Research into the instructional effectiveness of computer-based simulations has yielded inconsistent results. Part of this inconsistency can be attributed to the inappropriate instructional roles for which simulations are used. Two of the most promising roles of simulations in instruction are to: 1) establish a cognitive framework or structure to accommodate further learning in a related subject area, and 2) provide an opportunity for reinforcing, integrating and extending previously learned material. Thus, the effectiveness of a given simulation may depend upon when it is administered within an instructional sequence. The purpose of these two studies was to: 1) ascertain the value of a particular simulation to the learning of genetics principles, and 2) determine whether the position of the simulation, within the sequence of instructional events, altered its effectiveness. In both studies, students receiving the stimulation as a framework for understanding prior to formal classroom instruction scored significantly higher on an applications posttest than did students using the simulation as an integrating activity following formal instruction. Both groups scored higher than a control group which did not use the simulation prior to the posttest.

The effect of chronic cold stress for periods of 0, 3, 5, 10, 20 and 30 days on metabolic activity in vitro, testis weight, total lipid, total carbohydrate, total carbohydrate on lipid free residue, ribonucleic acid (rna), deoxyribonucleic acid (dna) and percentage of lipid free dry weight of the testis was determined. Metabolic activities measured were endogenous oxygen consumption and oxygen uptake in the presence of exogenous glucose, succinate and a Krebs' cycle reaction system. Carbon dioxide, lactic acid production and glucose uptake were also determined. Cold exposure caused a significantly decreased rate of body weight gain and a highly significant transient hypertrophy of the adrenals. There was no significant change in the metabolic activity and chemical constituents of the testes. These data indicate that cold stress for 30 days has no significant effect on testis size, composition or metabolic activity in mature rats in which the hypothalamo\p=m-\adeno-hypophysial\p=m-\gonadal axis was stimulated by constant light.

and Implications The objectives of this study were to compare the behavior of the laying hen kept in a cage system when offered a pre-molt calcium treatment and low-energy molt diets versus a traditional feed-withdrawal during induced molt. A total of 144 Hy-Line W-36 laying hens (85 wk of age), weighing 1.7 ± 0.2 kg, were used. Laying hens were housed 3 per cage (30.5 cm wide × 40.6 cm deep × 44.5 cm high), providing 413 cm 2 per hen. Six treatments were compared in a 2 × 3 factorial design with 2 Ca (coarse and fine) pre-molt treatments and 3 molt diets: feed withdrawal (FW), soybean hulls (SH), and wheat middlings (WM). The Ca pre-molt treatment was defined as the period when the hens received either a combination of fine (0.14 mm in diameter) and coarse (2.27 mm in diameter) CaCO 3 or an all-fine CaCO 3 mixed into a commercial diet for 1 wk. Both diets were formulated to contain 4.6% Ca, such that only the particle size of the CaCO 3 differed between the 2 treatments. Hens had free access to feed and water and had a 24-h photoperiod. The 3 molt diets were applied (FW, SH, or WM) for a total of 28 d. The hens assigned to the FW diet were deprived of feed for 7 d with free access to water followed by 21 d of skip-a-day feeding restricted to 60 g of feed/hen per feeding day. The hens fed the WM and SH molt diets were given free access to feed and water during the entire 28 d molt period. Lighting was reduced to 8 h for the first 3 wk and was then increased to 12 h at the start of the last week of molt. Behavior was recorded by camera once before molt, twice during molt, and twice post-molt for 2 h in the morning and 2 h at night. The acquisition of 2 postures and 5 behaviors were obtained by 2 experienced observers who viewed the recordings using 24 h mode onto the Observer software using a 1 min scan sampling technique. Postures and behaviors were not different among treatments during the baseline period. The Ca pre-molt treatment had no carryover effect during or post-molt. The hens assigned to the FW molt diet spent more time in active postures and feeding and drinking behaviors during molt compared to hens fed the other 2 molt diets. Post-molt, all hens, regardless of molt diet, spent the same amount of time in each of these behaviors. The hens assigned to the FW molt diet spent more time preening during molt compared to post-molt, whereas the hens fed the WM and SH molt diets did not differ between the 2 periods (Table 1). In conclusion, these low-energy molt diets did not adversely affect the postures and behaviors of the laying hen and are therefore acceptable dietary alternatives to FW for inducing molt.

