Radioimmunoassay and related techniques to improve artificial insemination programmes for cattle reared under tropical and sub-tropical conditions

CONSTRAINTS LIMITING THE EFFICIENCY OF ARTIFICIAL INSEMINATION OF CATTLE IN BANGLADESH. The aim of the present study was to identify the factors that influence postpartum intervals to first detected luteal activity, first service and to conception, and the conception rates of cows in the artificial insemination (AI) programme in Bangladesh. A baseline survey (investigations 1, 2 and 3) was made on 444 milking cows of Mymensingh District to 6 AI centres and sub-centres. Each cow was then examined three times after each AI until she stopped returning to oestrus. Sixty to 120 days after the last AI, the cows were examined per rectum to confirm the pregnancy. Milk progesterone data on Day 0 and Day 21–24 contributed to a clear diagnosis with respect to pregnancy in 82.5% cows indicating a possible use of this progesterone assay schedule for pregnancy diagnosis in AI programmes. The intervals to first service and to conception varied from 31 to 427 days (median = 184; n = 444) and 40 to 426 days (median = 184; n = 232) respectively, and conception rate from 32–58% (average 46.2%; n = 444). Prolongation of weaning age of calves resulted in long intervals to first service and to conception (P <0.001); weaning age varied from 6 to 19 months (median = 10). Cows with body condition score (BCS; 1–5 scale) of 3 or more and cows calved during July to September had shorter intervals to first service and conception than those with BCS less than 3 and those calved during March. The conception rate was influenced by cattle rearing systems (intensive vs. extensive), purpose of rearing cows (dairy vs. dairy + draught), BCS and milk production (P <0.05). The degrees of vulvar swelling, nature of genital discharge, tonicity of uterus, and interval between oestrus and AI had significant effects on the conception rate. Bulls classified as good and poor on the basis of semen evaluation data differed with respect to the conception rate in AI (P <0.001); this indicates a way of discriminating to some extend between bulls likely to have higher or lower fertility. In Investigation 4, milk progesterone was monitored two times in a month with a 10–day interval in 88 cows. The samples were taken between 10 days after calving and the first detected oestrus followed by two more samples 10 days apart. The proportion of cows accurately detected in oestrus was 30%. Another 30% were stated to be in oestrus when they were not (false positive) and 40% were not detected when they were in oestrus (false negative). The intervals between calving and oestrus, and luteal activity were 40–362 (median = 120, n = 82) and 34–398 (median = 111, n = 64) days, respectively. The BCS at calving and at the initiation of luteal activity influenced the interval between calving and luteal activity (P <0.05). Cows suckled twice daily initiated luteal activity earlier than their counterparts suckled several times daily (P <0.05). Investigation 5 demonstrated a reduction in sperm motility (P <0.05) due to dilution of fresh semen, and chilling, freezing, storing and transportation of frozen semen. The prolonged postpartum interval between calving and conception and low conception rate are the major constraints limiting the success of AI for cattle development in Bangladesh. The nutritional condition of the cow at calving and thereafter, weaning age of calves, frequency of suckling, cattle rearing system, accuracy of heat detection, interval between oestrus and AI, the oestrus signs and semen quality are the important determinants of the interval to conception and conception rate.