Literary data are presented and their analysis is conducted regarding the mode of use of ram-sires and their effect on sexual activity and sperm productivity. The results of research of scientists with recommendations of optimal modes of use of fetuses for semen production and its cryopreservation in non-pairing and steaming periods are presented. According to the results of the analysis of many researchers, the activity of the sexual reflexes of the rams in the spring and summer decreases by 1.4 times compared to the winter. At the same time quantitative indicators of sperm productivity decrease. However, M.M. Aibazov (1987) experimentally confirmed that sheep-breeders of the Caucasian fine-breed and Australian merenos breed exhibit high sexual activity and produce sperm of satisfactory quality in all seasons. Similar results were obtained by British researchers in the study of sexual activity and sperm productivity of ram-sires of British breeds. A.A. Ivanov (1987) indicates the regime of use of ram sires, for five years with obtaining and subsequent freezing in the unpaired period 6 ejaculates (2 doublets 3 times) per week and in the breeding season 10 ejaculates (2 doublets 5 times) week. P.P. Kundyshev (2004) considers it possible and proposes to obtain from the breeding rams for cryopreservation and storage during the year, both unpaired and steaming periods, with daily ejaculate production. This mode, according to the author, provides a sufficiently high fertility sperm up to 50.3 percent. In the study of sexual activity and sperm productivity of ram-sires of different breeds, including the North Caucasian meat-wool, jalgin merino, Soviet merino, maniche merino, Russian meat merino, Edelbaev, polldore P.P. Mammoth and others. (2018) found that the most active were the rams of the Edinburgh breed, which took 22 seconds. ejaculate secretion, and the slowest texel breeders, which took 39 seconds to ejaculate. The rams of the other breeds listed above spent 25 to 34 seconds to ejaculate. In addition, rams of Texel breed produced the lowest activity sperm, and therefore only 19 sperm were frozen from one ejaculate, with an average of 20 to 26 sperm species tested.
The article presents in retrospect the methods of cryopreservation of sperm of bulls and breeding rams. It is indicated that the first methods were proposed by I.V. Smirnov in 1947–1951, which ensured the production of viable lambs and calves. The significant contribution to the development of the method of cryopreservation of bull sperm by British scientists Polge C. and Rawson L. and Japanese scientists Nagase H. and Niwa T. The methods developed by them, with minor changes, have been used by scientists and breeding specialists for many decades. Modern technologies of cryopreservation of bull sperm are represented, in particular: Kharkiv in coated granules (author FI Ostashko and others), French company IMV-R-Cassou, German company Minitub, which are currently used in most countries with developed animal husbandry. It is noted that the first attempts to freeze the sperm of breeding rams were made by E. M. Platov in 1965. It is noted that in the cryopreservation of sperm the importance of adaptation and equilibration processes is important. The role of glycerin as a cryoprotectant in freezing the semen of male farm animals has been elucidated. The optimal concentration of glycerin in the media for cryopreservation of sperm of fetuses has been established. It is noted that the basis of “temperature shock” of sperm is damage to the sperm membrane, which is caused by balancing the concentration gradient that occurs at the boundary of cell-medium division with a sharp change in temperature. A high correlation between the physiological quality of the acrosome of sperm and its fertilizing ability is indicated. Studies of the chemical composition of the sperm of breeding rams have shown that it differs from the sperm of other animal species by a slightly higher content of proteins, lipids of lactic acid and a lower concentration of minerals. Proteins contain much more amino acids. Sheep sperm do not tolerate aerobic conditions, it is proved that damage to sperm by oxygen occurs mainly after its dilution and equilibration, and not during cryopreservation. Under aerobic conditions, one amino acid is cleaved from the molecule of lecithin, which is part of the membranes of sperm, with the formation of toxic lysolecithin. The most critical zones at thawing of deep-frozen sperm are shown. It has been experimentally established that the rate of the recrystallization process can be reduced by using cryoprotectants in environments, as well as by increasing the rate of thawing. An important influence in the thawing of sperm has the selection of the optimal mode of thawing. Analysis of literature data revealed that in practical conditions in the process of freezing ‒ thawing about 50% of sperm lose activity, which indicates that currently available methods of freezing sperm of breeding rams are imperfect and need further study and improvement.
