Diagnosis and effects of cobalt deficiency in the pregnant ewe

Fisher, George Edward John (1988) Diagnosis and effects of cobalt deficiency in the pregnant ewe. PhD thesis, University of Glasgow.

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Abstract

The literature relating to the diagnosis and effects of cobalt (Co) deficiency, particularly in the pregnant ewe, was reviewed. Two housed experiments, both with 60 hill ewes, were undertaken with the aim of characterising the effects of Co deficiency on reproductive performance. The diagnosis of sub-clinical Co deficiency was also studied. Three treatment groups of 20 ewes each were established in both experiments. The NS (non-supplemented) groups of both experiments were maintained on a Co-deficient intake for the whole of pregnancy. Sheep in the HS (half- supplemented) group of Experiment 1 received a Cosufficient intake until mid-pregnancy after which they were maintained on a Co-deficient diet. The HS group of Experiment 2 received a Co-deficient intake until midpregnancy, after which it was replenished with Co. The FS (fully-supplemented) group of both experiments received a Co-sufficient intake for the whole of pregnancy. Co status of the ewes was monitored by fortnightly sampling and analysis for serum vitamin B12 and methylmalonic acid (MMA) concentrations. Serum B12 was determined by either microbiological assay or radio- immuno assay (RIA). In Experiment 1 the NS and HS ewes were sub-clinically Co-deficient before lambing. In Experiment 2 the NS and HS sheep were sub-clinically Co-deficient at the start of tupping and the clinical disease was detected in the NS ewes at the start of lambing. After Co repletion from mid-pregnancy, serum B12 and MMA concentrations in the HS sheep returned to normal levels and they were Cosufficient before lambing. The FS ewes of both experiments were Co-sufficient throughout the investigations. In Experiment 1 and 2 the differences amongst treatments for serum B12 and MMA concentrations were significant (P<0.001). Concentrations of MMA in serum were a more accurate and precise marker of sub-clinical and clinical Co deficiency, than serum B12 levels. Within treatments, serum B12 concentrations were more variable than serum MMA levels and could imply false positive diagnoses. In contrast, there were no problems from diagnosing false negatives with serum MMA concentrations. However, there was evidence to suggest that liver damage could lead to incidences of very high levels of MMA in serum. Concentrations of B12 in serum provided an effective indication of Co intake and responded to declining Co status before serum MMA levels. Thus, the joint analysis of serum B12 and MMA concentrations was necessary for the prognostic, as well diagnostic, detection of Co deficiency. The microbiological assay and RIA of serum B12 both provided effective diagnostic data. However, for ewes fed a diet high in concentrates, mean serum B12 concentrations determined by the RIA were 20 percent lower than those measured by the microbiological assay (r = 0.97, P<0.001). The diagnostic criteria applied to RIA data therefore required alteration in this situation. For the microbiological assay, values between 200 and 400 ng/1 were regarded as indicative of sub-clinical disease. If ewes were fed a high concentrate ration, the range 160 to 340 ng/1 applied to data from the RIA provided the same diagnostic inference. A small housed experiment with wethers was undertaken to determine the presence of diurnal fluctuations in serum B12 and MMA concentrations. Endogenously stimulated fluctuations, of either marker, were not detected. However, serum levels of both B12 and MMA in Co-deficient and sufficient sheep showed inconsistent but marked rises in response to the exogenous stimulation of twice daily feeding. The consequences of the results for the diagnosis and effects of Co deficiency in pregnant ewes in the field situation were discussed. A survey of Co status in pregnant sheep on 15 farms in Scotland with a history of Co deficiency, was also undertaken. However, the use of one sampling during pregnancy was not adequate to indicate the Co status of flocks during tupping, pregnancy and lactation. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: A MacPherson
Keywords: Animal sciences
Date of Award: 1988
Depositing User: Enlighten Team
Unique ID: glathesis:1988-73403
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56
URI: http://theses.gla.ac.uk/id/eprint/73403

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