Brewers spent grains in ruminants
The feeding of cattle represents more than 70% of the total cost of a productive system. The increase in the price of conventional raw materials in diets such as cereals makes the characterization and use of unconventional foods (by-products, crop wastes, fruits of destry, etc.) of extraordinary current and future interest. In general, these materials contain high amounts of fiber (cellulose, hemicellulose, lignin, pectins etc.) and can be reused as food for ruminants thanks to the ability of these animals to degrade fiber.
This special capacity is due to: i) The rumination, a process that helps the degradation of foods rich in fiber and consists of the regurgitation of a part of the contents of the rumen, which reaches the mouth where the animal swallows the liquid fraction and chew again and insalivate the solid fraction; ii) The extraordinary development of one of the digestive pre-stomachs of these animals, the rumen, and iii) The presence in the rumen of numerous and diverse microorganisms (bacteria, protozoa, fungi, archaea, viruses).
This ability of ruminants to degrade fibrous foods, which can not be used by other animals (monogastric) or by humans, and transform them into milk and meat makes the ruminant occupy an extraordinarily important ecological niche. In contrast, as a result of the fermentation that takes place in the rumen, ruminants contribute to the emission of greenhouse gases, mainly methane.
The inclusion of by-products and waste in the diet of ruminant has several advantages: it allows to have sources of nutrients in times and areas of scarcity and poverty of natural pastures, recycle by-products with potential to contaminate, reduce the cost of feeding animals that they consume them etc. In addition, this way of recycling by-products and waste through the feeding of livestock, can have an added value of great interest for its beneficial effect on the health and welfare of the animal and on the quality of meat, milk and derivatives Dairy products due to special components such as fatty acids and secondary metabolites with antioxidant, anti-methanogenic, antiparasitic, etc. properties. present in those waste and by-products.
The fatty acids that contain foods of animal origin have focused a great scientific interest during the last 20 years due to their relationship with the incidence of cardiovascular diseases, diabetes, overweight, etc. in the consumer. Recently, studies have been carried out that indicate that some fatty acids can be beneficial for the health of the consumer, being possible to modify the acid profile of milk fat and in the meat of ruminants through changes in the diet of the animal. Thus, the inclusion of alperujo (set of skins, bone and olive pulp and water), a by-product of the extraction of olive oil, tomato and cucumber waste, citrus pulp or by-products of brewing in the diet has been shown to decrease the amount of saturated fatty acids in goat milk and increases the unsaturated fatty acids and rumenic acid, considered healthy for the consumer. However, the complexity of lipid metabolism in ruminants and the unknowns that still exist require a great research effort to know the mechanisms of action, identify ruminal microorganisms involved in the metabolism of fatty acids and their activity, etc.
Also the inclusion of by-products and greenhouse waste (tomato and cucumber) can have an added value due to the decrease that they promote from the emission of methane, representing an alternative to strategies aimed at reducing those emissions in ruminants through the use of chemical additives or essential oils. It has been observed that diets that include tomato and cucumber waste, mixtures of tomato waste, bagasse and beer yeasts and citrus pulp can reduce (30-40%) methane production.
The sustainable production of ruminants, through food strategies that imply the use of land not suitable for cultivation or by-products, crop residues, waste, etc., may represent a decrease in the economic and environmental costs of production and allow the ruminant contribute in a very important way to the generation of nutritious and healthy foods to meet the nutritional needs of a growing world population.