Handling frozen bovine semen — Factors which influence viability and fertility

Effect of Different Thawing Methods for Frozen Bull Semen and Additional Factors on the Conception Rate of Dairy Cows in Artificial Insemination

Simple Summary

Today, recommendations for thawing methods for frozen bull semen vary, and clear data to assess their influence on fertility are contradictory. Under present practical conditions, no differences between the three different thawing methods could be detected, so no clear recommendation for semen thawing methods in dairy reproduction can be made based on our data. Study results provide evidence that inadequate reproductive performance of high-producing, lactating dairy cows is a multifactorial consequence of farm and fertility management; accordingly, the livestock industry should focus more on cow health to avoid reproductive disorders and further improve the reproductive performance of dairy cows in the future.

Abstract

Recommendations for thawing methods of frozen bovine semen vary and clear data evaluating their influence on fertility are contradictory. In this respect, the aim of this study was to investigate the influence of different thawing methods of frozen bull semen in artificial insemination (AI) of dairy cows on conception rate (CR) under practical conditions and to determine further possible influencing factors on the success of AI in order to provide recommendations for practical use. From 2017 to 2019, 3393 AI were performed in a dairy farm in eastern Germany, distributed randomly into three groups of thawing methods: group A: n = 426 (11 s, 38 °C water bath); group B: n = 348 (35 s, 38 °C water bath); group C: n = 385 (30 s, “in the cow”). We observed no significant difference in CR from the general linear mixed model between the thawing methods (method A/B/C, 28.5%/26.6%/24.7%), but data analysis revealed effects of lactation number, month of insemination and AI method (natural heat vs. OvSynch) on CR. Based on our data, no clear recommendation for semen thawing method in dairy reproduction can be made. Our findings suggest that the main factors of influencing reproductive performance in the field are represented by the cow-side of fertility, e.g., insemination in natural heat, lactation number and season of insemination. Therefore, dairy farmers should focus more on cow conditions to further improve reproductive performance.

Strategies for Highly Efficient Rabbit Sperm Cryopreservation

The rabbit is a valuable animal for both the economy and biomedical sciences. Sperm cryopreservation is one of the most efficient ways to preserve rabbit strains because it is easy to collect ejaculate repeatedly from a single male and inseminate artificially into multiple females. During the cooling, freezing and thawing process of sperms, the plasma membrane, cytoplasm and genome structures could be damaged by osmotic stress, cold shock, intracellular ice crystal formation, and excessive production of reactive oxygen species. In this review, we will discuss the progress made during the past years regarding efforts to minimize the cell damage in rabbit sperms, including freezing extender, cryoprotectants, supplements, and procedures.

Effect of semen preparation on casa motility results in cryopreserved bull spermatozoa

Computer-assisted sperm analyzers (CASA) have become the standard tool for evaluating sperm motility and kinetic patterns because they provide objective data for thousands of sperm tracks. However, these devices are not ready-to-use and standardization of analytical practices is a fundamental requirement. In this study, we evaluated the effects of some settings, such as frame rate and frames per field, chamber and time of analysis, and samples preparations, including thawing temperature, sperm sample concentration, and media used for dilution, on the kinetic results of bovine frozen-thawed semen using a CASA. In Experiment 1, the frame rate (30-60 frame/s) significantly affected motility parameters, whereas the number of frames per field (30 or 45) did not seem to affect sperm kinetics. In Experiment 2, the thawing protocol affects sperm motility and kinetic parameters. Sperm sample concentration significantly limited the opportunity to perform the analysis and the kinetic results. A concentration of 100 and 50 x 10(6) sperm/mL limited the device's ability to perform the analysis or gave wrong results, whereas 5, 10, 20, and 30 x 10(6) sperm/mL concentrations allowed the analysis to be performed, but with different results (Experiment 3). The medium used for the dilution of the sample, which is fundamental for a correct sperm head detection, affects sperm motility results (Experiment 4). In this study, Makler and Leja chambers were used to perform the semen analysis with CASA devices. The chamber used significantly affected motility results (Experiment 5). The time between chamber loading and analysis affected sperm velocities, regardless of chamber used. Based on results recorded in this study, we propose that the CASA evaluation of motility of bovine frozen-thawed semen using Hamilton-Thorne IVOS 12.3 should be performed using a frame rate of 60 frame/s and 30 frames per field. Semen should be diluted at least at 20 x 10(6) sperm/mL using PBS. Furthermore, it is necessary to consider the type of chamber used and perform the analysis within 1 or 2 min, regardless of the chamber used.

