Influence of macronutrients and polyethylene glycol on intake of a quebracho tannin diet by sheep and goats.

We determined if supplemental macronutrients or polyethylene glycol (PEG) influenced intake of a tannin diet. Sheep (lambs 5 mo age, 36 kg) and goats (kids 7 mo age, 32 kg) were fed supplements high in either energy or protein or offered a choice between the two supplements before and after receiving a meal containing 15% quebracho tannin. The effect of PEG, a compound that attenuates the negative effects of tannins, was assessed by offering PEG while animals consumed the tannin diet for 4 h/d. Intake of the tannin diet was influenced by both macronutrients and PEG. Animals that chose their own supplements or that received the high-protein supplement, consumed more of the tannin diet than animals fed the high-energy supplement: 34 and 36 vs 31 g/kg(0.75) (lambs) and 41 and 39 vs 34 g/kg(0.75) (kids), respectively (P < 0.05). Animals supplemented with PEG ate much more of the tannin diet than unsupplemented animals: 70 vs 39 g/kg(0.75) (lambs) and 63 vs 34 g/kg(0.75) (kids), respectively (P < 0.001). Sheep and goats consumed more tannin food when given PEG than when supplemented with macronutrients (51 and 38 g/kg(0.75), P < 0.001). Sheep and goats offered a choice between supplements consumed more CP than animals fed the high-energy supplement and more ME than animals fed the high-protein supplement (P < 0.05). In so doing, they selected a combination of foods that yielded a more balanced intake of macronutrients, while achieving high levels of intake of the tannin food. Sheep and goats can be used as an environmentally safe and economically sound means to reduce the abundance of tannin-rich vegetation. Macronutrients and PEG enhance use of tannin-containing plants, which may increase production of alternate forages and create a more diverse mix of species in a plant community.

Influence of macronutrients and activated charcoal on intake of sagebrush by sheep and goats.

We determined if supplemental macronutrients or activated charcoal influenced intake of sagebrush, a shrub that contains terpenes. Sheep (lambs 3 mo age, 33 kg) and goats (kids 5 mo age, 28 kg) were fed supplements high in energy, high in protein, or offered a choice between the two supplements before and after receiving sagebrush for 4 h/d. The effect of activated charcoal, a compound that reduces bioavailability of toxins, was assessed by offering charcoal mixed with a carrier or the carrier alone while animals consumed sagebrush for 4 h/d. The effects of supplemental macronutirents were tested before and after charcoal supplementation. Activated charcoal did not increase intake of sagebrush by sheep or goats (P > 0.05), but supplemental macronutrients influenced intake of sagebrush by both species (P < 0.05). Intake of sage-brush was markedly higher for animals fed the high-protein supplement than for animals fed the high-energy supplement (P < 0.05). Lambs (before and after charcoal supplementation) and kids (after charcoal supplementation) offered a choice between the two supplements used sagebrush at levels comparable to animals supplemented with protein. They consumed more CP than animals fed the high-energy supplement and more ME than lambs fed the high-protein supplement (P < 0.05). Thus, providing a choice between supplements enhanced intake of sagebrush and enabled animals to achieve a more balanced intake of macronutrients. Preference for supplement and sagebrush also depended on an animal's immediate past history with a supplement. Sheep and goats previously fed the high-energy or the high-protein supplement preferred, respectively, the high-protein or the high-energy supplement when given a choice (P < 0.05). The changes in preference for supplement caused a decreased intake of sagebrush by groups that preferred the energy concentrate, and an increased intake of sagebrush by groups that preferred the protein concentrate. Thus, supplements of different energy and protein densities consistently altered intake of sagebrush by sheep and goats.

Changes in preferences of gestating heifers fed untreated or ammoniated straw in different flavors.

