Anita Stevnebø defended her PhD thesis on December 18th 2009

Ane Gro Siri Skjelfjord

Barley varieties (Hordeum vulgare L.) with different proportions of amylose - Effect on starch degradation characteristics and performance of monogastrics and ruminants

Starch structure is considered to affect the rate of starch digestion of cereals, and is therefore an important factor to consider when optimizing starch quality in cereals for animal feeds. The main aim of the present thesis was to reveal possible effects of amylose content, starch particle size distribution and amylose-lipid complex content in barley on the digestion of starch in monogastrics and ruminants.

Twelve barley cultivars with low (LA: Candle; Alamo; Cindy; Cinober), normal (NA: Kinnan; Fager; Olsok; Thule) and high (HA; StS 2-11; SW 2904; HA-d; Glacier) amylose proportions were used in the experiments. Starch was isolated from the cultivars, and large (A) and small (B) starch granules were separated. The present work was divided into in vitro experiments for both monogastrics and ruminants (Paper I and III, respectively), followed by in vivo experiments with broiler chickens (Paper II) and dairy cows (Paper IV) to verify the in vitro results obtained.

In the enzymatic in vitro experiment (Paper I), a significantly higher degree of starch hydrolysis (DSH) was observed with LA barley compared to NA and HA for both milled barley grains and pure starch fractions. A significantly higher DSH with B granules compared to A granules was also observed, and was related to the higher surface area in relation to volume for B granules, and to a lower crystallinity. Also within the A and B granules, LA starches had significantly highest DSH. Amount of small particles per vol% was measured by Coulter Counter, and found to be highest in HA barley cultivars. The amylose-lipid complex content was determined by Differential Scanning Calorimetry (DSC), and was lowest in LA cultivars, as expected. The negative effect of barley amylose level on starch degradation that was observed in vitro was not confirmed in the in vivo experiment with broiler chickens, fed wheat-barley based diets (34% barley) with three different amylose levels of barley. In fact, the NA diet had the significantly highest total tract digestibility, compared to LA and HA diets, of which may be related to confounding effects with other feed components, such as beta-glucans. The results imply that the differences observed in vitro may be too small to be of practical importance. The amylose-lipid complex that was formed by adding akofeed fat to the diets reduced the jejunal starch digestibility. Despite the fact that amylose-lipid complex formation is facilitated by heat, the level of amylose-lipid complex was higher in pelleted diets compared to expander treated diets, and high amylose level in barley did unexpectedly not lead to higher formation of amylose-lipid complex.

In the gas in vitro study (Paper III), accumulated gas production was measured during fermentation in rumen fluid and buffer solution for 72 hours, and effective rate of fermentation (kd) was predicted from the gas curves obtained. The results showed a significantly higher effective kd for LA barley compared to NA and HA barley cultivars when incubating milled grains (P=0.010). The ranking of the cultivars were similar with incubated pure starch (LA>NA>HA), but the differences were only numerical. There was no significant difference between A and B granules in effective kd. Due to long lag phase with incubated pure starch, of which we expected would underestimate the effective kd, the effective kd of neutral detergent solubles (NDS) was estimated. This was done by substracting the NDF gas curves from the total gas curves. Effective kd did not differ significantly between amylose groups with NDS (P=0.366). The effective kd of aNDF, however, was significantly higher for LA cultivars compared to NA and HA cultivars, of which corresponded to the results obtained with milled grains. This implied that there may be other factors than starch structure per se that influenced the differences between barley cultivars in the effective fermentation rate. Results from the in vivo experiment (Paper IV) with rumen fistulated dairy cows, fed roller milled barley or maize (4x4 Latin square design), confirmed the results of non-significant effect of amylose level on starch digestion in vitro. Neither dry matter intake, nor intake of individual feed ingredients, differed significantly among barley cultivars. Ruminal digestibility of starch was not affected by amylose level, and accordingly VFA concentration and ruminal pH was unaffected by barley cultivar. Feeding maize, however, resulted in lower VFA concentration and higher ruminal pH compared to barley. Small and non-consistent effects of treatment on supply of nutrients for milk production were confirmed with non-significant effects of barley cultivar or maize on milk production and milk composition.

Updated: 23.12.09
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