In the first oftwo experiments, 123 calf-fed steers were used over a 2-yr period to evaluate the effects of trenbolone acetate (TBA)-based implants administered alone or in combination with zeranol implants on fresh beef muscle quality, color, and physiological maturity of the carcass. Implant treatments decreased (P < 0.05) a* values (d 0 and d 3 of retail display) and b* values (d 0, d 1, and d 3 of retail display) after 14 d of aging. Carcasses from cattle initially implanted with Revalor-S and reimplanted with Revalor-S on d 60 of the finishing period showed increased lean and bone maturity scores and ash content of the 9th to 11th thoracic buttons and Warner-Bratzler shear force values (WBS) compared to those initially implanted with Ralgro and subsequently reimplanted with Revalor-S or control cattle. In addition, implants decreased (P < 0.05) marbling, percentage of the carcasses grading Choice, and kidney, pelvic, and heart fat (KPH). Implant treatments increased (P < 0.05) ADG, hot carcass weights, and longissimus muscle (LM) area. In the second experiment over a 2-yr period, 166 steers fed as yearlings were allotted to one of two implant treatments and one of two vitamin D3 preharvest supplementation treatments. Implanted steers had heavier (P < 0.05) final body weights and higher (P < 0.05) ADG, less (P < 0.05) KPH fat, and larger (P < 0.05) LM. Also, implanted steers had more (P < 0.05) advanced bone maturity scores, higher (P < 0.05) ash content of the 9th to 11th thoracic buttons, and higher (P < 0.05) WBS values on 5-d postmortem loin steaks. Vitamin D3 feeding decreased (P < 0.05) final live weight, ADG (P < 0.05), and LM (P < 0.05), but did not significantly improve WBS values. In Experiment 2, neither implant treatment nor vitamin D3 supplementation had significant effects on L*, a*, or b* values of muscles in steaks before or during simulated retail display.

Students enrolled in an introductory animal science course (ASG 3003) at the University of Florida were surveyed (n = 788) over a 3-yr period to ascertain their current experience and career goals in animal agriculture. Sixty-one percent of the students indicated that they were from an urban background. Only 4% were raised on a farm or ranch where the majority of family income was attributed to production agriculture. Eighty-six percent of the students had minimal or no experience working with large domestic farm animals, but nearly 64% of the students wanted to pursue a career in veterinary medicine. Disciplinary and species interests of the students were highly associated with previous background experiences. Students from nonagricultural backgrounds, who were most likely to indicate a career interest involving veterinary medicine, were most interested (P < 0.05) in animal behavior, whereas the students of rural background were more interested (P < 0.05) in animal management. Thirty-three percent of students were primarily interested in small companion animals; 22% in horses; 20% in domestic farm animals, including beef, dairy, swine, or sheep; and 24% in undomesticated zoo animals or wildlife. The career goals indicated by most students necessitate practical application of animal husbandry skills that are often assumed as general knowledge. Thus, a multispecies large animal management and production practicum (ANS 3206) was developed to provide students with hands-on experience. It was an elective course, and students were encouraged to enroll for two consecutive semesters. Teams of students rotated responsibilities among four livestock species (beef, dairy, equine, and swine). Daily responsibilities at each of the units included feeding and monitoring growth of feedlot cattle and finishing swine, farrowing assistance and baby pig processing, and equine training and foaling assistance. Students were also involved with all facets of a working dairy. Additionally, students completed written assignments specific to their individual species responsibilities that included daily journals, worksheets, or calculation of performance measures. Weekly class meetings allowed for instruction and were used to manage the varied course activities. Using a 5-point scale (1 = poor, 5 = excellent), students indicated that the course further stimulated their interest (4.73) and facilitated their learning (4.63) of animal science concepts. Overall course evaluations ranged from 4.54 +/- 0.55 to 4.85 +/- 0.38 over a 4-yr period. As more students enter animal science programs with nonagricultural backgrounds, it will become necessary to reemphasize basic animal-handling skills and practical applications through experiential learning activities.

