The effect of different levels of supplementary feed on the production of finisher ostriches (Struthio camelus) grazing irrigated lucerne (Medicago sativa) pastures

[摘要] ENGLISH ABSTRACT: The purpose of this study was to evaluate the production of slaughter ostriches in a grazing environment atdifferent levels of supplementary feed.Two grazing trials were conducted. In the first trial, one group of finisher ostriches (six months old) was put intoa feedlot and received a complete finisher diet. The other four groups were allowed to graze lucerne pasture(stocking rate of 15 birds/ha) with 1500, 1000, 500, and 0g supplementary feed/bird/day. Pasture productionand intake were measured. There was no difference (P >0.05) between the end mean live weights of the feedlotostriches and those two grazing groups receiving 1500 or 1000g supplementation. The average daily gain(ADG) of the group receiving 1000g supplementation was lower (P <0.05) than the ADG of the group receiving1500g supplementation, but all three groups reached a mean target slaughter weight of 95kg within the 154 daysof the study. Therefore, pastures together with the correct supplementation (at least 1000g/bird/day) canreplace complete feeds in the finishing phase of slaughter ostriches and can play an important role in theproduction of these birds. For lucerne intake, a quadratic relationship (P <0.01) was found between pasture drymatter (DM) intake (g/bird/day) and supplementary feed intake (g/bird/day). The maximum lucerne intake level(1692.8g/bird/day) was achieved at 619.6g supplementary feed/bird/day.In the second grazing trial, finisher ostriches were allowed to graze lucerne pastures at two different stockingrates (10 and 15 birds/ha) while receiving either 0 or 800g supplementary feed/bird/day. Ostriches receivingsupplementation had higher (P <0.05) mean end live weights than ostriches receiving no supplementation.Ostriches receiving supplementation reached a mean target slaughter weight of 95kg within the timespan of thetrial, but ostriches receiving no supplementation did not. Stocking rate had no influence on mean end live weightof the birds. An interaction (P <0.05) was found between the level of supplementation and stocking rate for ADGof the birds. Stocking rate influenced ADG only for birds receiving no supplementation. As stocking rateincreased, ADG of birds receiving no supplementation declined. Results of the pasture data indicated anincreasing level of replacement of grazed lucerne DM by supplementary feed as the trial progressed and thiswas more pronounced at the higher stocking rate of 15 birds per hectare. A high stocking rate seems to havehad a gradual depressing effect on lucerne DM production, while the less severe levels of defoliation at a lowerstocking rate promoted lucerne DM production.A digestibility trial was conducted with mature ostriches (12 months old) to investigate the effect ofsupplementation on intake and digestibility of nutrients, as well as to investigate the substitution effect thatostriches may display when they receive supplementary feed in addition to grazing. The same dietarytreatments as in the first grazing study were given to ostriches while they were kept in metabolism crates. Thesediets were also fed to 20-week old roosters to obtain energy values for these diets for roosters. These energyvalues would be used to predict ostrich energy values for the same diets by means of a regression equation. For the roosters, each diet treatment was mixed with 50% maize to prevent digestive disorders and ensuremaximum feed intake. Ostriches started to substitute supplementary feed for pasture when supplementationwas supplied at levels higher than 62% (i.e. 1000g supplementary feed/bird/day) of total feed intake. For eachincrease of 100g in supplementary feed intake, pasture was replaced at a rate of 4.9%. Higher (P <0.05) totalfeed intakes were reached by ostriches if they grazed lucerne pastures and received supplementation than ifthey grazed pasture alone. Pasture grazing alone had lower (P <0.05) dry matter digestibility (DMD) andapparent metabolizable energy (AME) values for both ostriches and roosters than if pastures were supplied witha supplement. A significant stepwise regression could not be computed for the prediction of ostrich AME valuesfrom rooster AME values.The economics of different feeding systems (extensive versus intensive) were evaluated with an economicanalysis, which was based on the same materials and methods and results of the first grazing trial. A marginabove feed cost (MAFC) analysis was performed to evaluate the economic viability of the different feedingsystems. The present value (PV) of the MAFC for the pasture-based system with 1000g/bird/daysupplementation was only 8.3% lower than that of the feedlot system over a period of six years, while the PV ofthe cost of the same pasture-based system was 78.4% lower than that of the feedlot system. Birds finished onlucerne pasture with 1000g supplementation led to a saving of 57% in feeding costs if compared to a feedlotsystem. A sensitivity analysis of the MAFC revealed that the pasture-based system was less sensitive tochanges in feeding costs than the feedlot system. Therefore, the unique circumstances of each ostrich producerwill play a role in the decision whether to raise ostriches in a feedlot or on pastures.

[发布机构] Stellenbosch University