Effect of hormones, season and lactation on follicular size, oocyte competency and embryo production in sahiwal cattle

Transvaginal ultrasound-guided ovum pick-up (OPU) and in vitro embryo production (IVEP) techniques are widely used for enhancing reproductive efficiency. The number and quality of embryos have been reported to be influenced by various factors like source of hormones, season, lactation in cattle.

Twenty-one multiparous, normal cyclic Sahiwal cows (aged: 6-8 years; lactating: n-11 and non-lactating: n-10) were selected randomly and the experiment was conducted during hot (April to September) and cold (October to March) seasons. All the donor cows were administered 10 μg GnRH at random stage of oestrous cycle followed by FSH (Folltropin-V™ or Stimufol) at the rate of 100, 60 and 40 mg after 48, 60 and 72 h of GnRH administration. After 24 hours of coasting period, follicular aspiration was performed by stabilizing the targeted follicles with the help of ultrasonography. The procedures of COCs grading, in vitro maturation, fertilization, followed by culture were performed as per the standard protocols.

The hormonal treatment was effective in improving the oocytes’, developmental competency and in vitro embryo production; with no statistical differences between the two sources. The follicle size distribution revealed a lower (P<0.05) medium-sized and small-sized follicular proportion during the hot season with a higher average count of dominant (large-sized) follicles. While, good quality (A+B+C) oocytes, matured and fertilized oocytes were significantly higher (P<0.05) in non-lactating donors, especially among cool-season collections.