Digestibilidade total e parcial e balanço nitrogenado em bovinos em pastejo no período das águas recebendo suplementos com nitrogênio não-proteico e/ou proteína verdadeira

Abstract

<jats:p>Objetivou-se avaliar o efeito de diferentes relações entre proteína verdadeira e nitrogênio não-proteico sobre a digestibilidade, a síntese de proteína microbiana e o balanço de compostos nitrogenados em bovinos em pastejo durante o período das águas. Foram utilizados cinco novilhos mestiços Holandês × Zebu, castrados, com peso vivo inicial de 335±35 kg fistulados no rúmen e no abomaso. Os tratamentos foram: controle (somente pasto); e suplementos com ureia; com 2/3 de compostos nitrogenados oriundos da ureia e 1/3 de compostos nitrogenados oriundos da albumina; com 1/3 de compostos nitrogenados oriundos da ureia e 2/3 de compostos nitrogenados oriundos da albumina; e com albumina. Foram fornecidos 200 g/dia de proteína bruta (PB) a partir dos suplementos. O experimento foi conduzido segundo delineamento em quadrado latino 5 × 5, com cinco períodos experimentais, cada um de 15 dias. A suplementação não afetou os coeficientes de digestibilidade total nem o teor de nutrientes digestíveis totais da dieta; elevou as estimativas do coeficiente de digestibilidade aparente ruminal da PB, que migraram de negativa, no tratamento controle, para positivas, porém não diferentes de zero, nos tratamentos envolvendo suplementação. O fornecimento de suplementos elevou a concentração de nitrogênio amoniacal ruminal. O balanço de compostos nitrogenados aumentou com a suplementação. A substituição de ureia por albumina influenciou de forma cúbica o balanço de compostos nitrogenados, cuja estimativa foi maior para o suplemento com 1/3 de PB oriunda da ureia. A eficiência de síntese microbiana no rúmen não foi influenciada pelo fornecimento ou pela composição dos suplementos. A suplementação de bovinos em pastejo com fontes de compostos nitrogenados degradáveis durante o período das águas amplia a eficiência de uso do pasto, principalmente por ampliar a retenção de compostos nitrogenados no organismo.</jats:p>

Effects of varying ruminally undegradable protein supplementation on forage digestion, nitrogen metabolism, and urea kinetics in Nellore cattle fed low-quality tropical forage1

“…A mixture of pure casein (LabSynth, Diadema, São Paulo, Brazil), urea, and ammonium sulfate (53:9:1, respectively) was used as the source of RDP (Table 1). This ratio was based on a previous study conducted in tropical conditions (Costa et al, 2011), where the ratio of one-third of the supplemental N from NPN (urea:ammonium sulfate, 9:1) and twothirds of the supplemental N from true protein promoted greatest N retention in grazing cattle. Pure casein (Table 1) was selected as the RUP supplement because of its high protein content, its essentially complete digestibility in the small intestine (Wickersham et al, 2004(Wickersham et al, , 2009b, and the absence of other components (e.g., carbohydrates).…”

Performance and economic viability of protein supplementation for grazing cattle steers in the wet and dry-wet transition season

“…Even working with different supplements and protein sources, our results were similar to the experiments by Figueiredo et al (2008) and Zervoudakis et al (2002), where animals that consumed higher amounts of rumen degradable protein (RDP) via supplement had a superiority in ADG during the trial period. According to Detmann et al (2010), during the rainy period the mass of organic matter degraded in the rumen can be greater in about 80% relative to the dry period, which would expand in demand for urea (RDP) for maintaining microbial growth in the rumen.…”

“…Deficiencies of nutrients in tropical fodder are common and attempting to balance these nutrients with supplementation contributes to maintaining a standard of uniform fermentation, constant rumen fermentation and, consequently, increased availability of energy substrates (volatile fatty acids) and microbial protein (COSTA et at., 2011;PAULINO et al, 2002). However, these biological assumptions should be linked to the condition that the adoption of supplementation within the production system meets a favorable cost-benefit ratio.…”

Accuracy of the estimates of ammonia concentration in rumen fluid using different analytical methods

“…Those samples were taken at different times during the day and filtered through three layers of cheesecloth. For each sample, a 100-mL aliquot was then separated, fixed with 2.5mL H 2 SO 4 (1:1) and frozen at -20ºC (Costa et al, 2011).…”

“…Alternatively, Fenner (1965) has established the theoretical basis for N-NH 3 evaluation in rumen fluid by steam distillation in the presence of a potassium hydroxide solution. This basis has been adapted for use in the Kjeldahl distillation (KD) procedure, which has been used in several ruminant nutrition assays (e.g., Detmann et al, 2009;Souza et al, 2010;Costa et al, 2011). Nonetheless, no study has compared the accuracy of these methods in the estimation of N-NH 3 contents.…”