To evaluate the response of three tropical forage species to varying rates of nitrogen (N) fertilization [0, 39, 78, 118, 157 kg of N/(ha x cutting)] and five summer harvests, forage DM mass and nutritive value were evaluated in a randomized complete block design with a split-split plot arrangement of treatments. Plots (n = 60) were established in 1996, and five harvests were conducted every 28 d from June through September in 1997 and 1998, with fertilizer applications occuring after each harvest. Fertilization with 78 kg of N/(ha x cutting) increased forage mass in these grasses by 129% (P < 0.01) compared with no N fertilization. Additional N did not result in further increases of forage mass. Bermudagrass (Cynodon dactylon) produced more forage DM [P < 0.01; 1,536 +/- 43 kg/(ha x cutting)] than stargrass [Cynodon nlemfuensis; 1,403 +/- 43 kg/(ha x cutting)] or bahiagrass [Paspalum notatum; 1,297 +/- 43 kg/(ha x cutting)]. Peak forage mass for all species occurred in late June and July. In vitro organic matter digestibility (IVOMD) of stargrass increased (P < 0.01) linearly with fertilization. A quadratic response to N fertilization (P < 0.01) was noted in IVOMD of bermudagrass, whereas bahiagrass was not affected. Bermudagrass was more (P < 0.01) digestible (57.5 +/- 0.4) than stargrass (54.6 +/- 0.4) and bahiagrass (51.9 +/- 0.4%). As fertilization level increased, NDF decreased linearly (P < 0.01) in all three forages. Total N concentration increased (P < 0.01) linearly as N fertilization increased in all forages. Total N concentration was highest (P < 0.01) in stargrass (2.4%, DM basis) compared with bermudagrass (2.2%) and bahiagrass (2.0%). Total N concentration was depressed in all forages for late June and July harvests (P < 0.01). Fertilization increased (P < 0.05) the concentration (% of DM) of all protein fractions. In July and August, nonprotein N was reduced 11.8% (P < 0.01), whereas ADIN increased in July (P < 0.01). Bahiagrass had less N in cell contents than did bermudagrass and stargrass but had a greater concentration of N associated with the cell wall. Managerial factors, including rates of N fertilization and harvest dates, can have profound effects on the nutritional value of forage. An increased understanding of these effects is imperative to improve supplementation programs for ruminants.

The effects of laidlomycin. propionate (LP) on, beef bull growth performance and sexual development were determined in, all. 84 day study. Forty embryo transfer Angus bulls were fed three complete diets containing LP levels of either 0, 10 or 20 g/t. Bulls were fed daily using electronic feeders to obtain individual feed intake. Full weight and scrotal circumference (SC) were evaluated at 28 day intervals, Breeding soundness examinations were conducted to characterize semen. Muscle mass and body fat were estimated using real-time ultrasonography. Laidlomycin propionate did not influence daily gain, dry matter intake, feed efficiency, subcutaneous or intramuscular fat deposition, but Longissimmus muscle deposition was enhanced. Among treatments, bulls had similar (P>0.05) SC measurements and no detrimental effects on semen quality or sperm morphology were observed. Supplementing growing bulls with laidlomycin propionate for improved performance did not detrimentally affect sexual development.

As the source of students shifts from rural to urban and suburban communities, students entering agricultural programs have less practical livestock experience. The career goals indicated by most of these students require knowledge of and experience with practical applications of their course work. The objective of this study was to examine the profile of students enrolled in an experiential beef cattle course 1) to describe the demographic and occupational characteristics of students enrolled and 2) to assess the perceived value of course activities to graduates completing the course as related to their skill attainment and career development. The questionnaire was sent to all 312 students who were enrolled in the course from 1983 to 1996. Over 61% of the respondents indicated they had enrolled in the course to gain experience working with beef cattle. Over 39% took the course to enhance their application to the College of Veterinary Medicine. When asked to rate the value of the course, as it related to skill development, they noted it was most helpful in teaching cattle handling skills, growth performance measurement, live animal evaluation, nutritional management, carcass and meat product value determination, and breed identification.

