Genetic resistance of Ghezel and Ghezel-Baluchi crossbred lambs to gastro-internal nematodes

Received: July 28, 2015 Accepted: July 12, 2017 1MSc Student, Department of Animal Science, Faculty of Agriculture, University of Tabriz, Tabriz, Iran 2Professor, Department of Animal Science, Faculty of Agriculture, University of Tabriz, Tabriz, Iran 3Professor, Department of Pathobiology, Faculty of Veterinary Medicine University of Tabriz, Tabriz, Iran *Corresponding author: rafata@tabrizu.ac.ir
Nowadays, beside of production traits, the characteristics of genetic resistance to diseases is considered as animal breeding aims in animal breeding. There is a growing interest by producers and consumers in the production of meat animals with minimal chemical input to reduce chemical residues in the meat and to increase the sustainability of livestock production. Selection of superior sires with identified resistance should be possible because parasite resistance that usually measured by fecal egg counts (FEC) or blood packed cell volume (PCV), is moderately heritable. One option to control helminth infections is to breed sheep that are resistant to these parasites. Genetic variation in response to parasite infection has been documented in the previous studies in some sheep breeds, mostly involving tropical and subtropical breeds, such as the Red Maasai, St. Croix, Florida Native, and Barbados Blackbelly. These breeds have consistently been more resistant to trichostrongyle infections than temperate breeds, such as Dorset and Rambouillet. The objective of this study was to evaluate differences between blood packed cell volume (PCV), parasitic nematode eggs per gram of feces (FEC) and FAMACHA scores of Ghezel breed and Ghezel-Baluchi crossbreds and determine that which group is more probable resistant to nematode parasites.
Material and Data were obtained from 24 one year-old lambs belonging to two genetic groups. Genetic groups including Ghezel (n= 12) and Ghezel-Baluchi (n=12) crossbreds. Ghezel × Baluchi group was containing 50% of Ghezel breed and 50% of Baluchi breed. Samples were collected at two different times on the 2012/2/19 and 2012/3/4 in the Khalat pooshan research station, Tabriz, East Azerbaijan. All lambs were born in the winter of 2011 and they were not given anthelmintic before and they were at the same environmental conditions. Fecal samples were collected directly from the rectum of animals and samples were tested by the method of Clayton Lane. The FEC were obtained for nematodes of Nematodirus (spp.), Marshallagia(spp.), Trichuris(spp.) and unknown nematode eggs. The other measured traits included body weight, PCV and Famacha test. All data except PCV were analyzed by the MIXED procedure of SAS software.Birth weight and blood packed cell volume were analyzed by the procedure of the GLM.
Results showed that the effect of the genetic group on nematodes eggs per gram of feces and Famacha test was significant (P The Ghezel-Baluchi crossbred ewes appeared to be more resistant to infection than the Ghezel breed in natural grazing condition. Crossbreeding of Ghezel and Baluchi sheep breeds increased resistance to internal parasites of the traits measured in this study. As a general conclusion, this research attempted to find resistance traits in relation to domestic parasites in the domestic environment. These characteristics have been investigated by veterinary parasitologists for many years, but animal breeders also need to consider the issue of improving the genetic resistance of sheep to nematodes, and more precisely how they measure the relevant traits and expressions to use in selection of breeder rams and ewes. It seems that crossbreeding of the Ghezel sheep breed with Baluchi breed increases the relative resistance to internal parasites in terms of Famacha, EPG and PCV as measured in this research. In the future there are two needed subjects in this area of animal science: a) to do more investigations to find exactly genetic explication for the relative superiority of crossbreds to pure breeds; and b) the discovery of the nature of the polygonal or non-additive nature of genetic resistance to nematodes in small ruminants.