Nasim Ahmad

Date of Graduation

1996

Document Type

Dissertation/Thesis

Abstract

Two experiments were conducted to examine the effects of patterns of follicular development on fertility in beef cows. In Experiment 1, effects of persistent follicles (PF) on recovery of embryos, fertilization, and embryonic development were examined. PF cows (n = 20) received a low dose of progesterone, intravagianally on Days 4-13 after pretreatment estrus (Day 0) and two injections of 20 mg prostaglandin (PG) F{dollar}\\sb{lcub}2\\alpha{rcub}{dollar}, on Day 6. Cows with growing follicle (GF; n = 22) received only PGF{dollar}\\sb{lcub}2\\alpha{rcub}{dollar} on Day 6. Follicular development was monitored by ultrasonography. Mean estradiol-17{dollar}\\beta{dollar} (E{dollar}\\sb2{dollar}) in plasma during six days before estrus was higher in PF than in GF (5.7 {dollar}\\pm{dollar} 0.4 vs 2.6 {dollar}\\pm{dollar} 0.4 pg/ml; {dollar}P < 0.01{dollar}). Recovery of embryos on Day 6 was lower (70%) in PF than in GF (90%; {dollar}P < 0.05{dollar}). Fertilization rate (97%) and accessory sperm (38 {dollar}\\pm{dollar} 12) for recovered embryos did not differ with treatment. Fewer embryos had reached {dollar}\\ge{dollar}16 cell stage of development in PF (14%) and were good morulae (14%) than in GF (86% and 73%, respectively; {dollar}P < 0.01{dollar}). Death of embryos in PF could reflect effects of elevated E{dollar}\\sb2{dollar} on oocyte maturation or oviductal function. In Experiment 2 effects of two (2W) or three (3W) follicular waves before and during the equivalent of one estrous cycle after breeding and associated patterns of estradiol on pregnancy rate were examined. More of 59 animals with estrous cycles of 17-25 days had 2W (86%) than 3W (14%) during the estrous cycle before breeding ({dollar}P < 0.01{dollar}). Cycles averaged 1.1 days longer ({dollar}P < 0.10{dollar}) and corpora lutea regressed later ({dollar}P < 0.01{dollar}) in animals with 3W than in those with 2W, but patterns of estradiol before ovulation did not differ. Pregnancy rates, 82% in cows with 2W and 100% in cows with 3W, did not differ during the postbreeding period. After breeding, 49% of the animals had 2W and 51% had 3W and fewer animals with 2W than 3W after-breeding became pregnant (70 vs 96%; {dollar}P < 0.05{dollar}).

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