Bovine ostertagiasis

Anderson, Norman (1968) Bovine ostertagiasis. PhD thesis, University of Glasgow.

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Abstract

Following a study of nineteen outbreaks of naturally occurring bovine parasitic gastroenteritis, in which 45.5 percent of 337 young dairy cattle were clinically affected, O.ostertagi was the predominant nematode species found, The fields which wore used year after year for the raising of replacement calves, together with the practice of grassing spring born and autumn born calves in the same field, were factors which were considered to be major predisposing causes of outbreaks of this economically important disease. Three phases of bovine ostertagiasis could be dinstinguished on the basis of clinical, history and laboratory findings. TYPE I corresponded to the classical description of clinical parasitic gastritis in which calves, at grass for the first time, showed a loss of weight and diarrhoea which occurred at any time from late July until the end of the grassing season. The vast majority of the ingested larvae developed to maturity within, the expected period of three weeks, PRE-TYPE II was clinically not apparent though large populations of O.ostertagi were present, of which over 80 per cent were inhibited at the early 4th stage of larval development. These animals had grazed infected pasture until the late autumn, but had no history of diarrhoea and usually appeared healthy to the farmer. The second clinical phase, Type II, was different to the first in that calves, which had no history of diarrhoea or weight loss during the grazing season and which were well grown and in excellent condition , were taken indoors about the beginning of November. After a variable period of time, ranging from 3 weeks to k months, these animals started to lose weight and to show a prefuse watery diarrhoea. The appearance of the clinical signs coincided with the development to maturity and emergence from the abomasal mucosa -of large numbers of inhibited O.ostertagi larvae, which were ingested during the late autumn grassing period. In the diagnosis of bovine ostertagiasis the results of faecal worm egg counts must be interpreted cautiously. All calves with egg counts of 1,000 e.p.g, and over were clinically affected animals. Because of the gross variation in worm egg counts which occurred in individual cases B low egg counts could not exclude bovine ostertagiasis from the differential diagnosis. In contrast to the effect seen in Type 1 cases, the response of Type II affected animals to anthelminthic treatment was poor, consequently, the prognosis was grave in the latter category. Anaemia , hypoproteinaemia and hypoalbuminaemia were not detected in cases of Type I ostertagiasis. In cases of Type II there occurred - a moderate, normocytic, normochromic anaemia and a marked hypealbuminaemia. The plasma pepsinogen concentration of infected calves was increased, markedly so in clinical cases, and was correlated with the severity of the abomasal lesions and the numbers of O.ostertagi found at autopsy. The pH and sodium ion concentration of the abomasal contents was markedly increased in Type 1 end Typo IX eases, but was only slightly elevated in Pre-Type II affected animals. The physiological abnormalities wore associated with marked histopathological changes within the abomasum. These wore described as a loss of cellular differentiation of the specialised cells, hyperplasia of the mucous epithelium and infiltration by reticuloendothelial cells. Further study would be required to establish how the parasites caused' the abnormalities observed. A detailed study of the naturally occurring disease revealed that the numbers of larvae available on the pasture of the calf rearing fields increased progressively from May to July and reached a peak at the end of August. Type 1 disease occurred after 9 to 16 weeks gracing on these pasture and some 50,000 to 60,000 O.ostertagi were required to precipitate clinical signs in calves of 4 to 6 months of age. In contrast to the worm counts from calves autopsied prior to October, a marked increase in the numbers of early 4th stage parasites was found in both previously infected and worm free calves which had grazed the heavily contaminated pasture, for as short a period as 14 days, during the late autumn period. This phenomenon was caused by inhibition of development at the early-4th larval stage and was attributed to an unspecified physiological change within the host or the larvae at this time of the year.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: W I NcIntyre
Keywords: Animal diseases
Date of Award: 1968
Depositing User: Enlighten Team
Unique ID: glathesis:1968-73803
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/73803

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