Intake, partial and tract total digestibility, microbial protein synthesis and metabolizable protein requirements for maintenance of Nellore bovines / Consumo, digestibilidades total e parcial, produção microbiana e exigências de proteína para mantença de bovinos Nelore

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Two trials were conducted from May to November 2004. Each experimental period lasted 15 days nine for diet adaptation and six for collections. In the first experiment, twelve Nellore of three sexual categories (four heifers, four bulls and four steers) averaging 15 months of age and body weight of 235, 249, and 239 kg, respectively, were assigned to a completely randomized design with a 2 x3 factorial arrangement (two levels of concentrate 25 or 50% and three sexual categories) to evaluate intake, partial and total tract digestibility of nutrients, microbial protein synthesis and ruminal metabolism. The estimation of both fecal excretion of DM and duodenal DM flow was done using chromium oxide. The collection of ruminal fluid was done at and 2, 4, and 6 hours after-feeding to determine pH and ammonia concentration. Ruminal samples for bacterial isolation also was collected 6 hours post-feeding. With the exception of EE, no other significant effect of concentrate levels and sexual categories was observed on intake and partial or total tract digestibility of nutrients. The intakes of DM, OM, EE, CP, TDN (kg/day) and DM (% BW or g/kg075) were neither affected by the concentrate levels nor by sexual category. Increasing dietary concentrate levels decreased NDF digestibility. Average bacterial N contents ranged from 6.91 to 7.39. No significant effect of concentrate levels and sexual category was observed on duodenal flow of nutrients and microbial efficiency excepted when expressed as MicN/kgOMDR. Maximum ruminal NH3 concentration (14.55 mg/dL) was estimated at 1.83 hours after-feeding. It was concluded that increasing dietary concentrate levels did not affect intake, partial and total tract digestibility of most nutrients and microbial protein synthesis. In the second experiment, twelve Nellore bovines fistulated in the rumen and duodenum were allotted to three Latin squares (four animals, four CP levels: 7, 10, 13, and 15% and four periods) to evaluate the intake, partial and total tract digestibility of DM, OM, CP, EE, NDF, and NFC, microbial protein synthesis, ruminal metabolism, nitrogen balance and metabolizable protein requirements for maintenance. The samples were ruminally incubated in each sexual category to estimate total tract digestibility of ingredients. The collection of ruminal fluid was done at and after-feeding to determine pH and ammonia concentration. Ruminal samples for bacterial isolation also was collected at and 6 hours post-feeding. The urea concentrations were estimated in the urine (UU) and blood serum (US). Estimation of fecal DM output and duodenal DM flow was done using the internal marker indigestible acid detergent fiber. Total collection of urine was conducted from day 13 to day 14 on each period. Metabolic fecal nitrogen, urinary endogenous losses and total endogenous losses were all estimated using a regression approach. Para nenhum dos consumos dos nutrientes, houve efeito significativo da interação quadrado latino (condição sexual) e níveis de proteína nas dietas. With the exception of EE and NFC, no other significant effect of dietary CP levels on daily intake of all nutrients was observed. Increasing dietary CP levels affected (P<0.05) total tract digestibility of DM, OM, CP, NDF, and NFC digestions and also resulted in higher concentrations of US, NUS, and UU. Differently from pH results, significant effect (P<0.05) of dietary protein levels x collection times interaction on ruminal NH3 was observed. With the exception of CP, significant effects of sexual category neither on intake, total tract digestibility of nutrients, microbial protein synthesis nor on ruminal digestion were observed. It was concluded that increasing dietary CP levels affected intake and total tract digestibility of most nutrients. Significant effect of sexual category was observed only for N intake that was greater for steers than heifers. Nitrogen intake, urinary and fecal N excretions and N balance all increased linearly when the dietary CP varied from 7 to 15%. It was observed NMF of 6.69 of N/kg ingested DM and NUE of 0.133 g N/kg0.75. The net protein requirement was estimated as 0.431 gN/kg0.75 or 2.69 g of protein/kg0.75. No effect of sexual categories on metabolizable protein requirements for maintenance (approximately 4.0 g/kg0.75) was observed in this trial.

ASSUNTO(S)

níveis de concentrado intake concentrate levels nellore bovines performance registers consumo registros de desempenho nelore nutricao e alimentacao animal

ACESSO AO ARTIGO

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