Serum triiodothyronine (T3) and thyroxine (T4) levels in embryo donor and recipient cows

Serum triiodothyronine (T-3) and thyroxine (T-4) levels were measured in embryo donor (Sahiwal) and recipient (crossbred) cows in relation to superovulatory response and conception/no conception respectively. The level of T, was significantly higher (P<0.05) at superovulatory estrus as compared to normal estrus in good responders (> 5 CL), however, its increase in fair (3-5 CL) and non-responder (1-2 CL) animals was nonsignificant. The levels of T 3 on the day of normal and superovulatory estrus in good, fair and non responders were 1.21+/-0.07, 1.59+/-0.12; 1.25+/-0.06, 1.29+/-0.10 and 1.33+/-0.07, 1.46+/-0.05 ng/ml respectively. Thyroxine (T-4) levels also followed the same pattern in the good, fair and non-responder animals. The T4 level was significantly higher in the group yielding maximum embryos. The values of T-4 were 7.50+/-0.47, 8.90+/-0.62; 7.33+/-0.69, 7.82+/-0.49 and 6.34+/-0.72, 6.84+/-0.23 mug/100 ml on days of normal estrus and supcrovulatory estrus in good, fair and non-responder animals respectively. Significantly higher levels of T-3 and T-4 on the day of superovulatory estrus resulted in better embryo recovery compared to those having only little increase on superovulatory estrus. There was significant increase in the level of T-3 on day 14 post embryo transfer in non-pregnant animals and the values below 1 ng/ml on day 14 post ET,could be indicative of pregnancy. The T-4 values were also lower in pregnant animals compared to non-pregnant animals on day 14 post ET.