J. J. du Preez

A note on growth curves for the ostrich ( Struthio camelus )

The Gompertz equation was used to compute growth curves for three groups of ostriches (Struthio camelus), from Oudtshoorn in South Africa, the Namib desert in Namibia and from Zimbabwe. All were reared under typical intensive farm conditions with ad libitum feeding. There were no significant differences in mature mass between regions but the maximum daily weight gain for males occurred later (day 163) for Oudtshoorn birds, compared with day 121 for Namibian and day 92 for Zimbabwean. Oudtshoorn females reached maximum rate of gain on day 175 compared with day 115 for Namibian and day 114 for Zimbabwean. Comparisons might prove important when planning programmes for the genetic improvement of commercial flocks, but possible influences of food composition and environment should be investigated.

RESPONSE TO LONG-TERM SELECTION FOR EGG PRODUCTION IN LAYING HENS

1. A White Leghorn line was selected for part-record hen-housed number of eggs from 1962 to 1990. Genetic changes were estimated as deviations from its unselected control line. 2. Over the first 10 generations with selection almost exclusively for number of eggs to the age of 273 d, all traits, except rate of mortality, showed significant changes. Regressions per year were: 273 d production, 3.07 eggs; 497 d production, 5.18 eggs; production from 274 to 497 d, 2.43 eggs; age at first egg, -2.33 d; mean weight of first 10 eggs, -0.82 g; body weight at 497 d, -19.02 g and rate of mortality, 0.19%. 3. Over the rest of the period increasing selection pressure for egg weight has been applied. This resulted in positive changes for this trait and no or small negative changes in egg number. 4. In general, heritabilities and genetic correlations did not change over the period of selection. The heritability of the main trait of selection, production to 273 d was 0.19 +/- 0.04 and heritabilities of egg size traits about 0.50. 5. The genetic correlation between egg production to 273 d and mean weight of first 10 eggs was estimated as -0.37 +/- 0.06 but from the observed response a realised genetic correlation of -0.97 was calculated.

True and apparent metabolizable energy values of lucerne and yellow maize in adult roosters and mature ostriches ( Struthio camelus )

In an experiment involving 30 roosters and 15 mature male ostriches the apparent metabolizable energy (ME) values, corrected for zero nitrogen retention (AME n ), were determined by balance method for maize and lucerne meal. A group of 10 roosters received maize as the sole dietary component. For the second group of 10 roosters a blend of 750 g/kg maize and 250 g/kg lucerne was prepared. The diet of the third group consisted of 500 g/kg maize and 500 g/kg lucerne meal. The ostrich basal diet consisted of 1000 g/kg lucerne, and was blended in the ratios 50 lucerne: 50 maize and 25 lucerne: 75 maize. Each dietary treatment was given to five ostriches, individually housed in metabolism crates. Food intake and excreta collection was carried out over a period of 5 days after the ostriches had been accustomed to the diets for 7 days. For roosters food intake and excreta collection lasted for 72 h after an adaptation period of 24 h. The AME n value for maize was 14·49 (s.e. 0·046) MJ/kg in roosters while in ostriches AME,, values of 14·3 (s.e. 1·81) and 14·5 (s.e. 0·845) MJ/kg for the 500 g/kg inclusion and 250 g/kg inclusion respectively were found. In roosters lucerne meal yielded AME,, values of 4·49 (s.e. 0·506) and 4·05 (s.e. 0·321) at 250 g/kg and 500 g/kg inclusion levels respectively. For the ostriches a value of 8·9 (s.e. 0·755) Mj/kg was found for lucerne. True ME, corrected for zero nitrogen retention, (TMEJ was computed by regressing gross energy output on gross energy input over all feeding levels. Maize yielded values of 14·65 (s.e. 0·0455) and 14·9 (s.e. 0·351) for roosters and ostriches respectively while corresponding values for lucerne were 4·03 (s.e. 0·118) and 8·6 (s.e. 0·296) MJ/kg. It was concluded that the ostriches were capable of digesting a high starch diet such as maize to the same extent as adult roosters but ostriches were capable of digesting a high fibre ingredient such as lucerne meal much more efficiently.

