm ± 14; mean ± standard deviation) had a normal distribution and was highly variable (83 to 172 mm) among the Gyr population. Our experimental hypothesis was partially supported by a phenotypic association of a greater number of total produced embryos (R2 = 0.023) as AGD decreased. Our results failed to support an increase in AMH concentration along with a decrease in AGD. In addition, positive and low genetic correlations were observed between AGD and viable oocytes (r = 0.08), and embryo rate (r = 0.20). A greater number of viable oocytes and embryos were observed in donors in the high compared with intermediate and low ROOC categories within both age categories. The age interval of 3 to <6 yr showed a greater number of recovered and viable oocytes for the high AMH compared with the low category, but no differences were observed among the AGD categories. In summary, for the Gyr breed, AGD was phenotypically inversely associated with a quantity-related parameter, such as the total number of produced embryos. In contrast, AGD showed a low genetic correlation with qualitative-related outcomes such as viable oocytes and embryo rate. Further studies should be performed to validate these retrospective analyses and to better understand the association between AGD and IVEP.
Subject(s)
Anti-Mullerian Hormone , Embryo, Mammalian , Cattle , Animals , Anti-Mullerian Hormone/genetics , Retrospective Studies , Oocytes , Fertilization in Vitro/veterinaryABSTRACT
The tested hypotheses were (1) LH/FSH pulses and F2 diameter are diminished by P4 and, (2) E2 increases during the transition to deviation and alters LH/FSH pulses. On Day 5 (Day 0 = ovulation), heifers were randomized into an untreated group (HiP4, n = 11), and a prostaglandin analog treated group (NoP4, n = 10). On Day 6, a follicular wave was induced by follicle ablation. Ultrasound and blood collections were performed every 12 h from Days 7 to 11. Blood was collected every 15 min for 10 h on Day 9 (largest follicle expected to be ~7.5 mm). Estradiol was ~75% greater (0.36 ± 0.14 vs 0.63 ± 0.19 pg/mL) in heifers with F1 ≥ 7.2 mm than in heifers with F1 < 7.2 mm. The HiP4 had smaller second largest follicle (F2) diameter, lower estradiol (P = 0.06), LH pulse baseline and peak concentrations (P < 0.007), in addition to half the frequency of LH/FSH pulses (4.1 ± 0.3 vs 9.6 ± 0.7 in 10 h) than the NoP4. Within HiP4, heifers with F1 ≥ 7.2 mm had ~25% fewer (P = 0.03) LH pulses compared to heifers with F1 < 7.2 mm. In contrast, within the NoP4, heifers with F1 ≥ 7.2 mm had ~75% greater LH (P = 0.05) and FSH (P = 0.08) pulse amplitude. We propose that greater F2 diameter at deviation in low P4 is related to greater LH baseline and peak concentrations, and greater frequency of LH/FSH pulses. A greater increase in E2 after F1 reaches ~7.2 mm results in further stimulation of LH/FSH pulse amplitude. Elevated P4 not only diminished frequency of LH/FSH pulses but also converted an E2 increase into a negative feedback effect on LH/FSH pulse frequency leading to smaller F2 at deviation.
