Biological and chemical assessment of feed proteins before and after rumen exposure

Intestinal digestibility of amino acids in rumen undegradable protein estimated using a precision-fed cecectomized rooster bioassay: I. Soybean meal and SoyPlus

The objectives of this experiment were to measure intestinal digestibility of AA in rumen undegradable protein (RUP-AA) in soybean meal (SBM) and expeller SBM (SoyPlus, West Central, Ralston, IA; SP) and to determine if these feeds contain a constant protein fraction that is undegradable in the rumen and indigestible in the small intestine, as assumed in the French Institut National de la Recherche Agronomique (Paris, France) and Scandinavian AAT-PBV (AAT = AA absorbed from small intestine; PBV = protein balance in the rumen) models. Three samples of SBM and 3 samples of SP were obtained from the Feed Analysis Consortium Inc. (Savoy, IL). To obtain the RUP fraction, samples were ruminally incubated in situ for 16 h in 4 lactating cows, and the collected rumen undegraded residues (RUR) were pooled by sample. Subsamples of the intact feeds and RUR were crop intubated to 4 cecectomized roosters, and total excreta were collected for 48 h. Intact feeds, RUR, and excreta were analyzed for AA. Basal endogenous AA loss estimates were obtained from fasted birds and were used to calculate standardized digestibility of AA in the intact feeds and RUP-AA. Indigestibility coefficients of the intact feeds were calculated as (100 - % standardized AA digestibility), and indigestibility of the RUR was calculated as [(100 - % ruminal degradation of AA) x [(100 - % standardized RUP-AA digestibility)]/100]. Results indicated that standardized digestibility of feed-AA was similar to standardized digestibility of RUP-AA for SBM and SP samples and that standardized digestibility of individual AA differed within samples. Standardized feed-AA and RUP-AA digestibility values were lowest for Lys and Cys and highest for Trp and Met. Results also indicated that SBM and SP did not contain a constant protein fraction that was both undegradable in the rumen and indigestible in the small intestine. Indigestibility values of RUR were lower than in intact feeds, suggesting that SBM and SP contain a protein fraction that is indigestible in the intestine but partly degradable in the rumen, digestible in the intestine after ruminal incubation, or both.

Concentrados protéicos para bovinos: 2. Digestão pós-ruminal da matéria seca e da proteína

O objetivo deste trabalho foi avaliar a digestão pós-ruminal de fontes protéicas. Utilizou-se a técnica de sacos de náilon móveis introduzidos no duodeno e colhidos nas fezes. Os alimentos introduzidos no intestino foram anteriormente incubados em sacos de náilon no rúmen ou foram separados das frações solúveis em água. O farelo de soja foi a fonte protéica de maior degradabilidade ruminal (73%) e altíssima digestibilidade intestinal (98%). O glúten de milho foi a fonte protéica menos degradada no rúmen (16%) e sua parcela sobrepassante foi altamente digerida no intestino (95%). Os farelos de algodão e de mamona mostraram características semelhantes com digestibilidade total da proteína de 95% e em torno de 65% de degradabilidade ruminal. O farelo de palmiste foi menos digerido (87% digestibilidade total quando incubado). Farinhas de origem animal foram menos digeridas no intestino e também no rúmen (fora o glúten), com digestibilidades totais de 75% para farinha de carne e ossos, 85% para farinha de penas e vísceras e farinha de peixe I, 67% para farinha de peixe II e apenas 46% para farinha de sangue.

Amino acid profile of escaped feed protein after rumen incubation and their intestinal digestibility

The crude protein content and amino acid profile of seven feedstuffs (linseed meal, maize gluten meal, rapeseed meal, rapeseed meal protected, soybean meal, fullfat soybean extruded and sunflower meal) were determined before and after ruminal incubation for 16 h in three bulls with large rumen cannulas. The intestinal disappearance of amino acids was measured using mobile bag technique. Ruminal incubation affected amino acid profile of all experimental feedstuffs. Crude protein degradation varied from 29.3% for maize gluten meal to 86.4% for rapeseed meal. A tendency towards increased disappearance was observed for glutamic acid, histidine, lysine and proline and decreased disappearance for branched-chain amino acids. The intestinal crude protein digestibility was higher than > 80%, except rapeseed meal (66.4%) and sunflower meal (77.8%). The least digestible individual amino acids were methionine and isoleucine in rapeseed meal, histidine and methionine in rapeseed meal protected and arginine in sunflower meal. In general, the lowest amino acid digestibilities were found in feedstuffs with the highest fibre content. The feedstuffs show that they have different potential for supplying of limiting amino acids. Of particular value are the feedstuffs with low crude protein degradability in the rumen and high intestinal digestibility of amino acids.