Selektive Futteraufnahme von Broilern bei Zinkmangel

Evidence of a dietary selection for methionine by the piglet

The objective of the current study was to investigate if there is a preference of piglets for diets varying in Met content and whether these preferences change with time. For this purpose, a feeding trial was carried out over a period of 6 wk. Piglets (equal numbers of males and females) with an initial BW of 7.2 +/- 0.1 kg were randomly subdivided into 4 groups of 12 pigs each. Two reference groups were fed either 0.19% Met (low-Met group) or 0.26% Met (high-Met group) diets. Two other groups had the choice between 2 diets containing 0.19 or 0.23% Met (Met-choice 1 group), or 0.19 or 0.26% Met (Met-choice 2 group). Compared with the low-Met group (397 g), daily feed intake was increased by 43%, 60%, and 82% (P < 0.05) in the Met-choice 1, Met-choice 2, and the high-Met group, respectively. Piglets on the Met-choice 1 and Met-choice 2 groups, respectively, selected 72 and 80% of the higher Met diet. In the first week, piglets on both Met-choice groups selected the diets at random, but they increased their preference for the diets higher in Met up to 81 and 89%, respectively, in the last experimental week. For the total experiment, mean Met contents of total diets were 0.22 and 0.25% in the Met-choice 1 and Met-choice 2 groups, respectively. Average daily gain of 195 g in the low-Met group was more than doubled (P < 0.05) in the high-Met group. Daily gains of 306 and 366 g in the Met-choice 1 and 2 groups, respectively, were (P < 0.05) improved compared with the low-Met group but lower (P < 0.05) than in the high-Met group. Plasma Met concentration of 46.3 micromol/mL in the Met-choice 2 group was greater than in the low-Met or the Met-choice 1 groups (25.3 and 32.8 micromol/mL, respectively) but lower (P < 0.05) compared with the high-Met group (59.6 micromol/mL). Conversely, the sum of essential AA showed a greater (P < 0.05) concentration in plasma from pigs on the low-Met and Met-choice 1 groups than in plasma from pigs on Met-choice 2 group and the high-Met group. In conclusion, the present data demonstrate that piglets are able to discriminate among diets of varying Met content. When given a choice, they prefer a diet better balanced for Met to a Met-deficient diet. As a result of the altered feeding pattern, piglets are able to partly redress the depressed performance and altered plasma AA pattern resulting from the ingestion of the diet more limiting in Met concentration.

Choice feeding of selenium-deficient laying hens affects diet selection, selenium intake and body weight

Inadequate selenium (Se) supply often in combination with low vitamin E status causes deficiency symptoms in many species. It is likely that a vague discomfort or sickness is perceived before clear deficiency signs become apparent. We investigated whether Se-deficient hens reduce their Se deficit by selecting a diet containing more selenium when offered two diets with different Se concentrations. A Low-Se diet (0.07 mg Se/kg) was supplemented with Se-enriched yeast (Sel-Plex 50) to produce Medium-Se (0.20 mg Se/kg) and High-Se (1.50 mg Se/kg) diets. Each of two consecutive study parts (I and II) with the same hens and treatments began with a 6-wk baseline period (Medium-Se diet), subsequently followed a 9-wk depletion period (Low-Se diet or Medium-Se diet), then a 6-wk choice feeding period in which two diets with different Se concentrations (Low-Se and Medium-Se, Medium-Se and High-Se, or Low-Se and High-Se) were offered. A control group received the Medium-Se diet throughout the study. Daily Se intake, calculated from daily feed intake, followed similar patterns in both parts of the study, but Se-deficient hens preferred (P < 0.05) the High-Se diet to the Low-Se diet during the first 3 wk of choice feeding only in part I. We conclude that young Se-deficient laying hens reduce their Se deficit if they have a choice between a Low-Se and a High-Se diet by preferentially selecting the High-Se diet, possibly based on learned place preference and/or learned taste aversion to the Low-Se diet, presumably in response to discomfort due to Se-deficiency.

[Estimation of the zinc requirement for broilers using their ability for selective zinc absorption and by dose-response relations]

Broiler chicks are able to select an adequate dietary Zn-concentration in choice-feeding. The zinc requirement should be ascertained by this method of self-selection. 72 day-old chicks were divided into 9 groups and were kept over 5 weeks in individual cages. By gradually supplementing ZnSO4.7H2O to a semisynthetic basal diet with isolated soybean protein 5 diets were made with Zn-concentrations of 14, 22, 30, 38 and 50 ppm, which respectively were fed to one group. The four other groups had to choose between two rations: 14/38; 14/50; 22/38; 22/50. Selective zinc intake was represented by a significant increase of dietary zinc concentration compared to random selection (mean of both diets). Feed intake, zinc intake and weight gain were measured daily and the end total feed consumption, live weight, feed conversion rate, plasma-zinc concentration and plasma-zinc binding capacity at the end of the experiment. In comparison optimal dietary zinc levels were estimated by dose-response relations, both by sigmoid growth curves and by broken-line model. With 30 ppm Zn chickens reached a high fattening level with daily weight gains of 60 g. Feed intake and growth rate were markedly reduced at a dosage of 14 and 22 ppm Zn, feed conversion rate was tendentially decreased below a level of about 34 ppm, whereas above zinc binding capacity reached a plateau. Birds self-selected a dietary zinc level of 32 ppm, which were adequate for the criteria feed intake and weight gains. Zinc requirements of about 40 ppm were assessed by conventional methods.

The role of experience in the development of selective zinc intake in pullets

Selective food intake behaviour was studied in pullets that were subjected to different zinc supply in early life. During the first four weeks post-hatching three groups, totaling 72 birds, were fed either a low zinc diet (25 ppm), a complete diet (50 ppm) or both diets in a choice situation. The prior feeding experience was investigated during the subsequent ontogenetic development in two-choice dietary tests. Chicks first exhibited a preference for the high zinc diet as deficiency symptoms can be seen in depleted birds. Juvenile pullets did not prefer any diet for the duration of experimental period. Layers were initially indifferent to the supplemented zinc diet, but after reaching high laying capacity they began preferentially to select the complete diet. The results indicate that early experience with diets different in zinc content have no influence on subsequent diet preferences at choice. The ability to select is based on association learning following ingestion. A conditioned diet aversion first developed in phases of high zinc requirement as a result of negative feedback mechanisms produced by the deficient diet.