Food industry  by-product  strategies to enhance  carbohydrate  fraction  digestion  and to limit fossil energy intensive cereal  starch needs in cereal-residue diets for beef cattle

A Araba, F M Byers^*, F Guessous

 Département des Production Animales,
Institut Agronomique et Vétérinaire Hassan II, Rabat Morocco
* Animal and Natural Resources Institute, USDA ARS, BARC, Beltsville MD 20705.
(This project was supported in part by funding from USDA ARS and USAID, and the Institut Agronomique et Vétérinaire Hassan II.)

Abstract

As part of a study on strategies to limit needs for energy intensive cereal grains and enhance utilization of by-products for beef production,  a digestibility trial was conducted with  40 growing cattle given diets containing four levels of molasses (0, 20, 40 and 60% of the diet dry matter) as a replacement for ground barley grain. The basal diet consisted of chopped wheat straw (12%), barley (from 70 reducing to 21%), sunflower meal (from 7 to 2%) and urea (1%) and minerals (4%). The protein level was 15%. Digestibility coefficients for dry matter, gross energy and cell wall constituents were determined mid-way through a growth trial (from 180 to 420 kg live weight) using the "Acid Insoluble Ash" (AIA) method.  

There was a close curvilinear relationship (R²>0.93) between molasses level and the digestibility coefficients for dry matter, energy and cell wall constituents, with optimum values being observed with 40% molasses in the diet dry matter. It appears that replacing barley with molasses up to the 40% level of diet dry matter had a favourable effect on the rumen ecosystem leading to increases in the microbial breakdown of the cell wall constituents in the diet. Increasing the molasses to 60% of the diet DM tended to reduce slightly this effect, although NDF digestibility on this diet was still higher than on the barley control diet (0M).

Molasses, produced as a by-product of the sugar industry, provides important opportunities to enhance utilization of the cereal residue forage carbohydrate fractions.  This can enhance production of meat and milk with lesser environmental impacts, reflecting the reduced fossil energy needed when there is less cereal grain in the diet.

Keywords: Cell wall constituents, barley, molasses, digestibility

Introduction

Most studies conducted for selecting energy supplements for forage-fed animals were designed to compare starchy with fibrous feeds (Archimede et al 1996; Horn et al 1991; Chan et al 1991; Sanson 1993) and to assess effects of starch on animal performance and intake (Villalboa and Provenza 2000).  Limited research has been conducted to investigate the effect of substitution of molasses (sugars) for barley (starch) on forage or diet utilization.  There is controversy regarding the effect of molasses on the digestibility of diet components. A beneficial effect was observed by Greenwood et al (2000) and Huq et al (1996). In other studies, molasses was reported to depress the crude fiber digestibility of forages (Brown 1993) when it was substituted for by-products such as sugar beet pulp (Garrett et al 1989) or ensiled sisal pulp (Herrera et al 1981).  Animals fed sugar beet molasses are expected to have higher ruminal pH than when fed barley (Araba et al 2001) and as a consequence, substituting barley with molasses may reduce the expected negative associative effect of barley starch on digestion of dietary fiber fractions.  The negative associative effect involves a reduced ruminal cellulose digestion due to a less favorable ruminal environment (Satter et al 1999), i.e. lower pH, and less cellulolytic bacteria. 

The objective of the experiment reported here was to study effects of substituting molasses for barley in the diet of cattle on the digestibility of the cell wall components and of the dry matter and gross energy of the diet.
 

Materials and methods

Animals and diets

The study was done with 20 bulls and 20 heifers, of Holstein*Brown of Atlas and Holstein*Friesian genotypes, at the Gharb Experiment Station of the Hassan II Institute of Agronomy and Veterinary Medicine. The animals had been randomly allocated within sex and genotype to one of four complete diets (Table 1), which were fed in a growth trial over the live weight range of 180 to 420 kg.

The animals were individually fed in a tie-stall barn. The feed was offered ad libitum twice daily at 0800 and 1600h. Feed intake was recorded daily.  Feed samples were collected weekly for dry matter analyses.

