Table 6 Ž
. Ž
Intake gr15 min of foods by lambs fed a basal diet that was either low in energy and high in protein Food .
Ž .
P or high in energy and low in protein Food E during Trial 3
1
Food offered Day
SE 1
2 3
Familiar foods
a a
a
Food E 59
52 57
4
a a
a
Food P 46
42 39
4 Novel foods
a a,b
b
wheat 57
77 81
4
a b
b
soybean meal 20
21 31
4
1
Ž See Table 1 for composition of Foods P and E and Table 5 for composition of novel foods wheat and
. soybean meal .
a,b
Ž .
Means with different superscripts differ P s 0.05 .
P ate less Food P and more Food E than lambs fed basal diet E, whereas the reverse was Ž
. true for lambs fed basal diet E P - 0.007; Table 5 . Throughout the 3-day trial, lambs
Ž .
in both groups did not change the amount of Foods P and E eaten P 0.05; Table 6 , but intake of the novel foods — wheat and soybean meal — increased over days
Ž .
P - 0.002, Table 6 . Lambs increased the amount of novel foods eaten at the near Ž
. location 77 vs. 98 vs. 112 g , and did not change the amount of familiar foods eaten at
Ž .
Ž the far location 105 vs. 94 vs. 98 g from days 26 to 28 LSD
s 11; location = day
0.05
. interaction, P - 0.0007 .
4. Discussion
4.1. Familiar foods at constant locations We hypothesized lambs would forage at locations with foods that complemented the
macronutrient content of their basal diet. Lambs fed a basal diet high in energy and low Ž
. in protein fed at locations with food high in protein Food P , whereas lambs fed a basal
Ž diet low in energy and high in protein fed at locations with food high in energy Food
. E . Thus, our findings are consistent with the notion that food preference depends on
Ž .
nutritional state Villalba and Provenza, 1999 . Nevertheless, even within a 15-min meal lambs did not feed exclusively on Food E or Food P. Rather, they ate relatively more of
the food with the macronutrient most limiting in their basal diet. The ratio of protein to energy in the diet influences preference, even within a meal.
Ž .
For example, lambs ruminally infused with protein casein after eating flavored grape pomace subsequently decrease preference for flavored grape pomace paired with casein
and increase preference for differently flavored grape pomace previously paired with Ž
. infusions of energy starch ; conversely, after a meal of barley, preference for flavored
Ž .
pomace previously paired with energy starch decreases, while preference for flavored Ž
. Ž
. pomace paired with protein casein increases Villalba and Provenza, 1999 . In our
trials, lambs selected foods that complemented the protein:energy ratios in their basal
diets. Lambs fed the high-energy basal diet selected foods with a higher DP:DE ratio Ž
. Ž
than lambs fed the low-energy diet in Trials 1 116 vs. 24 g DPrMcal DE and 2 71 vs. .
24 g DPrMcal DE . When offered novel foods, lambs fed a high-energy basal diet Ž
selected foods in a higher protein to energy ratio than lambs fed a low-energy diet 75 .
vs. 35 g DPrMcal DE . Balancing the supply of fermentable carbohydrates and nitrogen within a meal is
likely to optimize microbial protein synthesis and maximize the retention of rumen Ž
. degradable nitrogen Sinclair et al., 1993 . When the rate of ammonia formation exceeds
the rate of carbohydrate fermentation, nitrogen is not used efficiently by microbes and a Ž
. large proportion of nitrogen is excreted as urea Huber and Herrera-Saldana, 1994 .
Conversely, lactic acidosis occurs when the rate of carbohydrate fermentation exceeds Ž
. what can be metabolized in the rumen and liver Yokoyama and Johnson, 1988 .
Excesses of nitrogen or energy can cause rapid decreases in food preference in Ž
. ruminants Provenza, 1995, 1996 .
A food’s flavor and nutrient composition interact to influence food preference Ž
. Provenza, 1996 . Sensory-specific satiety refers to the decrease in preference for the
Ž .
flavor of a food as it is consumed Rolls, 1986 , whereas nutrient-specific satiety refers Ž
. to the decrease in preference for a nutrient consumed in excess Provenza, 1996 .
Sensory and nutrient-specific satiety interact to diminish food preference during a meal. Sheep and cattle fed nutritionally balanced food in one of two flavors for as little as 1
day prefer the alternate flavor when offered a choice for 2 hrday for the next 5 days. The decrease in preference becomes more pronounced and persistent when a food is
Ž either deficient or too high in macronutrients sheep: Early and Provenza, 1998; cattle:
. Atwood et al., 2000 . Lambs prefer a variety of flavored foods when their basal diet and
the foods on offer are nutritionally similar, but variety of flavored foods is less important Ž
when the foods on offer differ nutritionally from their basal diet Scott and Provenza, .
