Barley grain for ruminants: A global treasure or tragedy

Abstract

Barley grain (Hordeum vulgare L.) is characterized by a thick fibrous coat, a high level of ß-glucans and simply-arranged starch granules. World production of barley is about 30 % of that of corn. In comparison with corn, barley has more protein, methionine, lysine, cysteine and tryptophan. For ruminants, barley is the third most readily degradable cereal behind oats and wheat. Due to its more rapid starch fermentation rate compared with corn, barley also provides a more synchronous release of energy and nitrogen, thereby improving microbial nutrient assimilation. As a result, feeding barley can reduce the need for feeding protected protein sources. However, this benefit is only realized if rumen acidity is maintained within an optimal range (e.g., > 5.8 to 6.0); below this range, microbial maintenance requirements and wastage increase. With a low pH, microbial endotoxines cause pro-inflammatory responses that can weaken immunity and shorten animal longevity. Thus, mismanagement in barley processing and feeding may make a tragedy from this treasure or pearl of cereal grains. Steam-rolling of barley may improve feed efficiency and post-rumen starch digestion. However, it is doubtful if such processing can improve milk production and feed intake. Due to the need to process barley less extensively than other cereals (as long as the pericarp is broken), consistent and global standards for feeding and processing barley could be feasibly established. In high-starch diets, barley feeding reduces the need for capacious small intestinal starch assimilation, subsequently reducing hindgut starch use and fecal nutrient loss. With its nutritional exclusivities underlined, barley use will be a factual art that can either matchlessly profit or harm rumen microbes, cattle production, farm economics and the environment.

Figure 1

Top: Varieties of two-rowed and six-rowed barley. Bottom: Whole barley (right), naked or hull-less barley (middle) and pearled barley (left).

Figure 2

Available energy for 18 samples of barley fed to livestockad libitum(Adopted from[10]).

Figure 3

Rumen dynamics of processed barley compared with other cereals. Barley has one of the fastest degradation rates, preceded only by dry-rolled wheat.

Figure 4

Circadian and post-feeding rumen pH and total volatile fatty acid patterns in 8 cows fed a barley-grain based high-concentrate mixed ration once daily at either 0900 h or 2100 h[38],[48].

Figure 5

Top right: The slower rate of dietary energy vs. protein fermentation. Top left: Relationships among rumen pH, differential volatile fatty acids and lactate concentrations and prevalence of cellulolyric versus amylolytic bacteria. Bottom: Rumen release of rapidly (A, X), moderately (B, Y) and slowly (C, Z) degradable carbohydrates and nitrogen fractions over time for microbial mass yield. The AX and BY curves would represent post-feeding fermentation patterns of barley and corn respectively ([1,5,12,54,55]). Increased asynchrony of carbohydrate and protein release and prolonged rumen acidosis can make a tragedy from the treasure barley.

Figure 6

Ruminal lipopolysaccharides (LPS, log10 endotoxin units/mL; Figure A), haptoglobin (Hp; Figure B), and serum amyloid-A (SAA; Figure C) in steers fed chopped alfalfa hay only (days −2 and −1) and barley-wheat based pelleted concentrate (days 1 to 5). Diet 1 = 4 kg of barley-wheat pellets and 6 kg of chopped alfalfa hay offered daily; Diet 2 = 5 kg of barley-wheat pellets and 5 kg of chopped alfalfa hay offered daily; Diet 3 = 6 kg of barley-wheat pellets and 4 kg of chopped alfalfa hay offered daily. Different letters declare statistical significance. Daily duration of time at which pH was below 5.6 (as an indicator of subacute rumen acidosis) was 42, 117, and 134 min/d for Diets 1, 2, and 3, respectively [42].