School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemA study of weight-loss and compensatory gain in sheep( 1971)Two experiments of similar nature were conducted. In the first experiment 49 Corriedale wethers at approximately 8 months of age were allocated to four experimental groups and, within groups, to various slaughter weights which were spaced at 5 kg intervals. Group I animals were fed ad libitum and slaughtered - over a body weight- range of 38 - 63 kg inclusive. Groups II and III animals were fed ad libitum until 48 kg body weight hereupon intake was restricted to achieve a body weight loss of 0.9 kg/week until body weights were reduced to 38.5 kg and 34.5 kg, respectively. Ad libitum feeding was then resumed and animals were slaughtered up to 63 kg body weight at the same weight intervals as in Group I. Group IV animals were fed ad libitum until 48 kg body weight and then, food was adjusted to maintain body weight at 48 kg. Four animals were slaughtered after 60 days and a further four after 120 days of maintenance of body weight. In the second experiment, 15 wethers of similar age, breed and nutritional history as those used in Experiment 1, were allocated to four slaughter groups in a treatment similar to that of Group III in Experiment 1. Four animals were slaughtered at 33 kg body weight at the beginning of the first period of ad libitum feeding; three animals slaughtered at 45.5 kg at the end of the first period of ad libitum feeding; three animals slaughtered at 33.5 kg at the end of the weight loss phase; and five animals slaughtered at 46.5 kg at the end of the second period of ad libitum feeding. The compensatory growth rates of animals in Groups II and III were greater than those of Group I in each of the successive 5.5 kg increments in body weight. By maintaining higher growth rates over the entire weight range, the largest animals of Groups I I and III were slaughtered at a similar age to those, of Group I. Similarly, in Experiment 2, the compensatory growth rates (Group VI) were greater than continuous growth rates (Group V) over the body weight range used in this experiment. The data was transformed to logarithms in order to use Huxley's (1932) allometric growth equation in the linear form for an analysis of covariance. During continuous growth (Groups I and V), the empty body weight (EBW) increased as a proportion of full body weight (FEW) whilst during the compensatory growth which followed weight loss (Groups II, III and VI) the proportion of EBW remained constant. At the same FEW the EBW of Groups I I and III was less than that of Group I. Similarly, the EBW of animals maintained at a constant body weight (Group IV) was less, at the same FBW, than that of Group I. Carcass weight (CW) increased as a proportion of EBW as EBW increased in Groups I and V but the proportion remained constant in Groups II, III and VI. At the geometric mean FEW, treatment did not affect CW. However, the apparent dressing percentage (CW / FBW x 100) was 2% less during compensatory growth compared with that during continuous growth. The carcass length of animals in Groups II, III and IV was greater than that of animals in Group I.
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ItemChoosing sheep for lifetime profitability( 2004)This project investigated the selection of wool sheep for lifetime profitability by measuring the lifetime productive phenotypes of breeding ewes, their lambs and the rams to which the ewes were mated, on a commercial farm in East Gippsland. The measurements were recorded from 1992 to 2002. The seasons varied during this time, including a severe drought from 1996 to 1998. The results clearly demonstrate that the environment, its resources and demands, limit the full phenotypic expression of the genotype of the sheep. This expression varies over the lifetime of the animal. The results identify the sheep that were most suited to their environment. Phenotype interaction: It was found that enhancement of any single profitable phenotypic character resulted in changes to all other profitable phenotypic characters, usually in a negative direction. These phenotypic interactions frequently show curvilinearity and nonlinear relationships, demonstrating that to select on a linear model is frequently not appropriate for profit indicators or biological reality. Measurement of ewe body weight and the weight gain ratio of lambs A method is described for measuring the yearly and lifetime body weights of sheep from which the changing wool weights and weight due to pregnancy were removed. Birth weight, wool weight and weight gain of the suckling lamb were then expressed as a percentage of the body weight of the ewe. This resulted in a clearer understanding of how the ewe allocates metabolic resources. It also demonstrated that too high a bodyweight was itself an excessive user of resources. When the average daily weight gain of the lamb from birth to weaning was expressed as a percentage of the weight of the mother the results provided an early prediction of lifetime profitability of the lamb and indirectly of the mother. This percentage had a strong positive relation to the birth weight, weaning weight, greasy fleece weight of the lamb and to the survival rate of the progeny and the test ewes during the drought. However prediction of the fibre diameter required an independent measurement. Measuring the value of a sheep's wool: A method is described for assessing the value of wool. This eliminates the influence of monetary inflation and helps the farmer make a more accurate judgement of the wool value in the selection of his sheep. Auction prices from all districts of Victoria based on the 1987-1997 auction prices of wool were converted into a Price fibre-diameter ratio. This ratio