School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemUtilization of protein and energy in growing lambs( 1970)Extensive pasture improvement throughout large areas of Australia in recent years has emphasized the need for more efficient methods of pasture utilization. This has been achieved to some extent by an increase in sheep stocking rates. However, the benefits from high stocking rates are far greater when used for the production of wool from dry sheep than when applied to breeding flocks producing prime lambs. Results from many experiments with wethers (Arnold & McManus, 1960; Drake & Elliott, 1963; Bishop, Birrell & Tew 1966; Morley & Ward, 1966) indicate that as stocking rate is increased total wool production per acre increases substantially. The relationship between total wool production and stocking rate is curvilinear (Bishop et al., 1966) and although the stocking rate which results in the maximum production per acre is higher than that which achieves the greatest economic return (Lloyd, 1966),a considerable increase in farm income can be obtained when the stocking rate of wethers is raised above conventional levels (Chisholm, 1965). The improvement in pasture utilization when wethers are grazed at high stocking rates is brought about by an increase in competition between individual sheep and the consumption of much of the poorer quality and damaged pasture which is otherwise rejected. Increasing competition eventually results in a reduction in feed intake with a concomitant lowering of production. However, the adverse effects of a reduced intake are less for wool growth than for most other forms of production. For example, the results of Bishop et al. (1966) indicate that wool growth of Corriedale - Polwarth cross wethers will continue at a rate of approximately 14 g/day inspite of the fact that feed intake was insufficient to produce a gain in live-weight. A reduction in feed intake has more serious repercussions in a breeding flock. A nutritional stress on the ewe can lead to (a) low live-weight at mating with its effect on ovulation (Edy, 1968) and lambing percentage (Coop, 1962) , (b) small live-weight gains during gestation with low birth weights of lambs from multiple births (Wallace, 1948) and high perinatal mortality (Alexander, 1962), (c) poor lactation and reduced lamb growth rates (Wallace, 1948). The presence of lambs accentuate the decline in food availability and as a result of the low intake of both milk and pasture the lambs grow poorly. Arnold and Bush (1962) found that meat production from a prime lamb flock did not increase when stocking rates were raised from 4 to 7 ewes per acre. In a more recent study (G.W. Arnold, A Axelsen & M.E. Bourke, 1965 - personal communication) it was found that as the ewes were increased from 5 to 7 per acre the number of lambs reared remained constant at 6.2 per acre, but the meat production declined. Many prime lamb producers in southern Australia have attempted to increase stocking rates, but, poor growth of lambs has generally resulted in a large percentage of them remaining unfattened at the end of the period of pasture growth. These lambs are often carried through to the following autumn and further reduce the feed available in the winter. The poor response in meat production associated with increased stocking rates was considered to be of sufficient importance for the Reserve Bank of Australia to provide finance to investigate "the problems of high stocking rates in the prime lamb industry". It seemed logical that the production of meat may be improved if the competition between the ewes and lambs could be reduced. The most common methods by which this is done is to either creep graze or early wean the lambs, thereby giving them access to more pasture of high quality. The results of several studies in England (Spedding & Large, 1959; Dickson, 1959) and Tasmania (Jefferies, Dreaver & Wilson, 1961) suggest that creep grazing systems do produce faster growth rates in lambs when stocking rates are high. However, limited evidence from the Australian mainland (Arnold & Bush, 1962; Fletcher & Geytenbeek, 1968) indicates that the creep feeding of pasture is not advantageous and that the creep feeding of lucerne produces only slight improvements in growth rates. Lambs weaned at 2 to 3 weeks of age can survive at pasture, but their growth is poor (Spedding, Large & Brown, 1961). Wardrop, Tribe & Coombe (1960) found that lambs weaned at 7 weeks of age could grow as well as unweaned controls, but that their response was sensitive to the quality and quantity of feed. However, the results of Cannon & Bath (1967) indicate that, in conditions typical for southern Australia, stocking rates must be raised above 9.6 lambs per acre before any advantage in meat production can be obtained by weaning lambs at 10 weeks of age. Therefore, it seemed that the early weaning of lambs at pasture would not greatly improve production from prime lamb when high stocking rates were used. Because the response to both early weaning and creep feeding was dependent upon the quality and quantity of the pasture, it was reasoned that these systems may be more successful if the lambs were given concentrate diets formulated to meet their nutrient requirements. However, a survey of the literature revealed that there was a dearth of information on the nutrient requirements of lambs and that many recommendations were contradictory. Because concentrate diets which would satisfy the nutrient requirements of lambs could not be formulated with confidence, the major portion of this thesis has been concerned with determining the protein requirements of young, meat producing lambs.
