Includes bibliographical references (leaves 98-128). / iv, 128 leaves, [22] leaves of plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates protein secretion by bovine Sertoli cells in culture. Cultures were obtained from bulls at all stages of post natal development and from sexually mature animals. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Sciences, 1987

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Call number: LD2668 .T4 1955 G64 / Master of Science

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Photocopy of typescript. / Digitized by Kansas Correctional Industries

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Although the occurrence of ketosis is a postpartum phenomenon, recent studies have focused on the prepartum period as key in the development of the disorder. Indicators of prepartum energy status, such as depressed dry matter intake (DMI) and elevated plasma non-esterified fatty acid (NEFA) concentrations have been associated with the occurrence of ketosis. The objective of this study was to investigate the role of phosphoenolpyruvate carboxykinase (PEPCK) in the periparturient and ketotic cow. The enzyme PEPCK catalyzes the rate limiting step in gluconeogenesis in hepatocytes. Whereas, in adipocytes, it has been suggested that PEPCK functions in the synthesis of glycerol for the formation of triacylglycerol (TAG) when plasma glucose concentrations are low. Thirty-four pregnant multiparous Holstein dairy cows were fed a single prepartum ration that consisted of 50% oat hay, 18% corn silage and 32% grain mix (DM basis). The ration was formulated to meet or exceed NRC requirements of 14% CP and 1.6 Mcal/kg NE[subscript L]. At calving, cows were transitioned onto one of two postpartum diets: control (n=14) or 3.5% supplemental fat (n=20). The postpartum diets, fed from wk 1 to 3, were formulated to isonitrogenous and to meet NRC requirements. Both diets consisted of 25% alfalfa, 25% corn silage and 50% grain mix. The control and fat diets contained 17.2 and 17.6% CP and 1.67 and 1.74 Mcal/kg NE[subscript L] respectively. Liver biopsies from 28 cows and adipose tissue biopsies from 6 cows were collected at -14, 2 or 3 and 14 d relative to calving. Tissue samples were analyzed for PEPCK mRNA and activity. All results were analyzed by period: prepartum (-21 to -2 d), freshening (2 to 7 d) and postpartum (8 to 21 d). In a previous study in our lab, 25 and 75% cows on the control and fat diets, respectively, experienced ketosis. In the current study there a 40% occurrence of ketosis for both control and fat diet groups. The high occurrence in both diets may be attributed to the rapid transition from the dry cow ration (70:30 forage to concentrate ratio, DM basis) to the lactating cow ration (50:50 forage to concentrate ratio, DM basis). The cows on the fat diet had lower serum glucose at freshening. Cows with ketosis had higher prepartum body weights (788 kg) than non-ketotic cows (743 kg; P<.1). No prepartum differences were seen in body condition score, DMI, NE[subscript L] balance, NEFA, glucose or ��-hydroxybutyrate concentrations were detected between ketotic and non-ketotic cows. Expression of adipose PEPCK mRNA was not different between ketotic and non-ketotic cows. However, hepatic PEPCK mRNA expression was higher in non-ketotic cows at freshening when compared to ketotic cows. Cows that experienced ketosis had lower hepatic PEPCK activity prepartum (6.6 vs. 9.3 units /min/g protein) and postpartum (7.6 vs. 10.2 units/min/g protein; P<0.5) when compared to non-ketotic cows. Our data indicated that hepatic PEPCK is a useful prepartum predictor of a cows susceptibility to ketosis. / Graduation date: 1998

This study was designed to determine the potential biological effects of electric and magnetic fields (EMF), generated by 735 kV alternating current (AC) high tension lines upon the hormonal profile, some health-related parameters, stress response and productivity in dairy cattle. An EMF exposure chamber to house eight animals at one time was constructed. Forty-nine cows were divided according to their production stage; 8 pregnant non-lactating cows, 16 pregnant lactating cows, 16 non-pregnant lactating cows and 9 non-lactating non-pregnant heifers. They were exposed to an EMF of 10 kilovolts per meter (kV/m) and 30 micro-Tesla $( mu T)$ in two different fashions: (a) for three consecutive periods of 28 days in two sequences either with the EMF on/off/on or off/on/off, in a switch back design; (b) for three consecutive periods with the sequence OFF (5 days), ON (30 days) and OFF (5-12 days). The intensity of the EMF chosen for the experiments resembled a situation in which the cattle are standing continuously under a 735 kV AC high tension line when the line has a maximum load of current. In reality, these conditions are found only for a few days during the winter in the Province of Quebec. / Milk production and composition, feed consumption, blood hormonal profiles and cerebrospinal fluid (CSF) components were assessed during the different periods of exposure. Most of the variables assessed were not affected by EMF. However, there was a positive association between EMF and feed consumption, milk fat content, blood plasma progesterone during pregnancy and estrous cycle length. Also, there were changes in the mineral and neurotransmitter metabolite concentrations in the CSF that showed a relationship to the EMF. / In conclusion, it could be stated that EMF caused a biological response in dairy cattle. It is speculated that these changes do not represent a health hazard for exposed cattle, although they warrant further research.

This study consisted of a series of experiments designed to test the hypothesis that exposure to extremely low frequency (ELF) electric and magnetic fields (EMF), similar to those generated by power transmission lines, can modify the response to photoperiod in dairy cows. Thirty two Holstein cows, 16 pregnant and lactating and 16 non-pregnant and non-lactating, maintained under short photoperiod (8 h light, 16 h dark), were exposed to an electric field of 10 kV/m and a magnetic field of 30 muTesla for 16 h/d, using cross-over experimental designs with three-period sequences. These exposure conditions resembled those prevalent under a 735 kV line carrying an extreme current load. Feed consumption, milk yield and composition, body weight, circulating concentrations of melatonin, prolactin, IGF-1 and growth hormone were assessed, as well as estrous cycle traits. A positive association was found between EMF exposure and feed consumption, uncorrected milk yield at the end of the exposure period and blood concentration of IGF-1. EMF exposure was also associated with an increase in blood prolactin concentration and decreased melatonin levels during the photophase in lactating pregnant cows. Non-lactating cows exposed to EMF showed longer estrous cycles. It was concluded that exposure to ELF EMF similar to those found under power transmission lines under extreme conditions of load elicits a biological response in dairy cows. Some aspects of this response are consistent with the hypothesis of a modification of the response to photoperiod.