Sahiwal cow is the best milch breed among all Bos indicus throughout the Subcontinent. It is famous for heat resistance, tick tolerance, high milk production. It is also exported to different countries for its peculiar properties. These cows have low fertility when inseminated with frozen semen. Very little fragmented experimental data is available on reproduction of Sahiwal breed, which might be major reason of bad performance from reproduction aspect. The same rule of insemination as we know in Holstein (Bos taurus) when applied on our local animals did not yield similar results. The designed experiment was to determine appropriate time of insemination to improve reproductive efficiency in Sahiwal cows.
This experiment was conducted at Livestock Experimental Station Jahangirabad, District Khanewal Punjab. Eighty five (n=85) adult, multiparous, lactating Sahiwal cows having BCS ≥ 2.5 and weight 325–450 kg, more than 60 days post-partum with normal reproductive tract were selected for this study. Estrous detection was carried out twice daily with teaser bull for 30-45 minutes. Standing heat was considered when cow did not move away for 4-6 seconds with teaser bull being mounted on her. Cows were assigned randomly into four groups (0 h, 12 h, 24 h and 36 h) with respect to standing heat. Frozen semen from bull whose fertility is known to us having post thaw motility of 40% at least was used for insemination.
Ultrasound was used as tool for precise assessment of reproductive status of experimental animals. At the start of each replicate, both ovaries and uterus of all the adult Sahiwal cows were scanned with B-Mode Ultrasound console for presence or absence of fetus and CL or any structural abnormality, with help of 7.5MHz Trans-rectal probe. Pregnancy was diagnosed 35 day post AI. Results were analyzed by using statistical software (SPSS). Pregnancy per AI was compared amongst
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different insemination groups by using binary logistic regression test. Pregnancy was assessed retrospectively by plotting scatter graph using ovulation as our reference point.
The timing of ovulation was 20.64 hours from onset of standing heat. Mean size of ovulatory follicle at 0, 12, and 24 hour after standing heat was 13.52 mm, 14.52 mm and 15.39 mm respectively. The ovulation rate was 97%. Highest pregnancy per AI 57% (13/23) was observed in 0 h group, followed by 36% (8/22) in 12 h, followed by 25% (5/20) on 24 h group. Lowest pregnancy per AI 10% (2/20) was seen in group inseminated 36 hour after onset of standing heat (36 h). While retrospectively highest pregnancy per AI 67% (10/15) was observed in -18 h group, followed by 29% (6/21) in -6 h group and 32% (7/22) in +6 h group, while no pregnancy were observed 0% (0/12) in +18 h group. The overall pregnancy per AI was 33% (28/85) in Sahiwal cows.