Courtesy of the 41st Annual University of Nottingham Feed Conference
Our thanks to the author and Conference Organisers, a Committee consisting of both University and Industry colleagues.
The full paper will appear in the Conference Proceedings ('Recent Advances in Animal Nutrition - 2007', edited by Phil Garnsworthy and Julian Wiseman) published by Nottingham University Press in the autumn of 2007 www.nup.com
In the first part of this paper, a brief review and summary of data will be presented on glycerol for farm animals with emphasis on ruminants which will encompass the following topics: quality criteria for glycerol, rumen events, dietary energy value, and effects on feed intake and performance of dairy cows.
In the second part, again putting an emphasis on ruminants, the feeding value of rapeseed products such as rapeseed meal (solvent-extracted) and rapeseed cake (mechanically extracted; synonym: rapeseed expeller) will be briefly considered, because further increases in the demand for and production of glycerol will also increase the amounts of rapeseed meal and cake.
For the benefit of a fail-safe usage of glycerol in diets of all farm animals, methanol should be removed from the glycerol as far as technically possible. Glycerol inclusion levels of 50, 100 and 150 g/kg concentrate dry matter (DM) and storage of concentrates under good (15 °C and 60% relative humidity) or bad (20 °C and 70% relative humidity) environmental conditions for four or eight weeks revealed that physical quality of pellets was not affected by purity of glycerol or by glycerol concentrations of up to 150 g/kg DM.
Glycerol at different purities may help to stabilise the hygienic quality of pelleted compound feeds without compromising physical quality of pellets. Glycerol is a versatile feedingstuff in particular for ruminants but is different from propylene glycol. Data on ruminal turnover of glycerol would suggest that it should replace rapidly fermentable carbohydrates and thus, is not a direct competitor of propylene glycol. Mature cattle can consume (and like!) considerable quantities of glycerol (1 kg/d). Further, it may be speculated that the sweet taste of glycerol may improve intake of diets with inferior palatability (containing, e.g., extensively fermented silages) but this still needs to be investigated.
The net energy for lactation (NEL) concentration of glycerol for ruminants is approximately 9.5 MJ/kg. Conflicting results from trials on dairy cows indicate that more research is necessary to define conditions that allow glycerol to be used advantageously.
The most recent data indicate that complete diets containing glycerol may be (slightly) more palatable than diets supplemented with propylene glycol, thus stimulating DM intake. As greater intakes by cows did not result in an increased milk or milk component yield, processes of energy and nutrient conversion in the propylene glycol groups of these two trials likely were more efficient than those in the glycerol groups. Further labour is thus required to fully explore the potential of glycerol in dairy cow diets but type of diet and route of glycerol administration seem to play important roles.
Other rapeseed products for ruminants, such as rapeseed meal (RSM), compare well with soybean meal (SBM) for dairy cows if fed on an isonitrogenous basis.
Recent research on rapeseed meal has shown that RSM can fully replace soybean meal in dairy cow diets when fed on an approximate isonitrogenous and isocaloric basis, i.e. without considering differences in ruminal degradation and (or) amino acid pattern. Milk and milk component yields were similar for diets containing soybean meal or rapeseed meal.
Rapeseed cake needs further consideration and more reliable data because variations in the processing conditions result in varying chemical composition, particularly regarding the crude fat content and this currently hampers the prediction of its feeding value for all categories of farm animals.
The value of rapeseed cake would benefit from a standardization of the composition, because varying crude fat and crude protein concentrations makes the feeding value difficult to predict and could also affect storage stability of the cake.Author: K.-H. Südekum
Institute of Animal Science, University of Bonn, Endenicher Allee 15, 53115 Bonn, Germany