Abstract
The objective of this study was to evaluate the flow of nitrogenous compounds, protein degradability, rumen degradation of total carbohydrate and organic matter and microbial efficiency in heifers subjected to diets containing corn silage, sugarcane or Tifton. For this purpose, the 2,6-diaminopimelic acid (DAPA) technique was adopted and analytical procedures for amino acids by HPLC were adapted. Six rumen-fistulated Holstein-Zebu heifers with 480 kg of initial BW and at 24 months of age kept in individual tie stalls were assigned to two 3 × 3 Latin squares. Omasal digesta dry matter and microbial dry matter flows were determined using the isolated, purified and enriched lignin (LIPE®) and DAPA markers, respectively. Isolated bacteria from rumen showed on average 5.84 g/100 g microbial N, 0.25 g/100 g DAPA in dry matter and 44.61 DAPA:N ratio. The forage sources did not influence the flows of nitrogen compounds, except for total omasal flow and non-ammonia N in relation to N intake for the corn silage diet, for which there was an upward trend compared with the other diets. The degradation of the organic matter and total carbohydrates did not differ, averaging 6.1 kg/day and 5.2 kg/day, respectively. The studied forage sources do not influence the flows of nitrogen compounds, except for total omasal flow and non-ammonia N in relation N intake for the corn silage diet, for which there is an upward trend compared with the other diets. Protein degradability and microbial efficiency are similar between evaluated diets.
Highlights
The protein requirements of ruminants are met through the absorption of amino acids in the intestine, and 60% of these amino acids come from microbial protein synthesized from the symbiosis between animal and ruminal microbiota
The studied forage sources do not influence the flows of nitrogen compounds, except for total omasal flow and non-ammonia N in relation N intake for the corn silage diet, for which there is an upward trend compared with the other diets
Another compilation made by Valadares Filho (1995) with results of studies conducted in Brazil showed variations from 81.1 to 95.7 g/100 g as fed for dry matter and 5.2 to 8.7 g/100 g DM for total nitrogen compounds, which are consistent with the values obtained in this study, mainly because these values were obtained in tropical conditions
Summary
The protein requirements of ruminants are met through the absorption of amino acids in the intestine, and 60% of these amino acids come from microbial protein synthesized from the symbiosis between animal and ruminal microbiota. The microbial protein, whose intestinal digestibility is approximately 85% (Storm and Orskov, 1983), has a relatively constant amino acid profile, containing all amino acids, including the essential ones, in a proportion very close to the ideal, regardless of the protein composition ingested by the animal. Those selected were corn silage, due to its high content of soluble carbohydrates, which provide a good fermentation pattern, thereby placing it on the level of ideal grass and most used in ensiling processes, and Tifton hay, whose morphophysiological characteristics allow for a more uniform drying, generating a hay that maintains the quality and nutritional value of the fresh forage
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