Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Animal Science

First Advisor

Robert A. Godke

Abstract

In the first experiment, the temperature humidity index (THI) was compared with pregnancy rates (PR) in bovine females under two different environmental cooling systems. The PR decreased if the THI was greater on the second day prior to or after mating compared with that of the day of mating. In the second experiment, the stages of embryo mortality in the first 40 days of gestation were identified in the hot and cool seasons of the year. At day 13 or 14 of pregnancy 27% of embryos were viable in the hot months, which was less than 60% at day 13 or 14 in the cool months. The results suggest that embryonic loss after day 6 or 7 of pregnancy is a problem for high producing cows in this hot climate. In a third experiment, conceptus loss (CPL) $\geq$40 days of gestation was evaluated in 2,874 dairy cows. Overall conceptus loss occurred in 16.5% of the females. Results indicate that CPL continues to be a problem in dairy cattle after 40 days of gestation. In the fourth experiment, conceptus death was induced in beef females between days 25 and 50 of gestation by intrauterine infusion of colchicine. The results verify that luteal activity is maintained after conceptus death and that the interval to estrus may be reduced by administering prostaglandins after diagnosis of conceptus death. In a fifth experiment, day-6 bovine embryos received either an acute stress prior to co-culture at 38.6$\sp\circ$C, cultured-continuously at 38.6$\sp\circ$C or cultured continuously at 40$\sp\circ$C on an oviductal monolayer. Results show that a chronic heat stress is detrimental to embryo viability but that an acute stress significantly improved embryo development in vitro. In a final experiment, pregnant beef females were superstimulated with gonadotropin treatment at each trimester of gestation. Sixty oocytes from first trimester pregnant females were exposed to IVF resulting in 20% developing to the 2-cell stage with 50% of these reaching the morula stage. Results suggest that oocytes from early gestating females were capable of fertilization and development to the morula stage in vitro.

Pages

267

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