Typescript (photocopy) By using a regression equation relating the difference between dye binding and Kjeldahl values with the total protein concentration of the milk, the accuracy of estimates of casein in milk from individual cows was improved.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 85-94). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 85-94). Also available on the Internet.

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The effects of insulin on milk production were tested employing two different approaches. Firstly, 12 Holstein cows were used to determine the effects of feeding calcium propionate (Ca prop) on dry matter intake (DMI) and production traits. The experimental design was a switchback with 2 treatments (Ca prop at 0 or 300 g/d). The DMI was lower when animals received Ca prop. Ca prop did not affect the yield of milk and its components; however, Ca prop increased protein content. The (acetate+butyrate)/propionate ratio in rumen fluid 2 h after feeding was lower when cows received Ca prop. Plasma insulin concentration was not different between treatments and the putative effect of propionate as an insulin secretagogue was probably related to the maintenance of insulin levels when DMI was lower. In conclusion, Ca prop is a potential feed ingredient to increase protein content in milk. The second approach consisted of intravenous infusion of insulin. A trial was designed to test the effects of insulin, recombinant bovine somatotropin (rbST) and their interaction in lactating dairy cows. Eight Holstein cows were used in a Latin Square design with 4 treatments: (1) intravenous infusion of saline, (2) infusion of saline and administration of 40 mg of rbST per day, (3) intravenous infusion of 12 mg of insulin per day coupled with glucose infusion and (4) rbST administration combined with insulin and glucose infusion. The theory that rbST causes a peripheral resistance to insulin was confirmed. Insulin infusion increased percent protein, percent casein and decreased milk urea content regardless of rbST administration. For milk yield, protein yield, casein yield, lactose percent and lactose yield, there was an interaction between insulin and rbST administration. Similarly, there was an interaction between insulin and rbST on plasma IGF-I levels. Fat yield was higher, with a higher content of long chain fatty acids, during rbST administration, regardless of insulin infusion. I

Experiments were conducted to investigate the effects of formulating rations using different ingredients and of manipulating the cation-anion balance of the rations on production, acid-base status, metabolism of macrominerals and renal function of dairy cows. The effects of dietary cation-anion balance were studied during early, mid and late lactation as well as during the dry period. Feeding an alfalfa-haylage based diet vs a corn silage based diet, both having the same cation-anion balance did not affect the voluntary consumption, milk yield or milk composition of cows in early lactation. The acid-base status of the animals was not affected by dietary treatment. The lower urinary bicarbonate concentration observed with the alfalfa haylage-based diet was not associated with a lower total urinary bicarbonate excretion since urine volume was significantly higher than when cows were fed the corn silage-based diet. Manipulating dietary cation-anion balance, however, resulted in changes in acid-base status at all stages of lactation studied. Urinary bicarbonate concentration and total daily excretion were increased by a higher dietary cation-anion balance at all stages of lactation. Similar effects of dietary cation-anion balance on urinary bicarbonate did not, however, translate into similar changes in production or intake by cows at differing stages of lactation. Cows in early and mid lactation seemed to have benefited more from a highly positive dietary cation-anion balance than cows in late lactation or dry period.

This study presents a production function analysis of fresh milk producers in the Highlands of Eritrea for the year 2002, dealing with the most important factors of production. Most dairy farmers are located in the Central Zone and Southern Zone (Mendefera and Dekemhare) areas of the Highlands of Eritrea. To ensure representative production functions, the Highlands of Eritrea were divided into three respectively homogenous study areas, namely Central Zone, Mendefera and Dekemhare. Most data for this study were collected by survey using a questionnaire, as dairy farms' recorded data were scarce. The annual milk yield record and purchased concentrates per farmer were obtained from their respective milk collecting centres and Dairy Associations belonging to each study area. Basically, an attempt was made to pool the data of the three study areas, using dummy variables to test if the three study areas' regressions have a common intercept and a common slope. However, from the analysis, the intercept and slope dummy coefficients for the pooled data were found to be statistically significant at the 1 % and 5% levels of probability. Thus, it was not economically as well as statistically practical to pool the three areas' data to determine a common function that represents the sample dairy farmers of the Highlands of Eritrea as a whole. For this reason, a separate analysis was conducted for each study area. The analysis used the Cobb-Douglas function (double-log) form using multiple regressions. However, while analysing the data using ordinary least squares (OLS) regressions, strong intercorrelations were encountered among some factors of production. These intercorrelations resulted in some of the parameters having negative production coefficients where, a priori, all such coefficients are assumed to be non-negative. Thus, to tackle the multicollinearity problem, a ridge regression technique was used at different levels of the biasing constant, c, where the regression coefficients in the ridge trace start to stabilize and the variance inflation factor (VIF) of each parameter and the average of the VIFs are close to one. The final fitted model includes those variables, which were significant at the 1 % and 5% levels of probability. However, for the Mendefera study area those variables significant at 10% level of probability were included as their t-statistic values were considerably greater than one and nearly significant at the 5% level of probability. From the regression coefficients of the final fitted model for each study area, the elasticities of production with respect to the factors of production, ceteris paribus, were estimated. The highest response in production to a one percent change, ceteris paribus, is due to milking cows followed by concentrates and labour for the Central Zone Dairy farmers . However, for the Southern Zone (Mendefera and Dekemhare) the highest response next to milking cows came from forage and labour. The regression coefficients of all the factors of production in each study area were greater than zero and less than one, implying rational use of the resources. However, the sum of the elasticities of production was found to be greater than one for each area of production, indicating increasing returns to scale. Components of the production function and cost calculations including marginal product (MP), values of marginal product (VMP), marginal rate of substitution (MRS), least-cost combinations of inputs, profit maximizing combinations of inputs and the short-run cost functions for each category within the sample of dairy farmers in each study area were estimated. All the VMP's of the resources for the Central Zone dairy farmers were found to be greater than the corresponding unit price of the resources. This implies that the resources are utilized inadequately. However, for the Southern Zone (Mendefera and Dekemhare) the variable concentrates is over-utilized, as the VMP is less than the unit price of the input. The marginal rate of substitution of concentrates for forage, ceteris paribus, showed that the Central Zone sample dairy farmers were utilizing the two resources almost equally. But for the Southern Zone sample dairy farmers the MRS of the mentioned resources showed a higher dependence on concentrates than forage. From the least-cost combination of concentrates and forage analysis it was found that none of the sample of dairy farmers was allocating resources on a least-cost basis. The profit maximizing combination of inputs showed generally a considerable improvement of milk yield and margins for all the sample of dairy farmers relative to the present situations. However, the profit maximizing criteria (i.e. VMPx = Px), assumes perfect knowledge, a risk free environment and competitive marketing systems. This has to be considered when advising sample farmers as to the optimal combination of concentrates and forage. The short-run cost function also indicates use of resources at below optimum levels. When the average variable cost of the resources is less than the unit price of output, then use of the resources is in the rational area of production. Based on the analysis of the three study areas, the average variable cost of the lower one-third group of sample dairy farmers of the Southern Zone was found to be greater than the unit price of output. This means that the farmers were not covering the short-run costs of production. The MC of concentrates for the lower one-third group of sample dairy farmers was found to be greater than the price per litre of fresh milk in the Southern Zone. This implies more than optimum use of the input (i.e. where MC = Py). / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

