Mehraban Sheep Response to Monensin Applied and Physical Form of Barley Grain- Emphasis on Protein Metabolism

In ruminants, dietary manipulation such as applying feed additive or increasing fermentable carbohydrate in diet, improve rumen fermentation and enhance animal performance. Monensin, as a feed additive, increases propionate production, decreases ammonia production and protein degradation in rumen, this lead to improving energy and protein utilization. In addition, grain processing effects on starch fermentation; this could be increasing availability of energy for ruminal microorganisms. One of these processing methods is cracking barley grain. Since, monensin may be influenced on this processing and starch fermentation pattern, therefore the aim of this study, was evaluated the effects of monensin applied in diet and grain processing (cracked barley grain) on nutrients digestibility and protein metabolism in Mehraban sheep.  In this trial, 24 Mehraban male sheep with an average body weight of 52.98 ± 6.15 kg were used on 2 × 2 factorial experiment in a completely randomized design. Experimental factors were included the effects of monensin (diets containing monensin vs. without monensin) and physical form of barley grain (whole grain vs. cracked grain) as fallowing explanation. Sheep were kept in individual stalls for compatibility to the new environment and experimental conditions for 7 days. Then, were randomly divided into 4 groups (treatments) based on body weight and transferred to metabolic cages to determine the nutrients digestibility and nitrogen retention. The treatments were: Barley grain, Barley grain + monensin, cracked barley grain and cracked barley grains + monensin. Monensin was added to the related treatments in 30 mg per kg of feed intake. Determination of nutrients digestibility was conducted by directly collection of feces (in vivo method) for 14 days (the feces and urine samples were taken at the 7 final days). The experimental diets (40% forage and 60% concentrate) were offered twice in daily at morning (8:00 h) and evening (16:00 h). Urinary nitrogen, allantoin excretion, and chemical composition of feeds and feces (dry matter, organic matter, crude protein, ether extract, crude fiber and nitrogen free extract) were determined. Microbial protein synthesis was estimated by measuring the urinary allantoin excretion. Blood samples were taken on the final day (at 0 and 5 hours after the morning feeding) for determination of plasma glucose and urea concentration.  The results have shown that the physical form of barley grain significantly decreased dry matter and organic matter digestibility (P<0.05). Dry matter and organic matter digestibility in treatments with whole barley grain were 73.82 and 74.94 and in treatments with cracked barley grain were 71.58 and 72.84 percentage, respectively. Other nutrients digestibility (crude protein, ether extract, crude fiber and nitrogen free extract) were not affected by physical form of barley grain. Also, using of monensin and physical form of barley grain had no effect on dry matter and nutrients digestibility. Nitrogen metabolism parameters (nitrogen intake and % nitrogen in feces, urine and retention) were not affected by physical form of barley grain. Since, crude protein percentage in all treatments was equal, and dry matter intake was adjusted based on animal body weight and was in a similar range, therefore the nitrogen intake was similar in all treatments and there was no differences between them. But, % nitrogen retention significantly was increased by monensin using (P<0.05) and its amount were 21.23 and 26.33 (% of N intake) for treatments with and without monensin, respectively. Monensin prevents the ruminal proteolytic bacteria, and decreases ammonia production and deamination of amino acids in rumen. Thus, it prevents the loss of protein in the rumen, which result is increasing nitrogen retention. Allantoin excretion, microbial nitrogen synthesis, efficiency of microbial nitrogen and urinary urea were similar in the treatments with whole barley grains and cracked barley grains and there were no significant differences between them. Using of monensin significantly decreased allantoin excretion (P<0.05) and its value were 0.32 and 0.23 g/dl in treatments with and without monensin, respectively. Plasma glucose and urea concentrations (at 0 and 5 hours after the morning feeding) were not affected by the physical form of barley grain, monensin and treatments response. Plasma glucose and urea concentrations were 63.52, 67.88, 64.26, 65.48 mg/dl and 17.05, 15.70, 15.74, 14.75 mg/dl for treatments 1, 2, 3 and 4 at 0 hour after morning feeding, respectively. These parameters were 67.50, 66.86, 71.48, 68.06 mg/dl and 17.06, 14.04, 16.94, 14.87 mg/dl at 5 hour after morning feeding, respectively. Generally, nutrients digestibility, nitrogen retention and microbial nitrogen synthesis were not increased by physical form of barley grain. But, increased nitrogen was found by monensin in the sheep.