The results of studies on the semen production of ram-sires of three European meat breeds, such as texel, oxford down and Vvalais blacknose in the process of preparing for a breeding season or taking semen on an artificial vagina for further use for deep freezing, are presented. During the preparatory period, from each group of rams, 120 ejaculates were obtained, 12 ejaculates in the first and second subperiods, 18 ejaculates in the third and fourth and 60 ejaculates in the fifth subperiod. Differences in the semen production performance of the breeders of the studied breeds were determined. At the end of the preparatory period, the volume of the ejaculate of the rams of the oxford down breed was greater than that of texel by 34.8%, of the valais blacknose sheeps – by 53.1%. When comparing the volume of the ejaculate of the rams of the breed of texel and valais blacknose sheeps, the latter was lower by 12.0%. The concentration of semen in the ejaculate was the highest in the Valais rams and amounted to 3.24 billion/ml, which is 3.9% higher than the oxford down rams, and 14.9% is the texel breed. According to the activity of fresh semen, the difference between the breeds was insignificant and ranged from 2.4 to 4.3%. However, the activity of the frozen-thawed semen varied from 6.4% to 14.0%, the highest among the breeders of the oxford down ‒ 3.65 points, the lowest ‒ 3.20 points in rams of the Valais Blacknose breeds. A slight 2.2 – 4.4% deviation between breeds was noted for the resistance of semen to cryopreservation. The smallest number of cryopreserved semen with acrosome damaged in oxford down breeders was found to be 39.14%, which is 3.5% less than that of texel sheep breed and 6.7% more than that of valais blacknose breed breeders. The conducted researches have experimentally confirmed that indicators of semen productivity of ram-sires are improved in accordance with the term of their preparation. Therefore, to train rams to give semen to artificial vagina before the beginning of the steaming season, or to obtain it for cryopreservation, followed by artificial insemination of sheep, is required after careful preparation of the rams for 50‒60 days, with the provision of optimal conditions of keeping and feeding. The main studied parameters of sperm production of ram-sires in the preparatory period, significantly higher values of volume of ejaculate, activity of fresh and preserved semen, their resistance to freezing and the preservation of acrosomes in the breeders of the oxford don was established. The lowest studied indices were found in rams of the valais blacknose breed. Texel breeders occupy an intermediate position for the indicated indices between the studied breeds.
The article presents the results of experimental studies on the effect of the quality of ram-sires' thawed sperm during the breeding and non-breeding periods under different modes of using the breeders. It is established that the acrosome preservation under the mode of using the ram-sires to receive 4 ejaculates per week compared to 6 and 8 ejaculates during the nonbreeding period was higher by 3.5 and 6.0%, respectively, and by 2.5 and 5.0 percent during the breeding period. Kinetic parameters of sperm motion during both periods of seasonal activity were also higher under the mode of receiving 4 ejaculates per week by 2.6-14.0 percent on average. The fertilizing ability of thawed sperm from the first insemination of ewes under the mode of receiving 4 ejaculates per week compared to the above mentioned modes was higher by 3.2 and 7.2% during the non-breeding period, and by 7.3 and 10.6% during the breeding period; while fertility at lamb birth-by 1.7 and 3.8%, and by 1.0 and 8.1 percent, respectively.
The retrospective analysis of the invention of synthetic extender for ram’s semen cryopreservation, developed by different authors, is presented in the article. It has been shown, that in order to ensure the biological usefulness of the extenders for semen, they should contain phospholipids, electrolytes, non-electrolytes, cryoprotectants, biologically active substances and other ingredients, due to the many physical and chemical processes that occur in the process of cooling and deep freezing of spermatozoa. Researchers have established the protective role of phospholipids from chicken egg in protecting sperm from cold stroke. It has been proven that the usage of dried yolk and egg powder in extenders during the cryopreservation of sperm provides a high protective effect of sperm at the level of natural yolk. The degree of effectiveness of different electrolytes in preventing cold shock has been indicated. Their protective function not only for the creation of buffer properties of extender, but also for the reduction of freezing point of aqueous solutions has been emphasized. The importance of sugars in the composition of ram’s semen cryopreservation extenders has been proven. They reduce the conductivity of semen, thereby reducing sperm agglutination, act as antioxidants, inactivate spermolysins, increase the viscosity, structure water, prevent excessive hydration of proteins and organelles are used by sperm for respiration and glycolysis. It has been experimentally proven by a number of researchers, who studied the protective effect of antioxidants for the development of synthetic extender, that the process of cryopreservation intensifies the lipids peroxidation, which disrupts the orderliness of the sperm membranes structure and thereby the oxidation products damage the plasma membrane and adversely affect on the energy of sperm. A perspective direction in the development of new extenders for animal reproduction biotechnology has been highlighted, both for in vitro fertilization of oocytes and for freezing and thawing of semen using the metal nanoparticles.
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