In the first of three experiments, four Holstein multiparous dairy cows, equipped with ruminal and duodenal cannulas, were used to determine the impact of different methods of treating soybean meal (SBM) on ruminal degradability and intestinal digestibility of CP and amino acids (AA). Solvent extracted SBM (SE), expeller SBM (EP), lignosulfonate SBM (LS) and heat and soy hulls SBM (HS) were incubated in the rumen, in nylon bags, for various intervals up to 48h. Additional samples incubated for 16 h were pre-treated with pepsin HCI, and then used for determination of intestinal digestibility either in situ (mobile bag technique) or in vitro. Treatment of SBM (EP, LS, HS) increased rumen undegradable protein (RUP), and AA availability in 30%. Estimates of intestinal digestibility of AA and CP were lower when measured in vitro than in situ. Among the treated SBM products, four EAA (Ile, Leu, Phe and Val) showed differences in availability, with values consistently lower for HS than for LS. The second experiment involved a comparative assessment of the availability of lysine in SE and rumen protected SBM products (EP and LS). Lysine availability was assessed either by the increment in plasma flux of 15N lysine, the increment in intestinally digestible lysine (using chromic oxide as a digesta marker) or by the use of a "plasma lysine response curve" designed to predict intestinally available lysine. The plasma Lys flux was not different between the different SBM products. However, SE + 70 g.d-1 omasal infusion of Lys (SE70) increased Lys flux by exactly 70 g.d -1 above the SE treatment. No differences were observed on duodenal Lys flow, post-ruminal digestion and digestible Lys between the SBM diets (SE, EP, LS). Irrespective of the method of assessment, lysine availability was not altered by the method of treating SBM. The third study evaluated the relative impact of supplying rumen-undegraded protein (RUP) versus altering the carbohydrate source on milk yield and efficiency N usage for milk production. Protein supplementation (SE and EP) increased DMI, whereas the inclusion of beet pulp (BP) replacing 50% of high moisture shelled corn decreased DMI. The results of this research suggest that, under normal conditions of feeding, supplying rumen protected SBM to enhance the supply of intestinally available essential AA does not improve lactation performance; providing beet pulp as a source of readily fermentable fibre also failed to affect milk yield or efficiency of N usage for milk production by dairy cattle.

The influences of some environmental and genetic factors on the incidence of abnormal test-days in milk-recorded cows enrolled in the Quebec Dairy Herd Analysis Service (QDHAS) was determined in this study. Conditions Affecting Records (CAR) codes, collected monthly by QDHAS's supervisors, are possible explanation for a reduced production in the day of test. For the purpose of this study, CAR codes were used to analyze the incidence of health problems under generalized linear models methodology. Poisson and logistic regression model analyses were able to model the number of cases of abnormal test-days and health problems per lactation. Herd, testing program, parity number, and stage of lactation were important systematic effects included in the analysis. However, calving year, season of calving, and herd production level were not statistically significant in most analysis. Sires significantly differed in the incidence of some health problems of their daughters. Low heritability values, between 0.02 and 0.05, were found showing that most variability was explained by non-genetic factors. Regardless of the low heritability, the genetic variability has been shown to be considerable, suggesting that a significant genetic improvement of the disease resistance is achievable if proper procedures are adopted.