Thesis (doctoral)--Universiteit Utrecht, 2003. / Includes bibliographical references (158-171).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1987. / Vita. Abstract. Includes bibliographical references (leaves 52-57). Also available via the Internet.

Thesis (M.S.)--Ohio State University, 1985. / Includes bibliographical references (leaves 54-59). Available online via OhioLINK's ETD Center

Milk fever (parturient paresis / hypocalcaemia) is a metabolic disorder that usually occurs near parturition and at the onset of lactation in high producing multiparous dairy cows. Milk fever can indirectly contribute to an increased incidence of several diseases in early lactation. This study was conducted to compare two different feeding strategies to prevent milk fever, namely (i) the established concept of feeding a diet with a negative DCAD and (ii) a feeding strategy combining a negative DCAD supplement with 25-hydroxyvitamin D3 (25-OH-D3). Thirty dairy cows were used in a randomized block design and were selected and blocked by parity (second parity and later), 305 day mature equivalent milk production in the previous lactation and expected calving date. Within each of the 15 blocks, the cows were allocated to two experimental groups named DCAD and DCAD + HyD. Fifteen animals in the DCAD + HyD group received a daily oral dosage of 3 mg of 25-OH-D3. Plasma samples were collected from day 21 prepartum to 10 days postpartum and were analysed for 25-OH-D3, 1,25-dihydroxyvitamin D3, total and ionized calcium, phosphorus and magnesium. Samples were collected on day 21, 14, 10 prepartum and every second day to calving, 4 and 6 h postpartum and every second day up to day 10 after calving. Urinary samples for determination of macro minerals (calcium and phosphorus) were collected via manual stimulation on day 21, 14, 8 and 4 prepartum and day 4 postpartum. These samples were used to ensure that mild metabolic acidosis was achieved in both treatment groups. The metabolic acidosis was demonstrated by decreased urinary pH. Milk samples were collected on day 1, 4 and 10 postpartum and used for macro mineral (calcium and phosphorus) determination. This study did not achieve all of the expected results observed in similar experiments. No treatment differences could be detected for plasma Ca2+ concentrations (P>0.05) and the mean plasma Ca2+ concentrations were [1.086a mmol/L ± 0.010 (DCAD treatment) and 1.083a mmol/L ± 0.010 (DCAD + HyD treatment)] respectively.   Furthermore 1,25-(OH)2D3 plasma concentrations did not indicate any treatment differences (P>0.05). These results could be due to the fact that the experimental animals were not sufficiently challenged and therefore the combination of a low DCAD diet and Rovimix HyD did not influence the calcium homeostatic mechanisms as expected. A clear correlation between plasma 25-OH-D3 concentration and treatment duration was however demonstrated (P<0.001), indicating effective absorption of orally supplemented 25-OH-D3. Several authors demonstrated that feeding massive doses of vitamin D2 (30 million units) for extended periods led to clinical evidence of vitamin D toxicity. When 10 million IU of vitamin D3 were however administered intramuscularly within 10 days of parturition, a reasonable measure of protection against toxicity could be provided. It can be concluded from this study that longer feeding periods (± 21 days) than the proposed 10 days prior to calving can safely be implemented when feeding 3 mg 25-OH-D3 per animal per day (=240 mg Rovimix HyD 1,25%). Copyright / Dissertation (MSc(Agric))--University of Pretoria, 2012. / Animal and Wildlife Sciences / unrestricted

