Effect of corpus luteum: quality and recovery rate of buffalo (Bubalus bubalis) oocytes

* Correspondence: [email protected] India has the highest buffalo population in the world. In terms of meat, milk, and draft work, the indigenous river buffalo is the major contributor and is considered the leading dairy animal in the country. Due to its ability to survive in harsh climatic conditions, in comparison with cattle the buffalo is considered as the animal of the future in India. While buffalo have several advantages over cattle, poor availability of superior germplasm is a major problem in buffaloes. Inherent problems like delayed maturity, seasonality of breeding, poor conception rate, silent estrus, low germ cell reserve, higher rates of follicular atresia, high rate of incidence of early embryonic death, longer inter-calving period (1), poor freezability of semen, and susceptibility to thermal stress (2) are all limitations to the reproductive performance and productivity in the species. Therefore, attempts have been made to produce elite animals through advanced reproductive technologies, requiring large number of oocytes from ovaries of abattoir origin/live animals. Retrieval of good quality oocytes and average number of oocytes per ovary in buffaloes are low (3–6). Recovery rate and quality of oocytes is influenced by season, and significantly higher numbers of good quality oocytes were obtained during the winter season as opposed to the summer season. Moreover, during the winter season, significantly higher numbers of good quality oocytes were obtained from the ovaries during days where the temperature was lower than 25 °C (7). Little information on recovery rates of different grades of oocytes from buffalo ovaries is available. The present study highlights number of oocytes recovered per ovary having CL and without CL in buffaloes, and their relevant percentage of different grades of oocytes recovered from abattoir-collected ovaries. Buffalo ovaries from slaughtered animals were immediately collected from the Delhi slaughterhouse between February and April of 2001.The ovaries were thoroughly washed to remove tissue debris and blood clots, and transported to Karnal in a thermos flask at 32– 35 °C with fresh saline solution within 3–4 h of collection. The ovaries were again thoroughly washed in normal saline and were classified into 2 groups, with CL and without CL, and transferred separately into 2 sterile separate glass beakers. Later they were put on sterile filter paper to remove excess water. All the surface follicles of 3–10 mm diameter were aspirated in phosphate buffered saline albumin (PBSA) medium using a 5-mL plastic syringe (tissue culture grade) and a 19-gauge needle. The oocytes thus collected were kept in a petri dish with PBSA and examined under a microscope with 45× magnification. The oocytes were searched, separated, washed thoroughly, and classified into 4 grades. The criteria used for grading was as described by Singla (8) with some modification: Grade-A: Oocytes with a compact cumulus complex and 3 or more layers of cumulus cells. Grade-B: Oocytes with compact cumulus complex and 1–3 layers of cumulus cells. Grade-C: Oocytes with expanded and partially denuded cumulus cells. Grade-D: Oocytes without cumulus cells. Abstract: Recovery rate and quality of oocytes were investigated from abattoir collected ovaries with and without corpora lutea (CL). The oocytes were categorized into four grades: grade-A, grade-B, grade-C, and grade-D based on the presence of the cumulus cells complex around the oocytes. The number of oocytes per ovary were 1.7 ±0.1 and 1.5 ±0.1, obtained from ovaries without CL and with CL, respectively. Recovery rate of different grades of oocytes from ovaries with CL and without CL were almost identical.