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.

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.

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.

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)