Epsilon Open Archive

Abstract

This thesis presents studies of the reproductive and lactation performance of dairy cattle in the Oromia Central Highlands of Ethiopia, with particular emphasis on diagnosing and monitoring pregnancy. In an introductory study, early abortions were induced in four heifers with cloprostenol and monitored using ultrasonography. Prior to cloprostenol injection, plasma concentrations of bovine pregnancy-associated glycoprotein 1 (bPAG1), prostaglandin F2α (PG metabolite), and progesterone (P4) varied from 8.4–40 ng/mL, 158–275 pmol/L, and 20.7–46.9 nmol/L, respectively. After foetal death and subsequent expulsion, the bPAG1 level began to decrease, though the decrease was small and gradual. The PG metabolite level started to display short lasting peaks within three hours, while the P4 level dropped sharply. A cross-sectional study was followed by two years of longitudinal observation to examine the reproductive and lactation performance of smallholder dairy cows in Selalle, central Ethiopia: these studies involved 300 and 24 randomly selected smallholder dairy farms, respectively. The geometric means of the calving-to-conception interval (CCI) and duration after last calving as determined in the cross-sectional study were 187 and 201 days in pregnant and non-pregnant cows, respectively. While, the means of calving interval (CI), CCI and first observed oestrus after calving as determined by the longitudinal observations were 516, 253, and 141 days, respectively. Production system, district (location), and suckling status influenced these intervals considerably. Based on milk P4 profiles, the mean first onset of luteal activity (OLA) after calving was 52 days and was significantly influenced by suckling and parity number. The prevalence of pre-weaning calf mortality was quite high, up to 17.4%. The mean lactation length was 54.4 weeks, while the mean milk yield for the first 43 weeks of lactation was 11.7 L/day for crossbred cows. Suckling status, season of calving, and parity number significantly influenced the daily milk yield. A further follow-up study described the serum profiles of pregnancy-associated glycoprotein (PAG), oestrone sulphate (E1-S), and P4 during gestation in both Borana and crossbred cattle. Accordingly, the PAG concentrations at the 4th week post conception were 1.5–5.5 ng/mL and 2.1–4.7 ng/mL in Borana and crossbred cattle, respectively, and increased progressively, peaking approximately at the time of calving. The serum E1-S concentrations at the 17th week of pregnancy were 0.3–2.6 and 0.9–5.7 ng/mL in Borana and crossbred cattle, respectively, and increased progressively until calving. Breed, parity status, dam body weight, foetal sex, and foetal birth weight (only for PAG) significantly influenced PAG and E1-S concentrations. The P4 concentrations at the 4th week of pregnancy were 3.2–5.1 and 1.7–8.9 ng/mL in Borana and crossbred cattle, respectively, and remained elevated throughout gestation. In conclusion, the smallholder dairy cows in the study area experienced prolonged CCI and CI, and thus, their reproductive performance was unsatisfactory. Moreover, the observed pre-weaning calf mortality rate is quite high. The serum PAG and P4 levels at the 4th and the E1-S levels at approximately the 17th week of pregnancy were well above the required levels for pregnancy testing in both Borana and crossbred cattle. Moreover, the observed serum profiles of PAG, E1-S, and P4 throughout gestation (and 10 weeks postpartum for PAG) were comparable to those reported for other breeds of cattle.