A comparative study between mature ostriches (Struthio camelus) and adult cockerels with respect to true and apparent metabolisable energy values for maize, barley, oats and triticale

1. In three successive trials with cockerels and mature ostrich males the apparent and true metabolisable energy values, corrected for nitrogen retention (AMEn and TMEn) were determined by a balance method for malting barley, oats, triticale and yellow maize. All these ingredients were used as sole dietary components with the exception of triticale for ostriches which was diluted with 440 g/kg lucerne meal. The balance trial lasted for 5 d after an adaption period of 7 d for ostriches, and 3 d after an adaption period of one day for cockerels. 2. AMEn values for cockerels of malting barley, oats, triticale and maize were 11.6, 10.48, 11.44 and 14.42 MJ/kg respectively. Significantly higher values of 14.21, 12.65, 12.60 and 14.89 MJ/kg were determined for malting barley, oats, triticale and maize for ostriches. 3. TMEn values determined by regression yielded values in ostriches of 13.92, 12.27, 13.21 and 15.22 MJ/kg for malting barley, oats, triticale and maize respectively. The corresponding TMEn values in cockerels were 11.33, 10.63, 11.82 and 14.07 MJ/kg. 4. The ostrich is capable of utilising fibre more efficiently than poultry. The higher energy values observed for the various ingredients also indicated that the non-starch polysaccharides such as beta-glucans and arabinoxylans in the more fibrous energy sources had little if any effect on the available energy of these ingredients as found with poultry. 5. The potential of ostriches to utilise the more fibrous energy sources like barley, oats and triticale allows for their economical use in diet formulation. This possibility may result in markedly lower food costs for ostriches.

Molecular divergence of Grapevine virus A (GVA) variants associated with Shiraz disease in South Africa.

Shiraz disease (SD) is a highly destructive, insect-transmitted disease of noble grapevine cultivars, such as Shiraz and Merlot, in South Africa. Earlier studies revealed that, of the three molecular groups of GVA that were detected in local vineyards, variants of group II are closely associated with expression of this disease, and variants of group III are commonly present in GVA-infected SD-negative plants [Goszczynski, D.E., 2007. Single-strand conformation polymorphism (SSCP), cloning and sequencing of Grapevine virus A (GVA) reveal a close association between related molecular variants of the virus and Shiraz disease in South Africa. Plant Pathol. 56, 755-762]. Among many GVA variants transmitted to Nicotiana benthamiana from various grapevines with different SD status, a variant of group II, referred to here as GTR1-2, was also isolated from a consistently SD-negative Shiraz plant. The genome of this variant, along with 7 other GVA variants of the 3 molecular groups, including 4 variants of molecular group II associated with strong symptoms of SD, were sequenced. Results of comparative analysis of these genomes, with emphasis on differences between GTR1-2 and other variants of molecular group II, are presented. Among the many differences that were found, a 119 nt ORF2-related fragment was discovered within the native ORF2 of a GVA variant, P163-M5. This variant was isolated from a grapevine used by local industry as a reliable positive control for SD in woody indexing. The variant induced symptoms in N. benthamina that were significantly more severe than those of other variants of molecular group II.

Protein and energy requirements of the Pearl Grey guinea fowl

The ideal protein and effective energy requirements of the growing Pearl Grey guinea fowl up to 20 weeks of age were determined according to the Edinburgh model. Guinea fowl have their highest protein requirements between 5 and 10 weeks of age. Protein requirements of females are lower than those of males up to 10 weeks of age, after which the situation is reversed. Energy requirements from 10 weeks of age are also higher for females than for males.

