Comparative Growth Characteristics of Emus (Dromaius novaehollandiae)

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1 2003 Poultry Science Association, Inc. Comparative Growth Characteristics of Emus (Dromaius novaehollandiae) L. A. Goonewardene,*,1 Z. Wang,* E. Okine, M. J. Zuidhof,* E. Dunk,* and D. Onderka* *Livestock Development Division, Alberta Agriculture Food and Rural Development, Street, Edmonton, Alberta, Canada T6H 5T6; and Department of Agriculture Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5 Primary Audience: Researchers, Emu Producers, Poultry Extension Personnel SUMMARY The objective of this study was to model the growth process, derive growth parameters in emus, compare the parameters using broilers as a benchmark, and identify opportunities to improve the efficiency of emu production. The Richard s growth model fitted the weight and age data of emu and broilers very well with R 2 estimates that were 99%. The mature weights of emus were estimated to be 49.5 kg, and broilers were estimated to be 4.6 kg. Lifetime absolute growth rate of emus was 68.4 g/d, and they matured 12.5 times slower than broilers. Inflection age and weight were 105 d and 9.8 kg, respectively, for emus and 36 d and 1.67 kg, respectively, for broilers. Because emus are slaughtered late, growth efficiency is poor, and the feed cost per kilogram of gain is high. Characterizing the growth process is a valuable strategy that could be used to selectively breed emus that grow and mature rapidly and have high gain to feed ratios. Key words: broiler, emu, growth curve, maturing rate 2003 J. Appl. Poult. Res. 12:27 31 DESCRIPTION OF PROBLEM Emus (Dromaius novaehollandiae) belong to the ratite family, which includes other flightless birds such as the ostrich, rhea, and kiwi. They are not aggressive toward people and are reared commercially for meat, leather, and oil. The emu and rhea industries in Canada are new, and in 1999, it was estimated that 61,308 emus and rheas were produced on 967 farms in Canada [1]. The average carcass weight is approximately 37 kg with 54% dress out. Approximately 60% (12 kg) of the dressed weight is muscle and 40% (8 kg) is fat [2]. Emus are reported to have a feed conversion ratio of 6:1 [3], which is less efficient than that of broiler chickens estimated at <2:1 [4]. However, the relationship between feed efficiency of emus and their lifetime growth process is not known. Broiler lines that show rapid growth, good feed conversion, and early maturity have been developed through selective breeding [5, 6], and the same may be possible with emus. The process of growth has been mathematically modeled, and equations that describe the growth of animals have been developed [7, 8]. The Richard s and Gompertz models have been shown to give good descriptions of growth in species such as cattle, elk, chickens, and emus [9, 10, 11, 12, 13]. The Richard s model is a more generalized, four-parameter function with 1 To whom correspondence should be addressed: laki.goonewardene@gov.ab.ca.

2 28 a variable inflection point that provides a more complete description of the growth process in a variety of animal species [9, 10, 11]. Such growth models (curves) can be fitted to individuals or groups, and the parameters derived from these models can be biologically interpreted, making it possible to compare growth characteristics of different individuals, groups, and species [11]. The growth and maturity parameters identify the velocities of growth, maximum body sizes, and maturing rates relative to age. Based on such information, optimal feeding and management regimes can be formulated for animals. However, little or no information on growth and maturing patterns is available for emus. The objective of the study was to model the growth process in emus and use the growth characteristics of broiler chickens as a benchmark in order to identify opportunities to improve the efficiency of emu production. MATERIALS AND METHODS JAPR: Research Report Data were obtained from two sources, a commercial emu farm (n = 36) and the Poultry Research Centre (n = 72) at the University of Alberta, Edmonton, Canada. The emu chicks were hatched over a period of 43 d in February and March Emus were raised from birth to 60 d of