Discussion
Sheep is considered as one of the important sectors in livestock production. Sheep may be affected with many diseases which decrease production. Parasitic gastroenteritis is one of them causing many economic losses (Miller and Horohov, 2006).
Concerning the prevalence of parasitic nematodes, out of 319 examined sheep, 199 (62.38%) were proved to be infested with parasitic gastrointestinal nematodes via flotation concentration technique. Nearly similar prevalence was reported by El-Fayoumi (1989),(65.83%). Higher prevalence was reported by Al-Gaabary et al. (2007),(71.69%). Lower prevalence (42.66%) was reported by Abdel-wahed and Salem (1999). The variations between the prevalence in different studies may be attributed to the type of rearing, hygiene and control measures where, sheep raised on high protein diet developed resistance to parasitic gastroenteritis (Knox and steel, 1999). In addition, the changes in climatic condition may affect the degree of infection where rain may lead to increase infection with parasitic gastroenteritis.
Highest infestation was recorded by Trichostrongylus species (59.25%) and the lowest one recorded by Nematodirus (0.63%). Similar results were recorded by Hashem and El-Sayed (1997) and Al-Gaabary et al. (2007) who found that Trichostrongylus was the predominant species in percent of 46.4% and 64.92% respectively.
Our results differed from that recorded by Gharib (1998) who found that Trichuris ovis was the most common species of gastrointestinal nematode.
Concerning the seasonal distribution of parasitic infestation,the highestprevalence was recorded in spring(71.59%) and the lowest one was recorded in summer (43.01%). Similar result obtained by Altaif and Issa (1983); results may be attributed to pregnancy and lactation that cause rising in fecal egg count (Vlassoff et al., 2001).The rise in fecal egg count in female with specific physiological status may be attributed to relaxation of immunity and resistance (Valderrábano et al., 2006).
Some parasitologically positive animals appeared clinically normal. The clinical signs were severe emaciation, easily detached wool, pale mucous membrane and diarrhea in addition to bottle jaw in 2 cases. Our results were similar to those obtained previously by Yacob et al. (2009)who noticed that the severity of the clinical signs was related to the intensity of infection.
These clinical signs may be attributed to the decrease in the levels of serum total protein, albumin and globulin which lead to bottle jaw (Radostits et al., 2010). Beside that there was significant decrease in serum calcium (Hasan et al., 1986) and alkaline phosphatase. Moreover, there was significant reduction in bone mineral density (Thamsborg and Hauge, 2001). All these factors may lead to poor growth rate and emaciation. In addition, ulceration in abomasum and inflammation in intestinal wall interfere with digestion and absorption leading to diarrhea, emaciation and detached wool (Radostits et al., 2010). Severe anemia recorded byYacob et al. (2009) caused pale mucous membrane.
The hematological changes associated with parasitic gastrointestinal nematode in sheep showed negative correlation between the degree of infestation and the levels of RBCs, Hb and PCV. There were significant decrease in levels of RBCs and PCV and a significant decreases in serum total protein, albumin and globulin levels. In addition, there were in all infested animals. These results agree with the results obtaind by Radostits et al. (2010). In addition, there was a significant decrease in levels of MCV and MCH in severely infected animals only. Our results nearly similar to results
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who recorded that the peaks of worm egg counts occurred in spring and in autumn.
Our results differed from the results of Aly et al. (1994) who found lowest infestation during autumn and spring and Khalafalla et al. (2011) who reported lowest infestation during spring.
The prevalence of the recovered 3rd stage nematode larvae from fecal culture revealed that the predominant species in winter, spring and autumn were Haemonchus (30%) while in summer Bunstomum (30%). Nearly similar results were obtained by Reynecke et al. (2009)who recorded that Haemonchus species was the predominant during wet seasons from October to March. Our results differed from that obtained by Horak (2003) who recorded Haemonchus species as the predominant nematodes in summer season.
Concerning age predisposition, parasitic gastrointestionl infestation was significantly different (P<0.05) among age groups, where the prevalence was higher in the animals over 2 years (78.46%) followed by animals from 1 to 2 years (72.27%) and lastly in that below 1 year age (45.93%). Similar results were recorded by Ramadan et al. (1992)who recorded highest worm burden in adult and old sheep. On the other hand, our results were different from that obtained byKhan et al. (2010)who found high nematode infestation in young animals than adults.Vlassoff et al. (2001)attributed these results to development and increase in immunity during increase of age. On the other hand Bonfoh et al. (1995)observed no relation between animal age and prevalence of parasitic gastroenteritis.
Concerning sex predisposition, significant variation was recorded within different sex where the prevalence rate in female animals was 75.86% and in male animals was 38.79%. Similar results were obtained by Khan et al. (2010). These obtained by Yacob et al. (2009) who found that low levelofinfestation with Haemonchus contortus leading to normochromic normocytic anemia. These results may be attributed to the effect of the hemolytic factor that released from adult Haemonchus contortus on the surface of sheep RBCs lead to hemolysis(Fetterer and Rhoads, 1998).Moreoversignificant decrease in serum total protein, albumin and globulins levels were recorded. This may be attributed to the inflammatory enteropathy that occurred in the gastrointestinal tract and, in turn, the alteration of the intestinal micro-circulation, permeability and motility leading to albumin lossing enteropathy (Nesheim, 1993).Moreover, Rhodes et al. (1978)claimed that albumin might serve as a nutrient for the growing parasites and this might be responsible for the recorded hypoalbuminemia.
Post mortem examination of abomasum of sheep infected with Haemonchus contortus revealed thickening, hyperemia and small ulceration in addition to petechial hemorrhage at the site of worm attachment. The abomasal contents were dark in color and the adult worm was noticed grossly. Histopathologically, there were mononuclear cell infiltration in between mucosal glands and lamina propria beside necrosis and sloughing of mucosal epithelium and presence of adult worm. Similar results were previously obtained byHertzberg et al. (2000).
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