Inclusion of glycerol affects broiler growth

*Dr. William A. Dudley-Cash is a poultry and fish nutritionist and has his own consulting firm in Modesto, Cal. To expedite answers to questions concerning this column, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 5810 W. 78th St., Suite 200, Bloomington, Minn. 55439, or email [email protected]

GLYCEROL is the primary byproduct generated in the conversion of vegetable oils to biodiesel. Approximately 10% of the oil is recovered as glycerol.

The production of biodiesel is relatively expensive, and the economic viability of the industry is, to a large extent, dependent on finding a market for the glycerol.

Refined glycerol has an established market for thousands of uses that vary from cosmetics and pharmaceuticals to the starting point for the synthesis of other chemicals. However, this market is quite small. The volume of glycerol from biodiesel production easily overwhelms this market.

For example, in 2007, the refined glycerol price was painfully low, approximately 30 cents/lb. (compared to 70 cents/lb. before the expansion of biodiesel production) in the U.S. Accordingly, the price of crude glycerol decreased from about 25 cents/lb. to 5 cents/lb.

There is a great deal of interest in developing new markets for crude glycerol, and the animal feed industry is one potential large-volume market.

Glycerol is a good source of energy in animal feeds. It is readily absorbed and is converted to glucose for energy production in the liver of animals by the enzyme glycerol kinase.

Some researchers have referred to glycerol as a potential replacement for feed fats; however, glycerol is clearly not a feed fat. While glycerol may have some of the physical characteristics of a feed fat (a liquid at room temperature and lubricant in pelleting), chemically and metabolically, glycerol is a carbohydrate with a nutrient contribution similar to starch.

E. Topal of the Turkish Ministry of Agriculture & Rural Affairs and M. Ozdogan of the Adnan Menderes University Faculty of Agriculture in Turkey recently published a paper in the Journal of Applied Poultry Research on the use of glycerol in broiler feeds. The objective of the experiment was to investigate the effect of glycerol inclusion on the growth performance, internal organ weights and chemical composition of the drumstick muscle in broiler chickens.

A total of 360 one-day-old Ross 308 broiler chicks were placed in 12 pens (30 birds per pen) and randomly assigned to three dietary treatments (four replicates per treatment). All broilers were fed a starter diet (0-21 days of age) and a finisher diet (22-42 days of age). The experimental treatments consisted of either 0% (GLYC-0), 4% (GLYC-4) or 8% (GLYC-8) crude glycerol added to the diet. The crude glycerol was obtained from a commercial biodiesel production facility that used sunflower, corn and soybean oil in the production of biodiesel.

The crude glycerol was analyzed to contain 82.6% glycerol, 0.03% methanol, 11.8% moisture, 0.64% crude protein, 0.1% ether extract and 4.81% ash. The metabolizable energy (ME) of the glycerol had previously been measured at 3,527 kcal/kg.

The composition of the experimental diets is shown in Table 1. The diets were formulated to provide nearly equal nutrient contents associated with the three levels of glycerol. The glycerol primarily replaced corn (starch) in the diet, with a stepwise reduction in ether extract content.

Weight gain, feed consumption and feed conversion were measured from 0 to 21 days and from 22 to 42 days of age. At the end of the experiment, 48 broilers were randomly selected for analysis of serum, carcass yields and internal organ weights (two males and two females from each pen).

The average bodyweights of the randomly sampled male and female broilers were 2,919.8 g and 2,408.7 g, respectively. The bodyweights of the selected males and females were similar to the average pen weights observed.

After slaughter, the carcasses were dissected and the internal organs (liver, kidneys, proventriculus, gizzard and heart) were weighed. The carcass without giblets was weighed to determine hot dressed yield. The weights of the internal organs relative to bodyweight were calculated. The drumstick muscle was separated from the left tibia by removing the skin, bones and connective tissue. The muscle tissue was analyzed for dry matter, ether extract, crude protein and ash.

The growth performance results are shown in Table 2. The addition of 4% and 8% glycerol significantly increased bodyweight gain during days 0-21. There were numeric increases in weight gain over days 22-42, but these differences were not statistically significant. When combined for the overall 42-day experimental period, only the 8% glycerol addition resulted in bodyweight gains that were significantly larger than the 0% glycerol control.

For feed consumption, there were numeric increases during both days 0-21 and days 22-42, but these differences were not statistically significant.

Feed conversion followed the pattern of bodyweight gain, with statistically improved values for the 4% and 8% addition of glycerol from 0 to 21 days and from 0 to 42 days.

The researchers suggested that the positive effects of glycerol inclusion during days 0-21 may have been related to undeveloped gastrointestinal organs of chicks at zero to seven days of age. Others have stated that the gastrointestinal organs secrete insufficient amounts of digestive juices and that the villi are not well developed during the first weeks of life.

Glycerol may be a source of easily digested energy. The bioavailability of glycerol in broilers is thought to be higher than other energy sources, except for oils and glucose.

The inclusion of glycerol in the diet did not affect the internal organ weights (liver, kidney, gizzard or proventriculus) of male and female broilers, with the exception of the heart weights for males receiving the 8% glycerol diet (Table 3). The relative weights of some internal organs, such as the heart and liver, are known to be related to bodyweight. The researchers concluded that the difference observed for heart weights of males receiving 8% glycerol was not a direct result of feeding the glycerol.

A significant decrease was observed in the ether extract content of the drumstick muscle in both male and female broilers consuming either 4% or 8% glycerol (Table 3), which the researchers suggested was due to decreased ether extract levels in the diets that resulted from reducing the level of corn when glycerol was added.

 

Comment

The crude glycerol used in this research was exceptionally high quality, containing more than 80% glycerol and less than 1% methanol, but the quality can vary widely.

An unrelated study of 11 crude glycerol products collected from seven Australian biodiesel producers showed that the glycerol content ranged from 38% to 96%, and some of the samples included more than 14% methanol and 29% ash. Methanol is toxic, and a level of more than 5% should be considered unacceptable.

It is imperative that the nutritionist have a robust quality control program and analyze samples of crude glycerol from all suppliers.

 

The Bottom Line

The results of this research show that high-quality crude glycerol is very effective in broiler diets at levels of 4% and 8%. The use of the crude glycerol significantly improved bodyweight gain and feed conversion, particularly during the feeding period from 0 to 21 days.

In this era of crippling feed ingredient prices, crude glycerol represents another potentially economical source of energy.

A significant increase in the relative weight of the heart in males and a decrease in the ether extract content of the drumstick muscle were interesting results that deserve more research.

 

Reference

Topal, E., and M. Ozdogan. 2013. Effects of glycerol on the growth performance, internal organ weights and drumstick muscle of broilers. J. Appl. Poult. Res. 22:146-151.

 

 

 

 

Volume:85 Issue:22