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ItemEstimation of the available amino acid contents of feeds for pigs with Tetrahymena pyriformis w( 1973)Experiments were conducted to evaluate the usefulness of the Tetrahymena assay for predicting the available amino acid content of feeds for pigs. In collaborative studies the Tetrahymena lysine values were also compared with values from the Silcock technique for a series of feeds and attempts were made to evaluate which technique was more applicable to pigs. The pig experiments were conducted with pigs fed individually once daily during the 20 to 45 kg growth phase. Pig response was assessed in terms of live-weight gain, feed conversion efficiency and carcass lean as estimated by joint dissections. 1) The 4-day incubation period for the assay of proteins by Tetrahymena as recommended by Stott and. Smith (1966) was found to be adequate for buttermilk powder but not for fish meal or meat and bone meal. By extending the incubation of the latter two meals to 7 days, complete hydrolysis was achieved. Experiments with pigs fed diets formulated with values from either the 4-day or the 7.-day incubation periods for fish meal and meat and bone meal indicated that values obtained with the Tetrahymena assay after complete hydrolysis of the meals were more applicable to pigs than were those estimated after 4-days. 2) For cereals a 10-day incubation period for estimates of lysine and tryptophan with Tetrahymena was found necessary for maximum hydrolysis, and there was good agreement between these values and the response in pigs. 3) There was close agreement between Tetrahymena and Silcock estimates for lysine in samples of soyabean meal that were autoclaved for varying times. In a pig experiment the additions of lysine, methionine and tryptophan to diets containing the autoclaved soyabean meal restored only 43% of the effects of the heat damage. 4) This raised the question as to whether the supplements of free amino acids had been efficiently utilised by the pigs. A pig experiment was conducted to examine the effect of feeding a ration containing free lysine either once daily or in six equal portions at three hourly intervals. The results indicated that only 43% of the free lysine was utilised with once daily feeding relative to the frequent feeding regime. Thus the inability of the amino acids added to the autoclaved soyabean meal to compensate for the effects of heat damage may have been due to inefficient utilisation of the added amino ' acids by the pigs and not to inapplicability of the estimates of heat damage. 5) The amount of protein used in the Tetrahymena assay was found to govern the subsequent hydrolysis of the protein. Attempts to promote more vigourous hydrolysis of small amounts of protein by increasing the amount of inoculum were unsuccessful. Vigourous hydrolysis of the protein was obtained by the addition of 0.25 mg L-lysine-HC1 to each assay; this stimulated the initial growth of Tetrahymena, then vigourous hydrolysis resulted. 6) The rate of release of lysine from protein concentrates by Tetrahymena varied. Buttermilk powder and skim milk powder required 2 days, peanut meal 3 days, soyabean meal 4 days, safflower meal 5 days, rapeseed meal 6 days and fishmeal and meat meal 7 to 8 days. Free lysine was utilised within 4 days. 7) The Tetrahymena and Silcock lysine values for different protein concentrates showed no consistent pattern. For soyabean meal the Tetrahymena lysine values were greater than the Silcock values, for peanut meal the estimates were similar, and for the other proteins the Tetrahymena values were lower than the Silcock values. This was particularly so for a meat meal and rapeseed meal where the Tetrahymena values were approximately half the Silcock estimates. 8) An attempt was made to supplement cereal-based diets with protein-bound lysine to achieve diets of similar lysine content; both the Tetrahymena and the Silcock values were used to compute the amount of supplementary protein needed. Diets formulated according to these two values were then fed to pigs in an attempt to decide which value was the better indicator of lysine availability to pigs. This experiment proved inconclusive as factors other than lysine appeared to have influenced the results. This aspect of the comparison of the two methods of assay needs to be examined using feeding trials on a larger scale to eliminate these complicating factors. 9) In Appendix 1, the modifications made to the Tetrahymena assay to allow complete hydrolysis of proteins are Outlined.