No description available.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

LD2668 .T4 1942 E4 / Master of Science

Call number: LD2668 .T4 1963 H36 / Master of Science

Call number: LD2668 .T4 1951 B87 / Master of Science

Numerous investigations have been made on the contribution of butter cultures to the flavor of cultured cream butter, but production of uniform cultured cream butter has not been possible in industry. Therefore, it was desirable to investigate in detail the qualitative and quantitative chemistry of the flavor of high quality butter cultures, and to examine more closely some of the aspects of flavor production by butter culture organisms. Volatile flavor components of high quality butter culture and control heated milk were isolated from intact samples by means of a specially designed low-temperature, reduced-pressure steam distillation apparatus. Most of the flavor compounds present in the resulting distillate fractions were tentatively identified by gas chromatographic relative retention time data. Flavor concentrates obtained by ethyl ether extractions of aqueous distillates were also separated by temperature-programmed, capillary column gas chromatography, and the effluent from the capillary column was analyzed by a fast- scan mass spectrometer. Many of the flavor compounds in the flavor concentrates were positively identified by correlation of mass spectral and gas chromatographic data. In addition, supporting evidence for the identification of some flavor components was obtained through the use of qualitative functional group reagents, derivatives and headspace gas chromatography. Compounds that were positively identified in butter culture include ethanol, acetone, ethyl formate, methyl acetate, acetaldehyde, diacetyl, ethyl acetate, dimethyl sulfide, butanone, 2-butanol, methyl butyrate, ethyl butyrate, methane, methyl chloride, carbon dioxide and methanol; also included were 2-pentanone, 2-heptanone, acetoin, formic acid, acetic acid, lactic acid, 2-furfural, 2-furfurol, methyl hexanoate, ethyl hexanoate, 2-nonanone, 2-undecanone, methyl octanoate and ethyl octanoate. Compounds that were tentatively identified in butter culture include hydrogen sulfide, methyl mercaptan, n-butanal, n-butanol, 2-hexanone, n-pentanal, n-pentanol, 2-mercaptoethanol, n-butyl formate, n-butyl acetate, 2-methylbutanal, 3-methylbutanal, methylpropanal, methyl heptanoate, n-octanal, 2-tridecanone, methyl benzoate, methyl nonanoate, ethyl nonanoate, ethyl decanoate, methyl dodecanoate, ethyl dodecanoate, delta-octalactone and delta-decalactone. Compounds that were positively identified in control heated milk include acetaldehyde, ethyl formate, ethyl acetate, 2-heptanone, 2-furfural, 2-furfurol, 2-nonanone, 2-undecanone, ethyl octanoate and methyl decanoate. Compounds that were tentatively identified in control heated milk include dimethyl sulfide, hydrogen sulfide, ammonia, methyl mercaptan, methyl acetate, acetone, methanol, butanone, butanal, n-butanol, methyl butyrate, ethyl butyrate, 2-pentanone, 2-hexanone, 2-mercaptoethanol, 2-furfuryl acetate, ethyl hexanoate, methyl heptanoate, 2-tridecanone, ethyl decanoate, ethyl dodecanoate, delta-octalactone and delta-decalactone. The data indicated that the qualitative flavor composition of control heated milk and butter culture were very similar. Diacetyl, ethanol, 2-butanol and acetic acid were noted to be consistently absent in the data for the control heated milk. Other compounds were not observed in the heated milk fractions, but were also absent from some of the culture fractions. This was attributed to their presence in low concentrations, chemical instability or inefficient recovery. A modified 3-methyl-2-benzothiazolone hydrazone spectrophotometric procedure was adapted for the determination of acetaldehyde produced in lactic starter cultures. The procedure was applied in conjunction with diacetyl measurements in studying single- and mixed-strain lactic cultures. The diacetyl to acetaldehyde ratio was found to be approximately 4:1 in desirably flavored mixed-strain butter cultures. When the ratio of the two compounds was lower than 3:1 a green flavor was observed. Acetaldehyde utilization at 21°C by Leuconostoc citrovorum 91404 was very rapid in both acidified (pH 4.5) and non-acidified (pH 6.5) milk cultures. The addition of five p.p.m. of acetaldehyde to non-acidified milk media prior to inoculation greatly enhanced growth of L. citrovorum 91404 during incubation at 21°C. Combinations of single-strain organisms demonstrated that the green flavor defect can result from excess numbers of Streptococcus lactis or Streptococcus diacetilactis in relation to the L. citrovorum population. Diacetyl, dimethyl sulfide, acetaldehyde, acetic acid and carbon dioxide were found to be "key" compounds in natural butter culture flavor. Optimum levels of these compounds in butter culture were ascertained by chemical or flavor panel evaluations. On the basis of these determinations, a synthetic butter culture prepared with heated whole milk and delta-gluconolactone (final pH 4.65) was flavored with 2.0 p.p.m. of diacetyl, 0.5 p.p.m. of acetaldehyde, 1250 p.p.m. of acetic acid, 25.0 p.p.b. of dimethyl sulfide and a small amount of sodium bicarbonate for production of carbon dioxide. The resulting synthetic butter culture exhibited the typical aroma, flavor and body characteristics found in natural high quality butter cultures, except that the delta-gluconolactone was found to contribute an astringent flavor. / Graduation date: 1965