age on an emu starter diet that contained 14.0% CP, 12.0% acid detergent fiber (ADF), 3.57 Mcal/kg digestible energy (DE), 4.0% crude fat, 0.22% Ca, and 0.38% P. From 61 to 255 d, the birds were on a grower diet containing 16.8% CP, 17.8% ADF, 3.28 Mcal/kg DE, 7.5% crude fat, 0.92% Ca, and 0.55% P. They were weighed monthly from d 1 to 240 ± 14 d. All emus were housed in heated indoor pens at 18 C for 8 wk and then transferred to outdoor pens during the summer months. In the fall (November), the birds were placed in three pens in an unheated covered barn. The broiler chickens were raised under environmental conditions that allowed the birds to express their genetic potential for growth. The broilers were started at 35 C with the temperature decreasing 5 C per week until 18 C was reached. A temperature gradient and adequate floor area was available in the pens to allow birds to find a thermoneutral space. They were fed diets that met the NRC [14] requirements for energy and provided 105% of the recommended CP and the first five limiting amino acids: lysine, methionine, methionine + cystine, arginine, and threonine. Body weights were recorded at weekly intervals to 42 d. The diets, housing conditions, and other management practices for the two species were similar to a commercial emu and broiler operation in Canada and were cared for in a manner similar to the guidelines of the Canadian Council of Animal Care [15]. The Richard s growth model [8] was fitted to the body weight and age data of emus and broiler chickens, using the NLIN procedure of the SAS software [16]. Further, the same model was fitted to weight-age data provided for emus by Scheideler and Sell [3] under two scenarios: average management (average) or above-average management that assumed better-than-average genetic potential and moderate ambient temperature (potential). These data were used as a comparison with our (Canadian) emu data. The Marquardt iterative procedure was used to reduce the residuals and improve the fit [16]. The Richard s model derived the following parameter estimates: A = asymptote (mature weight) when time (t), b = an integration constant, k = coefficient of relative growth also called a maturing index (where a smaller value of k indicates late maturing, and a larger value of k indicates early maturing) establishing the rate at which weight (Wt) approaches the mature weight A, and m = a shape parameter that determines the time of inflection (T I ) and the weight at inflection (W I ). The time of inflection is defined as the point on the growth curve when the velocity of growth is maximum, and the weight at inflection is the body weight corresponding to the time of inflection [7]. The first derivative of the function with respect to age (dwt/dt) expresses the instantaneous lifetime absolute growth rate at time t and the general rate of change in Wt was referred to as the average lifetime absolute growth rate (AGR) [7]. The instantaneous maturing rate is the instantaneous growth rate relative to the mature weight A, and the general rate of change was the average lifetime absolute maturing rate (AMR). The relative growth rate was the instantaneous growth relative to current weight, and the general rate of change averaged over the growth curve was the average lifetime relative

3 GOONEWARDENE ET AL.: COMPARATIVE GROWTH CHARACTERISTICS OF EMUS 29 TABLE 1. Parameter estimates and growth characteristics of emus, broilers and published emu industry data based on the Richard s model Parameter/character A Symbol Units Emu B Average C Potential C Broiler D Asymptote (mature wt) A kg Constant b Maturing rate k /d Shape parameter m Time of inflection T I d Weight at inflection W I kg Absolute growth rate AGR g/d Absolute maturing rate AMR /d Relative growth rate RGR g/d Degree of maturity at T I UT I % A A = asymptote or mature weight when time (t), b = an integration constant, k = coefficient of relative growth also called a maturing index establishing the rate at which weight (Wt) approaches the mature weight A, m = shape parameter that determines the time of inflection (T I ) and the weight at inflection (W I ), AGR = the first derivative of the function with respect to age (dwt/dt), AMR = the instantaneous growth rate relative to