Subject(s)
Follicle Stimulating Hormone , Luteinizing Hormone , Animals , Cattle , Female , Estradiol/pharmacology , Follicle Stimulating Hormone/pharmacology , Ovarian Follicle/physiology , Progesterone , SteroidsABSTRACT
Double ovulation and twin pregnancy are undesirable traits in dairy cattle. Based on previous physiological observations, we tested the hypothesis that increased LH action [low-dose human chorionic gonadotropin (hCG)] before the expected time of diameter deviation would change circulating FSH concentrations, maximum size of the second largest (F2) and third largest (F3) follicles, and frequency of multiple ovulations in lactating dairy cows with minimal progesterone (P4) concentrations. In replicate 1, multiparous, nonbred lactating Holstein dairy cows (n = 18) had ovulation synchronized. On d 5 after ovulation, all cows had their corpus luteum regressed and were submitted to follicle (≥3 mm) aspiration 24 h later to induce emergence of a new follicular wave. Cows were then randomized to NoP4 (untreated) and NoP4+hCG (100 IU of hCG every 24 h for 4 d after follicle aspiration). Ultrasound evaluations and blood sample collections were performed every 12 h for 7 d after follicle aspiration. All cows were then treated with 200 µg of GnRH to induce ovulation. In replicate 2, cows (n = 16) were resubmitted to similar procedures (i.e., corpus luteum regression, follicle aspiration, randomization, ultrasound evaluations every 12 h, GnRH 7 d after aspiration). However, cows in replicate 2 received an intravaginal P4 device that had been previously used (â¼18 d). Only cows with single (n = 15) and double (n = 16) ovulations were used in the analysis. No significant differences were detected for frequency of double ovulation, follicle sizes, and FSH concentrations across replicates (NoP4 vs. LowP4 and NoP4+hCG vs. LowP4+hCG), so data were combined. Double ovulation was 40% for control cows with no hCG (CONT) and 62.5% with hCG (hCG). Double ovulation increased as the maximum size of F2 increased: <9.5 mm and 9.5-11.5 mm (7.7%) and ≥11.5 mm (94.1%). The hCG group had more cows with F2 > 11.5 (69%) than with 9.5 ≥ F2 ≤ 11.5 (25%) and F2 < 9.5 (6%). In agreement, F2 and F3 maximum size were larger in the hCG group, but FSH concentrations were lower after F1 > 8.5 mm compared with CONT. In contrast, FSH concentrations were greater before deviation (F1 closest value to 8.5 mm) in cows with double ovulations than in those with single ovulations, regardless of hCG treatment. In addition, time from aspiration to deviation was shorter in cows with double rather than single ovulation and in cows treated with hCG as a result of faster F1, F2, and F3 growth rates before diameter deviation. In conclusion, greater FSH and follicle growth before deviation seems to be a primary driver of greater frequency of double ovulation in lactating cows with low circulating P4. Moreover, the increase in follicle growth before deviation and in the maximum size of F2 during hCG treatment suggests that increased LH may also have a role in stimulating double ovulation.
Subject(s)
Follicle Stimulating Hormone , Lactation , Animals , Cattle , Chorionic Gonadotropin/pharmacology , Estrus Synchronization/methods , Female , Follicle Stimulating Hormone/pharmacology , Gonadotropin-Releasing Hormone/pharmacology , Humans , Lactation/physiology , Luteinizing Hormone , Ovulation , Pregnancy , ProgesteroneABSTRACT
The side of ovulation (left ovary, LO; right ovary, RO) and side of the next ovulation were compared between (1) beginning and end of an interovulatory interval (IOI) and beginning and end of consecutive sets of two and three IOI (n = 900 IOI), (2) beginning and end of the IOI for two and three follicular waves per IOI (n = 1300), and (3) beginning of pregnancy and first postpartum ovulation (n = 793). Pairs of sides of ovulation were designated LL (LO and LO), RR, LR, and RL. The frequency of ovulation pairs for two ends of an IOI was not different from two ends of two or three consecutive IOI indicating that differences between LO and RO were more likely inherent than from factors that developed in each IOI. For each end of an IOI or two consecutive IOI, the least frequency (P < 0.05) was for LL (16 %) with no differences among RR, LR, and RL (28 % for each). Frequencies between ipsilateral (LL, RR) and contralateral (LR, RL) ovulations pairs were not different for two-wave IOI (48 % compared with 52 %) but differed (P < 0.0001) for three-wave IOI (32 % compared with 68 %) and for pregnancy/postpartum (34 % compared with 66 %). In pregnancy/postpartum, each pair was different (P < 0.05) from each other: LL (13 %), RR (21 %), LR (30 %), RL (36 %). The lesser frequency for LL than for any of the others for an IOI, consecutive IOI, and pregnancy/postpartum indicated a ubiquity of the small propensity for LO ovulation.
