Estrus has been synchronized in cattle with progestogens, prostaglandins (prostaglandin F2 alpha and its analogues), progestogen-estrogen combinations and progestogen-prostaglandin combinations. Progestogens administered for 14 to 20 d are effective in synchronizing estrus; however, fertility at the synchronized estrus is subnormal. Duration of progestogen treatment can be reduced by combining it with an estrogen. Syncro-Mate B is a progestogen-estrogen combination that results in a tightly synchronized estrous response. Prostaglandins can be used in double- or single-injection programs. Fertility of the estrus after prostaglandin treatment is similar to that of controls. Estrus also has been synchronized effectively by combining a 5- to 9-d progestogen treatment with prostaglandin at or near the end of treatment. When prostaglandin is used alone, cattle in the late stages of the luteal phase (d 11 to 15 of the estrous cycle) at the time of prostaglandin injection have a higher estrous response and may be more fertile than those injected with prostaglandin in the early part (d 6 to 9) of the luteal phase. More recently, a 14-d progestogen treatment has been combined with a prostaglandin injection given 16 to 18 d after progestogen withdrawal. This system places cattle in the late luteal phase of the estrous cycle at the time of prostaglandin injection and has resulted in an estrus with greater fertility than that immediately following progestogen treatment.

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To determine whether an increase in serum lipids alters the area occupied by lipid droplets in steroidogenic luteal cells and(or) clearance rates of progesterone from serum, pregnant beef heifers received control (n = 6) or treatment (n = 5) diets. To increase serum lipids, the treatment diet contained calcium soaps of fatty acids. Control and treatment diets were formulated to be isocaloric and isonitrogenous. Feeding of diets was initiated approximately 100 d before parturition and continued through the third postpartum estrous cycle. On d 12 or 13 of the third postpartum cycle, corpora lutea were collected by ovariectomy and a center slice was processed for electron microscopy. Eight samples from each slice were sectioned, stained, and examined at a magnification of 2,500x. Five micrographs per sample were analyzed for area occupied by small (SLC) and large (LLC) luteal cells, percentage of the area of each steroidogenic cell type occupied by lipid, and total steroidogenic area (SLC + LLC) occupied by lipid. Jugular blood was collected before and after ovariectomy, and progesterone, cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) were quantified. Cows consuming treatment diets had approximately twice (P < .05) the concentration of cholesterol, HDL, and progesterone in serum that controls had. The percentage of the area of SLC, LLC, and total area occupied by lipid was greater (P < .05) in treated than in control cows. The average time required for serum concentrations of progesterone to decrease by 50% after ovariectomy was greater (P < .05) in treated than in control cows (170 +/- 16 vs 113 +/- 15 min).(ABSTRACT TRUNCATED AT 250 WORDS)

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