Masters Theses

Date of Award

8-1998

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

F. Neal Schrick

Committee Members

Fred Hopkins, Richard Heitmann

Abstract

Cycling (n = 90) and pregnant (n = 51) beef cows were utilized as oocyte donors to examine the effects of body condition and pregnancy status on oocyte development. Cows were scored for body condition (BCS, scale 1-9) immediately prior to slaughter and classified as either good (BCS = 5-6) or thin (BCS = 3-4). Blood samples were collected for determination of progesterone (P4), insulin (INS), non-esterified fatty acids (NEFA), and blood urea nitrogen (BUN) at exsanguination. Ovaries were collected approximately 15 minutes postmortem and separated into one of four groups based on body condition and pregnancy status: good non-pregnant (GNP; n = 96), good pregnant (GP; n = 54), thin non-pregnant (TNP; n = 84), and thin pregnant (TP; n = 48). Blood samples and ovaries from cows greater than the first trimester of pregnancy were discarded. At the laboratory, the number of small (< 5 mm), medium (6-10 mm), and large (>10 mm) follicles per ovary and the presence or absence of a corpus luteum were recorded. Oocytes were collected from follicles and subjected to identical in vitro maturation, fertilization, and culture procedures. Only oocytes with a compact layer of cumulus cells and an evenly granulated cytoplasm were utilized. Total number of oocytes utilized per group were 306, 249, 225, and 252 for GNP, GP, TNP, and TP, respectively. Embryos were fertilized with proven quality semen and cultured in simple media. On days three and eight post-fertilization, cleavage, 8-cell, and blastocyst development was recorded. Blood samples were statistically analyzed by BCS, while follicular populations and embryonic development were analyzed in a 2 x 2 factorial by BCS, pregnancy (PREG) status, and the interaction between BCS and PREG. Good and thin conditioned cows exhibited no differences in concentrations of P4 (P = .77), NEFA (P = .52) or BUN (P = .65). Insulin concentrations were lower in thin (.5 ± .04 ng/ml) compared to good conditioned cows (.67 ± .04 ng/ml; P = .0003). Results of metabolic assays indicate that thin cows were not nutritionally stressed and any effects measured were due to BCS alone. Body condition and PREG did not affect the number of oocytes recovered, nor embryonic development to the cleaved, 8-cell, or blastocyst stages. Total numbers of follicles per ovary were greater in pregnant cows (13.3 ± 1) compared to cycling cows (10.5 ± .8; P = .006). Furthermore, thin body condition and TNP cows exhibited a strong tendency to be lower than all other groups (P = .09; P = .07, respectively). Numbers of small follicles were greater in good body condition cows (11.6 ± .7) compared to thin cows (9.9 ± .7; P = .05), and pregnant cows (12.3 ± .8) compared to non-pregnant cows (9.2 ± .6; P = .0001). Medium and large follicles did not differ between BCS and PREG. In conclusion, body condition and pregnancy status did not influence developmental potential of oocytes to the blastocyst stage.

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