Subject(s)
Cattle/physiology , Ovary/physiology , Ovulation/physiology , Pregnancy, Animal , Animals , Female , Pregnancy , Pregnancy, Animal/physiologyABSTRACT
Studying selection of multiple dominant follicles (DFs) in monovulatory species can advance our understanding of mechanisms regulating selection of single or multiple DFs. Carriers of the bovine high fecundity Trio allele select multiple DFs, whereas half-sib noncarriers select a single DF. This study compared follicle selection during endogenous gonadotropin pulses versus during ablation of pulses with Acyline (GnRH antagonist) and luteinizing hormone (LH) action replaced with nonpulsatile human chorionic gonadotropin (hCG) treatment in Trio carriers (n = 28) versus noncarriers (n = 32). On Day 1.5 (Day 0 = ovulation), heifers were randomized: (1) Control, untreated; (2) Acyline, two i.m. doses (Days 1.5 and D3) of 3 µg/kg; (3) hCG, single i.m. dose of 50 IU hCG on Day 1.5 followed by daily doses of 100 IU; and (4) Acyline + hCG. Treatments with nonpulsatile hCG were designed to replace LH action in heifers treated with Acyline. Acyline treatment resulted in cessation of follicle growth on Day 3 with smaller (P < 0.0001) maximum follicle diameter in Trio carriers (6.6 ± 0.2 mm) than noncarriers (8.7 ± 0.4 mm). Replacement of LH action (hCG) reestablished follicle diameter deviation and maximum diameter of DFs in both genotypes (8.9 ± 0.3 mm and 13.1 ± 0.5 mm; P < 0.0001). Circulating follicle stimulating hormone (FSH) was greater in Acyline-treated than in controls. Finally, Acyline + hCG decreased (P < 0.0001) the number of DFs from 2.7 ± 0.2 to 1.3 ± 0.2 in Trio carriers, with most heifers having only one DF. This demonstrates the necessity for LH in acquisition of dominance in Trio carriers (~6.5 mm) and noncarriers (~8.5 mm) and provides evidence for a role of GnRH-induced FSH/LH pulses in selection of multiple DFs in Trio carriers and possibly other physiologic situations with increased ovulation rate.
Subject(s)
Chorionic Gonadotropin/pharmacology , Guanine Nucleotide Exchange Factors/metabolism , Luteinizing Hormone/pharmacology , Oligopeptides/pharmacology , Ovarian Follicle/drug effects , Protein Serine-Threonine Kinases/metabolism , Animals , Cattle , Chorionic Gonadotropin/administration & dosage , Female , Gene Expression Regulation, Enzymologic/drug effects , Gonadotropin-Releasing Hormone/antagonists & inhibitors , Guanine Nucleotide Exchange Factors/genetics , Hormone Antagonists/pharmacology , Oligopeptides/administration & dosage , Ovarian Follicle/physiology , Protein Serine-Threonine Kinases/geneticsABSTRACT
The aim was to develop a program for resynchronization of ovulation (ReBreed21) that allowed reinsemination of non-pregnant Bos indicus heifers every 21 d using timed AI (TAI) without the need for detection of estrus. The Rebreed21 program begins 12 d after previous TAI (Day 0) by inserting an intravaginal P4 implant (Day 12) that is removed 7 d later (Day 19) combined with treatment with 300 IU of eCG. On Day 21, early pregnancy diagnosis (Doppler PD) is performed based on CL vascularity. Non-pregnant (NP) heifers immediately received AI combined with 100 µg of GnRH. The program is replicated 12 d after second TAI to produce a breeding season (BS) of 42 d with 3 potential TAIs. Two experiments were conducted as a proof of concept for this rapid rebreeding program. In Experiment 1, 76 heifers were enrolled in ReBreed21, as explained above. In Experiment 2, 300 Nellore heifers were synchronized for 1st TAI and randomly assigned to one of two groups: ReBreed21 (n = 147) or another early resynchronization procedure, Resynch14 (n = 153) with P4 implant inserted 14 d after previous TAI plus 50 mg of long-acting injectable P4; 8 d later P4 implant removed (Day 22) and early Doppler PD performed; NP heifers received 150 µg of cloprostenol, 0.5 mg of ECP, and 300 IU of eCG with TAI on Day 24. In both experiments, the largest follicle (LF) was measured at each Resynch TAI. Ultrasound was later used to confirm the early Doppler PD and to determine ovulation (OV) to Resynch at 12 d after TAI in ReBreed21 (Day 33 of pregnancy) and 14 d after TAI in Resynch14 (Day 38 of pregnancy). Final PD was performed 40 d after 3rd TAI. Results for Experiment 1 were: diameter of LF 11.8 ± 0.23 mm; 88.9% OV; 20.5% false positives; 38.1% P/AI at 1st TAI; 44.4% overall P/AI for ReBreed21 TAIs; 72.3% total pregnant at end of BS. In experiment 2, Rebreed21 vs. Resynch14 were different for: diameter of LF (10.9 ± 0.17 vs. 10.0 ± 0.17 mm, P = 0.0003), heifers with LF < 8.5 mm (10.2 vs. 26.4%, P = 0.04), or LF ≥ 11 mm (50.0 vs. 37.2%, P = 0.001), and P/AI at first TAI (29.3% [43/147] vs. 20.3% [31/153], P = 0.074) but similar for OV (overall 86.8% [239/275], P = 0.82), false positives (P = 0.52) overall P/AI for Resynch TAIs (33.6 vs. 28.8%, P = 0.4), and total pregnant at end of BS (58.5% [86/147] vs. 55.6% [85/153], P = 0.64). In addition, median time to pregnancy was 9 d earlier (P = 0.0007) for ReBreed21 than Resynch14. Thus, ReBreed21 is a novel protocol that allows earlier reinseminations than Resynch14 but with similar fertility.
