The concern with productive efficiency in the milk chain is obvious considering that the industry markets are increasingly competitive. The concentrates have high market value, thus one should exploit the use of forage in diets of dairy cows in order to reduce feed costs that are around 50-60 % of the total cost of milk produced. Thus, the use of roughage quality or making them highly digestible in the rumen by means of additives can improve the performance of these animals thus providing greater profitability. In an attempt to improve the fermentation profile enhancing nutrient utilization by the animal, various additives are being currently developed, among which we can cite the growth promoters (ionophore antibiotics), probiotics and fungal cultures. Latter are purified exogenous enzymes, which may have different activities, among them the one that is exposed here, fibrolytic activity. In literature there are studies showing the effectiveness of the use of exogenous fibrolytic enzymes on performance of dairy cows, increasing milk production by improved fiber digestibility, and consequently of the total diet. The scientific hypothesis to be evaluated in this project is that exogenous fibrolytic enzyme Fibrozyme® (Alltech Inc., Nicholasville, KY) positively influences improving performance, digestion and metabolism in lactating dairy cows. This study will be conducted to evaluate the use of growing doses of exogenous fibrolytic enzyme in the feed of dairy cows in an attempt to establish an ideal for this type of animal dose. Twenty-four Holstein cows that will be distributed in six Latin Squares (LS) 4x4, contemporary and balanced, with two compounds LS for cannulated cows rumen (8 cows) and 4 LS not cannulated cows (16 cows) will be used. The experiment will consist of four periods, compound for 21 days each, with the first 14 of diet adaptation and the other to evaluate the variables measured. The experimental diets are as follows: 1) Control (C) composed of a basal diet without the addition of fibrolytic enzyme (Fibrozyme ®); 2) F7,5 with addition of 7.5 g / cow/day of fibrolytic enzyme (Fibrozyme®); 3) F15 with the addition of fibrolytic enzyme 15g/cow/day (Fibrozyme®); 4) F30 with the addition of fibrolytic enzyme 30g/cow/day (Fibrozyme®). Will be evaluated its possible effect on dry matter intake and total apparent digestibility of dry matter and nutrients, fermentation and synthesis of rumen microbial protein, production and milk composition, metabolic profile and nitrogen balance.
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