the mature weight A, RGR = instantaneous growth rate relative to current weight, and UT I = degree of maturity at inflection (T I ). B Emu weight-age data modeled from 1 to 240 d from the present study. C Emu weight-age data (average and potential) obtained from Scheideler and Sell [3] and modeled from 1 to 270 d using the Richard s function. D Broiler weight-age data modeled from 1 to 42 d from the present study. growth rate (RGR) [7]. The degree of maturity (U) at any time on the growth curve was defined as the weight at time t relative to the mature weight A [11]. Based on the parameter estimates obtained by fitting the Richard s function, the following formulae were used to calculate the growth information: T I = k 1 lnmb, W I = A[(m 1)/m] m, AGR = 0.5Amk/(2m 1), AMR = 0.5mk/ (2m 1), RGR = mk/(m 1) and U = Wt/A [11]. RESULTS AND DISCUSSION The Richard s growth model fitted the weight and age of emu and broiler data very well with R 2 estimates that were 99%. The parameter estimates and growth characteristics for Canada emus and broilers and published data based on the Richard s growth model are shown in Table 1. The growth parameters derived for our data were similar to the estimates derived for the published data, but the Canada emus grew and matured more slowly and reached slightly higher mature weights compared to the emus in the published data. The asymptotic (mature) weight of emus was estimated to be 49.5 kg and for broilers was 4.6 kg. The body weights of emus have been reported to be about 40 kg at 64 wk of age [17], 40.6 kg at 70 wk of age [18], and approximately 55 kg at maturity [19]. The maturing rate, AMR, and RGR were 12.5, 4.4, and 8.4 times lower, respectively, for emus when compared to broiler chickens. The velocity of growth was maximum (inflection) at 105 d of age when the emus were 9.8 kg. Inflection in emus and broilers occurred when birds had reached 19.8 and 36.3% of their mature body size, respectively. In dairy cattle and elk, inflection occurs when they are approximately 24% mature [10, 11]. The AGR was 68.4 g/d for emus and 54.0 g/d for broilers. At these daily growth rates, emus would reach mature body weight at 722 d and broilers would reach mature body weight at 84 d of age. Growth rates of 111 g/d to 20 wk and 88 g/d to 64 wk of age for emus have been reported [17]. AGR values ranging from 135 to 150 g/d for elk and 264 to 455 g/d for cattle have been reported in the literature [9, 10, 11]. Based on the Richard s model, Canada emus matured more slowly and took more time to reach mature body weight than broilers (0.0037/ d vs /d). The maturing rates of cattle and elk have been reported to be /d [9] and /d [11], respectively. Based on the Richard s model, Canada emus would take approximately 584 d to reach a live market weight of 40 kg [3, 17], whereas broiler chickens would take 45 d to attain a live market body weight of 2.5 kg. At slaughter, emus would be 81% mature

4 30 and at the decelerating phase of the growth curve (i.e., beyond inflection) for 479 d, whereas based on the growth curve, broilers would be 54% mature and only 13 d beyond inflection at slaughter. The further an animal is on its growth curve beyond inflection (point of the highest growth velocity and the lowest cost per unit of gain), the higher the cost per unit of weight gain due to the increased maintenance requirements [7]. Because the emu industry average slaughter weight is about 40 kg, it is evident that emus are marketed when their growth efficiency is extremely poor. It has been recognized that the cost of weight gain is an important determinant of the total cost of production in broilers [20]. Although no feed to gain ratios were calculated in our study, literature estimates the feed to gain ratio for emus to be 6:1 [3] and 2:1 for broilers [6]. Assuming similar densities for emu and broiler feeds, an emu would need approximately g (6 68.4) of feed/d, and the total JAPR: Research Report feed required to carry an emu to a slaughter end point of 40 kg (584 d) would be 239 kg of feed. Broiler chickens, on the other hand, would need a total of 5 kg of feed to reach a slaughter weight of 2.5 kg. Thus, a single emu would consume the equivalent feed of 48 broiler chickens, yet produce only 16 times the