Abstract:
Animal Production in Australia 1998 Vol. 22 DEVELOPING A PELLETISED FEED FOR FARMED SALTWATER CROCODILES R. J. MAYER and S. K. J. PEUCKER Dept of Primary Industries, PO Box 1085, Townsville, Qld 4810 Crocodile farms in Australia use a variety of fresh meat (beef, kangaroo, chicken, pork, horse) and occasionally fish to feed their grower stock. These diets all need to be supplemented with vitamins and minerals. Using fresh meat requires high transport, freezer storage and manual labour costs (eg cutting up frozen meat, mincing and mixing with additives). Also, the hot, humid conditions in which crocodiles are reared in Northern Australia is conducive to spoilage of meat and potential disease problems. Other industries which rear animals intensively (pigs, poultry) have long ago developed pellet diets based on optimal nutritional profiles and least-cost formulations. The aim of this research was to develop and evaluate a pelleted food for juvenile saltwater crocodiles (up to one year of age) using specific research facilities established at the QDPI veterinary laboratory in Townsville. Ridley Agriproducts Pty Ltd was a cooperator in this work and manufactured the dry food components. The research facility, with 12 independent tanks and carefully controlled environments, supported a replicated design. Because there was such a large variation in size of the six month old animals at the start of this work (130 to 860g), and the larger animals in any group display aggressive social behaviour, it was necessary to divide the animals into two size classes within each experiment. In the first experiment the basic raw ingredient was a dry mash consisting of a variety of animal based products, with plant ingredients kept to a minimum because of concerns with digestion. This was formed into a mash pellet by first mixing with water (4:1 ratio) and putting the mix through a mincing machine. This diet was compared with a standard meat diet (minced chicken heads and kangaroo meat supplemented with vitamins and minerals) and with a 50:50 mixture of minced meat and mash. The subsequent two experiments (using the same animals but re-allocated into even groupings on liveweight) evaluated commercially produced pellets, both as a pure diet or mixed with meat. For both animal sizes growth rates for the dry product were lower than for meat (Table 1). The combined meat/dry formulations in the first two experiments produced the best growth rates among the larger sized animals. In terms of efficiency of converting food eaten into increased liveweight, Experiment 1 recorded optimal rates for the mixture while in Experiments 2 and 3 the smaller sized animals were less efficient on the pellet diet. The efficiency rates are comparable with rates of 0.26 to 0.33 (Webb et al. 1990) for saltwater crocodile hatchlings fed a daily diet of chicken heads, pork and supplements. Table 1. Response of two size groups of crocodiles (S/M = small/medium, M/L = medium/large) fed different diets in experiments (E) corresponding to growth stages 26-34, 34-42 and 42-54 weeks of age E1 (14/10 - 9/12/96) Response d cd e E 2 (9/12/96-30/1/97) Meat/pellets ab E3 (30/1-21/4/97) Meat 6.3 a 8.3 0.17 0.17 a a a Size class Meat Meat/mash Mash pellets Meat ab Pellets 2.0 a 6.4 0.14 0.23 b b a Pellets 1.3 ab 5.0 c 0.05 b 0.10 b Liveweight gain S/M 4.5 5.5 2.0 5.7 5.6 b a c a a (g/animal/day) M / L 8.8 11.0 5.6 9.0 9.8 c b c a a Food conversion S/M 0.23 0.43 0.23 0.27 0.26 A c a c a a Ratio M / L 0.27 0.53 0.29 0.25 0.28 A Liveweight gain expressed as a ratio of weight of food eaten (wet weight basis) Within an experiment values followed by a similar letter do not differ significantly (P>0.05) Emphasis of the current research has been on diet acceptance, following several years of failures of earlier harder formulations of pellets. This has been achieved but the current dry food ingredients are nutritionally no better than the current industry diets of fresh meat. Further research to address this issue is of high priority and will be pursued in collaboration with the food manufacturer. WEBB, G.J.W., MANOLIS, S.C. and COOPER-PRESTON, H. (1990). Proceedings of the tenth working meeting of the IUCN Crocodile Specialist Group, Florida, pp. 254-73. 326