Studies on the hatching, growth and energy metabolism of ostrich chicks : Struthio Camelus var. Domesticus
Thesis (PhD(Agric) Animal Sciences))--University of Stellenbosch, 1988.
Farming with ostriches became established as a new stock-farming activity in South Africa around 1863. Ostrich feathers were then the only commercial product of that activity and fifty years later still held fourth place on the list of exports from South Africa - after gold, diamonds and wool (Smit, 1963). However during the world depression of 1914 - 1945 the appeal of ostrich feathers vanished and the industry collapsed. Today commercial farming with domesticated ostriches (Struthi0 camelus var. domesticus), originating from a cross (Duerden, 1910; Smit, 1963, 1984) between the South African (Struthio camelus australis) and the North African ostriches (Struthio camelus camel us), is again a rapidly expanding activity in South Africa's Little Karoo. This is the only region in the world where farming with ostriches is still encountered at a commercial scale, and although relatively small in the general stock-farming scenario, it provides a livelihood for about 400 farmers who run some 150 000 ostriches. Feathers, together with ostrich leather and meat are all prominent export products that account for foreign exchange earnings of more than R30 million. In terms of monetary value the ostrich industry has grown by more than 300% over the past decade and by al most 100% in the 1ast 5 years. This high growth rate is primarily due to the steady development of the slaughter bird industry in which leather, meat and feathers account for more than 80% of the entire industry's turnover. Ostrich products, however, are primarily exclusive fashion products, of which more than 90% is exported. Because the world market is relatively small, expansion prospects for the industry are limited and sensitive to supply and demand. To ensure the industry's continued economic well-being, ostrich research pays particular attention to production techniques that will help to improve efficiency and result in better product quality and profitability. For the purpose of increased ostrich chick production, ostrich eggs are presently being incubated in large quantities (ca 200 000 eggs per annum). However, hatching success of ostrich eggs in incubators is considerably below that of natural nests, and Burger & Bertram (1981) suggested that it may be due to high humidities (63% relative humidity) commonly used in ostrich incubators. Investigations were undertaken to measure incubation temperatures and humidities during the complete course of 41 days of natural incubation in 6 ostrich nests. In addition, the water vapor conductance of the eggs was measured, as well as the incubation water loss which in other species averages 15% of the initial egg mass and has been proposed as an optimal condition for hatching success (Ar & Rahn, 1978; Rahn 1984). The natural incubation parameters measured during these experiments were adapted and applied to conditions of artificial incubation. This improved the realized hatchability from 50 to 75%. Furthermore the intensive production and finishing of slaughter birds on complete dry meal diets under feedlot conditions is a new development which contains exceptional possibilities for the industry (Swart & Kemm, 1985). Economically and biologically, efficient diet formulation has accordingly become essential for profitable slaughter bird production. The nutritional value of feed constituents for ostriches is, however, still unknown and without it effective least cost diet formulation and programming is not possible. Present growth and finishing diets for ostriches are based on energy values of the dietary components which have been derived from poultry (Blair, Daghir, Morimoto, Peter & Taylor, 1983; Du Preez, Duckitt & Paulse, 1986) and pig values (Kemm & Ras, 1981; NRC, 1973; IAFMM, 1985). This approach may, however, result in unreal estimation of the actual nutritional value of feed constituents for ostriches, so that quantification of their nutritional value has consequently become necessary. During 1985 a multi-disciplinary research programme on ostriches was initiated, the objective being to investigate the energy metabolism and the efficiency of energy utilization in growing farm ostriches. For the purpose of these experiments all ostrich chicks were incubated in an ostrich egg incubator, maintained at a dry bulb temperature of 36°C and a wet bulb temperature of 24,0 ± 1,0°C. These temperature settings were extrapolated from the natural incubation parameters measured in the six naturally incubated nests (Swart, Rahn & De Kock, 1987; Swart & Rahn, 1987). An important aspect of the studies on energy metabolism was to determine the extent to which plant fibre is digested in various segments of the gastrointestinal tract of growing ostriches and whether these birds utilize the end products of fibre digestion, namely volatile fatty acids such as acetic acid, efficiently. The possible use of metabolizable energy to evaluate feedstuffs for ostriches was an initial aim of this study. Subsequently the effect of crude fibre or energy concentration on the digestibility of gross energy, energy loss as methane, heat expenditure, and the effect on the efficiency of ME utilization were investigated. Finally accretion patterns and the partition of metabolizable energy during growth were studied in the young ostrich chick. The findings of the studies on incubation aspects (Section 1) are presented in Chapter 2 and 3 and that of the metabolism studies (Section 2) are presented in Chapters 4, 5, 6, 7 and 8 of this dissertation.