Diet digestibility

Digestibility coefficients for dry matter, gross energy and cell wall constituents were determined mid-way through the growth trial using the "Acid Insoluble Ash" (AIA) as an internal marker (Van Keulen and Young 1978).  The collection period lasted five days.  Fecal samples were collected daily by rectal palpation from each animal.  Samples were collected the first day at 0800, the second day at 1300, the third day at 1800, the fourth day at 2300, and the fifth day at 0400.  Feed samples of each of the 4 diets were collected for 5 consecutive days starting 2 days before initiating fecal collection.  Feed and fecal samples were dried in a forced air oven at 60°C for 72 h.  Daily samples of diets and of feces were composited and ground in a laboratory mill with a 2 mm screen for subsequent ADF, NDF, and energy analyses. ADF and NDF were determined using the procedure of Goering and Van Soest (1970). Gross energy of the samples was determined by adiabatic bomb calorimetry of dried feeds and feces.

Digestibility coefficients of energy, dry matter, NDF and ADF were statistically analyzed using the SAS GLM procedure (SAS 1986).  The models included the main effects of diet, genotype and sex, and interactions.

Results and discussion

There were no effects of sex or genotype on any of the measured parameters and no interactions. The results are therefore discussed only in terms of effects of diet.

Diet composition

Sugar beet molasses is composed of soluble sugars and minerals and contains no fiber (FAO 2001), thus one effect of substituting barley by molasses was to decrease the concentration of all cell wall components in the diets (Table 2).

Digestibility coefficients       

There was a close curvilinear relationship (R²>0.93) between molasses level and the digestibility coefficients for dry matter, energy and cell wall constituents, with optimum values being observed with 40% molasses in the diet dry matter (Table 3 and Figures 1 and 2). It appears that replacing barley with molasses up to the 40% level of diet dry matter had a favourable effect on the rumen ecosystem leading to increases in the microbial breakdown of the cell wall constituents in the diet. Increasing the molasses to 60% of the diet DM tended to reduce slightly this effect, although NDF digestibility on this diet was still higher than on the barley control diet (0M).   

Figure 1: Coefficients of apparent digestibility of DM, energy, NDF and ADF for diets
with increasing levels of molasses (M) replacing barley grain

Figure 2: Relationships between level of molasses (% of diet dry matter) and coefficients
of apparent digestibility of DM, energy, NDF and ADF in low-roughage diets

There is some controversy in the literature regarding the effect of molasses on digestibility.  Fermentation conditions are known to alter digestibility of specific fiber sources and types (Varadyova et al 2000).  Furthermore, kinetics of fiber degradation vary with fiber types, (Bruno-Soares et al 2000; Sahoo et al 1999) and thus impacts of different carbohydrates on this process are expected to vary as well. Our results are similar to those of Hatch and Beeson (1972) who found that the apparent digestibility of DM and energy were significantly improved when molasses was substituted for either 10 or 15% of the maize grain in the diet.    Brown (1993) showed that supplementing hay with molasses alone or with cottonseed meal increased OM digestibility, whereas apparent digestibilities of NDF and hemicellulose were decreased, and ADF digestibility was not affected.  Also, Brown and Johnson (1991) found that sugars from molasses increased apparent DM or OM digestibility, but decreased fiber digestibility. Nguyen Van Thu and Preston (1999) observed an improved ruminal environment but no change in degradability of a fibrous feedstuff when a molasses urea cake was fed to swamp buffalo.  Petit and Veira (1994) found that, when incorporating 7.5 and 15% molasses (DM basis) in a silage based diet, DM digestibility was not affected, but ADF, NDF and energy digestibilities were reduced. Molasses included at 10, 20, 30 and 40 % of a bagasse pith based diet in replacement of maize did not have any effect on DM, OM and nitrogen digestibilities but the digestibility of the crude fiber decreased with the 30 and 40% molasses diet (Carrasco et al 1993). A reduced fiber digestibility was reported by Herrera et al (1981) when molasses was added to a basal diet of sisal pulp.

Negative associative effects of the energy source on forage digestibility have been reported by Kennedy and Bunting (1992), Satter et al (1999) and on overall energy utilization by Kirkland and Gordon (1999). Thus the evidence is conclusive that the capacity of the rumen ecosystem to digest cell wall constituents is adversely affected when molasses is added to a forage-based diet (high in cell wall constituents). There are fewer reports of effects of adding molasses to grain-based diets (low in cell wall constituents), but it appears that this can have a positive effect on cell wall digestion.