Subject(s)
Estrus Synchronization , Insemination, Artificial , Animals , Cattle , Estrus , Female , Gonadotropin-Releasing Hormone , Insemination, Artificial/veterinary , Ovarian Follicle , Ovulation , Pregnancy , ProgesteroneABSTRACT
Sides of ovulation at beginning and end of an interovulatory interval (IOI) were studied for 10 successive ovulations in each of 100 heifers (1000 ovulations, 900 IOI). The frequency of side for 1000 ovulations was less (P < 0.0002) for the left ovary (LO or L; 44.4 %) than for the right ovary (RO or R; 55.6 %). Number of observed ratios of L to R was determined within each of 100 sets of 10 ovulations per set (eg, L2 to R8, L6 to R4). Expected ratios were calculated by combinatorics using the criterion that side of ovulation was an independent event. Differences in ratios between observed and expected were significant supporting the hypothesis that side of ovulation is dependent on the side of the previous ovulation. Number of pairs of ovulations for each end of the 900 IOI was significantly less for the LL pair (144, 16.0 %) than for the pairs of RR (255, 28.3 %), LR (247, 27.5 %), and RL (254, 28.2 %). The hypothesis was supported that the frequency of the pairs of ovulations at the beginning and end of an IOI differed among LL, RR, LR, and RL pairs. Novel observations were that frequency was lowest for the LL pair and similar among the the RR, LR, and RL pairs. These observations indicated that the greater frequency of RO ovulation was mathematically and functionally related to lower frequency of LO ovulation. The interpretation was that intraovarianism in the LL pair accounted for the lower frequency of LO than RO ovulation.
Subject(s)
Ovarian Follicle/physiology , Ovary/physiology , Ovulation/physiology , Animals , Cattle , Corpus Luteum/physiology , FemaleABSTRACT
Previous research demonstrated that acute treatment with GnRH antagonist, Acyline, allowed follicle growth until ~8.5 mm and no dominant follicle was selected. This study evaluated whether deficient LH was the underlying mechanism for Acyline effects by replacing LH action, using human chorionic gonadotropin (hCG), during Acyline treatment. Holstein heifers (n = 24) during first follicular wave were evaluated by ultrasound and randomized into one of three treatments: Control (saline treatments), Acyline (5 µg/kg Acyline), or Acyline+hCG (Acyline plus 50 IU of hCG at start then 100 IU every 12 h). Pulses of LH were present in Control heifers (9 Pulses/10 h) but not during Acyline treatment. Data were normalized to the transition to diameter deviation (day 0; F1 ~7.5 mm). Diameter deviation of the largest (F1) and the second largest (F2) follicle was not observed in Acyline-treated heifers, whereas control heifers had decreased growth of F2 at F1 ~7.5 mm, indicating deviation. Selection of a single dominant follicle was restored by providing LH activity in Acyline+hCG heifers, as evidenced by F1 and F2 deviation, continued growth of F1, and elevated circulating estradiol. Separation of F1 and F2 occurred 12 h (~7.0 mm) earlier in Acyline+hCG heifers than Controls. Circulating FSH was greater in Acyline than Controls, but lower in Acyline+hCG than Controls after day 1.5. In conclusion, dominant follicle selection and growth after follicle deviation is due to LH action as shown by inhibition of this process during ablation of GnRH-stimulated LH pulses with Acyline and restoration of it after replacement of LH action by hCG treatment.
