School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemComposition of commercial pig diets and utilization of piggery wastes( 1977)The work presented in this thesis was part of an integrated study conducted by the School. of Agriculture and Forestry into various aspects of piggery waste utilization. Particular attention was given to the occurrence and source of mineral elements in pig diets and piggery wastes. Results of analysis of commercial pig diets and piggery wastes are discussed in relation to nutritional requirements and toxicities and from environmental and legislative aspects. The Literature Review in Chapter 2 describes how similarities in the atomic orbital configurations of some transition elements and oxy-anions can explain the synergisms and antagonisms displayed by these chemical entities in biological systems. In particular, the concept of orbital equivalence is used to explain some of the better known cases of mineral antagonisms affecting the health and nutrition of livestock. The antagonism between sulphate and molybdate ions is discussed relative to their ionic structures and to their respective involvements in copper metabolism. The interactions of copper, zinc and iron are examined, particularly in relation to pig nutrition. Interactions between copper, zinc and cadmium are related to their orbital structures and to their ability to form metallothioneins. The ability of high levels of copper and zinc to induce selenium deficiency in chicks is discussed and associated with the similar orbital configurations of zinc, copper and selenate ions. Caution is proposed in the formulation and mineral supplementation of multi-constituent diets used in intensive animal production. Procedures used in the development and calibration of analytical techniques for the determination of eleven elements in pig faeces and pig diets are described in Chapter 3. Copper, zinc, iron, cadmium, lead; sodium, potassium, magnesium, calcium and phosphorus were measured from a single sample digestion using a nitric-perchloric acid mixture. Phosphorus content in the digest was determined colorimetrically and the remaining elements by atomic absorption spectrometry. A separate digestion procedure was required for arsenic which was then measured by atomic absorption spectrometry after generation of arsenic as its hydride. Accuracy and precision of the techniques were rigorously tested using standard addition and recovery procedures- and comparison of values obtained after analysis of the U.S. National bureau of Standards Reference Material ''Orchard Leaves". Chapter 4 reports the chemical composition of pig diets, ingredients of diets and mineral-vitamin supplements collected from 24 commercial piggeries in Victoria. An evaluation of the diets relative to the suggested dietary mineral requirements for grower pigs proposed by the Agricultural Research Council (A.R.C.) indicated that mineral imbalances occurred in many of the diets. High levels of cadmium and lead found in some diets originated principally as contaminants of mineral additives and from meat meals, meat and bone meals and fish meals. The mineral content of the diets was found to be highly variable and indicated differences in choice of dietary ingredients and in the practice of mineral supplementation. Copper, zinc, and iron levels in the diets were particularly variable and in the case of zinc and iron were present at concentrations far in excess of the levels suggested by.the A.R.C. Chapter 5 describes the chemical composition and in vitro organic matter digestibility (OMD) of pig faeces samples collected from 24 piggeries in Victoria. Pig faeces are shown to be highly variable in chemical and nutrient content and, in some instances, to contain high levels of potentially toxic mineral elements such as copper, cadmium, lead and arsenic. Wide ranges in in vitro OMD values, proximate constituent concentrations and cell wall composition were also recorded. Multiple regression analysis associated low in vitro OMD with high values of cell wall content, phosphorus, copper and lignin/cell wall. Standard additions of phosphorus and copper to pig faeces samples undergoing in vitro fermentation significantly lowered the OMD values of these samples, contributing further evidence of the possible inhibitory effects of these elements to the digestive processes of the ruminant. Some health aspects of refeeding pig faeces as an ingredient in diets for ruminants are discussed, particularly in relation to the presence of toxic minerals such as copper, cadmium and lead. In Chapter 6 a procedure is described for calculating the chemical composition of pig manure using dietary composition, recommended feed intakes, published retention values for each element and estimated excreta outputs fin. an "average" pig of 45 kg liveweight. The variability in the calculated composition of manure is discussed in relation to existing and proposed guidelines limiting the rates of application of pig manure to land. Some aspects of the proposed guidelines for Victoria are discussed; particularly in relation to the suggested maximum rates of manure application to provide not more than 500 kg of nitrogen or 300 kg of potassium/hectare/ annum. Because of the range in the estimated nitrogen content of pig manures, the quantities of manure supplying 500 kg of nitrogen were calculated to range from 46 - 123 tonnes with an average of 63 tonnes. Included in these quantities were widely varying amounts of other elements which would be applied to land with 500 kg of nitrogen; some of which are known to pose environmental problems through leaching to ground water, as run-off to waterways or through ingestion by grazing animals. The potential environmental hazards of applying large amounts of minerals, including heavy metals, to land are discussed and a method is proposed which would permit a more accurate estimate of manure loading rates to provide 500 kg nitrogen/ hectare of land.