and ImplicationsThe objectives of this study were to compare stress measures and bone quality of laying hens when offered a Ca pre-molt treatment followed by low-energy molt diets versus a traditional feed withdrawal before, during, and after an induced molt. A total of 189 Hy-Line W-36 laying hens (85 wk of age, 1.7 ± 0.2 kg), housed 3 per cage, (413 cm 2 /hen) were used. Six treatments were compared in a 2 × 3 factorial design with 2 Ca (coarse and fine) pre-molt treatments (coarse and fine) and 3 molt diets: feed withdrawal (FW), soybean hulls (SH), and wheat middlings (WM). The Ca pre-molt treatment was defined as the period when the hens received either a combination of fine (0.14 mm in diameter) and coarse (2.27 mm in diameter) CaCO 3 or an all-fine CaCO 3 mixed into a commercial diet for 1 wk. Both diets were formulated to contain 4.6% Ca, such that only the particle size of the CaCO 3 differed between the 2 treatments. Hens had free access to feed and water and had a 24-h photoperiod. The 3 molt diets were applied for a total of 28 d. The hens assigned to the FW molt diet were deprived of feed for 7 d with free access to water followed by 21 d of skip-a-day feeding restricted to 60 g of feed / hen per feeding day. The hens fed the WM and SH molt diets were provided free access to feed and water during the entire 28 d molt period. Lighting was reduced to 8 h for the first 3 wk and was then increased to 12 h at the start of the last week of molt. During the 22 wk postmolt, hens were fed a laying hen diet and lighting was increased by 1 h each week to 16 h. None of the treatments resulted in an increased heterophil to lymphocyte ratio during or post-molt compared to baseline values, which would have suggested increased stress in the laying hen. Additionally, any changes reported during molt in bone quality returned to baseline values during the post-molt period. Therefore, these treatments are acceptable for inducing molt in the laying hen.

and Implications The objectives of this study were to compare the production of laying hens when offered a Ca pre-molt treatment and low-energy molt diets versus a traditional feed-withdrawal (FW) before, during, and after an induced molt. A total of 792 Hy-Line W-36 laying hens (85 wk of age, 1.7 ± 0.2 kg), housed 3 per cage, (413 cm 2 /hen) were used. Six treatments were compared in a 2 × 3 factorial design with 2 Ca (coarse and fine) pre-molt treatments and 3 molt diets: FW, soybean hulls (SH), and wheat middlings (WM). The Ca pre-molt treatment was defined as the period when the hens received either a combination of fine (0.14 mm in diameter) and coarse (2.27 mm in diameter) CaCO 3 or an all-fine CaCO 3 mixed into a commercial diet for 1 wk. Both diets were formulated to contain 4.6% Ca, such that only the particle size of the CaCO 3 differed between the 2 treatments. Hens had free access to feed and water and had a 24-h photoperiod. The 3 molt diets were applied for a total of 28 d. The hens assigned to the FW molt diet were deprived of feed for 7 d with free access to water followed by 21 d of skip-a-day feeding restricted to 60 g of feed/hen per feeding day. The hens fed the WM and SH molt diets were provided free access to feed and water during the entire 28 d molt period. Lighting was reduced to 8 h for the first 3 wk and was then increased to 12 h at the start of the last week of molt. During the 22 wk postmolt, hens were fed a laying hen diet and lighting was increased by 1 h each week to 16 h. The fine-Ca pre-molt treatment was more effective than the coarse-Ca pre-molt treatment at decreasing egg production during molt and increasing egg production after molt regardless of which molt diet was fed (P < 0.05). The FW molt diet resulted in the most complete molt with a greater decrease in egg production during molt (P < 0.05). The SH molt diet compared to the WM molt diet was more effective at inducing molt with lower egg production and ovary and oviduct weights during molt (P < 0.05), however, the WM molt diet resulted in the highest egg production and body weight post-molt compared to the other 2 molt diets (P < 0.05). In conclusion, a fine-Ca pre-molt treatment and a low-energy molt diet containing WM or SH can be useful alternatives to a FW molt.