School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemEffect of body condition at calving on milk yield of the dairy cow( 1978)The experiments reported in this thesis were done at the Dairy Research Institute (Ellinbank), Department of Agriculture, Victoria. This Institute is situated 100 kilometres east of Melbourne in the West Gippsland Region. The information currently available on the effect of precalving feeding on subsequent milk yield of grazing dairy cows is limited and largely of a qualitative nature. This thesis attempts to provide quantitative information on which feed management decisions can be made in the precalving period with some degree of confidence. The design, analysis and interpretation of the two experiments reported in this thesis were done primarily by myself. I was also actively involved in development of the condition scoring system reported in this thesis and in collecting, analyzing and interpreting data in order to provide an objective description of the condition scoring system. Chapter 1 reviews the literature on precalving feeding of the dairy cow indicating the apparent conflict in the results of different experiments which cannot be explained because of the confounded design and inadequate reporting of the results of experiments. Gaps in our current knowledge of precalvins feeding are also highlighted. Chapter 2 reports on an experiment which was done as part of a series of three experiments at Ellinbank to determine the relative importance of precalving liveweight change and body condition at calving on milk yield of dairy cows. These three experiments have been written up and accepted for publication in the Australian Journal of Experimental Agriculture and Animal Husbandry. Chapter 3 describes a system for scoring the body condition of dairy cows which was developed at Ellinhank with the assistance of the author. Chapter 4 reports on an experiment which quantifies the effect of body condition score at calving on milk yield under two levels of feeding after calving. This experiment and a more recently completed experiment with stall- fed cattle in different condition scores are to be combined and submitted shortly to the Australian Journal of Experimental Agriculture and Animal Husbandry. In Chapter 5 the experimental results are discussed in the light of continuing work and the industry significance of the work is emphasized.
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ItemLactation in mice as a model to study genetic improvement of dairy cattle in the tropics( 1989)In chapter one of this thesis aspects of reproduction and production, mainly milk production were reviewed. Components of reproductive efficiency such as the fertility components: age at calving, service periods, days open, calving interval and non return rate; were also investigated. The physiological relationship between those traits and milk production and persistency, in both temperate and tropical environments, was also considered, as well as longevity or stayability as other alternatives for evaluating reproduction. Attention was put on first and second lactation performance. With a view towards understanding physiological aspects of reproduction and production in dairy cows, the nature of lactation in mice was reviewed from the relatively few works that have been done. The papers reviewed included the role of pre-natal and post-natal maternal effects and the relationship between littersize and milk-yield. Daily yield and lactation from a number of studies were compared. Theories of genotype-environment interaction (GM) and adaptation, as well as their implications, were reviewed in the subsequent part of. chapter 1. Evidence of GEE in dairy cattle (Friesian, Holstein or Friesian-Holstein, crossbred with Friesian, and native) in both reproductive characters and milk production throughout the tropic regions were examined particularly closely. Mating systems and selection responses in genetic improvement programmes also were reviewed. Constraints and shortcomings for the achievement of genetic progress through natural mating, AI and progeny-testing in the tropics were examined in conjunction with attainment of high milk production in the temperate countries. The use of new technology (MOET) for manipulating reproductive efficiency was also introduced in the hope that it can be used to increase breeding efficiency in the tropics. The milk-yield and reproductive . characters, of two genotypes of mice (one genotype had been selected for high early reproductive and milking performance and the other was a random bred control) were measured in the normal and a hot environment to check if GEI were present. Both genotypes had been developed in the normal temperature. Evidence of interaction was found in the second parity and only in reproductive traits, e.g. fecundity, interval between mating and birth of second parity. These results are supported by many studies of GEI for both milk-yield and reproductive characters in dairy cattle in the tropics. Milk production does not show GEI, if the environment is defined merely as temperature. The previous selection of the improved genotype had resulted in positive correlated responses in: litter size and litter weight at birth in the first parity, production characters (growth characters and preweaning weight of the litters) in both parities, and on milk production but not on persistency. The selected line did maintain its superiority across environments. However females from the improved genotype performed worse in almost all characters in the hot environment compared to the normal environment. In an analogy with dairy cattle, the high production capacity of the selected line was not exhibited in the adverse environment. Problems of genetic improvement in the tropics were discussed. They included the use of appropriate selection criteria based on . more knowledge of both physiological and genetical relationships between milk-yield and other-characters, with the aim of increasing adaptability and productivity in the target environment. Other possibilities for genetic improvement of dairy cattle in the tropics and the use of synthetic breeds for overcoming the problems in the long term were also discussed.
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ItemThe nutritive value of white clover pasture for cows in mid-lactation when supplemented with maize silage( 1992)In a completely randomised grazing trial, 8 cows in mid-lactation were offered white clover pasture (35kg DM/cow/day) with 4 of the cows given a supplement of maize silage (8 kg DM/cow/day). Factors evaluated over a 28 day period were total DMI, pasture DM/maize silage DM substitution rate, herbage selection in the pasture, milk yield, fat and protein concentration. Supplementing cows with maize silage increased total DMI by 22% and lowered pasture herbage DMI by 21%; equivalent to a substitution rate of 0.5 kg pasture DM /kg of maize silage DM. Selection of herbage in the pasture was not affected by supplementation, but cows on both treatments selectively grazed the white clover. Supplementing cows with maize silage increased milk yield by 34%, fat yield by 35% and protein yield by 35% (P<0.05), but did not affect milk fat and protein concentration. In a metabolism trial, 6 rumen fistulated cows in mid-lactation were fed similar diets in a crossover experiment but with white clover fed ad libitum. Digestibility, nitrogen balance, milk yield, fat and protein concentration were evaluated over a 7 day period. Maize silage DM and white clover DM digestion in the rumen were evaluated by DM disappearance rates from nylon bags over a 96 hr period. Measurments of rumen fluid volume, fluid mean retention time, fluid outflow, pH, ammonia and VFA concentration and the acetate/propionate ratio were estimated over a 24 hr period. Supplementing cows with maize silage increased total DMI by 34%, without affecting DM digestibility (DMD). However, OMD was reduced by 5% and fibre digestion by 18% (P<0.05). Supplementing cows with maize silage did not affect the rate of digestion of maize silage DM or white clover DM in nylon bags, but white clover was digested at a faster rate than maize silage (P<0.05). The increased DOMI by cows supplemented with maize silage was highly correlated with a 24% increase in milk yield (P<0.05; iI=61 ) but had no effect on milk fat and protein concentration. At similar nitrogen intakes cows supplemented with maize silage produced 2.3 kg more milk (P<0.050='66) but there was no effect on milk fat and protein concentration. Rumen fluid volume, mean retention time and fluid outflow rate were not significantly altered by the maize silage supplement, although rumen pH and ammonia concentration were significantly lower (P<0.05). Total VFA concentration was not significantly different between the two diets, but acetate concentration was significantly lower (P<0.05), while propionate concentration was significantly higher (P<0.05) in supplemented cows. The reduction in acetate and the corresponding increase in propionate, lowered the acetate/propionate ratio. Butyrate concentration was not affected. It was concluded that for cows in mid-lactation fed on good quality white clover dominant pasture, maize silage supplementation can increase milk yield, without affecting milk fat and protein concentration. The increase in milk yield was attributed to increased apparent energy intake as nitrogen intake did not change markedly. However further work is required to quantify whether increased nitrogen utilization occurred and whether the lower ammonia concentration in maize silage supplemented cows were due to improved rumen microbial synthesis. The possibility also exists that improved milk yields were due to by-pass rumen starch, thereby providing glucose to the animal, after enzymatic digestion in the small intestine.