Pregnancy Rate from Timed-artificial Insemination and Natural Service of Oestrus Synchronized Kedah-Kelantan and Crossbred Cows in Two Management Systems

Improved reproductive efficiency is the outcome of herd management and could involve a decision to choose between artificial insemination (AI) and natural service (NS). The objective of the present study was to determine the time of ovulation and pregnancy rate (PR) following timed AI (TAI) and NS, and frequency of TAI of two different management systems in oestrus synchronized Kedah-Kelantan (KK) and KK crossbred (CB) cows. Cows were assigned to two management systems: pen (A, n=80) and pasture (B, n=70). The cows were synchronized with controlled internal drug release (CIDR) device for 7 d, and injected intramuscularly with 500 μg of synthetic prostaglandin (PGF) analogue 2 d prior to CIDR withdrawal. Seventeen KK and 47 CB cows were scanned for follicular mapping to determine the ovulation time. Cows were later bred in A using NS (n=20) or TAI at 56 h (ATAIS56, n=20), 65 h (ATAIS65, n=20) and 72 h (ATAIS72, n=20) and in B using TAI at 56 h (BTAIS56, n=16), 65 h (BTAIS65, n=18) and 72 h (BTAIS72, n=16) following CIDR withdrawal. KK and CB cows were then compared for number of AI services conducted: one service (S56S, n= 20) and two services (S56D, n= 20) of TAI. Mean ovulation time of the cows studied was 85.1±1.6 h. Cows managed on pasture and inseminated at a fixed time of 65 h showed higher (22%, p>0.05) PR compared with the other groups studied. The percentage of pregnant cows managed on pasture was higher (p>0.05) for cows bred with TAI at 65 h than at 56 h and 72 h and all groups under NS kept in the pen. There was no significant difference between TAI and NS groups managed on pasture. Pregnancy rate of cows with one-service TAI (25%) was higher than those with two-service TAI (20%) done at 56 h and 96 h. It can be concluded that ovulation occurs at 85.1 h after CIDR withdrawal, and the pregnancy rate is not affected by the management system and the number of services of TAI.