It has been reported world wide that over the past fifty years production has dramatically increased in dairy cattle but at the same time fertility rates have steadily declined, particularly in mature cows. Fertility of heifers that were bred for the first time has not been affected. One of the major reasons for such fertility decline in mature cows could be impaired progesterone production. Therefore relationships of parity with reproductive performance, its effect on progesterone concentrations and genes associated with progesterone synthesis were examined in this thesis. In the first experiment, breeding records of 163 Holstein heifers and cows in 1st, 2nd, and 3rd/4th parities were used to compare pregnancy rates among heifers and parity cows and between parity cows. Progesterone levels of heifers, 1st, 2nd, and 3rd/4th parity (10 animals each group) were measured from milk and blood samples. First and second inseminations pregnancy rates were higher in heifers compared to other parity cows. Furthermore 1st parity cows showed higher pregnancy rates than 2nd and 3rd/4th parity cows. However, P₄ levels were not significantly different among animals of different parity. In the second experiment, expression levels of steroidogenic genes – StAR, P450scc, 3-β HSD; apoptotic genes Bax and Bcl-2; and HSP70 in corpus luteum obtained from six heifers and three 2nd/3rd parity lactating cows were compared using RT-PCR. Relative optical density with house keeping gene was obtained for each gene. Analysis of variance revealed that expression levels of steroidogenic and Bax genes are higher (p<0.05) in cows than heifers. HSP70 gene and Bcl-2 gene expressions were not different (P>0.05) between the two groups. This study confirmed a clear relationship between parity and reproductive performance. There was no significance relationship between parity and circulating progesterone levels. Steroidogenic genes expression was higher in lactating cows than heifers and no differences were seen in mRNA levels of Bcl2, and HSP70 genes between heifers and mature cows. Bax mRNA expression was higher in mature cows suggesting that the lifespan of corpus luteum may be compromised in 2nd and 3rd parity cows, resulting in early embryonic mortality and reduced pregnancy rates.

Thesis (Ph. D.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xvi, 218 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 92-114).

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 126-145). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 126-145). Also available on the Internet.

Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains viii, 71 p. : ill. Includes abstract. Includes bibliographical references (p. 60-71).

It has been reported world wide that over the past fifty years production has dramatically increased in dairy cattle but at the same time fertility rates have steadily declined, particularly in mature cows. Fertility of heifers that were bred for the first time has not been affected. One of the major reasons for such fertility decline in mature cows could be impaired progesterone production. Therefore relationships of parity with reproductive performance, its effect on progesterone concentrations and genes associated with progesterone synthesis were examined in this thesis. In the first experiment, breeding records of 163 Holstein heifers and cows in 1st, 2nd, and 3rd/4th parities were used to compare pregnancy rates among heifers and parity cows and between parity cows. Progesterone levels of heifers, 1st, 2nd, and 3rd/4th parity (10 animals each group) were measured from milk and blood samples. First and second inseminations pregnancy rates were higher in heifers compared to other parity cows. Furthermore 1st parity cows showed higher pregnancy rates than 2nd and 3rd/4th parity cows. However, P₄ levels were not significantly different among animals of different parity. In the second experiment, expression levels of steroidogenic genes – StAR, P450scc, 3-β HSD; apoptotic genes Bax and Bcl-2; and HSP70 in corpus luteum obtained from six heifers and three 2nd/3rd parity lactating cows were compared using RT-PCR. Relative optical density with house keeping gene was obtained for each gene. Analysis of variance revealed that expression levels of steroidogenic and Bax genes are higher (p<0.05) in cows than heifers. HSP70 gene and Bcl-2 gene expressions were not different (P>0.05) between the two groups. This study confirmed a clear relationship between parity and reproductive performance. There was no significance relationship between parity and circulating progesterone levels. Steroidogenic genes expression was higher in lactating cows than heifers and no differences were seen in mRNA levels of Bcl2, and HSP70 genes between heifers and mature cows. Bax mRNA expression was higher in mature cows suggesting that the lifespan of corpus luteum may be compromised in 2nd and 3rd parity cows, resulting in early embryonic mortality and reduced pregnancy rates. / Land and Food Systems, Faculty of / Graduate

The objective of this study was to examine hepatic steroid inactivation and luteal function throughout bovine gestation. In pregnant beef cows, cytochrome P450 3A activity decreased from mid- to late-gestation, while progesterone concentrations tended to increase from mid- to late-gestation. Uridine diphosphate-glucuronosyltransferase activity per kg of body weight was increased in pregnant vs non-pregnant dairy cows. Total corpus luteum (CL) blood perfusion tended to be increased in pregnant vs non-pregnant dairy cows. Hepatic portal blood flow per kg of body weight was increased in pregnant vs non-pregnant dairy cows. Hepatic steroid inactivating enzyme activity, CL blood perfusion, and portal blood flow did not differ between pregnant and non-pregnant beef cows. There was no difference in progesterone concentrations in pregnant vs non-pregnant dairy or beef cows. The current study highlights the relevance of further investigation into steroid secretion and inactivation and their impact on the maintenance of pregnancy in cattle.

