Abstract
Simple SummaryCorn straw (Zea mays, CS), rice straw (Oryza sativa, RS), and wheat straw (Triticum aestivum, WS) are the three main crop straws worldwide. Few studies on indigestible neutral detergent fiber (iNDF) and total-tract digestibility (TTD) of crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) of these crop straws are available, which limits their utilization in dairy diets. Here, we compared the ruminal degradability, iNDF288 content, intestinal digestibility, and TTD for the CP, NDF, and ADF of these three crop straws with alfalfa hay (Medicago sativa, AH) and corn silage (Zea mays, CSil). The results showed that CS, RS, and WS had higher ruminal potential NDF degradation, intestinal digestible CP, and lower iNDF288 content compared to AH. Greater accuracies for regression equations capable of predicting the iNDF288 content and TTD were also generated based on chemical composition and ruminal degradation kinetics. Incorporating this information into rations could improve our ability to optimize the utilization of main crop straws in balanced dairy diets.Three main crop straws including corn straw (Zea mays, CS), rice straw (Oryza sativa, RS), and wheat straw (Triticum aestivum, WS), and two forages including alfalfa hay (Medicago sativa, AH) and corn silage (Zea mays, CSil) were analyzed in order to compare their ruminal degradability, indigestible neutral detergent fiber (iNDF), intestinal digestibility (ID), and their total-tract digestibility (TTD) of crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) using both an in situ nylon bag technique and a mobile nylon bag technique. The forage samples were incubated in the rumen for 6, 12, 16, 24, 36, 48, 72, and 288 h, respectively, to determine their ruminal degradability. Prior to intestinal incubation, forage samples were incubated in the rumen for 12 h and 24 h to determine the ruminal degradable content of CP, NDF, and ADF, respectively, and for 288 h to determine their iNDF288 content. Residues from the ruminal undegradable fractions (12 h for CP, 24 h for NDF and ADF) were subsequently inserted into the duodenum through a cannula to determine their intestinal digestible content. Here, the TTD of CP, NDF, and ADF were determined as the ruminal degradable content + intestinal digestible content. The results showed that AH had the highest iNDF2.4 (calculated as acid detergent lignin content × 2.4) and iNDF288 values (379.42 and 473.40 g/kg of NDF), while CS and CSil had the lowest iNDF2.4 values (177.44 and 179.43 g/kg of NDF). The ruminal degradability of CP, NDF, and ADF for CS, RS, and WS were lower than those of AH and Csil during the first 48 h of incubation. The potential degradation fraction of CP, NDF, and ADF for CSil was the highest; CS, RS, and WS were intermediate; and AH was the lowest (p < 0.05). CS, RS, and WS had a lower intestinal digestibility with respect to their rumen undegradable content of NDF (p < 0.05), and lower TTD of CP, NDF, and ADF (p < 0.05) compared to AH and CSil. General regression equations with satisfactory accuracy (R2 ≥ 0.828) were derived to predict iNDF288 and TTD based on their chemical compositions and the ruminal degradation kinetics of different forages. Incorporating this information into rations could improve our ability to optimize main crop straws utilization and milk production.
Highlights
Corn straw (Zea mays, CS), rice straw (Oryza sativa, RS), and wheat straw (Triticum aestivum, WS) are the main crop straws due to the fact that corn, wheat, and rice are the main grain crops consumed worldwide [1]
The nutritional value of crop straws was reported to be low due to their low contents of crude protein (CP), metabolizable energy (ME), minerals, and vitamins, and high contents of polysaccharides, lignin, and silica content, which may restrict their use as feed for ruminants [11,12,13]
Raffrenato et al analyzed more than two hundred samples of several forage species from Australia and South Africa; the results indicated that the lignin and indigestible neutral detergent fiber (iNDF) were highest in legumes and C3 forages on neutral detergent fiber (NDF) basis [48]
Summary
Corn straw (Zea mays, CS), rice straw (Oryza sativa, RS), and wheat straw (Triticum aestivum, WS) are the main crop straws due to the fact that corn, wheat, and rice are the main grain crops consumed worldwide (with a production of 1125, 775.8, and 505 million metric tons, respectively, in 2020–2021) [1]. The lactational performance of dairy cows and the total-tract apparent digestibility of all the nutrients significantly decreased when replacing the alfalfa hay (AH) with corn stover and RS as the main forage (30% of DM diet) of isonitrogenous diets [14]. Similar milk yield and total-tract digestibility (TTD) were observed when the dairy cows were fed equivalent concentrations of neutral detergent fiber (NDF) from corn silage (CSil), AH, WS, and corn stover (50.8–101 g/kg of diet DM) [12]. Different forages vary in their digestibility of NDF, which is the most important trait in feed value determinations, and dominate the variability in total diet digestibility, helping in predicting DMI and lactating performance of dairy cows [16,17,18]. Forage is important in ruminant nutrition, as a source of ME and contains sufficient physically effective neutral detergent fiber (peNDF) to stimulate rumination and saliva production, which buffers the rumen and promotes rumen health [19]
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