We determined how a food's flavor and digestibility, along with an animal's recent experiences, influenced food preference and intake. In three experiments, pregnant heifers were fed a basal ration (7.75 kg/animal) of alfalfa, barley, corn silage, and a vitamin/mineral supplement from 1500 to 2200. Exp. 1 determined the influence of recent exposure to flavored straw. Animals were divided into two groups (n = 16/group) and fed either untreated or ammoniated straw with digestibilities of 43 and 58%, respectively. Within each group, half of the heifers were fed maple-flavored straw and the other half were fed coconut-flavored straw from 1100 one day to 0900 the next day, with no base ration. We then offered straw in both flavors from 1000 to 1200 for the next 5 d. Animals fed maple-flavored straw for 1 d generally preferred coconut- over maple-flavored straw for the next 5 d, whereas animals previously fed coconut-flavored straw preferred maple-flavored straw (P < 0.001). The change in preference was stronger when animals were fed untreated compared with ammoniated straw. Experiments 2 and 3 determined the influence of offering straw in different flavors, either in sequence (Exp. 2) or simultaneously (Exp. 3). In Exp. 2, we offered heifers (n = 16) straw in three flavors (maple from 0900 to 1100, coconut from 1100 to 1300, and unflavored from 1300 to 1500) and compared their intake with that of heifers (n = 16) offered unflavored straw throughout the day. In Exp. 3, we compared intake of heifers (n = 16) simultaneously offered straw in three flavors (coconut, maple, and unflavored) with that of heifers (n = 16) offered only unflavored straw from 1000 to 1500. In both experiments, straw intake and preference differed between heifers offered straw in a variety of flavors as opposed to only unflavored straw (P < 0.05), but animals fed a variety of flavors did not consistently eat more than those fed only one flavor. During a post-trial preference test, heifers previously restricted to straw in one flavor for 5 d preferred straw in alternative flavors, whereas heifers fed straw in all three flavors preferred unflavored straw. Changes in preference were stronger for heifers fed untreated compared with ammoniated straw. Collectively, our results suggest that palatability, as evidenced by changes in preference and intake, is dynamic and depends on a food's flavor and nutritional quality and an animal's recent experiences with the food.

Influence of free-choice vs mixed-ration diets on food intake and performance of fattening calves.

Research findings and management recommendations typically emphasize responses of the "average" individual, yet more than half of the animals in a group may differ significantly from the mean regarding food preference and intake. The productivity of a herd may be adversely affected if animals differing from the mean are fed a uniform diet formulated to meet the needs of the "average" individual. We compared the intake and performance of beef calves offered a choice or no choice among foods. Diets consisted of ad libitum access to either a chopped, mixed ration of rolled barley (31.3%), rolled corn (31.3%), corn silage (15.5%), and alfalfa hay (18.9%) (n = 16 calves) or a choice among those foods offered individually (n = 15 calves). Averaged across the 63-d trial, the two groups did not differ in ratios of protein to energy ingested (43 vs 43 g CP/Mcal ME; P = 0.50), but preference for foods high in energy or protein varied markedly for animals fed free-choice: on d 21 they had protein:energy ratios higher than those of animals fed the mixed ration, on d 2 the ratios were equal, and on d 40 they had protein:energy ratios lower than those of animals fed the mixed ration. Throughout the trial, no two animals consistently chose the same ingredients, and none selected a diet similar to the nutritionally balanced mixed ration, yet each animal ate a diet adequate to meet its needs. Animals offered the mixed ration tended to eat more than animals offered a choice (109 vs 102 g/kg MBW/d; P = 0.10), but they did not gain at a faster rate (0.89 vs 0.92 kg/d; P = 0.65). Gain/unit of food consumed also was similar for both groups (0.09 vs 0.10 kg/kg; P = 0.38). However, food cost/day was higher for animals fed the mixed ration than for those offered a choice ($1.58 vs $1.36; P = 0.03). Consequently, cost/kilograms of gain was higher for the mixed ration than for the choice group ($1.84 vs $1.49/kg; P = 0.045). These findings suggest that 1) animals can more efficiently meet their individual needs for macronutrients when offered a choice among dietary ingredients than when constrained to a single diet, even if it is nutritionally balanced; 2) transient food aversions compound the inefficiency of a single mixed diet by depressing intake even among animals suited to that nutritional profile; and 3) alternative feeding practices may allow producers to efficiently capitalize on the agency of animals, thus reducing illness and improving performance.