Biomedical subjects

J D Crouse

Publications and source records attributed to J D Crouse.

44 records · Page 3Linked to original sources

PubMed1981

Photoperiodic regulation of growth: a photosensitive phase during light-dark cycle.

Growth and performance of 72 young ram lambs were evaluated for susceptibility to exposure to three different photoperiods. Lambs were penned in groups of two and exposed to either short (8L:16D), long (16L:8D), or split (7L:9D:1L:7D) photoperiods. Lambs exposed to 16L:8D and 7L:9D:1L:7D photoperiods ate more feed (P less than 0.01), gained weight more rapidly (P less than 0.01), and required less feed per unit gain (P less than 0.01) than did lambs exposed to the 8L:16D photoperiod. Final weight and carcass weight were increased (P less than 0.01) as a result of exposure to 16L:8D and 7L:9D:1L:7D photoperiods; however, carcass attributes were not affected. Lambs exposed to the 7L:9D:1L:7D photoperiod had elevated prolactin concentrations that generally paralleled the prolactin profiles of lambs exposed to the 16L:8D photoperiod; however, concentrations of luteinizing hormone and testosterone were not affected by photoperiod. Lambs exhibited a daily feed-intake rhythm that was closely associated with daily photoperiod. These rhythms could account in part for the increased feed intake and performance of lambs exposed to 16L:8D and 7L:9D:1L:7D photoperiods. From these results, we conclude that 1) light is an important Zeitgeber for the regulation of feed intake, prolactin secretion, and growth rate in young lambs, and 2) a photosensitive phase exists for these functions during the light-dark cycle in sheep.

Aging↗

PubMed1980

Testosterone influences on growth, performance, carcass characteristics and composition of young market lambs.

Ram lambs, wethers and wethers implanted with Silastic capsules containing crystalline testosterone were placed on test at 14.9 +/- 1.1 kg and evaluated for differences in growth, performance, carcass characteristics and composition. Silastic implants that were able to maintain physiological concentrations of serum testosterone provided appropriate replacement therapy in wethers. Growth rate, efficiency of feed utilization and carcass yield of intact ram lambs and testosterone-implanted wethers were superior to the corresponding traits of wethers. Wethers had greater backfat thickness and percentage kidney and pelvic fat, and their carcasses graded higher than those of ram lambs or wethers implanted with a high dosage of testosterone. Empty body composition was significantly affected by treatment. Thus, intact rams contained more water and protein but less fat and gross energy than wethers. Testosterone-implanted wethers were intermediate in composition. Carcass water and protein were not significantly affected by treatment; however, carcass fat and gross energy were highest for wethers and lowest for intact rams. The relationship between testosterone and carcass fat and energy was dose dependent; i.e., decreased fat and energy were associated with increased serum testosterone. In conclusion, testosterone appears to be the principal testicular hormone responsible for the superior performance and preferred carcass traits characteristic of young market rams.

Animals↗

PubMed1980

Growth and performance of growing-finishing lambs exposed to long or short photoperiods.

The effects of photoperiod (8 hr light: 16 hr dark [8L:16D] or 16L:8D) on performance of growing-finishing lambs were evaluated in an experiment with 24 rams and 24 wethers. All lambs were caged in groups of two in a controlled environment and fed a pelleted diet ad libitum for the duration of the study (10 to 22 weeks of age). Performance and carcass data showed that both photoperiod and sex of lamb affected growth rate (P less than .01) and feed efficiency (P less than .05) but that only sex of lamb affected carcass quality (P less than .05) and yield (P less than .10). A sex by photoperiod interaction not observed for any of the traits measured. Average daily gain (grams/per day) and feed efficiency (feed/gain) for lambs in the four treatment groups tested were: rams (16L:8D), 410 and 4.3; rams (8L:16D), 340 and 4.5; wethers (16L:8D), 345 and 4.6, and wethers (8L:16D(, 300 and 4.8 respectively. Carcass weight, like slaughter weight, was affected by photoperiod (P less than .01) and sex of the lamb (P less than .05); both rams and wethers exposed to long photoperiods had the heaviest carcasses. Ram carcasses were leaner, had better yield grades and were heavier than wether carcasses, yet both ran and wether carcasses graded Choice. Testosterone concentrations in serum were undetectable (less than .2 ng/ml) at 22 weeks of age in wethers but were elevated (P less than .01) in ram lambs exposed to short (3.4 +/- 1.4 ng/ml) or long (.8 +/- .2 ng/ml) photoperiods. Prolactin concentrations, on the other hand, were not influenced by sex of lamb but were influenced (P less than .01) by photoperiod; i.e., prolactin concentrations were high in rams (190 +/- 34 ng/ml) and wethers (178 +/- 28 ng/ml) exposed to long photoperiods and low in rams (43 +/- 9 ng/ml) and wethers (27 +/- 11 ng/ml) exposed to short photoperiods. These results suggest that testosterone and prolactin may independently affect growth and performance of growing-finishing lambs.

Animals↗

PubMed1975