Effect of age of exposure on consumption of a shrub by sheep.

We investigated the influence of age of exposure to a specific forage on its consumption by young sheep both during and after that exposure. Prior exposure to the shrub Cercocarpus montanus enhanced subsequent consumption (P less than or equal to .05) of that shrub by lambs and yearlings during two experiments in consecutive years. Effects of prior exposure persisted as long as 9 mo without intervening exposure. Age of exposure influenced consumption in lambs both during the period of exposure (P less than or equal to .0001) and during feeding trials following exposure (P less than or equal to .07) in Exp. 1. Lambs exposed at 1 to 5 wk of age, when they are nonruminant and normally are dependent on the dam, browsed less of the time while at the shrub (P less than or equal to .02) and consumed less of the shrub (P less than .02) at a slower rate (P less than or equal to .03) than did lambs exposed at older ages. Lambs exposed at 4 to 8 wk of age, a period corresponding to the transition from nonruminant to ruminant digestion, consumed more shrub following exposure than did lambs exposed at younger or older ages (P less than equal to .05, unprotected least significant differences test). In Exp. 2, which compared naive yearlings with the experienced yearlings exposed as lambs in Exp. 1 the previous year, age of exposure did not influence consumption by yearling sheep following exposure; however, the number of months that had elapsed from the period of exposure varied from 0 to 13 among experimental groups and may have confounded results. Learning of forages appeared poor among nonruminant lambs; data were inconclusive concerning the efficiency of learning of lambs in the transition to ruminant digestion.

The establishment and persistence of food preferences in lambs exposed to selected foods.

Our study determined whether lambs' food preferences developed as a result of exposure to specific foods early in life and whether the presence of the mother affected the development of dietary preferences. In the first experiment, lambs were fed wheat (W) and mountain mahogany (MM) (Cercocarpus montanus) from 50 to 110 d of age. After exposure to W and MM, lambs preferred (P less than .05) W when offered with barley (B) but did not prefer (P greater than .05) MM when offered with serviceberry (SB) (Amelanchier alnifolia), probably because lambs were reluctant to eat mountain mahogany during exposure. Persistence was determined by dividing lambs exposed to W or MM into four groups: 1) continued exposure to W (MM); 2) exposure to B (SB); 3) no further exposure; and 4) exposure to W + B (MM +SB). Preferences for wheat persisted (P less than .05) regardless of the second exposure. In the second experiment, lambs were exposed to W (MM) either alone or with their mothers. Persistence was determined after 21 d of exposure to B (SB). Lambs preferred (P less than .05) W and MM whether they were exposed alone or with their mothers. However, preferences persisted longer in lambs exposed with their mothers. Finally, lambs exposed to either SB or MM with their mothers were later allowed to choose between SB or MM. Lambs strongly preferred (P less than .05) the shrub to which they were exposed early in life.

Effects of predator fecal odors on feed selection by sheep and cattle.

The effectiveness of predator fecal odors in modifying feeding selection by sheep and cattle was investigated in two trials. In trial 1, animals could select from feed bins contaminated with coyote, fox, cougar, or bear fecal odor, and oil of wintergreen, or select the control feed. All odors were rejected (P<0.01) by sheep and cattle, except bear odors by sheep. In trial 2, animals could select feed during 10-min periods in an open 11-m × 16-m arena. Fecal odor did not influence approaches to feed bins, or head entries into bins. Only coyote fecal odor reduced (P<0.05) the time spent feeding in the contaminated bin, and increased (P<0.05) consumption from the control bin by both cattle and sheep. Some animals on some test days refused to feed from either feed bin, although cattle and sheep closely inspected bins. Results suggest that fecal odors may not prevent livestock from entering a treated area but may reduce the time spent grazing in such an area.

The reproductive cycle of male uinta ground squirrels: some anatomical and biochemical correlates.

1. Maximum testicular development and plasma testosterone levels occurred at spring emergence from aestivation-hibernation (A-H), followed by a regression to basal state in June. 2. A slight testicular recrudescense occurred just prior to immergence into A-H, but this development was not accompanied by a definitive increase in plasma testosterone levels or seminal vesicle weights. 3. Four lines of evidence were consistent with the hypothesis that FSH stimulates testicular MAO activity. 4. Changes in pituitary and hypothalamic MAO activity suggested a functional role for this enzyme in controlling releasing factor and gonadotropin production by these organs.