Subject(s)
Chorionic Gonadotropin/pharmacology , Gonadotropin-Releasing Hormone/antagonists & inhibitors , Hormone Antagonists/pharmacology , Oligopeptides/pharmacology , Ovarian Follicle/drug effects , Ovulation/drug effects , Animals , Cattle , Estradiol/blood , Female , Follicle Stimulating Hormone/blood , Ovarian Follicle/diagnostic imaging , Ovarian Follicle/growth & development , Ovulation/physiology , UltrasonographyABSTRACT
Initiation of luteolysis in ruminants is variable due to ill-defined mechanisms. Cycles of two follicular waves are shorter and have earlier luteolysis than three-wave cycles. This study validated a cytobrush technique for evaluating dynamics of endometrial gene expression and associated changes in mRNA with timing of luteolysis, based on circulating progesterone and ultrasound-determined changes in blood flow and volume of corpus luteum (CL). On day 8 (ovulation = day 0), Holstein heifers were randomized into two groups: cytobrush group (n = 9) had an endometrial sample collected every 48 h from day 8 until end of luteolysis (CL blood flow ≤ 20%) and control group was sampled only once either before (day 12; n = 4) or at the end of luteolysis (n = 5). Concentrations of progesterone, CL blood flow, CL volume, and the frequency of two and three-wave cycles were similar between groups. Endometrial mRNA for progesterone receptors and estradiol receptors 1 and 2 was greater on day 8 and decreased thereafter similarly in two and three-wave cycles. Oxytocin receptor mRNA increased earlier in two vs three-wave cycles (day 14 vs 18), and the increase was associated with the onset of luteolysis. In conclusion, the cytobrush technique allowed in vivo collection of multiple endometrial samples during the estrous cycle. Endometrial mRNA expression of steroid receptors did not explain the variability in timing of onset of luteolysis in heifers while the later onset of luteolysis in three-wave cycles was associated with later up-regulation of oxytocin receptor mRNA.
Subject(s)
Endometrium/metabolism , Luteolysis/physiology , Receptors, Oxytocin/metabolism , Up-Regulation , Animals , Cattle , Corpus Luteum/metabolism , Estrous Cycle/genetics , Estrous Cycle/metabolism , Female , Receptors, Estrogen/genetics , Receptors, Estrogen/metabolism , Receptors, Oxytocin/genetics , Receptors, Progesterone/genetics , Receptors, Progesterone/metabolismABSTRACT
This study aimed to assess characteristics of bovine cryopreserved sperm and evaluate its relation to field fertility in fixed-time artificial insemination (FTAI). Semen samples of 16 bulls were used to inseminate 811 Nellore cows, and four of these bulls were also used to inseminate 101 Nellore heifers. Samples of the same ejaculate used for FTAI from each bull were analysed in the laboratory after thawing. Sperm motility and vigour were subjectively assessed by light microscope, and integrity of the plasma and acrosome membranes, and H2 O2 production were evaluated by flow cytometer. Relation among sperm characteristics and pregnancy rate of cows and heifers were evaluated by univariate and multivariate logistic regression. Subjective sperm motility and vigour did not affect the probability of pregnancy in cows or heifers. In univariate analysis for pregnancy in cows, sperm traits related to acrosome injury positively affected probability of pregnancy mainly when associated with plasma membrane integrity; H2 O2 production seems to be less important than plasma membrane integrity in affecting probability of pregnancy. In multivariate analysis, sperm traits related to injured acrosome positively affected probability of cow and heifer pregnancies while intact acrosome was negatively related to cow pregnancy. Intact plasma membrane and high H2 O2 production were positively related to cow pregnancy but negatively related to heifer pregnancy. Results suggest that a capacitation-like status of the acrosome may benefit probability of pregnancy in cows.