The use of radioimmunoassay in early diagnosis of non-pregnancy in smallholder dairy herds of Kenya

Kenya's smallholder dairy sector produces 85% of the total milk marketed in the country. The majority of cows in this sector have long calving intervals, leading to low lifetime production of milk and calves. Determining non-pregnant cows early by measuring progesterone levels at 23 days after artificial insemination (AI) can help reduce calving intervals, thus improving productivity. A study was conducted on 481 cows subjected to AI, to determine the timeliness of AI, cycle and pregnancy status. Milk samples (10 mL) were collected from each cow on day 0 (day of AI) and on days 13 and 23 after AI. Data pertaining to the farm, cow, heat period, AI technician and semen batch were recorded. Progesterone concentration was measured in skim milk using a solid-phase radioimmunoassay. Rectal palpation was done 90 days after AI to confirm the predictions made from hormone assay. The overall conception rate (CR) was 53%. Mean progesterone levels in pregnant cows were 0, 5.3 and 10.1 nmol/L at the three stages of sampling, while in non-pregnant cows they were 0.59, 2.69 and 0.46 nmol/L, respectively. Low progesterone was found in 83% of the cows at the time of AI, but of these 46% did not conceive, indicating that they were either non-cyclic, had fertilization failure or suffered early embryonic loss. At the time of AI 14% of the cows were in the luteal phase, while 32% were not cycling. Cows were inseminated on average 19 hours after onset of heat. The interval from calving to first AI averaged 5 months. There were no differences between breeds in CR, but cows inseminated during April to June (long rain period) had higher CR than those inseminated during July to September. The accuracy for prediction of non-pregnancy by progesterone assay was 99% and that for predicting pregnancy was 95%. It is concluded that this technique can identify open cows by day 23 after AI, thus reducing the time required to rebreed, which will lead to shorter calving intervals. (author)