Date of this Version
Thesis (M.S.)—University of Nebraska—Lincoln, 1968. Department of Animal Science.
Restricted energy intake before calving has been shown to delay the onset of post-partum estrus in the lactating bovine; this effect is most pronounced in young cows and is produced even when high levels of energy are fed after calving.
Little research has been conducted to determine the changes in the reproductive system that account for the differences in post-partum reproductive performance. The present experiment was conducted to determine the differences in pre-partum and post-partum ovarian and uterine function in two-year old beef female subjected to high and low levels of energy prior to calving.
Seventy-four pregnant yearling Hereford heifers were randomly assigned to two pre-calving diets (high energy diet and a low energy diet) and seven slaughter groups approximately 140 days prior to calving. Heifers were slaughtered initially (140 days prior to calving) and from each ration treatment at 45 days pre-calving, zero (within 24 hours), 15, 30, 45 days and day 10 of the second post-partum estrous cycle post-calving.
Changes in ovarian activity were determined in each heifer by measuring changes in ovarian weight, follicular fluid weight, corpus luteum weight, progesterone content of the corpus luteum and number and size of follicles. Changes in uterine activity were determined by measuring changes in uterine weight, thickness of the uterine layers, number of glands, percent of glandular epithelium, glandular size, glandular and stromal secretions in the endometrium and collagen content, edema, and hypertrophy of the endometrial and myometrial layers.
Some of the results of this study show, heifers on the high-energy diet before calving gained more weight prior to calving (34 vs. 2 kg., P<.01), produced heavier calves at birth (30 vs. 26 kg., P<.1) and exhibited estrus sooner after calving (37.3 vs. 59.8 days, P<.01) than heifers on the low-energy diet.
High-energy heifers demonstrated greater overall ovarian activity both before and immediately after calving. Ovarian weight and follicular fluid weight were significantly heavier for the high-energy heifers, but the advantage was not consistent over all pre-calving and post-calving stages.
Advisor: Dwane Zimmerman