Title: Soyhull energy availability when fed alone or in forage mixtures
Abstract: Three experiments were conducted to examine the digestibility and/or metabolizability of energy of soyhulls (SH) when fed as varying fractions of forage diets. In expt. 1, SH were fed ad libitum to mature ewes as 0, 25, 50, 75, and 100% of the diet with the balance as chopped millet straw &/or supplement in a replicated incomplete block design (2 ewes/treatment, each of 3 periods). Diet nutrient intakes and fecal outputs were measured by 7-d balance and methane with 2-d opencircuit chambers. In expt. 2, SH were fed ad libitum to 55 kg wethers in a randomized complete block design with 2-periods and 4 SH levels in the diets (0, 33, 66, and 100%), the balance being chopped alfalfa hay. Particle passage rates were determined by single dose of Yb (SH), Cr-mordant (alfalfa) and C0-EDTA (liquid) at the beginning of 7-d digestion trials. During expt. 3, the kinetics of SH digestion was measured in situ, by incubations in the rumen of cannulated steers fed either SH or alfalfa with or without buffer. When SH were fed with varying ratios of straw (expt 1) intake increased linearly (P < 0.01) from 43 to 89 g/BW.75 as SH level increased. Nutrient digestibilities and ME increased linearly (P < 0.01) to a maximum when the diet contained 75% SH, and then declined (quadratically, P < 0.05) as SH increased to 100%. Energy yielding nutrient digestibilities of the SH/alfalfa mixtures (expt 2) exhibited similar positive associative effects to those in expt. 1, with linear increases, then quadratic decreases in DE (P < 0.05) in response to SH level. Contrary to expectations, however, the particle passage rates of SH were not increased and did not explain the depressed digestibilities when the wethers were fed the 100% SH diet. When SH or alfalfa were incubated in the rumen of steers fed SH (expt. 3), the in situ rate of DM and NDF disappearance was markedly depressed (P < 0.05) as compared to incubation in the rumen of steers fed alfalfa. Inclusion of buffers only partially restored the digestion rates of these fibrous substrates in the rumen of steers fed SH. Thus, the cause of low availability of energy from SH fed alone is unexplained and not apparently due to accelerated particle passage and only partially due to depressed rumen pH. Additional factor(s) such as an anti-quality factor e.g., tannin, are likely involved.
Publication Year: 2003
Publication Date: 2003-10-10
Language: en
Type: book-chapter
Indexed In: ['crossref']
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