In the present study, the improvement in DM and energy digestibility was probably the direct result of increased dietary density of readily fermentable carbohydrate as the organic matter in molasses is completely digestible. However, the improvement in digestibility of the cell wall fraction is more probably the result of an improved rumen environment for cellulolysis caused by a increase in rumen pH when barley is replaced by molasses as reported by Araba et al (2001).  The other positive effect to be expected from addition of molasses to a grain-based diet, and the associated rise in rumen pH, is an increase in the numbers of rumen protozoa (Preston et al 1967). These organisms ingest large amounts of starch and the associated starch-fermenting bacteria (Jouany 1996). The resultant reduction in the rate of starch fermentation would be expected to have a positive outcome for digestion of cell wall constituents.

However, the positive effects of molasses on apparent digestibility of the gross energy and cell wall constituents of the diet were not reflected in the growth performance which was negatively related to the level of molasses in the diet (Araba and Byers 2002). These authors reported live weight gains of 0.96, 0.96, 0.72 and 0.69 kg/day, and feed conversion rates of 9.0, 9.5, 10.6, and 11.8 kg DM/kg live weight gain, for molasses levels of 0, 20, 40 and 60% respectively.  These contrasting findings support the arguments of Preston and Leng (1987) that expressing the nutritive value of a diet in terms of digestible and metabolisable energy values can be highly misleading when the feeds contain ingredients that result in markedly different balances among the critical nutrients (ie: amino acids and glucose in relation to total volatile fatty acids),  required for demanding production functions such as growth, reproduction and lactation.

Conclusions

Replacing barley with sugar beet molasses in a low-roughage diet for growing cattle led to curvilinear increases in apparent digestibility of dry matter and cell wall constituents with the optimum response being achieved with 40% molasses in the diet. However, these improvements in digestibility of the overall diet and the fibrous fraction of the diet were not reflected in animal performance, which deteriorated as the level of molasses in the diet was increased.

Molasses produced as a by-product of the sugar industry provides an opportunity to enhance utilization of the fibrous fraction, and to raise the overall energy density, of ruminant diets thus sparing the use of cereal grains. There will also be potential for indirect environmental benefits from making greater use of molasses in ruminant diets, because of the reduced fossil energy needed  to produce molasses, especially molasses derived from sugar cane, compared with grain. However, this potential will only be realised in practice when the improved supply of digestible energy at the level of the rumen is reflected in improved animal performance, which requires a concomitant improvement in the balance of essential nutrients available for metabolism by the animal.  

References

Araba A and Byers F M 2002  Environmentally friendly beef production of bulls and heifers from two genotypes fed cereal/molasses diets. Submitted to Livestock Production Science.

Araba A, Byers F M and Guessous F  2001  Patterns of rumen fermentation in cattle fed cereal/molasses diets.  Animal Feed Science and Technology  (submitted for publication).

Archimčde H, Sauvant D, Hervieu J, Ternoisa F and Poncet C  1996  Effects of the nature of roughage and concentrate and their proportion on ruminal characteristics of non lactating goats, consequences on digestive interactions. Animal Feed Science and Technology 58: 267-282.

Brown W F  1993  Cane molasses and cottonseed meal  supplementation of ammoniated tropical grass hay for yearling cattle. Journal of Animal Science 71: 3451-3457.

Brown W F and Johnson D D  1991  Effects of energy and protein supplementation on ammoniated tropical grass hay on  the growth and carcass composition of cull cows. Journal of Animal Science  69:348.
 

Bruno-Soares A M, Abreu J M F, Guedes C V M and Dias-da-Silva A A  2000   Chemical composition, DM and NDF degradation kinetics in rumen of seven legume straws. Animal Feed Science and Technology  83: 75-80.          

Carrasco E, Stuart R, Fundora O and Febles I  1993  Consumption and digestibility in sheep fed different proportions of final molasses/maize in bagasse pith rations. Cuban Journal of Agricultural Science 27 (3): 275-279.

Chan W W, Hibberd C A, Scott R R and Swenson K  1991  Corn vs. soybean hulls supplements for beef cows fed low  quality native grass hay.  Oklahoma Agricultural  Experiment Station  MP-, 134:172. Stillwater.

FAO 2001 Tropical Feeds. FAO, Rome.
 http://www.fao.org/WAICENT/FAOINFO/AGRICULT/AGA/AGAP/FRG/

Garrett J E, Guessous F and Eddebbarh A  1989  Utilization of sugar beet molasses and monensin for finishing dairy bullocks.  Animal  Feed Science and Technology  25: 11-21. 

