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Protein degradation in the rumen often proceeds at a rate which exceeds the ability of the microbial population to utilize the resulting breakdown products. Bacteria are the most active proteolytic organisms in the rumen, and many species of rumen bacteria are known to be proteolytic (Wallaceet al., 1985). The commonly isolated proteolytic bacteria are also able to break down peptides and amino acids, and it was assumed that they were responsible for the ruminal degradation of intact protein through to ammonia. However, studies comparing the specific activities of ammonia production between mixed ruminal bacteria and the well-known proteolytic bacteria noted that no individual bacterium had an activity which could explain the activity of the mixed ruminal culture (Russellet al., 1988). Subsequently, three gram-positive, monensin-sensitive, ammonia hyper producing (HAP) bacteria were isolated from the rumen. The present study reports the sequence of 16sr RNA for ruminal ammoniabacters of Iranian Holstein cows.

Prolactin (PRL) is a polypeptide hormones produced by cells of the anterior pituitary. The bovine PRL gene consists of 4 introns and 5 exons, located on chromosome 23. Different biological functions of PRL were subdivided into five broad categories: reproduction, osmoregulation, growth, integument, and synergism with steroids. Also, It has been shown to be important for control of mammary growth, lactogenesis and lactation (Skinkyteet al., 2005). Chung et al, (1996) showed that PRL-RsaI locus had a significant effect on milk fat percent in dairy cattle. Therefore the PRL gene was chosen as a candidate gene for milk traits in dairy cattle. The objective of this study was to evaluate the association of genetic differences in bovine PRL gene and milk fat content in Iranian Sarabi cows.

Candidate gene approaches facilitate discovering and localizing causative genes for quantitative traits and polymorphisms within selected candidate genes can be tested for association with variationin the quantitative trait (Campbell et al., 2003). Leptin is a 16-kDa protein that is synthesized and secreted predominantly by white adipocytes tissue and its expression is regulated by body fatness and energy balance. Leptin gene expressed in a variety of tissues including adipose tissue, placenta, mammary glands, skeletal muscles, gastric mucosa, brain and pituitary glands. In cattle, the leptin gene is located on chromosome 4 and consists of three exons. Several studies shown the association between polymorphism at the leptin gene and feed intake, energy balance, fertility and immune functions. It has been shown that leptin gene influences milk performance in cattle and reproduction in beef cattle(Liefers et al., 2002). Buchanan et al. (2002) described a cytosine (C) to thymine (T) substitution in exon 2 of the leptin gene of the B. taurus breeds, suggesting the existence CC, TT and CT genotypes. The aim of this study was to identify the single nucleotide polymorphism of exon 2 in Iranian Taleshi cattle.

DNA-based molecular methods have made possible genotyping of animals of any age and sex for milk and meat genes, thus providing a potentially more efficient and flexible selection tool. Among specific genes that may affect economically important traits in sheep, the Beta-lactoglobulin (BLG) locus has been extensively studied [Barillet et al., 2005]. The genotype BB of BLG seems to be associated with higher milk yield; on the other hand genotypes AA and AB seem to be superior in protein and casein content and crude yield [Garzon et al., 1992]. Another genes intensively investigated in farm animal are that of calpastatin (CAST) and calpain (CAPN). Calpastatin and calpain (CAPN) deserves special attention because of their major role in meat production. The calpain-calpastatin system (CCS) comprises a family of calcium dependent neutral proteases. The CAPNs have been shown to play the major role in post mortem tenderization in beef, lamb, and pork by degrading specific muscle structural proteins. The aim of the present study was to identify genotypes of BLG, CAST and CAPN genes in Kurdi sheep breed by PCR.

Rumen is an area with high potential for growing of diverse living organisms including anaerobic fungi. The most studies on rumen fungi focused on anaerobic fungi classified asChytridiomycetes, familyNeocallimasticaceas, while few studies have done on determination ofZygomycetesthat can be native in the rumen. The most fungi within the subkingdomZygomycotinabelong to the classZygomycetes. Fungi in this class possess some distinctive properties that contain rapid growth, nonseptate mycelium, reproduction by sporangiospores (Pittet al., 1985) and production of some hydrolytic enzymes (Vinogradovaet al.,2003). The aim of this study was microscopic examination and molecular analysis of nuclear small subunit (SSU; 18S rDNA) of ruminal fungi,Zygomycete, and its reproductive manner in sheep.