Intake and digestibility in cattle fed low-quality tropical forage and supplemented with nitrogenous compounds

Isis Lazzarini,Edenio Detmann,Mário Fonseca Paulino,Cláudia Batista Sampaio,Marjorrie Augusto De Souza,Fabrício Albani Oliveira,Sebastião De Campos Valadares Filho

doi:10.1590/s1516-35982009001000024

Isis Lazzarini, Edenio Detmann + Show 5 more

Open Access

https://doi.org/10.1590/s1516-35982009001000024

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Abstract

The objective of this study was to evaluate the effects of supplementation with nitrogenous compounds on intake, digestibility, and rumen microbial synthesis in cattle fed low-quality tropical forage. Five crossbred heifers, averaging 209 kg and fitted with ruminal fistulla, were used. The animals were fed ad libitum with signal grass (Brachiaria decumbens Stapf.) hay, which had crude protein (CP) content of 5.08%, as dry matter (DM) basis. The five treatments were defined according to the increasing level of CP in the diet (0, 3, 5, 7, and 9 percentile points above the forage CP level). The supplement consisted of the following nitrogen sources: urea, ammonium sulfate and albumin (4.5:0.5:1.0, respectively). The experiment was carried out according to a 5 × 5 Latin square design, with five experimental periods. The average CP levels in the diets were: 5.28, 8.08, 9.82, 11.87, and 13.63% on DM basis. The intakes of DM, organic matter (OM), and neutral detergent fiber (NDF) showed a quadratic response according to CP levels in the diet, with maximum responses at 10.83%, 10.78%, and 10.37% CP, respectively. The digestibility coefficients of OM and NDF showed a linear-response-plateau response according to CP levels, with the plateau beginning (maximum response) at 7.93% and 7.55% CP, respectively. The average daily concentration of rumen ammonia nitrogen (RAN) was positively related with CP levels. The RAN estimate associated with the maximum DM intake was 15.33 mg/dL. It was observed that intestinal flow of microbial nitrogenous compounds and nitrogen intake became equivalent to each other at 7.13% of CP.

Highlights

Pasture is the main nutrient resource for cattle production in Brazil and stands out from other feed sources due to lower cost and practical utilization (Paulino et al, 2006)
The intakes of dry matter (DM), organic matter (OM), and neutral detergent fiber (NDF) showed a quadratic response according to crude protein (CP) levels in the diet, with maximum responses at 10.83%, 10.78%, and 10.37% CP, respectively
The average CP levels in the diets, which were calculated as the ratio of the total CP intake on the total DM intake, were 5.28, 8.08, 9.82, 11.87 and 13.63%, on DM basis, for the supplementation levels of 0, 3, 5, 7 and 9 percentile points, respectively

Summary

Introduction

Pasture is the main nutrient resource for cattle production in Brazil and stands out from other feed sources due to lower cost and practical utilization (Paulino et al, 2006). The change from rainy to dry season causes an abrupt fall in pasture production and digestibility and is the main limiting factor to animal production in the tropics (Leng, 1984). Under these conditions the nutritional deficiencies are assumed to be multiple, but the nitrogenous compounds deficiency must be considered as priority, since this implies suboptimal rumen conditions that limit microbial activity, forage intake and digestibility, and animal performance. Supplementation is the main strategy for avoiding these limitations and adjusting the nutritional imbalance in tropical pastures (Paulino et al, 2006). Supplementations endeavors to increase pasture utilization by optimizing digestion, increasing the rate of passage of indigestible residues and, as consequence, improve the total digestible nutrients (TDN) intake (Paulino et al, 2004)

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