was used to determine a commercial wool value (Ewe wool score) for each test ewe. For each of the test ewe's male and female progeny, the same ratio was used to obtain a wool score (up to two years of age). These progeny values of all her lambs were added to provide a Progeny wool score for each test ewe. A Combined wool score combined both the ewe's own woolscore and the woolscore of her progeny. The top ten test ewes were identified for each category then compared to the subjective assessments of a sheep classer, the farm manager and the wool classer. Sheep that had high Combined wool scores and were therefore the most profitable over two generations had different phenotypes from those with high individual wool scores. It should be noted that while wethers might be chosen for wool score only, ewes should be chosen for wool score and the ability to produce profitable progeny. This thesis has highlighted the fact that selection for lifetime profitability will differ for ewes and for wethers. Using the Statistica 4.1 (1994) for McIntosh program stepwise multiple regressions were carried out on the test ewes for Ewe wool score, Progeny wool score and Combined wool score. The factors with significant influence (p-level < .05) on each of the three wool scores were identified. For the Ewe wool score, the factors in order of importance are, average fibre diameter (negative), greasy fleece weight, average visual assessment of the fleece and lambs alive December 1996 (negative). Those four factors "explain" 42% of the sums of squares in the Ewe wool score. For the Progeny wool score, the factors in order of importance are, lambs alive in December 1996, which was the end of the recording of the test ewes, and the average fibre diameter (negative). These two factors "explain" 64% of sums of squares in the Progeny wool score. In the Combined wool score, the factors in order of importance are, lambs alive in December 1996, average fibre diameter 1992-6 (negative) and average greasy fleece weight 1992-6 (negative). These three factors "explain" 60% of the sums of squares in the Combined wool score. The negative partial regression for fibre diameter is explained by the position of the average fibre diameter on the Price-fibre diameter curve (finer fibres bring higher prices). The negative partial regression of the Combined wool score on greasy fleece weight suggests that there is competition between resources required for producing wool and for successful reproduction. Heritability estimates: Heritability estimates were calculated from intra-sire regressions of progeny on dams. This was done for body weight, greasy fleece weight, fibre diameter and the visual assessment of the fleece at specific ages over the years for which paired data for the test ewes and their progeny were available. Such estimates were available for hoggets and 2,3,4 and five-year olds of both the dams and progeny, with a varying numbers of pairs at different ages. The results varied between ages and between the sexes of the progeny. There were more data available (pairs of dams and progeny) from the middle age-years. 'When the male and female progeny were considered together, the corrected body weight in years two and four gave highly significant results of 0.45 and 0.44 respectively. Year three had significant results of 0.27. Years one and five were not significantly different from zero. Fibre diameter had highly significant results of 0.89 in year one and significant results of 0.28 in year two and 0.32 in year three. Years four and five were not significant. Greasy fleece weight had significant results of 0.70 in year one. Other years were less than 0.30 and were not significant. Fleece visual assessment had highly significant results of 0.35 in year three; the other years were not significant. One wool classer classified all the fleeces subjectively at shearing over an eight-year period giving a yearly visual score to each fleece. He was unaware of the identity of the fleeces. The results showed a high degree of consistency. The above results shows that visual scores can be heritable. Fibre diameter, greasy fleece weight and their interaction: Fibre diameter was examined for lifetime variation in individual sheep and groups of sheep selected on micron. Lifetime group measurement of fibre diameter was highly predictable. This allows a fanner to get a reasonable lifetime group fibre diameter result from one year of measurement. Lifetime measurements of fibre diameter for individuals were less predictable. Fibre diameter was also examined for the effect of resources and their availability, heritability, ageing, lambing and lactation, and the health of the sheep. The two-generation realized heritability of fibre diameter for the test ewes in 1995 and the one-year old progeny in 1993 to 1995 was 0.50. Greasy fleece weight was examined for lifetime variation, in individual and group measurements, for the effect of the availability of resources, the variations of ageing and the health of the sheep. Greasy fleece weight had lower heritability estimates at hogget age than did fibre diameter. Group measurements of greasy fleece weights had more lifetime variation than did fibre diameter. Therefore a single greasy fleece group measurement would not be as reliable an indicator for lifetime results as a single measure of fibre diameter. Using 1992-6 average values, the fleeces of the Tubbut flock were examined for the relationship of the fibre diameters to greasy fleece weights, from the finest to the broadest fibre diameters. This relationship was not linear. From 25-21 microns the decrease of the greasy fleece weight for each decrease of one micron was 5.7%, from 21-18 microns the result was 9.6 %, from 17-16 microns the result was 11.4%. The