1998 . When flavors and macronutrients vary in foods offered during a meal, lambs Ž
. prefer foods high in macronutrients regardless of flavor Wang and Provenza, 1997 .
Thus, while flavor and nutrients interact to influence preference, flavor is secondary to macronutrients in importance.
4.2. Familiar foods at different locations As the locations of nutritious foods changed, lambs changed foraging locations.
Lambs fed at the location nearest the shelter that contained the macronutrient deficient Ž
in their diet. Intake at the mid location changed as the type of food offered changed i.e., .
Food P on day 24 and Food E on day 25 ; lambs fed basal diet E ate more at the mid location on day 24 and lambs fed basal diet P ate more at that location on day 25. Thus,
the preference for location was most likely a result of the food offered at the location. Conditioned place preferences can result from the pairing of nutrient feedback at a
Ž .
location with external location cues Carr et al., 1989 . For instance, rats spend more Ž
time at locations where they consume sucrose compared to saccharin White and Carr, .
Ž .
1985 . Nevertheless, the results of this and other experiments Scott et al., 1995 suggest that food does not necessarily condition persistent place preferences. Even when lambs
prefer one location to another for reasons other than food, they still spend more time and
eat more food at less preferred locations when foods they prefer occur at those locations Ž
. Scott and Provenza, 1998 . When a preferred food is moved to a new location marked
by a visual cue, sheep initially return to the original location, and then move to the new Ž
. location based on the visual cue Edwards et al., 1996 . Cattle quickly learn the locations
of nutritious foods, but when the locations change constantly, cattle spend more time Ž
. searching and less time eating Laca, 1993 .
Lambs fed at a variety of locations, rather than exclusively at the location with a Ž
. variety of foods i.e., the ‘‘ variety’’ location with both foods . If lambs had preferred the
location with the most food, then they should have fed at the variety location. However, Ž
. they consumed only 12 of the food offered at the variety location 52 of 450 g .
Lambs also might be expected to consume all of the food at the first location Ž
. encountered. However, on average they consumed 26 43 g of the food offered at the
Ž .
Ž .
near location, 62 105 g of food at the mid location, and 12 20 g of the food offered at the farthest location. Thus, lambs fed at all three locations and did not
consume all of the food at any one location. Lambs’ fed a high-protein diet were influenced more by the variety of food choices at
a location than lambs fed a high-energy diet. Lambs fed a high-protein diet consumed more Food E when it was offered with Food P than when it was offered alone, whereas
lambs fed a high-energy diet did not eat more Food P when it was offered with Food E. Rats, too, increase intake of high energy foods when their food choices differ in flavor
Ž .
and texture Naim et al., 1986 . 4.3. NoÕel and familiar foods at constant locations
Animals fed nutrient-deficient diets sample novel foods more readily than animals fed Ž
. adequate diets Wang and Provenza, 1996a . Thus, we wanted to determine whether
lambs readily ingested novel foods high in macronutrients — wheat and soybean meal — even though they had access to familiar foods — P and E — that contained needed
macronutrients. All lambs ate significant amounts of the novel foods, relative to the
Ž .
familiar foods, even from day 1 of the trial Table 6 . Lambs increased consumption of both novel foods throughout the trial, but they ate more wheat than soybean meal.
Wheat and soybean meal are both good sources of macronutrients, though soybean meal is much higher than wheat in protein. Thus, we expected lambs fed basal diet P to
prefer wheat and lambs fed basal diet E to prefer soybean meal. However, lambs in both groups preferred wheat to soybean meal. Lambs may have generalized a preference from
Ž .
Ž .
a familiar grain barley to the novel grain wheat , and in the process showed a greater preference for wheat than soybean meal. All lambs had extensive experience eating
barley as part of their basal diet prior to our trials. Grains such as barley and wheat are about 80 starch and lambs generalize preferences from familiar foods high in starch to
Ž .
novel foods high in starch Villalba and Provenza, 2000a . Thus, the macronutrients provided by wheat, along with its relative familiarity, likely contributed to the lambs’
preference for wheat. Ž
. Ž
. Protein sources in the novel i.e., soybean and familiar i.e., bloodmeal foods
differed greatly in chemical characteristics. Thus, intake of the novel protein food may
have been lower as compared to the novel energy food because sheep did not generalize based on a common flavor. In addition, bloodmeal is less ruminally degradable and has
Ž .
a higher N escape than soybean Loerch et al., 1983 . Soybean meal, on the other hand, Ž
. is converted more readily than bloodmeal to NH in the rumen Sultan et al., 1992 .
3
5. Conclusion
