Thirty mares in late gestation were used in a 3-yr study to assess effects of the tall fescue endophyte Acremonium coenophialum on serum prolactin (PRL) and progesterone. Two paddocks of each treatment, 0 or 100% infected 'Kentucky 31' tall fescue, were grazed by the mares for 21 d. Blood was collected three times per week until parturition. At 7-d intervals, mares were challenged with thyrotropin-releasing hormone (TRH) while grazing and blood was collected postinjection. Mares grazing 100% infected tall fescue (E+) had decreased serum PRL compared with mares grazing the 0% infected tall fescue (E-) in 2 of 3 yr. Within 8 d postgrazing, serum PRL for E+ mares equaled or surpassed values of the E- mares. Serum PRL was not different during the 3rd yr. In response to TRH, serum PRL rate of increase was similar between treatments but remained elevated (P less than .01) in the E+ mares at the 180-, 240-, and 300-min sample times. Serum progesterone was lowered (P less than .05) by E+ but increased to control values within 10 d postgrazing. It is concluded that serum PRL and progesterone in the gravid mare were decreased by the presence of A. coenophialum in 'Kentucky 31' tall fescue grass but normal levels were reestablished within 2 to 3 wk.

Plasma and pineal melatonin (MEL) and selected pineal neurochemicals (5-hydroxytryptophan, serotonin, N-acetylserotonin, dopamine, norepinephrine) associated with MEL synthesis were determined in steers grazing Acremonium coenophialum (endophyte)-infected 'Kentucky-31' tall fescue paddocks. Paddock treatments included low (LE, 33%) or high (HE, 74%) endophyte at either low (134 kg.ha-1 x yr-1, LN) or high (335 kg.ha-1 x yr-1, HN) nitrogen fertilization. Twelve pairs of yearling Angus steers were randomly assigned to three replications of the paddock treatments (LEHN, HEHN, LELN, and HELN). One steer in each of the 12 paddocks received per os either a dopamine antagonist, metoclopramide (MC; 15 mg/kg), or sucrose (S; 15 mg/kg) three times weekly for 10 wk. Blood was collected via jugular cannulas during the day and night for plasma MEL analysis and pineal glands were collected at termination. Day and night plasma MEL in the S/HEHN steers was reduced by 31.7 and 35.4% (P < .05), respectively, compared with that in S/LEHN steers. Mean night plasma MEL in the S/HELN steers was reduced by 26.7% (P < .05) compared with that in S/LELN steers. Metoclopramide reduced mean day and night plasma MEL by 22.9 and 38.3% (P < .05), respectively, in the LEHN steers and increased night MEL in the HELN animals by 35.1% (P < .05). During the day and night, there was a MC x pasture treatment interaction (P < .05). No differences were observed in either pineal MEL or the pineal neurochemicals. Acremonium coenophialum-infected fescue reduced plasma concentrations of MEL in steers, whereas treatment with MC altered plasma MEL biphasically.(ABSTRACT TRUNCATED AT 250 WORDS)

Opioid modulation of LH and prolactin (PRL) concentrations in Angus steers was investigated. In Exp. 1, morphine sulfate (M) was administered at either 1, 2 or 3 mg/kg BW (n = 4) as an i.v. injection. Blood samples were obtained at 15-min intervals for 4 h pre- and post-treatment for serum hormone analyses. Mean serum LH concentration and number of LH secretory pulses decreased (P less than .1) for 2 h after M (4.1 to nadir of 2.4 ng/ml, and .33 vs. .21 pulses/h; pre- vs post-treatment). Luteinizing hormone pulse amplitude decreased (P less than .01; 7.3 vs 2.6 ng/ml; pre- vs post-treatment) during the 2 h following M. Prolactin concentrations increased 126.6%, 170.6% and 187.6% following 1, 2 and 3 mg M/kg BW, respectively (P less than .05, 1 vs 2; P less than .01, 1 vs 3). In Exp. 2, either saline solution (S, n = 6) or M (.31 mg/kg BW, i.v. injection followed by .15 mg/(kg.h) infusion; n = 6) was given for 7 h. Concentration of LH was unaffected. Response of LH to naloxone was determined in Exp. 3. Blood samples were obtained for 2 h pre- and post-administration of either naloxone (1 mg/kg BW, i.v. injection; n = 5) or S (n = 5). Response of LH at 15, 30 and 45 min posttreatment was greater (P less than .05) in naloxone- compared with S-treated steers. In summary, M had no significant effect on serum LH concentration or LH pulse frequency, but it decreased pulse amplitude and increased serum PRL concentrations. In contrast, naloxone increased LH secretion. These observations taken together indicate a physiological role for opioid modulation of LH and PRL secretion in the steer.

The South of the United States (13 southern states) is ecologically and socioeconomically well suited for reproducing ruminant animals. The South has a broad economic base, its climate is comparatively mild, much of its soil is easily eroded requiring vegetative cover, it receives comparatively abundant rainfall, and a diversity of plant species grow well, enabling a multitude of production and management alternatives. The South currently accounts for 46.3% of the beef cows in the United States. To assess current practices associated with the raising of replacement beef heifers, a questionnaire was sent to 60 extension beef cattle specialists in the 13 southern states. Twenty-four completed questionnaires revealed that much needs to be accomplished to improve replacement heifer production. Particularly deficient areas include lack of a limited breeding season, failure to check for pregnancy, inadequate health management, poor nutrition such that heifers do not calve at 24 mo of age, and often those that calve do not rebreed. These deficiencies result in reduced economic efficiency of replacement heifer development and could result in a significant reduction in profits of an entire beef cow-calf operation. Beef cattle specialists suggested that part of the problem associated with development of replacement heifers is a lack of defined objectives by producers.