Water buffaloes (Bubalus bubalis) are important in rural livestock production. The buffalo population in Egypt was predicted to be 3.7 million, producing around 45% (4.5 million tonnes/year) and 19% (367 thousand tonnes/year) of total milk and meat output, respectively [1]. On the other hand, Buffaloes are known to have a lower reproductive performance than cattle due to late puberty, weak estrus expression, and extended inter-calving intervals [2, 3], therefore, an increase in culling rate, costs of fertility treatment, and number of inseminations [4], consequently increasing the cost of each unit of milk that is produced [5].
In vitro embryo production (IVEP) has been introduced and applied to improve the poor reproductive efficacy of buffaloes [6]. Also, IVM is a critical component of IVEP, facilitating the utilization of a large number of oocytes inside an ovary [7]. However, in vitro oocyte maturation entails artificially removing COCs from follicles and cultivating them to the metaphase II stage. In addition, in vitro fertilisation (IVF) is now one of the most effective alternatives to ovarian hyperstimulation. However, only a small proportion of in vitro matured oocytes show full developmental potential to term [8]. It is likely that buffalo oocytes and embryos are very sensitive to oxidative stress due to their high lipid content.
One of the first media designed for this purpose was synthetic oviduct fluid (SOF), which was established from the composition of bovine oviductal fluid [9, 10]. SOF medium, which was originally based upon the biochemical and physiological analysis of sheep oviductal fluid [11], has been used in the IVM of oocytes in bovine [12, 13], goat [14], bitch [15] and in IVC of sheep embryos [16]. In human IVF, FertiCult is a chemically balanced salt solution (HEPES buffered) that also contains gentamycin, sperm washing, embryo replacement, and the sperm swim-up procedure. It was reported that Ferticult medium enhanced cumulus cell expansion and nuclear maturation more than tissue culture meium-199 (TCM-199), Ham’s F-10 medium, or minimum essential medium (MEM) in buffalo oocytes [17].
Amino acids can be categorised as either essential or non-essential. Essential amino acids are unable to be synthesised de novo and must be obtained from the diet, such as histidine and lysine [18–20], whereas nonessential amino acids are not required in the diet as they can be synthesised in vivo, such as alanine. However, some nonessential amino acids have been found to be essential in certain situations and disease states. These amino acids are called conditionally essential and must be obtained from the diet, such as tyrosine [21, 22]. Thus, amino acids are involved in several physiological processes that ensure the maintenance of cellular homeostasis. The major concern with the inclusion of amino acids in embryo culture medium is the production of toxic ammonium. Thus, to prevent the spontaneous breakdown of amino acids, medium should be stored at 4°C. Moreover, care should be taken to limit the amount of time the medium is exposed to 37°C prior to the addition of the embryo. If media are handled appropriately, amino acids confer immense metabolic and homeostatic benefits to the developing embryo [23].
The supplementation of amino acids to SOF medium may increase the pool size of endogenous amino acids and denovo protein synthesis [24]. Also, adding L-tyrosine to FertiCult could improve the IVM and IVF in buffaloes. Where the author also attributed those results to the contents of FertiCult medium, as it has in every 20 ml 0.4% HSA, L-glutamine, glycine, and taurine, which could enhance IVM rate [25].
To the best of our knowledge, there are scarce reports on the effect of essential amino acid addition on oocyte maturation as well as embryo cultivation media in buffaloes. The aim of the work was to evaluate the effect of amino acid addition (Histidine and L-Tyrosine) to the oocyte maturation medium on future IVM, IVF rates, and embryonic development in buffaloes.