The effect of Haemonchus contortus infection on haematological parameters in young Merino sheep and its significance for productivity

Abstract

1990). The effect of Haemonchus contortus infection on haematological parameters in young Merino sheep and its signicance for productivity. Animal Production, 50, pp 99-109 ABSTRACT Faecal egg counts, haematocrits, erythrocyte potassium contents and serum iron concentrations were determined in 1005, 3-to 5-month-old Merino lambs infected with a single dose of 11 000 Haemonchus contortus larvae. Live-weight gain and wool growth also were recorded. Lambs were infected in six different groups over a 3-year period. When infections were terminated after 5 weeks, faecal egg counts in the six infected groups had reached a peak of 5170 to 20 339 eggs per g (average 12 909), haematocrits had declined to between 196 and 309 ml/1 (average 233), erythrocyte potassium contents had risen to between 16-7 and 37-5 mequiv. per 1 (average 31-5) and serum iron concentrations, in some cases following an erratic course, had dropped to between 0-512 and 1-546 mg/1 (average 0-946).Of the three haematological parameters, haematocrit correlated best with faecal egg count (r = 0-7 in four of six infected groups). However, in two groups with low faecal egg counts this correlation was much lower (r = 0-3). Erythrocyte potassium concentration and serum iron concentration significantly correlated with variability of haematocrit not accounted for by faecal egg count, suggesting that both erythropoiesis and iron availability influence the degree of anaemia.The effect of H. contortus infection on productivity of lambs was best predicted by haematocrits: for each further 0-01 proportional decrease in haematocrit, a 0-03 reduction of live-weight gain over a 9-week post-infection period, a 0-007 reduction in clean wool growth and a 0-004 reduction in fibre diameter over a 4-to 9-week period were observed. Some evidence was obtained indicating a tolerance level of anaemia at approximately 280 ml/1 packed cell volume.

Genetic resistance of different genotypes of sheep to natural infections with gastro-intestinal nematodes

“…This finding is similar to that of Albers et al (1990) that live-weight gain in lambs infected with H. contortus was positively correlated with haematocrit and negatively correlated with EPG. This finding is similar to that of Albers et al (1990) that live-weight gain in lambs infected with H. contortus was positively correlated with haematocrit and negatively correlated with EPG.…”

Experimental infection of Ethiopian highland sheep by different infective doses of <em>Haemonchus contortus</em> (L₃): haematological and parasitological parameters, serum protein concentrations and clinical responses

“…Among important clinical responses, haematological parameters provide an excellent basis for judgment with respect to the nature of the disease, the extent of tissue and organ damage, the response of defence mechanism of the patient, in diagnosing the type of possible anaemia and may serve as an index to characterize health status of animals (Albers et al,., 1990). There are quantifiable variations in blood parameters particularly in haemoglobin concentration, RBC counts and PCV values between exotic and indigenous animals but these physiological values were not recorded for different species and breeds of indigenous animals in Ethiopia.…”

Trichostrongylus colubriformis and Haemonchus contortus infections in light bodyweight Merino lambs

“…Weaner Merinos show a decrease in daily weight gain once their H contortus worm egg count reaches 3000 eggs per gram 9 (Le Jambre personal communication), an egg count expected to result from a worm count of approximately 3500 10 . Thus all of the lambs in this experiment had worm burdens and worm egg counts in the pathogenic range (Figure 2).…”