Twelve control (C) and 12 prenatally androgenized (PA) lactating (L) first-calf heifers and five (two C and three PA) similar, nonlactating (NL) heifers were used to assess the effects of PA and L on the metabolic activity of s.c. adipose tissue (AT). Heifers were fed an 85% concentrate diet, and their calves were weaned at 112 +/- 1 d of age. Adipose tissue was biopsied at approximately 77 d (period 1, during lactation for L heifers) and 126 d (period 2, after L heifers had calves weaned) postpartum. The NL heifers gained .22 kg/d faster (P = .20) and had greater fat deposition than L heifers during period 1. The PA heifers were fatter and gained 14.6% faster than C heifers during lactation. Epinephrine (E) and norepinephrine (NE) increased in vitro fatty acid (FA) release 25 (P <.01) and 15% (P <.06), respectively, above basal rates. Near-maximal release of FA, as estimated by stimulation with E plus theophylline plus adenosine deaminase (ETAD), was 73% (4,110 vs 2,379 +/- 161 nEq/[2 h . 100 mg of tissue]; P <.01) above basal rates. Basal FA release was unaffected, but ETAD-stimulated rates were decreased (P <.04; 4,430 +/- 246 vs 3,789 +/- 209 nEq/[2 h . 100 mg of tissue]) by PA. Stimulation of FA release by E (P = .22) or NE (P = .31) did not differ between C and PA. For NL heifers, PA decreased (P <.02) FA release, which corresponded with their greater fat deposition, but PA did not affect L heifers (PA x L interaction, P =.14). The content of NEFA in s.c. AT (pool size) was 34% greater (P <.01) during period 2 than during period 1. Pool size was not affected (P = .72) by NE but was increased by E (1,628 vs 1,777 +/- 92 nEq/100 mg of tissue; P <.05) and ETAD (1,628 vs 2,176 +/- 93 nEq/100 mg of tissue; P <.01). For L heifers, PA tended (P <.07) to increase incorporation of acetate into FA during period 1. Thus, PA resulted in subtle increases in lipogenesis and decreases in lipolysis during the first lactation-weaning cycle that were consistent with greater rates of gain and fat deposition.

Three studies were designed using a 2 x 2 factorial arrangement of treatments within each experiment to evaluate the effects of various management techniques on growth and carcass traits of once-calved heifers. In Exp. 1, 33 yearling (16 control [C] and 17 prenatally androgenized [PA]) and 39 once-calved (20 C and 19 PA) nonpregnant heifers were used to evaluate the effects of age and PA. Once-calved heifers were approximately 31 kg heavier (P < .03) on-test, initially consumed 11% more (P < .01) DM, and gained 11% faster (P < .08), but had similar (P = .44) gain to feed ratios (.138 vs. .131) as yearlings. Growth performance was not affected by PA. The yearling and once-calved heifers were then slaughtered at approximately 707 and 1,080 d of age, respectively. Despite maturity differences (P < .01), marbling scores (P = .26) and percentage of choice carcasses (P = .27) were similar. However, on the basis of newly accepted grading changes, percentage of once-calved heifer carcasses grading choice decreased from 57.3 to 34.4%. Organoleptic properties did not differ. Experiments 2 and 3 were then conducted to evaluate effects of commercially available products (melengestrol acetate [MGA] and Synovex-H) on feedlot characteristics of heifers following weaning of their first calf. In Exp. 2, 48 once-calved Simmental-based heifers were fed during the summer to a constant compositional fat thickness of .8 cm. Experiment 3 was conducted in the late fall and early winter, during which 52 moderately sized heifers were fed for 116 d postweaning and slaughtered. Performance of heifers in Exp. 2 was not affected by MGA. However, heifers fed MGA in Exp. 3 gained 9% faster (P < .05) than controls. In Exp. 2, Synovex-H tended to improve ADG (P < .09) and feed efficiency (P < .07), but did not affect performance in Exp. 3. Most carcass traits were not affected by either treatment. Nonpregnant, once-calved heifers seem to have a large capacity for efficient weight gain as compared with yearling heifers. However, hormonal compounds, such as testosterone propionate provided pre- or postnatally (Synovex-H), and MGA do not appear to provide the consistent, positive responses often seen with younger, more typical feedlot heifers.

