Department of Animal Sciences

 

Making silage with shrimp or crab waste and straw.

Dale J. Evers and Diane J. Carroll
Department of Animal Sciences, Oregon State University, Corvallis, October 1996

RESEARCH QUESTION

Restrictions on field burning in Oregon have resulted in an abundance of grass seed straw. Changes in environmental laws have created a large quantity of shrimp and crab waste for which there is no readily available method of disposal. When mixed with grass straw, these high protein wastes could be incorporated into ruminant feeds in the form of silage. Ensiling fresh crustacean wastes on a daily basis is impractical, therefore, a means of preserving the waste for stockpiling before ensiling is needed. The goals of this study were to: 1) economically preserve fresh shrimp or crab waste for storage for 5 to 7 days prior to ensiling; and, 2) to identify the best combinations of waste, grass straw, molasses and inoculant to adequately ferment the silage.

LITERATURE SUMMARY Several researchers have successfully used organic acids such as propionic, formic, sulfuric, or acetic acid to preserve crab and shrimp waste. These acids are expensive and could be corrosive to processing plant equipment. Fresh crab and shrimp waste have been fermented with forages and successfully fed to sheep and cattle.

STUDY DESCRIPTION Two experiments were performed to evaluate the use of shrimp or crab waste in silage. The first experiment was designed to test two methods of preserving fresh crab or shrimp wastes for 5 to 7 days: wastes were mixed with 0, 10, 15, 20 or 25% dry molasses or 0, 2.5, 5, 7.5, 10 or 12.5% salt. The second experiment investigated mixing 7.5% salt-preserved shrimp or crab waste with 0, 10 or 20% molasses and grass straw to make a low, medium or high dry matter silage. All mixtures were tested in mini-silos (4 gallon buckets).

APPLIED QUESTIONS

What worked best to preserve the fresh crustacean wastes? Use of molasses to preserve the waste was unacceptable. Treatment of the shrimp or crab waste with 7.5% or greater salt was more effective at preserving the crude protein and minimizing odor than the molasses.

Can silage be made with the 7.5% salt-preserved wastes? None of the ensiled combinations used in our experiment adequately decreased pH. The final silage should have been less than 4.5 pH, had a lactic acid greater than 6%, and butyric acid less than .1%. It should not have smelled fishy or been moldy. The high amounts of waste used in our mixtures, the low level of carbohydrates and the high buffering capacity (CaCO3) of the shells were barriers to adequate fermentation. Below is a comparison of our mixtures with others who were able to decrease the pH.

Should I make some crustacean silage to feed my heifers? All of the variables that predict adequate fermentation are not known for this type of silage. Prior to ensiling large quantities of shrimp or crab waste, it is critical that small quantities of the proposed mixtures be made to assure that an adequate drop in pH and rise in lactic acid will occur.

Crustacean wastes silages mixed with molasses that range from 50 to 60% dry matter.
		Basis		Silage composition
Reference	Ingredients	Wet %	DM %	DM %	CP % DM	Lactic %DM	pH
Shrimp waste:
Stephenson	Shrimp waste	50	22	54.4	18.1	11.2	4.2
et al., 1991	Corn, cracked	20	32
	Cottonseed hulls	15	25
	Molasses, liquid	15	21
Evers and	Shrimp waste	48	22	49.5	11.2	1.5	7.0
Carroll, 1996	Grass straw	35	53
	Molasses, dry	17	26
Crab waste:
Stephenson	Crab waste	55	27	50.9	19.6	12.6	5.2
et al., 1991	Corn, cracked	20	34
	Cottonseed hulls	10	18
	Molasses, liquid	15	15
Abazinge	Crab waste	36	26	60.6	12.7	12.8	4.7
et al., 1993	Wheat straw	36	53
	Molasses, dry	14	21
	Water	14	- -
	Inoculant, 0.1%	- -	- -
Evers and	Crab waste	69	51	50.6	19.5	1.1	7.0
Carroll, 1996	Grass straw	11	17
	Molasses, dry	32	32

Evers, D.J. and D.J. Carroll. 1996. Preservation of fresh crab or shrimp waste. Animal Science Feed and Technology. 59:233-244.

Evers, D.J. and D.J. Carroll. 1998. Ensiling salt-preserved shrimp waste with grass straw and molasses. Animal Science Feed and Technology. Accepted 9/97.