The effects of energy balance on hormonal patterns and recovered oocytes were evaluated in 20 lactating Holstein cows during two trial periods (fall/spring). Cows were randomly selected and assigned to one of two dietary treatments formulated so that cows consumed 3.6% BW (HE- 1.78 mcal/kg; n=6 in fall, n=5 in spring) and 3.2% BW (LE-1.52 mcal/kg; n= 5 in fall, n=4 in spring). Body weight and body condition score (BCS) were recorded prior to parturition and weekly throughout the fall trial. Ultrasound guided transvaginal follicular aspirations were conducted twice weekly between d 30 and 100 of lactation. Follicle size and number were recorded. Follicular fluid (FF) was aspirated from the largest follicle, and serum samples were collected for hormone assay (IGF-1; estradiol (E2); progesterone (P4, serum ); LH and FSH). Oocytes were collected and graded based upon cumulus density and ooplasm homogeneity, then fertilized and cultured in vitro. Milk yield averaged 41.64 ± .3 kg/d (mean ± SE) for HE and 32.8 ± .3 kg/d for LE. There was a significant cubic day postpartum by treatment interaction for milk yield. Dry matter intake and BW treatment by week interactions were significant for the cubic and linear components, respectively. Oocyte numbers increased linearly from d 30 to 100 postpartum. HE cows produced more good + oocytes (1.5 ± .2 ) than LE cows (1.4 ± .1). Follicles less than or equal to 5 mm predominated throughout the study (6.4 ± 3.0). However, greater numbers of follicles 10 to 14 mm and greater than or equal to 15 mm were found in the fall (1.98 ± .08 and .50 ± .06) than spring (1.11 ± .3 and .23 ± .07). Follicular fluid IGF-1 was higher in HE (2.3 ± .2 ng/ml) than in LE cows (1.6 ± .2 ng/ml). Mean basal serum FSH concentration was lower at 28 d postpartum (173 ± 8 pg/ml) compared to later (521 ± 25 at d 60 and 650 ± 25 pg/ml at d 110). Serum P4 peaked at 35 d postpartum, with HE cows having 1 ng/ml higher P4 than LE cows. Low dietary energy reduced milk yield, DMI, BCS, FF IGF-1 and serum P4 and had a negative impact on oocyte quality. / Master of Science

The development of oocytes of differing quality retrieved using transvaginal follicular aspiration (TVFA) and following DNA injection was examined. Eight cows were subjected to twice weekly TVF A for 16 wk. Oocytes retrieved were graded and placed in an in-vitro maturation, fertilization and co-culture (IVMIIVFIIVC) program. Two thirds of oocytes were injected with DNA. Good quality oocytes from slaughtered cows (SH) were obtained once monthly and processed the same way. Good quality TVF A oocytes had a higher mean development score than poor quality oocytes, but not different from that of good quality SH oocytes. Good quality TVF A oocytes produced more viable embryos (31.7% blastocysts) than poor quality oocytes or SH oocytes (12.8% and 20.4% blastocysts, respectively). Embryo development following injection of DNA was the same for oocytes for each source-quality group (TVF A-good, 8.4; TVF A-poor, 5.5; SH-good, 6.3 % blastocysts). Development of good quality TVFA oocytes increased during the last 9 wk of the 16 wk collection period. Poor oocyte development increased slightly to 9 wk and then decreased. Development of TVF A oocytes injected with DNA did not vary during the experiment. However, development of controls increased from a mean score of2.50 at wk 1 to 4.17 at wk 16. Oocytes from TVFA produced more PCR positive blastocysts (95.0%) than SH oocytes (61.5%). More calves were born from the transfer of embryos injected with DNA from TVF A oocytes (3/5) than from SH oocytes (116), although not statistically significant. One calf was PCR positive in bone-marrow, but was negative in other tissues. The use of oocytes obtained by TVF A may improve the efficiency of producing transgenic cattle. / Master of Science