Twenty-four prenatally androgenized (PA) heifers, born to testosterone propionate-implanted cows, and 27 control (C) heifers, born to nonimplanted cows, were bred, calved, and placed in drylot pens, with calf at side, to assess the effects of PA on feedlot growth and lactational performance of heifers used in a single-calf heifer (SCH) system. Lactating heifers were fed an 85% concentrate diet, calves weaned at 117 d postpartum, and heifers slaughtered at a constant compositional end point of 1.1 cm of s.c. fat. Preweaning, PA heifers gained 22.5% faster (P < .01) and were 17.3% more efficient (P < .01) than controls. Prenatal androgenization of the heifer, however, did not affect calf growth performance. All calves gained more than 1.4 kg/d and had an average weaning weight of 159 kg at 117 d of age. Combining heifer-calf weights, PA and C pairs gained 2.88 and 2.53 kg/d, respectively. Correcting for DMI of calves, PA improved (P < .01) efficiency of beef production 10.8%. Four percent fat-corrected milk yield of PA and C heifers averaged 7.96 and 7.60 kg/d, respectively, and the percentage of milk protein and fat did not differ. Accounting for average BW, milk production, and DMI, PA and C lactating heifers should have gained 1.27 kg/d; however, gains were 137 and 127% of those predicted, respectively. Overall, pre- and postweaning, PA heifers required 10 fewer (P < .04) days on feed, gained 23% faster (P < .01), and were 16% more efficient (P < .02) than C heifers. At slaughter, PA and C heifers averaged 853 and 865 d of age, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Primiparous Angus x Simmental heifers (n = 43) in a single-calf heifer (SCH) system (i.e., heifers are bred, calved, and placed in drylot pens with their calves at side and fed to slaughter weights) were studied to evaluate the effects of prenatal androgenization on parturition and on periparturient reproductive and metabolic hormone concentrations. Seven prenatally androgenized (PA) and seven control (C) heifers were used for blood collection to characterize parturient and lactation endocrine profiles; all heifers were used for blood collection to characterize postpartum ovarian cyclicity. Serum concentrations of progesterone, estradiol, testosterone, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), and prolactin from 10 d before to 3 d after parturition were similar for PA and C heifers. Calf birth weights (34.7 +/- .9 kg) and calving ease scores (1.34 +/- .14) were similar between treatments. Postpartum ovarian cyclicity was similar; only 6 of 22 PA (27.3%) and 3 of 21 C (14.3%) heifers were cyclic by 70 d postpartum, based on weekly serum progesterone concentrations. Serum concentrations of insulin, triiodothyronine (T3), and prolactin at 35, 70, and 105 d of lactation were similar for PA and C heifers; thyroxine (T4) concentrations were similar at 35 and 70 d but greater (P < .01) at 105 d of lactation in PA heifers than in C heifers. Although mean serum concentrations of insulin, T3, and T4 were similar between treatments, prolactin concentrations were greater (P < .05) in C than in PA lactating heifers. We conclude that PA heifers are similar to C heifers with respect to parturition and to periparturient reproductive and metabolic hormone concentrations. Therefore, management requirements of PA primiparous beef heifers seem to be similar to those of C primiparous beef heifers, and PA heifers can be used successfully in a SCH system.

Over the past 3 yr, 100 carcasses (64 steers, 24 bulls, and 12 heifers) were fabricated into closely trimmed (6 mm maximum fat cover), boxed beef and further evaluated for percentage of retail yield at the Iowa State University Meat Laboratory. Hot carcass weight ranged from 235 to 399 kg with a least squares mean (LSM) and standard error across all sex classes of 318 +/- 3 kg. Additionally, fat cover ranged from .30 to 1.78 cm with an average of .91 +/- .05 cm. The LSM for longissimus muscle area (LMA) across all sex classes was 81.6 +/- 1.0 cm2. Bulls had significantly less subcutaneous fat (P less than .01) and greater LMA (P less than .01) than did either steers or heifers. Retail yield from the boxed chuck, expressed as a percentage of cold carcass weight, was 19.2 for bulls and 14.8 for steers. This difference was due primarily to a reduction of intermuscular fat. Similarly, bulls had a greater yield (P less than .01) of the boxed round than did steers. When cattle of differing frame sizes were compared, only percentage of retail yield of the boxed round was significant (P less than .01): large-framed cattle yielded 14.3 +/- .2%, compared with 12.8 +/- .2% for the small-framed cattle. When all possible regression analyses were run, sex class differences accounted for 25.7% of the variation in retail yield. The current USDA retail yield equation accounted for only 37.2% of the variation. Percentage of closely trimmed, boneless round had an R2-value of .57.(ABSTRACT TRUNCATED AT 250 WORDS)