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This Article Full Text (PDF) All Versions of this Article: jas.2008-1069v1 87/3/1058    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Pina, D. S. Articles by Valadares, R. F. D. Search for Related Content PubMed PubMed Citation Articles by Pina, D. S. Articles by Valadares, R. F. D.

Influence of different levels of concentrate and ruminally undegraded protein on digestive parameters in beef heifers

D. S. Pina^*,, S. C. Valadares Filho, L. O. Tedeschi^*, A. M. Barbosa and R. F. D. Valadares

^* Department of Animal Science, Texas A&M University, College Station, TX 77843-2471 Department of Animal Science, Universidade Federal de Viçosa, Viçosa, MG 36571, Brazil

luis.tedeschi{at}tamu.edu

Abstract

This experiment evaluated the effect of 2 levels of diet concentrate (20 and 40% of DM) and 2 levels of ruminally undegraded protein (RUP: 25 and 40% of CP) on nutrient intake, total and partial apparent nutrient digestibility, microbial protein synthesis, and ruminal and physiological parameters. Eight Nellore heifers (233 ± 14 kg BW) fitted with ruminal, abomasal, and ileal cannulas were used. The animals were held at individual sheltered pens of approximately 15 m² and fed twice daily at 0800 and 1600 h for ad libitum intake. Heifers were allocated in two 4 x 4 Latin square designs, containing 8 heifers, 4 experimental periods, and 4 treatments in a 2 x 2 factorial arrangement. All statistical analyses were performed using PROC MIXED of SAS. Titanium dioxide (TiO₂) and chromic oxide (Cr₂O₃) were used to estimate digesta fluxes and fecal excretion. Purine derivative (PD) excretion and abomasal purine bases were used to estimate the microbial N (MN) synthesis. No significant interaction (P > 0.10) between dietary levels of RUP and concentrate was observed. There was no effect of treatment (P = 0.24) on DMI. Both markers led to the same estimates of fecal, abomasal, and ileal DM fluxes, and digestibilities of DM and individual nutrients. Ruminal pH was affected by sampling time (P < 0.001), but no interaction between treatment and sampling time was observed (P = 0.71). There was an interaction between treatment and sampling time (P < 0.001) for ruminal NH₃-N concentration. A linear decrease (P = 0.04) over sampling time was observed for the higher level of RUP, whereas a quadratic effect (P < 0.001) of sampling time was observed for the lower level of RUP. The higher level of dietary concentrate led to greater MN yield regardless the level of RUP. The MN yield and the efficiency of microbial yield estimated from urinary PD excretion produced greater (P < 0.01) values than those estimated by either TiO₂ or Cr₂O₃, which did not differ (P = 0.63) from each other. However, all methods yielded values that were within the range reported in the literature. In conclusion, no interactions between dietary levels of RUP and concentrate were observed for ruminal and digestive parameters. Neither RUP nor concentrate level affected DMI. Titanium dioxide showed to be similar to Cr₂O₃ as an external marker to measure digestibility and nutrient fluxes in cattle.

Key Words: energy • microbial synthesis • Nellore • protein