Four experiments were designed to examine the contribution of the oocyte or the follicular, oviductal, or early uterine environments to low fertility associated with the first ovulation postpartum. At 17-25 days postpartum in experiments 1, 2, and 3, suckled beef cows were assigned at random to receive 6 mg norgestomet, via ear-implant, for 9 days (NOR) or to serve as controls (CON). Calves were weaned from all cows 7 days after assignment to treatment in order to induce estrus, an LH surge, ovulation, and subsequent formation of CL. As cows were detected to be in estrus, they were bred first by natural service and 12 h later by artificial insemination. In experiment 1, on Day 3 after estrus, the oviduct ipsilateral to the side of ovulation was removed and flushed for recovery of an embryo or oocyte. Rates of recovery (86%), fertilization (68%), and development of fertilized oocytes to the 4- to 8-cell stage (100%) did not differ between CON and NOR cows. In experiment 2, uteri were flushed nonsurgically on Day 6 after estrus. Rates of recovery of embryos from the uterus were similar between CON (86%) and NOR (71%) cows. In experiment 3, one half of the cows in each group (CON and NOR) were fed melengestrol acetate (MGA) beginning on Day 4 after estrus and continuing until Day 35. The remaining cows in each group served as controls. Treatment with NOR increased (p < 0.05) the proportion of cows that maintained pregnancy until Day 35 (9/22) as compared to controls (0/18).(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

The first two experiments examined the role of the uterus in low pregnancy rates of beef cows induced to ovulate by early weaning. At 20 to 25 d postpartum, one-half of the cows in Exp. 1 and 2 received a s.c. implant containing 6 mg of norgestomet (NOR) for 9 d (NOR-pretreated) and the remaining cows were untreated controls (CON). Lengths of first postpartum luteal phase after weaning of calves at d 7 after implant insertion were expected to be normal in NOR-pretreated and short in CON cows. In Exp. 1, cows of both groups received an implant containing 3 mg of NOR at d 4 after first estrus and a silastic implant with 15 or 25 mg of NOR at d 7 after first estrus. At 7 d after first estrus, two embryos were transferred into the uterus of each cow and pregnancy was diagnosed by ultrasonography at d 35. Blood samples were collected daily from onset of treatment to d 8 after estrus and then every other day to d 24. Only 4 of 22 cows were pregnant at d 35, concentrations of estradiol (E2) were elevated after luteolysis, and large follicles were present at d 35. In Exp. 2, all cows were injected with 100 mg of progesterone (P4) twice daily from d 4 to 35 after first estrus. Embryos were transferred, pregnancy was diagnosed, and blood samples were collected as in Exp. 1, except blood sampling was continued to d 34.(ABSTRACT TRUNCATED AT 250 WORDS)

COMBINATIONS OF INSULIN, SELENIUM AND TRANSFERRIN THAT MAXIMIZE MATURATION, FERTILIZATION AND CULTURE 2.1 INTRODUCTION 2.1.1 The selection of a buD for in vitro fertilization 2.1.2 Addition of insulin-transferrin-selenium (ITS) to maturation medium 2.1.3 The addition of insulin, selenium or transferrin individually or in combination to maturation, fertilization or culture medium 2.2 MATERIALS AND METHODS 2.2.1 Oocyte recovery and selection 2.2.2 In vitro maturation procedure 2.2.3 Maturation controls 2.2.4 Assessment of sperm motility and morphology 2.2.5 In vitro fertilization procedure 2.2.6 Fertilization controls 2.2.7 In vitro culture procedure 2.2.8 Experimental design and statistical analysis 2.3 RESULTS 2.3.1 Bull selection 2.3.2 Addition of ITS to maturation medium 2.3.3 Insulin, selenium and transferrin in the maturation, fertilization and culture medium 31 33