No description available.

Establishment and maintenance of pregnancy is a central concern to the cattle industry, as it strongly impacts efficiency and profitability of beef cow-calf operations. The objective of this study was to determine if nutrient restriction impacts ovulatory follicle size and corpus luteum (CL) development and function of Bos taurus cows enrolled in estrous synchronization. A total of 26 Angus cows were housed in a facility equipped with a Calan gate system for individual animal intake. Cows were stratified by body weight (BW), and randomly assigned one of two nutritional treatments: 1) 100% of nutrient requirements (MTN; n=13) or 2) 70% of nutrient requirements (REST; n=13). Individual daily intakes were measured and adjusted weekly based on BW. Cattle underwent an acclimation period of 14 days and were exposed to nutritional treatments for 30 days prior to estrous synchronization. Body weight was measured daily using an automated scale and a conventional livestock scale at the beginning and end of the experiment. Cows were synchronized using a 7-day CO-synch + CIDR protocol beginning on day -10. Ultrasonography of the ovaries was performed at each event of the estrous synchronization protocol on days -10, -3, 0, 5, and 7. Blood samples were taken on days -10, -3, and daily from day 0 through 7 to observe changes in progesterone (P4). Data were analyzed as repeated measures using the MIXED procedure of SAS. Initial BW tended to differ between treatments (P = 0.07; MTN 597 ± 32 kg, REST 604 ± 32 kg), but MTN had greater final BW (P < 0.001; 687 ± 24 and 556 ± 27 kg, respectively) and greater average daily gain (1.35 ± 0.18 and -0.72 ± 0.21 kg/d, respectively, P < 0.001) than REST. Diameter of the largest follicle was similar (P = 0.851) between treatments at CIDR insertion (12.6 ± 0.6 mm) and CIDR removal (12.9 ± 0.4 mm) but was greater (P < 0.05) for MTN than REST cows at 60 hrs after CIDR removal (14.01 ± 0.6 and 12.37 ± 0.5 mm, respectively). Volume of CL was similar (P > 0.1) at 5 (3211 ± 113 mm3) and 7 (5280.3 ± 212 mm3) days after ovulation. Concentration of P4 did not differ on days -10, -3, or 0-5. However, on days 6 and 7, P4 was greater (P < 0.05) for MTN than REST (2.07 ± 0.15 and 1.65 ± 0.15, and 2.27 ± 0.15 and 1.83 ± 0.15 ng/mL, respectively). In conclusion, nutrient restriction to 70% of maintenance during estrous synchronization negatively affects diameter of the ovulatory follicle and circulating P4, but it did not affect CL volume in multiparous Bos taurus beef cows. / Master of Science / Ensuring successful pregnancy in beef cow-calf operations is crucial for the efficiency and profitability of the cattle industry. This study investigates the effects of nutrient restriction on ovulatory follicle size and corpus luteum (CL) volume in Angus cows undergoing estrous synchronization. A total of 26 cows were subjected to either a maintenance diet meeting 100% of nutrient requirements (MTN) or a diet providing 70% of nutrient requirements (REST). Intakes were updated weekly using computer software. The cows underwent a 30-day nutritional treatment before synchronization of ovulation. Results revealed that cows on the maintenance diet exhibited greater final body weight and average daily gain compared to those on the restricted diet. While estrus expression showed a numerical increase in MTN cows, the impact was not statistically significant. Analysis of ovulatory follicle size demonstrated that MTN cows had larger follicles 60 hours after synchronization compared to REST cows. Surprisingly, corpus luteum volume did not differ between the two groups at 5 and 7 days after ovulation. Additionally, circulating progesterone (P4) levels were affected by nutrient restriction, with notable differences observed on days 6 and 7. In summary, nutrient restriction during ovulation synchronization negatively influenced ovulatory follicle size and P4 levels, but did not affect corpus luteum volume in mature Angus cows. These findings contribute valuable insights for the cattle industry, emphasizing the importance of proper nutrition for optimal reproductive health in beef cows.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Restricted until May 2007. Bibliography: leaves 97-114.