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Mature Hereford cows (n = 28) were used to determine the effect of percentage body fat on secretion of LH and content of GnRH in the infundibular stalk-median eminence (ISME). Cows were fed to maintain, lose, or gain weight to achieve body condition scores (BCS; 1 = emaciated; 9 = obese) of 3 to 7. Then cows were fed to maintain weight and body condition. Before slaughter, estrus was synchronized using two injections of prostaglandin F2 alpha(PGF) 11 d apart. Five d after the second PGF injection, cows were given 100 micrograms of GnRH (im) and serum samples were obtained. LH was quantified using RIA. The anterior pituitary and ISME were obtained within 45 min of death. Anterior pituitary weight and LH concentration, total GnRH in the ISME, total carcass fat, and percentage carcass fat were determined. BCS of cows at the time of slaughter influenced percentage carcass fat (P less than .001), total GnRH in the ISME (P less than .02), and maximum LH after GnRH treatment (P less than .09), but did not influence pituitary weight or concentration of LH in the pituitary. Content of GnRH in the ISME averaged 76 +/- 12, 32 +/- 14, 27 +/- 13, and 24 +/- 13 ng for cows with BCS of 3, 5, 6, and 7, respectively. BCS was correlated (P less than .001) with percentage carcass fat (r = .94) and total fat in the carcass (r = .92). Total GnRH in the ISME was negatively correlated (P less than .005) with BCS (r = -.54), percentage carcass fat (r = -.55), and total carcass fat (r = -.49).(ABSTRACT TRUNCATED AT 250 WORDS)

Three experiments were conducted to evaluate performance and fecal nematode egg counts in grazing stocker cattle receiving morantel tartrate (MT) in two continuously administered forms. In Exp. 1, 80 crossbred steers either received no anthelmintic (C) or were dewormed at the initiation of a 140-d bermudagrass grazing study with either levamisole injection (L) or MT in a sustained-release trilaminate (MSRT). Anthelmintics did not affect performance parameters, but fecal nematode egg counts were lowest from L, intermediate from MSRT, and highest from C at the end of the study. In Exp. 2, 60 crossbred steers grazing fall-regrowth smooth bromegrass were offered a mineral mixture of trace-mineralized salt and dicalcium phosphate (3:1 ratio) with 0 or 10% dried molasses and 0 or 5.58 mg/g MT. Steer gains were similar (P>.10) across treatments, but fecal egg counts were reduced (P

Growth, carcass, and meat quality traits of crossbred intact males and zeranol-implant steers were evaluated. Young bulls grew more rapidly (P

Eighty-eight spring calving and 58 fall calving Hereford and Hereford × Angus cows were wIntered on dormant native tallgrass range to study the value of wheat middlings (WM) as a source of supplemental CP and energy. Supplements consisted of soybean meal (SBM, 40010 CP), SBM and WM (32% CP), WM and SBM (24% CP), and WM (16% CP). Each supplement was individually fed and provided .36 kg CP daily from November 5 to December 9, and .54 kg CP from December 10 to May 4 for spring calving cows. Fall calving cows were fed .36 kg CP daily from November 29 to December 9 and .54 kg from December 10 to March 15. Precalving weight changes for spring calving cows increased linearly (P

One hundred twenty crossbred yearling heifers were used to compare a combination of MGA and prostaglandin F 2 α (PGF 2 α) as an estrous synchronization program to a conventional Al program. Heifers were stratified by estrous status (prepuberal or postpuberal) and assigned to receive MGA for 14 d followed by an injection of PGF 2 α 16 d post-MGA feeding (TRT) or to an untreated control group (CON). Puberty was determined by the detection of behavioral estrus or the presence of a palpable corpus luteum arid an increased level of serum progesterone. All heifers were observed for behavioral estrus and bred by Al during a 30-d breeding season. A higher percentage ( P P >.10) for the two groups. A higher percentage ( P 2 α injection (60%) compared with the CON group (5%) during the same time period. A higher percentage ( P 2 α was effective in estrous synchronization.

The feeding of antibiotics or ionophores in free-choice mineral mixtures was evaluated in four studies with stockers (heifers and steers) grazing native range. In trial 1, heifers with access to lasalocid in a free-choice mineral mixture consumed more mineral ( P P P >.05) in daily gain and in ruminal propionic acid. Both groups gained more ( P P P

Clenbuterol is a highly specific, long-acting (four to eight hours) beta-two sympathomimetic which causes bronchodilation and tocolysis (myometrial paralysis). The tocolytic effect was explored as a means to control parturition and reduce dystocia. Forty-six heifers were injected i.m. with either Clenbuterol or saline placebo in a randomly controlled experiment. Animals were treated when a cervical dilation of five centimeters or more was detected by vaginal examination. Length of first, second and third stages of parturition, ease of parturition, maternal pelvic area and calf viability were compared between treatment groups. Treatment with Clenbuterol increased (P