Four lactating Holstein cows fitted with ruminal and duodenal cannulae were used in a 4 x 4 Latin square design to determine the effects of feeding raw and heat-treated flaxseed on ruminal fermentation parameters, ruminal fatty acid biohydrogenation (BH), nutrient utilization in various segments of the gastrointestinal tract, and plasma and milk composition of lactating dairy cows. Four diets were formulated: a control diet with no flaxseed (C); a raw flaxseed (RF); a micronized flaxseed (MF); and an extruded flaxseed (EF) diet. Ruminal pH, NH3N and total volatile fatty acids were not affected by dietary treatments. However, feeding flaxseed decreased ( P < 0.01) molar proportion of acetate and increased ( P < 0.01) that of propionate. Ruminal fiber digestion was lower (P < 0.04) for cows fed the flaxseed diets relative to those fed C. Feeding flaxseed had no effect on milk yield, milk fat and protein content, and milk fat yield, but decreased (P = 0.02) milk protein yield. (Abstract shortened by UMI.)

No description available.

Three studies were conducted to determine the effects of roasting on ruminal degradability of sunflower seeds and the effects of feeding roasted sunflower seeds on ruminal fermentation, nutrient digestibility and milk yield and composition of dairy cows. Experimental treatments were a control diet with no added sunflower seed, a raw sunflower seed diet and a roasted sunflower seed diet. Sunflower seed diets contained 6% fat whereas the control diet contained 3% fat. In study one, two ruminally fistulated cows were used in a randomized complete block design to determine the effects of roasting on ruminal degradation of sunflower seeds. In the second study, three ruminally cannulated lactating Holstein cows were used in a 3 x 3 Latin square experiment to determine the effects of dietary treatments on ruminal fermentation and total tract nutrient utilization. In the last study, three primiparous and six multiparous Holstein cows were used in three 3 x 3 Latin squares to determine the effects of dietary treatments on milk yield and composition.

The objective of this study was to evaluate the effect of two different feeding systems and of four different energy sources (Grain diet) on lactation characteristics and milk composition of dairy cattle. A total of 8,808,798 test-day records from 566,736 Holstein cows in 5,183 different herds, and 416,883 test-day records from 26,973 Ayrshire cows in 652 different herds covering a period of five years were obtained from the Quebec dairy herd improvement agency (Valacta). In addition to test-day records, information on lactation, animal status, feed composition and feeding systems was also available. For both Ayrshire and Holstein cows the fixed effect of Feeding System*DIMB (Blocks of 15 days in milk) was a significant effect in predictive models of daily milk, milk-fat, protein, and lactose yields and on milk urea nitrogen (MUN) concentration. Cows served a diet prepared with a Total Mixed Ration (TMR) compared to cows served a diet in a Traditional way tended to have higher peak milk yields and appeared to have a stronger persistency after peak milk yield. TMR-fed cows also showed a tendency for higher milk-fat, protein, and lactose yields and lower MUN concentrations than Traditionally-fed ones. Significantly higher milk yields (peak to 135 days in milk) and higher milk-fat and protein yields (peak to mid-lactation) were found in TMR-fed cows compared to Traditionally-fed ones in 3rd parity Holsteins. Both milk-fat and protein-yield lactation curves of TMR-fed cows displayed a different pattern than Traditionally-fed cows. The fixed effect of the Grain diet*DIMB was found to be a significant effect in predictive models of milk and milk-protein yields of both Ayrshire and Holstein. It was also found to be a significant effect in predictive model of MUN concentration but only in 2nd parity Ayrshire. The effect was non-significant in predictive models of both milk-fat or lactose yields. A tendency for higher milk and milk-protein yields, and lower MUN values was seen when cows received Corn Grain or High Moisture Corn compared to Barley or Commercial Concentrate but no significant differences were observed. It was concluded that a tendency for higher milk and components yields can be observed when cows are fed with a TMR compared to a Traditional system.

Two experiments were conducted to investigate the effects of metabolic acid-base balance on feed intake and susceptibility of dairy heifers to ketoacidosis. Animals were fed two dietary cation-anion difference diets [dietary cation-anion difference is defined as mEq (Na++K+)-(Cl -+S2-) kg-1 dietary dry matter], a high dietary cation-anion difference (positive) and a low dietary cation-anion difference (negative). The heifers fed the positive dietary cation-anion difference had significantly higher blood pH, blood bicarbonate and dry matter intake than heifers fed the negative dietary cation-anion difference. There was an initial decrease in dry matter intake by the heifers fed the negative dietary cation-anion difference. However this difference was not significant by the end of the two week period. It is unclear whether the reduced dry matter intake in the heifers fed the negative dietary cation-anion difference is the result of metabolic-acidosis caused by the anionic salts, poor palatability of the anionic salts or a combination of both. Heifers were induced into a nervous ketosis by feeding 1,3-butanediol. There was no difference in the incidence of ketosis between animals fed positive and negative dietary cation-anion difference. Animals fed the positive diet tended to be more susceptible to anorexia.