amount of meat. Furthermore, in 584 d, at least 11 broiler cycles would be possible, assuming that the birds are marketed in 6 wk with 10 d for clean up between cycles. As the emu industry matures and the cost of producing emu chicks decreases, chick cost becomes a smaller part of the total cost of production, and, conversely, feed costs become more important. Further, the opportunity cost of tying up rearing facilities in order to raise emus to mature body weight becomes more important. Therefore, the emu industry should consider marketing birds at an earlier age closer to the point of inflection. CONCLUSIONS AND APPLICATIONS 1. Emus can achieve mature body weights of 49.5 kg, grow at an average growth rate of 68.4 g/ d from birth to maturity, and reach maximum velocity of growth at 105 d of age when they weigh 9.8 kg. 2. At inflection, emus are 19.8% mature, whereas broilers are 36.3% mature. 3. Because emus are processed at heavier weights, which are close to mature body weights, they are expected to have a high feed cost per unit of weight gain. Hence, for the emu industry to be sustainable, a premium price for meat, leather, and oil is necessary primarily to cover the cost of feed. An alternate possibility is to market birds earlier. 4. The growth process described for emus could be a valuable strategy to selectively breed emu chicks to grow rapidly over a short period with high gain-to-feed ratios and maturing rates. REFERENCES AND NOTES 1. Agriculture and Agri-Food Canada Pages 1 44 in Snapshot of the Canadian Ostrich, Emu and Rhea Industries. Agriculture and Agri-Food Canada, Ottawa, Ontario, Canada. 2. Jeffery, J. S., Emu production. Texas Agric. Ext. Serv. Texas A&M University, College Station, TX. 3. Scheideler, S. E., and J. L. Sell Nutrition guidelines for ostriches and emus. Neb Guide G A. Coop. Ext. IANR, University of Nebraska, Lincoln, NE. 4. Ingram, D. R., L. F. Hatten, III, B. N. McPherson Effects of light restriction on broiler performance and specific body structure measurements. J. Appl. Poult. Res. 9: Barbato, G. F Genetic architecture of growth parameters in chickens. Theor. Appl. Genet. 83: Havenstein, G. B., P. R. Ferket, S. E. Scheideler, and B. T. Larson Growth, livability and feed conversion of 1957 vs 1991 broilers when fed typical 1957 and 1991 broiler diets. Poult. Sci. 73: Brody, S Bioenergetics and Growth. Reinhold Publ. Co., New York. 8. Fitzhugh, H. A., Jr Analysis of growth curves and strategies for altering their shape. J. Anim. Sci. 40: Brown, J. E., J. A. Fitzhugh Jr., and T. C. Cartwright A comparison of non-linear models for describing weight-age relationships in cattle. J. Anim. Sci. 42: Perotto, D., R. I. Cue, and A. J. Lee Comparison of non-linear functions for describing the growth curves of three genotypes of dairy cattle. Canadian. J. Anim. Sci. 72: Goonewardene, L. A., R. J. Hudson, R. Weingardt, and B. Friedel Characterization of body and velvet growth in farmed wapiti (Cervus elaphus). Can. J. Anim. Sci. 78:

5 GOONEWARDENE ET AL.: COMPARATIVE GROWTH CHARACTERISTICS OF EMUS Hurwitz, S., H. Talpaz, I. Bartov, and I. Plavnik Characterization of growth and development of male British United turkeys. Poult. Sci. 70: Palmer, M., B. Phillips, and G. Smith Application of nonlinear models with random coefficients to growth data. Biometrics 47: NRC Nutrient requirements of poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC. 15. Canadian Council of Animal Care Guide to the Care and Use of Experimental Animals. Vol 1. CCAC, Ottawa, ON, Canada. 16. SAS Institute Inc SAS Stat User s Guide. SAS/STAT Version 6 Edition. SAS Inst. Inc., Cary, NC. 17. Mannion, P. F., P. B. Kent, K. M. Barram, P. C. Trappett, and G. W. Blight Production and nutrition of emus. Pages in Proc. 7th Aust. Poult. Sci. Symp. University of Sydney, NSW, Australia. 18. Frapple, P., and R. Hagan Taking the emu to market. Western Aust. J. Agric. 33: Grzimek, H. C. B Grzimek s Animal Life Encyclopaedia. Van Nostrand Reinhold Co., New York. 20. Groen, A. F., X. Jiang, D. A. Emmerson, and A. Vereijken A deterministic model for the economic evaluation of broiler production systems. Poult. Sci. 77: Acknowledgments The authors thank Garry and Sheila Boyd who collected all of the emu data on their farm.