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Our objective was to determine the relationship between energy balance and secretion of progesterone in lactating dairy cows. Eight primiparous and 24 multiparous lactating Holstein cows were studied from parturition to 100 d postpartum or conception. Cows calved normally and remained healthy throughout the study. All cows were fed ad libitum a total mixed(More)
The effects of energy balance on the corpus luteum may be mediated by IGF-I. Our objective was to determine whether negative energy balance decreases expression of IGF-I mRNA in the liver or corpus luteum of heifers. For four consecutive estrous cycles, 14 Holstein heifers were maintained in negative or positive energy balance to lose 510 g/d of BW or gain(More)
A factorial experiment was conducted to determine influence of energy balance (EB) and body condition (BC) on luteal function in heifers. Heifers with moderate (MBC) or fat (FBC) BC were fed individually to sustain positive EB (PEB) or to cause negative EB (NEB). Intake of feed was measured daily and body weight weekly. Progesterone was quantified daily in(More)
The objective of this study was to examine changes in intrafollicular concentrations of inhibins and steroids in heifers during growth of dominant follicles. To obtain dominant ovulatory follicles, heifers received injections of prostaglandin (PG) on Day 9 of an estrous cycle and were ovariectomized (OVX) 0, 24, 48, 60, or 72 h after injection. To obtain(More)
Luteal function was studied in the absence of non-ovulatory ovarian follicles to determine if these follicles are involved in luteal regression in cattle. After at least one estrous cycle, cows were assigned randomly to treatment (n=5) or control (n=5). All cows were laparotomized on day 10 postestrus (Estrus = day 0). During laparotomy of treated cows, all(More)
Destruction of ovarian follicles during diestrus prolongs the lifespan of corpora lutea in cows, but the site(s) of action is unclear. Thus, ovarian follicles were destroyed in 10 beifers (X-IRRAD) on Day 9 postestrus, while 10 additional beifers (SHAM) served as a control group. To investigate changes in luteotropic support resulting from destruction of(More)
The objective of our experiment was to examine changes in serum concentrations of estradiol in each utero-ovarian vein before, during and after gonadotropin surges. Four cows were given prostaglandin F2 alpha (PGF2 alpha) during diestrus and three cows were allowed to cycle spontaneously. All cows had a cannula in each utero-ovarian vein and in one jugular(More)
Our objectives were to determine whether or not ovarian follicles contribute to spontaneous luteal regression in heifers and, if so, when during diestrus do follicles exert their effect. Thirty-one Holstein heifers having displayed at least one estrous cycle (19 to 21 d) were assigned, as available, to randomized blocks for a factorial experiment.(More)
The objective was to determine effects of energy balance and body condition on estrous behavior and estrous cycles in Holstein heifers. Before the experiment heifers were fed so body condition remained moderate or they became fat. During the 2 x 2 factorial experiment, moderate and fat heifers were in positive or negative energy balance. Heifers were fed(More)