Mixed bacterial cultures derived from the rumen were grown in a remen fluid medium in a chemostat at three dilution rates (.02, .06, and .12 per h), each at four growth-limiting glucose concentrations (5.8, 9.9, 12.7, and 25.0 mM). Microscopic observations indicated that a relatively complex mixture of bacterial species was maintained and proportions of fermentations products were similar to those of the rumen except for elevated proportions of methane and acetate. Cell concentration increased linearly with increases in glucose concentration. The range of glucose concentrations had little effect on yields of cells or products produced per mole of glucose fermented. With increases in dilution rates, the amount of butyrate and methane produced per mole of glucose fermented decreased and the amount of propionate increased. Yield glucose (grams cells produced per mole of glucose fermented) increased from 42 at a dilution rate of .02 to 84 at a dilution rate of .12. These large increases are discussed in relationship to the energy requirements for maintenance of bacteria. A theoretical maximum yield glucose of 89.3 and a maintenance requirement of .26 mmol glucose per g cells per h were calculated. Moles of adenosine triphosphate produced per mole of glucose fermented and yield of cells produced per mole of adenosine triphosphate are discussed.

Forty-eight crossbred ewes were subjected to heat stress of short or long duration during the last third of gestation in a completely randomized design to determine the effects of maternal heat stress on lamb birth weight, lamb conformation and subsequent preweaning growth rate. Ewe treatments were spring range pasture, confinement on slotted floors in a heated room maintained between 28 to 38 C or in a slotted floor barn with feed intake equal to the feed intake of the 38 C housed ewes. Treatment exposure averaged 25 and 53 days for short and long duration, respectively. Lamb birth weights of heated, range and restricted fed ewes were 3.18, 4.57 and 4.16 kg, respectively. After adjustment for sex and multiple birth effects, birth weight of lambs from hot environment ewes were smaller (P<.01) for both durations of treatment. Lamb birth weights from heated ewes were smaller than those of lambs from restricted fed ewes (P<.05). Relative kidney and liver weights were greater in lambs from heated ewes (P<.05). Relative muscle weights and relative linear equivalent bone lengths were not different among ewe treatments. Lambs from heated ewes had 30 and 56-day weights similar to those of lambs from range and restricted fed ewe groups. Small Iambs resulting from maternal heat stress of 25 or 53 days duration are proportional dwarfs and occur independently of ewe level of nutrition. Department of Animal Science. 2Studies were conducted at the Dixon Springs Agricultural Center, Simpson, IL. The cooperation of Drs. M. E. Mansfield and D. Drori is gratefully appreciated.

The objective of this study was to determine whether increased amounts of collagen and (or) hydroxylysylpyridinoline crosslinks in longissimus muscle are partially responsible for decreased tenderness when callipyge lambs are compared to normal lambs. The longissimus muscle was used because we believe tenderness is a greater problem in loin chops of callipyge lambs than it is in other cuts. Ten normal and 10 half-sibling lambs expressing the callipyge gene were compared. Lambs were slaughtered at approximately 8 mo of age when they reached a target weight of 59 kg. Dressing percentages were higher for the leaner callipyge lambs that exhibited larger longissimus muscle areas and heavier leg weights (P < .01). Warner-Bratzler shear values for longissimus muscle from callipyge lambs were higher (P < .01) than those from normal lambs. The higher shear values were not explained by amount of muscle collagen or by hydroxylysylpyridinoline crosslink concentration because both collagen percentage (P < .09) and crosslink concentration (P < .04) were lower in callipyge lambs. Therefore, attempts to modify shear values and make loin chops from callipyge lambs more acceptable to consumers should focus on the myofibrillar fraction of muscle.

A metabolism study evaluated the influence of increasing quantities (O-30% dry matter basis) of mountain big sagebrush (Artemisia trident&a ssp. vaseyana Rydb. Beetle) on dry matter intake and in vivo digestibility of wether diets. Diets consisted of band-harvested, coarse-ground and frozen current year's growth of mountain big sagebrush leaves and twig tips mixed with chopped native grass hay. Dry matter intake decreased from 93 to 23 g dry matter day" kg metabolic weight' and in vivo dry matter digestibility from 59 to 0% with increasing levels of sagebrush in the diet. With increasing levels of sagebrush in the diet, water, lignin, and nitrogen contents increased in the diet, but decreased iu the dung, while fiber components decreased in both the diet and dung. Total nitrogen intake decreased from 1.58+0.041 to 0.406+0.070 g day" kg metabolic weight', and nitrogen retention decreased from 0.80 g day-' kg metabolic weight-' with no sagebrush to a slight loss of nitrogen with 30% sagebrush in the diet. Mountain big sagebrush was not readily consumed by wethers when fed together with grass; as low as 10% sagebrush in the diet seems to adversely influence intake and digestibility. Therefore, when other more favorable forages are not available, sheep and other ruminants with similar physiological responses to mountain big sagebrush may not meet their nutrient requirements through increased sagebrush consumption.

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