**1. Introduction**

The biotechnology of sex selection in animals is one of the most studied and also misunder‐ stood in the history. According Garner and Seidel [1], Democratis (470 – 402 AC) had sug‐ gested that the right testicle produces male sperm and the left female. For sure that is not true, once there are two sperm populations on the mammals ejaculate, being a portion of it carrier the X sexual chromosome and other Y. During years, researchers have been trying to manipulate the sex of the offspring before conception [1]. The selection of desired sex deliv‐ ered can be one of the determining factors to increase the genetic progress and farmer profit‐ ability in either beef or dairy cattle. For example, in dairy farms, the male calf has little or any zootechnical or economic value. However, in beef farms, the male calf is the product of interest due to its increased potential to produce meat. Considering these particularities, many researches have been developed to predict and/or manipulate the calf sex proportion. The separation of the Y sperm from the X is possible due to the differences on the DNA con‐ tent of these spermatic cells (X sperm has about 4% more genetic material than Y) by flow cytometry. Nowadays, this is the most efficient method to separate X from Y-spermatozoa in large scale. Some available biotechnologies in commercial scale are the use of the sex-sorted sperm by artificial insemination (AI) with estrus detection, timed artificial insemination (TAI), embryo transfer with superovulation (ET) and timed embryo transfer (TET).

© 2013 Guerino Macedo et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Reproductive programs based on TAI, have been continuously incorporated in routine of the reproductive management on farms. These programs represent a systematic approach to enhance the use of AI in dairy or beef farms, increasing the benefits of this reproduc‐ tive biotechnology.

Recent advances in the form of the tip of the flow cytometry, the positioning of the sperm cells at the moment of the passage through the laser, as well as changes in pressure and the type of staining cells have significantly improved separation process gametes X and Y [9]. The X-Y sperm separation speed is relatively slow with approximately 300,000 to 400,000 cells per minute. In this way, for a higher process efficacy, the semen dose in the straw nor‐

The Use Of Sex-Sorted Sperm For Reproductive Programs In cattle

http://dx.doi.org/10.5772/52180

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The process of sorting X and Y-bearing sperm likely results in some damage to the sperm that compromise fertilization [4, 10]. According to Gonsálvez et al. [11], the sorting process produce an interaction of the DNA with fluorophores, laser exposure, spermatozoa separa‐ tion in micro-droplets, acceleration of spermatozoa through geometrically-pressured fluid channels and centrifugation. All of these para-biological spermatozoa-media or mechanical interactions would theoretically have the potential to produce changes in cell structures, in‐ cluding the DNA molecule. When considering cell structures, spermatozoa appear to be par‐ tially capacitated during the flow cytometry process used for sex pre-determination [12]. This total or partial capacitation is induced by the conditions that sperm are subjected dur‐ ing preparation for flow cytometric-sorting and during sorting [13]. Lu and Seidel [12] em‐ phasize that it could be due to the condition that the sperm are pre-incubated with Hoechst 33342 at 34.5 8C for 45 min before sorting. During sorting, sperm are subjected to laser light and various physical forces, such as exiting the sorter at nearly 90 km/h before entering the collecting medium. The process of sorting results in an extremely diluted sample with 800,000 sperm/ml, and subsequently sperm are gently centrifuged to provide a concentrated

Thus, this process could also led to a shorter functional sperm life compared to non-sorted sperm [12, 14, 15], which could include pre-capacitation and a reduced number of viable spermatozoa for the insemination [6, 16]. The thermo-resistance test showed that the motili‐ ty decline in sex-sorted sperm was faster compared to non-sorted sperm. Also, there is an effect associated with samples from a specific bull and sex-sorted sperm insemination dose [5] and some samples from certain bulls can tolerate the stress of sorting in a more desirable

Although the above information stated, it is important to highlight that AI with sex-sorted sperm does not alter pattern of return to estrus and does not affect the likelihood of heifers to conceive from subsequent AI [18]. Also, Holstein heifers inseminated with sexed semen had similar pregnancy loss from 29 ± 1 to 50 ± 1 d after AI compared with heifers inseminat‐ ed with conventional semen [17], and there is no difference on abortion rate from 2 mo of gestation to parturition. Farmers in general are interested to know if calves produced by sexed semen are different that those from conventional semen. To address this question Tubman et al. [19] analyzed data from 1,169 calves produced from sexed semen and 793 calves from conventional semen. They did not observed difference in gestation length, birth weight, calving ease, calf vigor, weaning weight, abortion rate, and death rates (neonatal and through weaning) among calves produced by sexed or conventional semen. When *in vi‐ tro* models are used to verify the efficiency of sex-sorted sperm to produce embryos, there are inconsistent results concerning the embryo development which mainly depend on the

cells in a 0.25cc straw.

mally used is set to be 2.1 x 106

manner [17].

sample suitable for packaging and cryopreservation.

The ET technique has been used widely around the world once it increases the number of offspring that can be obtained from females with great genetic value [2, 3]. The use of sexsorted sperm could increase the production of a specific calf gender, which would benefit beef and dairy industries worldwide [4]. Likewise, the TET synchronizes the ovulation simi‐ lar to TAI; however, instead to inseminate before ovulation, the recipient cow receive an em‐ bryo fertilized *in vitro* with sex-sorted sperm seven days after ovulation.

Advances in sex sorting of sperm using flow cytometry have enabled its incorporation in‐ to commercial reproductive management. Despite the increased use of sex-sorted sperm, preg‐ nancy per AI (P/AI) is still less than when using non sex-sorted sperm [5]. Regardless of these reduced results, suitable spermatozoa concentration at AI time; longer intervals from the induction of ovulation to the AI (i.e., closer to the expected moment of ovulation); AI into the uterine horn ipsilateral to the expected ovulation; the size of the follicle from which ovulation occurs; occurrence of estrus from progesterone (P4) source removal to the TAI and the identification and use of bulls with proven fertility producing spermatozoa resist‐ ant to the sexing process have increased the likelihood of pregnancy in females inseminat‐ ed with sex-sorted sperm [6-8], thereby optimizing the use of sex-sorted sperm in TAI and ET programs.

There is a huge interest in sex-sorted sperm around the world. There are many opportuni‐ ties and challenges associated to the use of this semen in farms. The aim of this review is to bring into focus a summary of our current understanding of the use of sex-sorted sperm in TAI and ET programs and some strategies to optimize the use of sex-sorted sperm. Before describing the researches results and opportunities for its use, it is important to understand how sperm are sorted and the critical points associated to the process.