Dairy heifers were submitted to high or moderate plane of nutrition before and during first gestation. High plane of nutrition did not increase milk production but negatively affected reproduction and health. In addition, high plane of nutrition decreased growth hormone (GH) concentration and increased prolactin concentration during gestation. There was no effect of previous plane of nutrition on peripartum concentrations of hormones. Milk production was positively correlated with GH concentrations, but was negatively correlated to concentrations of insulin-like growth factor-1(IGF-1) concentrations postpartum. / The effect of GH administration on mammary vasculature and on paracrine secretion of growth factors was investigated in lactating and non-lactating dairy cows. The injection of GH induced a linear increase of IGF-1 concentration in blood and mammary primary lymph, but did not affect concentrations of prostaglandin E$ sb2$ (PGE$ sb2$) concentrations. However, the rate of IGF-1 increase was slower in lymph than in blood, suggesting that blood is the source of most lymph IGF-I. Therefore, GH did not seem to affect paracrine secretion of IGF-1 and PGE$ sb2$ by the bovine mammary gland. Growth hormone administration induced a gradual increase in mammary blood flow in lactating cows while it remained constant in non-lactating animals. Changes in lymphatic, but not blood, concentrations of a stable metabolite of the vasodilatator prostacyclin I$ sb2$ parallelled the changes in blood flow. This indicates that local secretion of this vasodilatator may be responsible for the effect of GH on mammary blood flow. / Mitogenic activity of mammary primary lymph samples taken at different physiological stages was evaluated on mammary epithelial and mammary fibroblast cell lines. The results indicate that the mitogenic activity of lymph in epithelial cells was not related to physiological stage but to PGE$ sb2$ concentration. In fibroblasts, mitogenic activity of lymph was not related to physiological stage or to the content in any of the growth factors assayed.

Twenty-five animals that were randomly selected on the basis of sex and age from among the animals feeding exclusively on communal grazing in Mogosane village and were used to investigate the mineral (P, Ca and Mg) status, especially P, based on blood and faecal P and to estimate the quantity of P they consumed from the pasture they were grazing. The project was conducted in the same area each month for one year, and no supplement was given. Months were blocks and seasonal changes were factors and the animals were experimental units within a block. Faecal, blood and grass samples were used as indicators of P, Ca and Mg minerals within experimental units, and Analysis of Variance was done to determine whether the P status of native pastures had a significant effect on the total P, Ca and Mg utilization and movement in and out of the blood and throughout the faeces during different periods the year. Body mass, condition scores and rainfall were also recorded during this trial. When the mineral status was investigated in this trial, it was found that mineral content in blood and faeces was directly related to the minerals in the pasture since these indicators were curvilinear increasing from winter months to spring months peaking in summer months with highly (P< 0.05) significant values when grazing was best and declining as the grazing became worse during autumn and winter months. The values of the body condition of the animals increased and declined with the values of body mass. Blood P .. concentration was very inconsistent and varied greatly and did not follow the same increasing and decreasing pattern followed by faeces and the grass. This emphasizes the fact that the P content of blood is not always good indicator of the P status in the animal. The mean faecal P concentration during winter was lower with the value of 1.23 ± 0.13 mg/g, during spring was low with the value of 1.8 ± 0.06 mg/g, during summer was higher with the value of 3.22 ± 0.12 mg/g and -( during autumn was high with the value of 1.98 ± 1.04 mg/g. The mean concentration of P in the grass during winter was lower with the value of 0.92 ± 0.04 mg/g, during spring was low with the value of 1.16 ± 0.08 mg/g, during summer was higher with the value of 1.68 ± 0.06 mg/g and during autumn was high with the value of 1.22 ± 0.09 mg/g. The seasonal rainfall correlated with the faecal and grass P values vary much with the value of 0 mm in the winter season, with the value of 26.33 mm in the spring, the value of 90.4 mm during summer and the value of 44.83 mm during autumn. Condition scores and body masses had the values of 2.08 units/20 1.4 Kg during winter season, had the values of 3.07 units/272.29 Kg in spring season, had the values of 3.88 units/371 Kg during summer season and the values of2.75 units/286.65 during autumn season, respectively. / Thesis (M.Sc. (Agric.) North-West University, Mafikeng Campus, 2005

No description available.

No description available.

The study was designed to test the hypothesis that P excretion in manure of dairy cattle could be reduced by manipulating electrolyte balance of the diet. Feces was the main route of P excretion, but fecal P was not affected by dietary cation-anion (DCAB) (P > 0.05). Plasma concentration of P tended (P < 0.10) to be higher at lower DCAB levels, implying that DCAB may have influenced P homeostasis. The overall P balance was not affected by the different DCAB levels. The range of DCAB where both P excretion and animal performance could be optimised is very narrow (+250 to +350 mEq/kg DM), so using DCAB to control P excretion in dairy cattle requires caution. (Abstract shortened by UMI.)