limitation of the environment: The data presented in this thesis clearly demonstrate, that with limited resources available from an environment, there is an overriding and fundamental response within animals to allocate those resources to maximize their survival and that of their progeny. Any artificial selection must be carried out with the knowledge, that over time, the animals will attempt to return to the allocation of resources that maintains the best chance of survival for themselves and their progeny. Within this thesis there are many examples where, if sheep had been artificially selected for one character this would have altered all or most of the other characters usually in a negative direction. It has been shown that high artificial selection tends to have that selection reduced in value over the animal's lifetime. Important principles: Results in this thesis highlight that in selecting for lifetime profitability breeders should note that 1) The environment, its resources and demands, limit the full expression of the genotype of the sheep. The effect varies over the lifetime of the animal. 2) In the selection of animals for particular traits, due regard must be given to the effects that the selection will have on the whole of the phenotype. 3) Increased profitability resulting from the selection of one trait may result in the overall loss of profitability from the decrease in other profitable traits. 4) Where research is carried out on one particular trait to either enhance or decrease that trait, the research needs to demonstrate the effect of that selection on the whole animal over its lifetime. 5) Sheep need to be selected for an increase in lifetime profitability in their own commercial environment. Taking note of these principles will ensure true progress is made in phenotypes and genotypes suitable for any particular environment. It will also produce greater profits for Australian farmers.
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ItemEffects of growth patterns on body composition and compensatory growth in sheep( 1977)The literature related to compensatory growth in ruminants, with particular reference to sheep, has been reviewed. An experiment was conducted which examined the effects of planned BW losses on growth rate, body composition, wool growth and nitrogen and energy utilisation of sheep when ad libitum feeding was resumed. Sheep were fed a pelleted ration throughout the experiment, and BW loss induced by reducing feed intake. Following developmental growth from 30 to 37.8 kg, Groups B and C lost 21% BW at 122 and 63 gd-1, respectively to reach 30.2 kg BW. Following developmental growth from 30 to 46.7 kg (Groups D and E), Group D lost 34% BW at 125 gd-1 to reach 30.8.kg BW, while Group E lost 23% BW at 157 gd-1 to reach 35.0 kg. Group A was a control group fed ad libitum throughout the experiment. When ad libitum feeding was resumed compensatory growth occurred in treatment groups for up to 10 kg recovery of BW. Group D showed the most persistent increases in growth rate compared with that of control sheep, however, above 50 kg BW there were no significant differences between groups in growth rate. Weight loss did not produce a reversal of the compositional changes which occurred with increasing BW during developmental growth, in the whole body, carcass or offal. However, differences in composition between groups at the end of weight loss were not significant. During compensatory growth there were few differences between groups in the relative growth rates of protein, fat, ash or water in the whole body, carcass or offal. There were some differences between groups in weights of components at specific BW, carcass weight (CW) and offal weight WW), most notably fat and ash. However, these differences appeared to be transitory, and reflected the composition of that portion of the animal at the start of realimentation, rather than an effect of weight loss which was maintained during compensatory growth. The body, carcass and offal composition of sheep appeared to be resilient to periods of nutritional stress, and tended to return to the "normal" composition expected at that weight. The effects of up to 18 weeks severe undernutrition, resulting in rapid BW loss, were able to be overcome during compensatory growth when feed was offered ad libitum. Compared with developmental growth, nitrogen retention increased during compensatory growth. However, the efficiency of ME utilization was not different during these two periods of growth, although DE requirements for maintenance were lower during compensatory growth, compared with developmental growth. Dry matter intakes (DMI) of treatment groups required up to 13 weeks to return to the DMI of sheep during developmental growth, once ad libitum feeding was resumed. Over their respective growth paths Groups A, B, C, D and E required the same amount of feed to reach 50 kg BW. Wool growth rate (WGR) responded more slowly than BW to changes in level of nutrition, both during weight loss and during compensatory growth. There was a lag phase of at least 30 days. WGR during compensatory growth was reduced and required up to 14 weeks to return to developmental WGR after ad libitum feeding was resumed. Total body water (TBW), estimated from tritiated water (TOH) space in sheep undergoing compensatory growth, was overestimated by at least 20%. TOH space was measured without imposing a period of prior starvation on the sheep, and this may have contributed to the large overestimate. Multiple regression equations including TOH space, BW and a maturity factor (M), were able to explain up to 95% of the variation in chemical composition of the body, but residual standard errors were still high.
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