The estimation of endogenous excreta and the measurement of metabolisable energy in poultry feedstuffs using four feeding systems, four assay methods and four diets

Abstract 1. Four different methods (dual semi‐quick (DSQ), conventional, a true metabolisable energy (ATM) method and Farrells rapid method) were used to measure in adult roosters the apparent metabolisable energy (AME) and true metabolisable energy (TME) of four maize‐based diets with bran inclusions of 0, 200, 400 and 600 g/kg 2. Daily food intakes per bird were 75 g (or ad libitum) (H), 35 g (M) and 10 g (L). AME values determined by DSQ, conventional and Farrell methods were not different at the two highest intakes but were depressed at L intakes. ATM method often gave different values from other methods, particularly at the lowest intake. 3. The linear relationships between food intake and excreta energy yielded intercept values of 13 to 32 kJ/d for three methods; but ATM method yielded intercepts of 31 to 52 kJ/d. In a separate experiment it was demonstrated that a linear model may not be the most appropriate fit to such data. Removal of data for the 10 g/d intake yielded linear regression equation...

Comparison of metabolisable energy values of different foodstuffs determined in ostriches and poultry

Apparent (AMEn) and true (TMEn) metabolisable energy values, corrected for nitrogen retention, of wheat bran, saltbush (Atriplex nummularia), common reed (Phragmites australis), lupins, soyabean oil cake meal (SBOCM), sunflower oil cake meal (SFOCM) and fishmeal were compared in 7 successive trials using 12 mature South African Black ostriches and 10 adult Australorp cockerels per ingredient. TMEn values of 11.91, 7.09, 8.67, 14.61, 13.44, 10.79 and 15.13 MJ/kg for wheat bran, saltbush, common reed, lupins, SBOCM, SFOCM and fishmeal, respectively, were found for ostriches in comparison to lower (P<0.05) values of 8.55, 4.50, 2.79, 9.40, 9.04, 8.89 and 13.95 MJ/kg for cockerels. The higher (P<0.05) ME values for ostriches confirm that the ostrich is capable of digesting foodstuffs, especially those with high fibre concentrations such as drought-resistant fodders, more effectively than poultry. Plant protein sources could make a considerable energy contribution to diets for ostriches. It is concluded that it is essential to use energy values of foodstuffs determined using ostriches and not extrapolated values derived from poultry in diet formulation for ostriches.

A comparative study between mature ostriches (Struthio camelus) and adult cockerels with regard to the true and apparent digestibilities of amino acids

1. A study was conducted to compare apparent and true digestibility of amino acids in a high protein experimental diet between young ostriches (7 months of age) and cockerels. 2. A mean value for true digestibility of amino acids (TAAD) of 0.837 +/- 0.0073 (range 0.780 to 0.862) was derived for ostriches, compared with a mean value of 0.795 +/- 0.0258 (range 0.723 to 0.825) for cockerels. 3. True retention of dietary protein was 0.646 +/- 0.0114 and 0.609 +/- 0.0643 for ostriches and cockerels respectively. 4. Results in the present study produced evidence that the method for determining metabolisable energy values of ingredients for ostriches is also suitable for measuring the digestibility of amino acids. 5. It was concluded that accurate diet formulation for ostriches requires the assessment of amino acid digestibilities for individual ingredients, because values derived from poultry would underestimate digestibilities for ostriches.

The additivity of TMEn values of various ingredients in a complete diet for ostriches and adult roosters

The additivity and accuracy of true metabolisable energy values, corrected for nitrogen retention (TMEn), of different diet ingredients previously determined for ostriches, were evaluated by feeding an experimental diet containing a number of these ingredients to ostriches and roosters. The TMEn value of the test diet was determined with 36 young ostriches (7 months old) by a balance method of continuous feeding for 5 days after an adaption period of 7 days. The test diet was also offered for 3 days to 10 adult roosters after an adaption period of 24 h. Theoretical values of 11.69±0.189 MJ/kg and 8.28±0.181 MJ/kg calculated for the test diet for ostriches and roosters, respectively, compared well with determined values of 11.25±0.072 MJ/kg and 8.02±0.445 MJ/kg, respectively. It was concluded that reliable energy values are now available for the establishment of energy requirements and diet formulations for ostriches.