Optimization of dietary protein to energy level for commercial emu (Dromaius novaehollandiae) production to maximize fat yield

Abstract

This research was conducted to study the optimum dietary protein and energy ratio of finishing diets to sub-adult emu birds for greater fat accretion. The research was done at African Emu Ranch in Muldersdrift, Gauteng. Twenty-six, four to five months old emu birds were reared to an average target weight of 30.72kg on a control diet containing 17% crude protein (CP). The birds were weighed fortnightly before and during the feeding trial. Dietary treatments, containing 14% and 20% CP were specially mixed by Rustia Feeds Company and proximate analysis was done to confirm the proximate composition. Crude protein (CP), nitrogen free extract (NFE) and ether extract (EE) % were determined and metabolizable energy (ME) of feed was calculated. The birds were randomly allocated into three groups of eight, and further assigned to two treatments and the control. Water and feed were given ad libitum. The feeding trial spanned eight weeks. The birds were slaughtered, and fat yield, gastrointestinal segments measurements, volatile fatty acid production and carcass weight were recorded. The fat was analyzed for lipid content and composition in terms of mono-, poly-unsaturated and saturated fatty acids. Repeated measures of ANOVA on the pre-trial growth levels as well as pre-trial average daily weight gain of the birds showed no significant differences between the groups (F=0.198, p=0.662). The growth rate and the average weight gain of the birds during the feeding trial under the respective treatments were analyzed but the results showed no statistically significant differences (i.e. no difference between subject factors’ effects (F=0.118, p=0.890). The standard variations were minimal. The average dressed out carcass weights for 14, 17 and 20 % CP groups were 16.75, 18.65 and 19.11 kg respectively. The results of the statistical analysis of the dressed out carcass weight showed that there was a significant difference between the respective groups (F=4.493, p=0.028). The percent dressed out carcass weight (or dressing percentage) between the groups also showed a significant difference (F=4.248, p=0.03). This implies that if the objective of an emu farmer is carcass production and depending on the cost of the protein, then a 20% CP diet could be fed. The variations in the standard deviations were not wide. Analysis of the results of the respective digestive segments “with and without” contents, as well as their lengths showed that there were no significant differences between the groups in terms of weight. Analysis of the volatile fatty acid (VFA) concentrations in the different intestinal segments showed no significant differences due to dietary treatments. The most abundant VFA collected from the distal and the proximal intestines was acetic acid (between 68 and 79.43 mmol). The highest concentration of acetic acid (79.43 mmol) was found in the distal ileum. The smallest volume was that of iso-butyric acid in the distal ileum. Total average fat yield (Subcutaneous fat + Skin fat + Omental fat) for the groups was 4.1, 4.2 and 4.4 kg respectively. There was no statistically significant difference in the average fat yield per group. It can therefore be concluded that, for economical production of emu oil, the birds should be finished on diets with low protein (in this case 14% CP) to energy ratio. The results of the analysis of the fat in respect of long chain fatty acids showed that there were no significant differences between the groups or treatments for all the different long-chain fatty acids. The results of the analysis of saturated fatty acids (27.74%), monounsaturated fatty acids (51.80%), and polyunsaturated fatty acids (20.45%) indicated that there were no significant differences between the treatment groups. The results of the analysis of lipid content indicated that the effect of anatomical location on the lipid content tended towards significance (p=0.064). The total mean lipid content in the omental and subcutaneous locations were 82% and 92.5% respectively. However the treatment and location/treatment effects were found to be insignificant (p=0.29 and p=0.719). The overall lipid content of the fat averaged 87.4%. It may be concluded that, considering the cost of protein, if the farmer’s objective is carcass production, then the birds could be finished on diets with a high protein to energy ratio. However, if the farmer’s objective is emu oil production, then diets with a low protein to energy ratio should be fed. Copyright