Nitrogen digestion and metabolism in sheep consuming diets containing contrasting forms and levels of N

Abstract

1. Nitrogen kinetics were studied in six sheep (45-55 kg live weight) consuming either a high-N grass silage or a low-N dried grass made from swards of perennial ryegrass (Lolium perenne). The diets were fed hourly at a level of 600 g dry matter/d and supplied 19.5 and 11.0 g N/d respectively.2. The amounts of organic matter (OM) consumed and flowing at the duodenum and ileum and excreted in the faeces were similar (P > 0.05) with both diets. Each diet supplied 23 g digestible OM/d per kg live eight^''^, which was sufficient to maintain body-weight.3. There were no differences (P > 0.05) between diets in rumen fluid volume, fractional outflow rate of fluid from the rumen, total concentration of volatile fatty acids or molar proportion of acetate in the rumen. The pH and molar proportion of propionate in rumen fluid were higher (P i 0.01), and molar proportion of butyrate lower (P < 0,001) when the silage was given. 4.There was a net loss of N (4.0 g/d) between mouth and duodenum when the silage was consumed but a net gain (5.5 g/d) when the dried grass was consumed. As a result, total non-ammonia-N (NAN) flow at the duodenum did not differ (P > 0.05) between diets. Rumen microbial NAN flow at the duodenum, based on 15N as the marker, also did not differ (P > 0.05) between diets but the efficiency of microbial N synthesis in the rumen (g/kg OM apparently digested) was higher (P < 0.05) with the dried grass.5. When the sheep were consuming silage they had a higher concentration of ammonia in rumen fluid (P < 0.01), a higher rate of irreversible loss of ammonia from the rumen (P < 0.05) and a higher rate of absorption of ammonia across the rumen wall (P i 0.01). The rate of absorption was found to be more closely related to the unionized ammonia concentration in rumen fluid (r2 0.85) than to the total ammonia concentration (r2 0.36).6. Endogenous N entry into the forestomachs was calculated to be 5.5 g/d when the silage was given and 9.4 g/d when the dried grass was given, of which 1.7 and 3.5 g/d respectively were in the form of urea. Thus, approximately 4-6 g N/d were derived from non-urea materials.7. Within the small intestine the apparent absorption coefficient of rumen microbial NAN (0.72) did not differ (P > 0.05) between diets but the apparent absorption coefficient of total NAN was lower (P < 0.05) when the I silage was given, owing to a lower (P i 0.01) absorption coefficient of the non-microbial NAN fraction (undegraded feed and endogenous). 8.Within the large intestine, diet had no effect (P > 0 05) on the apparent absorption coefficients of total N (0.22) and rumen microbial NAN (0.63). 9. Plasma urea concentration, the rate of urea synthesis in the body and urinary urea excretion were higher (P < 0.001) when the silage was consumed. However, the transfer of urea to the whole digestive tract and to the post-ruminal part of the tract did not differ (P > 0.05) between diets; urea transfer to the rumen was higher (P < 0.01) when the dried grass was given.10. The results were used to construct a whole-anim...

Effect of food intake on protein and energy metabolism in finishing beef steers

“…These values are compatible with those observed using detailed 15N tracer techniques to follow digestive processes at single intakes (e.g. Siddons et al 1985). The large contribution of fermentationderived N in urine, however, obscures significant changes in the amount of available N as intake is altered.…”

Concentração plasmática de uréia e excreções de uréia e creatinina em novilhos

“…Ambas as excreções de uréia aumentaram com o teor de PB da dieta, de acordo com TOPPS e ELLIOT (1967), SIDDONS et al (1985), SUSMEL et al (1994) e HENNESSY et al (1995, e, com relação à quantidade de FDN, apresentaram comportamento semelhante, indicando que, com a diminuição da energia da dieta, ocorreu aumento da excreção de uréia, devido às maiores perdas de amônia ruminal e concentração de NUP.…”

“…Já a transferência através do epitélio ruminal ocorre, provavelmente, por difusão passiva, sendo que a camada epitelial queratinizada constitui barreira para o movimento da uréia, mas é menos efetiva para a amônia formada, pela ação da urease produzida, pelas bactérias que proliferam nas camadas epiteliais cornificadas. Então, o potencial para transferência de uréia para o rúmen é aumentado, se há alta concentração sangüínea, grande atividade de urease, baixo pH ruminal e diminuição da concentração ruminal de amônia (SIDDONS et al, 1985;RÉMOND et al, 1993).…”

Utilização de amiréias (produto da extrusão amido + uréia) com diferentes proporções de uréia: 1. consumo e digestibilidade aparente da matéria seca, fibra em detergente neutro e fibra em detergente ácido

“…As dietas também apresentavam por volta de 13% PB e as ingestões diárias de MS não diferiram entre si, apesar de numericamente serem maiores e um pouco mais heterogêneas entre si do que as encontradas neste trabalho (71,4; 64,1 e 68,8 g.kg -1 PV 0,75 para o farelo, a uréia e a amiréia, respectivamente). Essa ocorrência parece vir de encontro à afirmação de Ørskov (1992), segundo o qual o nitrogênio suplementar pode não influir no consumo de matéria seca quando a dieta apresenta teores de proteína superiores a 12%, também relatado por Siddons (1985), que trabalhando com níveis crescentes de N dietético (que não foi o caso do presente ensaio), não observaram diferenças entre ingestões de MS em ovinos.…”