Current status of assisted reproductive technologies in buffaloes

Buffaloes are raised by small farm holders primarily as source of draft power owing to its resistance to hot climate, disease, and stress conditions. Over the years, transformation of these animals from draft to dairy was deliberately carried out through genetic improvement program leading to the development of buffalo-based enterprises. Buffalo production is now getting more attention and interest from buffalo raisers due to its socioeconomic impact as well as its contribution to propelling the livestock industry in many developing countries. Reproduction of buffaloes, however, is confronted with huge challenge and concern as being generally less efficient to reproduce compared with cattle due to both intrinsic and extrinsic factors such as poor estrus manifestation, silent heat, marked seasonal infertility, postpartum anestrus, long calving interval, delayed puberty, inherently low number of primordial follicles in their ovaries, high incidence of atresia, and apoptosis. Assisted reproductive technologies (ARTs) are major interventions for the efficient utilization of follicle reserve in buffaloes. The present review focuses on estrus and ovulation synchronization for fixed time artificial insemination, in vitro embryo production, intracytoplasmic sperm injection, cryopreservation of oocytes and embryos, somatic cell nuclear transfer, the factors affecting utilization in various ARTs, and future perspectives in buffaloes.

Quality analysis of buffalo blastocysts derived from oocytes vitrified before or after enucleation and reconstructed with somatic cell nuclei

We investigated the potential of vitrified-warmed buffalo oocytes to develop to blastocysts after parthenogenetic activation (PA) and somatic cell nuclear transfer (SCNT). In vitro-matured oocytes before and after enucleation (M-II oocytes and enucleated oocytes, respectively) were put in 7.5% DMSO and 7.5% ethylene glycol (EG) for 4, 7 and 10 min, and then vitrified (Cryotop device) after 1-min equilibration in 15% DMSO, 15% EG and 0.5M sucrose. Following 4-, 7- and 10-min exposure, proportions of the post-warm oocytes with a normal vitelline membrane were similar (66-71% in M-II oocytes and 69-71% in enucleated oocytes). However, 18-20% of the normal M-II oocytes had no detectable first polar body in their perivitelline space (no potential for subsequent enucleation). When the post-warm M-II oocytes were treated for PA by 7% ethanol, 10 microg/mL cycloheximide and 1.25 microg/mL cytochalasin-D, parthenogenetic development into Day-7 blastocysts occurred in 10-13% of cultured oocytes, lower (P<0.05) than fresh (control) oocytes (24%). In the absence of the cooling and warming, blastocyst rates in the 4-min exposure group (22%), but not in the 7-min and 10-min exposure groups (14-15%), were similar to that in the fresh group (23%). The total cell number (group average 117-132 cells) and the ICM ratio (22-24%) of the PA blastocysts derived from vitrified M-II oocytes were comparable with fresh oocytes (127 cells and 25%). After SCNT (with fibroblast cells and vitrified-warmed oocytes), blastocyst rates were similar for the three exposure periods for M-II oocytes (8-10%) and enucleated oocytes (7-9%), but were lower (P<0.05) than in the fresh group (15%). The total cell number of the SCNT blastocysts derived from vitrified M-II and enucleated oocytes (80-90 and 82-101 cells) was smaller (P<0.05) than from fresh oocytes (135 cells); the ICM ratio of blastocysts derived from the M-II and enucleated oocytes after vitrification in 7- or 10-min exposure groups (20-22%) was not different (P>0.05) from fresh control oocytes (24%) or those in 4-min exposure group (M-II 23%, enucleated 24%). Thus, SCNT of swamp buffalo oocytes following vitrification before or after enucleation resulted in blastocysts with a slightly decreased cell number.

Factors affecting cryosurvival of nuclear-transferred bovine and swamp buffalo blastocysts: effects of hatching stage, linoleic acid–albumin in IVC medium and Ficoll supplementation to vitrification solution

The objective was to determine whether the hatching stage of cattle and swamp buffalo somatic cell nuclear-transferred (SCNT) blastocysts affected cryosurvival after vitrification, and whether addition of linoleic acid-albumin (LAA) to the IVC medium and Ficoll to the vitrification solution improves cryosurvival. Fused couplets were activated with ethanol and cycloheximide-cytochalasin D (day 0), and were allowed to develop in the presence of 0.3% BSA or 0.1% LAA+0.2% BSA. Hatching blastocysts were harvested at day 7.0 (cattle) or day 6.5 (buffalo), and classified into one of three categories, according to the ratio of extruding embryonic diameter from zona to embryonic diameter inside the zona. The blastocysts were vitrified in 20% DMSO+20% ethylene glycol+0.5M sucrose, with or without 10% Ficoll in TCM199+20% FBS, using Cryotop as a cryodevice. The post-thaw survival of the blastocysts was assessed by in vitro culture for 24h. In cattle, when the LAA-supplemented IVC medium and the Ficoll-free vitrification solution were used, cryosurvival of the early-hatching blastocysts (77%) was not different from those of middle- and late-hatching blastocysts (74 and 80%, respectively). Inclusion of Ficoll in the vitrification solution did not improve the cryosurvival of SCNT blastocysts (54 to 68%). Early-hatching SCNT blastocysts produced in the absence of LAA were sensitive to the vitrification procedure (cryosurvival 56%; P<0.05 versus 80% in the late-hatching blastocysts). The full-term developmental potential of SCNT blastocysts was proven only in the non-vitrified control group. In buffalo, the mean cryosurvival of hatching SCNT blastocysts produced with LAA (89%) was not different from that of those produced without LAA (87%). In conclusion, bovine SCNT blastocysts, regardless of their hatching stage, were relatively resistant to vitrification by the ultra-rapid cooling procedure when the blastocysts were produced in the presence of LAA. Furthermore, swamp buffalo SCNT blastocysts were more tolerant of vitrification than bovine SCNT blastocysts.