Effect of different thawing rates on post-thaw sperm viability, kinematic parameters and motile sperm subpopulations structure of bull semen

The aim of the present study was to evaluate three thawing rates for bull semen frozen in 0.25-ml straws: placing the straws in a water bath at 37 degrees C for 40s, at 50 degrees C for 15s or at 70 degrees C for 5s. In a first experiment, the three thawing rates were compared in relation to post-thaw sperm motility, determined subjectively, and sperm plasma and acrosomal membrane integrity, examined by flow cytometry, after 0 and 5h of incubation at 37 degrees C. In a second experiment, the three thawing rates were evaluated based on post-thaw sperm motility, determined using a CASA system, after 0 and 2h of incubation at 37 degrees C. In addition, for the motile spermatozoa, the individual motility descriptors were analysed using a multivariate clustering procedure to test the presence of separate sperm subpopulations with specific motility characteristics in the thawed bull semen samples. Finally, it was investigated if the thawing rate had any influence on the relative frequency distribution of spermatozoa within the different subpopulations. In terms of overall post-thaw motility or plasma and acrosomal sperm membrane integrity there were no significant differences between the three thawing methods evaluated. The statistical analysis clustered all the motile spermatozoa into four separate subpopulations with defined patterns of movement: (1) moderately slow and progressive sperm (27%); (2) "hyperactivated-like" sperm (15.4%); (3) poorly motile non-progressive sperm (34.3%); (4) fast and progressive sperm (23.3%). The thawing rate had no significant influence on the frequency distribution of spermatozoa within the four subpopulations, but there was a significant effect (P<0.05) of the interaction between thawing rate and incubation time. Higher proportions of spermatozoa with fast and progressive movement were observed after 2h of post-thaw incubation when the thawing was at the faster rates (35 degrees C/40s: 8.3%, 50 degrees C/15s: 18.1% and 70 degrees C/5s: 16.5%). Whether this subtle difference might affect to the in vivo fertility of the thawed bovine semen is not known.

Straw-Thawing Method Interacts with Sire and Extender to Influence Sperm Motility and Conception Rates of Dairy Cows

Influence of interactions of straw-thawing method with sire and extender type (milk or egg yolk-based) on postthaw sperm motility and conception rates of dairy cows was assessed. In experiment 1, sperm from 10 Holstein sires were frozen in egg yolk citrate and heated whole-milk extenders using a split-ejaculate technique. Straws were thawed in a 37 degrees C water bath with or without 3 min of exposure to a 37 degrees C warming plate while wrapped in a paper towel (air-thaw). Percentage of motile sperm was assessed after 1 min and 3 h of incubation at 37 degrees C. In experiment 2, sperm from 3 Holstein sires were frozen in egg-yolk citrate and a nonheated whole milk extender using a split-ejaculate technique. Straws were thawed and motility was assessed as in experiment 1. Conception rates (n = 475) were compared in a single herd of Holstein cows after thawing straws in 35 degrees C water for 45 s or after air-thawing by wiping straws with a paper towel upon removal from the storage vessel and placing directly into the insemination gun. In each experiment, interactions between thaw method and sire, extender type, or both, indicated that conditions may be created that facilitate sperm tolerance of air-thaw procedures. When a significant thaw method effect was detected in either experiment, air-thaw was consistently associated with the lesser measure of sperm motility, conception, or both. In conclusion, although some sire x extender combinations seem to be tolerant of air-thaw procedures, other combinations are more sensitive, resulting in reduced postthaw sperm survival, conception rates of cows, or both, in response to air-thaw.

Synchronization of estrus in dairy heifers: a field demonstration

Use of prostaglandin F2 alpha to synchronize estrus was demonstrated over 3 yr with 2966 dairy heifers in 45 herds. Reproductive status of all heifers was determined before any injections occurred. Anovulatory heifers (8.3%) were not injected or inseminated. Ovulatory heifers received one intramuscular injection and most heifers received two injections of prostaglandin F2 alpha spaced 11 d apart. Observations for estrus and insemination were scheduled and performed by dairy farmers. Insemination of heifers occurred 12 h after detection of estrus or at 80 h after second injection of prostaglandin F2 alpha. Pregnancy rate averaged 50.9% but varied from 0 to 100%. Pregnancy rate after insemination according to estrus (62.8%) was greater than when insemination was at 80 h (39.1%). Low pregnancy rates were associated with limitations in basic management of heifers before or during insemination. Managerial limitations were in timing insemination, range of ages or weights of heifers housed together, number and types of vaccinations, season and diet, frequency of observing heifers for estrus, and number of straws of semen thawed concurrently. Managerial factors that affect fertility are similar whether or not estrus is synchronized. Although agents used to synchronize estrus do not affect fertility directly, managerial limitations on fertility may be accentuated by increased intensity of activity associated with synchronization.

Cryobiological principles of embryo freezing

During a cryopreservation process a preimplantation embryo has to undergo multiple changes in volume caused by osmotic forces. When parameters such as cryoprotectant and water permeability coefficients and their temperature coefficients are known, equations can be solved to predict the volume response of an embryo during cryopreservation. This approach will allow the development or modification of cryopreservation procedures using relatively few embryos.

Thawing time and nonreturn rate of bovine semen frozen in fine French straws

Bovine semen packaged in fine French straws was thawed for 8 or 25 s in warm water baths (38 +/- 2 degrees C). During 12 months, 43 inseminators performed alternately 87,486 first inseminations. The nonreturn rate was highly and significantly affected by month of first service, region, inseminator within region, herd with our without contract for progeny testing, parity group and the bull. When the semen was thawed for 25 s, the 75-day nonreturn rate was 0.54% and the 120-day nonreturn rate 0.45% higher than for 8 s. Though these differences were barely significant (P<.08, P<.16, resp.), they confirm nevertheless the observations of other authors. No significant interaction was found between thawing time and inseminator. According to the results of this trial, the semen temperature should be brought to the temperature of the water bath (38 +/- 2 degrees C) when thawed. A thawing time of 25 s is recommended.