Goering H K and Van Soest P J  1970  Forage fiber analyses : apparatus, reagents, procedures and some applications. Handbook 379, ARS, USDA.

Greenwood R H, Titgemeyer E C and Drouillard J S  2000  Effects of base ingredients in cooked molasses blocks on intake and digestion of prairie hay by beef steers.  Journal of Animal Science 78: 167-172.

Hatch C F and Beeson W M  1972  Effect of different levels of cane molasses on nitrogen and energy utilization in urea  rations for steers.  Journal of Animal Science,  35: 854-858.

Herrera F M Ferreiro, Elliot R and Preston T R  1981  The effect of molasses supplements on voluntary feed intake, live weight gain and rumen function of bulls fed basal diets of ensiled sisal pulp.  Tropical  Animal  Production  6: 178-185.

Horn G W, Bernardo D J, McMurphy W E, Cravey M D and McDaniel B G  1991  High-starch vs. high-fiber energy  supplements for stocker cattle on wheat pasture: Cattle  performance and economics.  Oklahoma Agricultural Experiment Station.  MP-, 134: 129.  Stillwater.

Huq M A, Akhter S, Hashem M A, Howlider M A R, Saadullah M and Hossain M M   1996  Growth and feed utilization in Black Bengal goats on road side grass based diet supplement with fish meal and ura molasses block. Asian-Australasian Journal of Animal Science 9 (2): 155-158.

Jouany J P  1996  Effect of rumen protozoa on nitrogen utilization by ruminants. Journal of Nutrition 126 (Supplement): 1335S-1346S.

Kennedy D W and Bunting L D  1992  Effects of starch on ruminal fermentation and detergent fibre digestion in lambs fed bermudagrass hay.  Animal Feed Science and Technology,  36: 91.

Kirkland R M and Gordon F J  1999  The metabolisable energy requirement for maintenance and the efficiency of use of metabolisable energy for lactation and tissue gain in dairy cows offered a straw/concentrate ration.  Livestock Production Science 61:23-31.           

Nguyen Van Thu and Preston T R  1999  Rumen environment and feed degradability in swamp buffaloes fed different supplements.  Livestock Research for Rural Development (11) 3.
 http://www.cipav.org.co/lrrd/lrrd11/3/thu113.htm

Petit H V and Veira D M  1994  Digestion characteristics of beef steers fed silage and different levels of energy with or without protein supplementation. Journal of Animal Science 72: 3213-3220.

Preston T R, Willis M B and Elias A 1967 Intensive beef production from sugar cane by-products 1.  Different levels of urea and molasses given ad libitum to fattening bulls as a supplement to a grain diet. Revista cubana Ciencia Agricola (Eng. ed.)   (1) :33

Preston T R and Leng R A 1987 Matching Ruminant Production Systems with Available Resources in the Tropics and Subtropics. PENAMBUL Books Ltd: Armidale NSW, Australia

Sahoo B, Saraswat M L, Haque N and Khan M Y  1999  Energy balance and methane production in sheep fed chemically treated wheat straw.  Small Ruminant Research 35: 13-19.             

Sanson D W  1993  Effects of increasing levels of corn or beet pulp on utilization of low quality crested wheatgrass hay by  lambs and in vitro dry matter disappearance of forages.  Journal of Animal Science  71: 1615-1622.

SAS  1986  General linear models.  SAS institute.  USA.

Satter L D, Jung H G, van Vuuren A M and Engels F M  1999  Challenges in the nutrition of high producing ruminants. In: Nutritional Ecology of Herbivores, H. Jung and G. C. Fahey Eds., Publication of American Society of Animal Science pp 609-646.

Van Keulen J, and Young B A  1977  Evaluation of acid-insoluble ash as a natural marker in ruminant digestibility studies. Journal of Animal Science 44: 282-287

Váradyová Z, Zeleák I, and Siroka P  2000  In vitro study of the rumen and hindgut fermentation of fibrous materials (meadow hay, beech sawdust, wheat straw) in sheep. Animal Feed Science and Technology 83: 127-138

Villalboa J J  and Provenza F D  2000  Postingestive feedback from starch influences the ingestive behaviour of sheep consuming wheat straw.  Applied Animal Behavior Science 66: 49-63.

Received 20 October 2001

Go to top