Effect of grain processing and silage on microbial protein synthesis and nutrient digestibility in beef cattle fed barley-based diets.
Effects of the extent of grain processing and the percentage of silage in barley-based feedlot diets on microbial protein synthesis and nutrient digestibility were evaluated using four steers (initial BW of 442 +/- 15 kg) with ruminal and duodenal cannulas. The experiment was a 4 x 4 Latin square with four periods of 21 d each. Dietary treatments were arranged as a 2 x 2 factorial with two levels of barley silage (20 and 5% DM basis) and two degrees of barley grain processing (coarsely and flatly steamrolled to a processing index [PI] of 86 and 61%, respectively). The PI was quantified as the volume weight of the barley grain after processing, expressed as a percentage of the volume weight prior to processing. Digest a flow (Yb) and microbial (15N) markers were continuously infused into the rumen for a period of 13 d. Ruminal, duodenal, and fecal samples were collected at various times over the last 6 d of marker infusion. Diurnal ruminal pH was measured for 48 h. Intake of DM averaged 1.8% of BW, and was not different among the dietary treatments (P > 0.10). Ruminal starch digestibility was higher (P < 0.05) for the more extensively processed grain and tended (P < 0.10) to be highest when the more extensively processed grain was combined with 5% barley silage. In contrast, ruminal fiber digestibility for the 5% silage diets was reduced (P < 0.05) when the grain was more extensively processed. There was, however, no effect of grain processing on ruminal OM digestibility (P > 0.10), and hence, no inhibitory effect on microbial N flow to the intestine (P > 0.10). There was also no effect of the level of silage on microbial N flow (P > 0.10), but there was a tendency for improved efficiency of microbial protein synthesis for the 20% silage diets (P = 0.072). Ruminal escape of nonmicrobial N (P = 0.003) was greater, and thus, protein flow to the intestine was greater for the 5% silage diets. Diurnal ruminal pH was lower (P < 0.05) for 11 of the 24 hourly time points in steers fed the 5% silage diets than those fed the 20% silage diets. In conclusion, barley grain rolled to a PI of 86 to 61% and combined with 20 and 5% barley silage had little effect on microbial protein supply. Microbial protein supply was not inhibited when the barley grain was extensively processed (PI of 61%) and the silage was limited to only 5% of the diet DM, but feed intake of steers in this study was lower than would be expected in the feedlot.
Agriculture and Agri-Food Canada, Research Centre, Lethbridge, AB, Canada T1J 4B1. koenig@agr.gc.ca
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Koenig
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Beauchemin
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Rode
D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001419:Bacteria / Q000378:metabolism; D001426:Bacterial Proteins / Q000096:biosynthesis; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary*; D004040:Dietary Carbohydrates / Q000378:metabolism; D004063:Digestion; D004386:Duodenum / Q000378:metabolism / Q000382:microbiology; D004435:Eating; D005511:Food Handling / Q000379:methods*; D001467:Hordeum; D008297:Male; D009584:Nitrogen / Q000378:metabolism; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism / Q000382:microbiology; D012820:Silage
D001426:Bacterial Proteins; D004040:Dietary Carbohydrates; D009584:Nitrogen