Biomedical subjects

J B Kjaer

Publications and source records attributed to J B Kjaer.

8 recordsLinked to original sources

PubMed2006

Altered circulating levels of serotonin and immunological changes in laying hens divergently selected for feather pecking behavior.

The aim of this study was to investigate the changes in immunological parameters as well as changes with respect to plasma levels of serotonin and tryptophan in lines selected for and against feather pecking (FP) behavior [high FP (HP) line and low FP (LP) line] for 5 generations. The hens from the HP line had a higher plasma serotonin level than those from the LP line (0.059 vs. 0.037 micromol/L, F(2,27) = 0.031, P < 0.05). The plasma level of tryptophan was, on average, 67.30 micromol/L and did not differ between the lines (68.3 vs. 66.3 micromol/L, F(2,28) = 0.36, P < 0.05). The HP line had a higher response to infectious bursal disease virus vaccination after 1 wk post-vaccination compared with the control and LP lines. The number of white blood cells (P < 0.0001) and the expression of MHC class I molecules on CD4 (P < 0.02), CD8beta (P < 0.006) and on B cells (P < 0.03) were highest in the LP line compared with the control and HP lines. Selection for or against FP, therefore, changes the number of white blood cells and the expression of MHC class I molecules on T and B cells, which may influence the health status of the birds.

Animals↗

PubMed2006

Divergent selection on feather pecking behavior in laying hens has caused differences between lines in egg production, egg quality, and feed efficiency.

The correlated changes in egg production, egg quality, and feed efficiency (FE) due to selection for feather pecking (FP) were investigated by analyzing the data from an experiment including 2 divergently selected lines and a control line. The experiment was conducted with hens from 42 to 46 wk (hatch 1) and 39 to 43 wk (hatch 2) of age in the fifth generation of selection. The number of FP bouts per hour in the low FP line (LFP) was lower than the high FP line (HFP; 0.38 vs. 2.01), and total plumage score in line LFP was better than in line HFP (16.9 vs. 11.6). During the 4 wk, egg number and egg mass in line LFP were higher than those in HFP (24.4 vs. 18.3 and 1,223 vs. 1,132 g, respectively). On the other hand, line HFP had greater egg weight (60.7 vs. 59.2 g), albumen height (73.0 vs. 64.9 in Haugh units), shell thickness (38.1 vs. 37.0 mm), and yolk percentage (30.6 vs. 29.5%) than the LFP line. The control line was intermediate for those traits. The residual feed consumption (RFC) was highest in line HFP, lowest in line LFP, and intermediate in line C. Partial regressions of feed consumption (FC) on BW gain and egg mass were not significantly different among the 3 lines, whereas a significant difference in regression on metabolic BW (32.6 g/d in line LFP, 38.0 g/d in control line, and 43.4 g/d in line HFP) was observed. In addition, there was a negative regression of FC per day on plumage score (-1.73 g). The adjustment for plumage score accounted for 60% of the difference between regressions on metabolic BW in lines LFP and HFP. These results indicated that selection for FP has led to a change in egg production, egg quality, and FE. The better FE in line LFP resulted from a lower requirement for maintenance energy. The later was partly accounted for by a better plumage cover.

Animal Nutritional Physiological Phenomena↗

PubMed2006

Foot pad dermatitis and hock burn in broiler chickens and degree of inheritance.

A total of 2,118 birds from 2 strains were allocated to 12 groups of 93 to 100 each in 2 time-separated replicates. The development of foot pad dermatitis (FPD) and hock burn (HB) were recorded weekly from d 8 to slaughter on a set sample of live animals (7 per group). In addition, feet and hocks of all birds were investigated at slaughter at either 4, 6 (fast-growing strain), 8, or 10 (slow-growing strain) wk of age. Lesions were scored for both the left and right foot and classified according to a scale from 1 (no lesion) to 9 (very severe lesions) for FPD and from 1 (no lesion) to 3 (very severe lesions) for HB. No FPD lesions and very few low-grade HB lesions were found in chickens from the slow-growing strain. In the fast-growing strain, the first signs of FPD and HB were seen in wk 2. The incidence of both types of lesions increased thereafter. Foot pad dermatitis was more frequent in females (49 vs. 36%, P < 0.05). Body weight did not affect FPD, but more HB were found at higher BW (P < 0.01). Egg weight influenced neither FPD nor HB. Variance and covariance components were analyzed using a multivariate animal model, in which scores for FPD and HB were transformed into logarithmic scale. The analyses were carried out using restricted maximum likelihood algorithm. Heritabilities were estimated to be 0.31 +/- 0.12 (SE) for FPD, 0.08 +/- 0.08 for HB, and 0.38 +/- 0.13 for BW. Genetic correlations among these traits were low and nonsignificant. Phenotypic correlation between BW and FPD was low and nonsignificant and between BW and HB was 0.17 +/- 0.05 (P < 0.01). The relative high heritability of FPD and the low genetic correlation to BW suggested that genetic selection against susceptibility to FPD should be possible without negative effects on BW gain.

Analysis of Variance↗

PubMed2005

Use of the range area in organic egg production systems: effect of climatic factors, flock size, age and artificial cover.

(1) To evaluate the effect of climate, flock size, age and artificial cover on the use of range area, a study was conducted in 1994 to 1998, involving 5 farms with a total of 37 flocks of layers kept in commercial, free-range, organic systems. Flocks were visited regularly during the production period to record the number and distribution of hens on the range. (2) On average 9% of the flock used the range area, but with large variations both within and between flocks, and this was partly influenced by climatic factors. Range use was affected by temperature, wind, precipitation, season and age, and there was a tendency for reduced numbers of hens on the range with the time of day and increasing flock size. (3) Eight flocks (including houses and range areas) were divided into 8 paired units, and the range area of one unit in each of the flocks was provided with artificial cover. There were more hens on the range when artificial cover was present and the presence of cover attracted more hens away from the area immediately outside the hen house.

Aging↗

PubMed2005

Variance components and selection response for feather-pecking behavior in laying hens.

Variance components and selection response for feather pecking behavior were studied by analyzing the data from a divergent selection experiment. An investigation indicated that a Box-Cox transformation with power lambda = -0.2 made the data approximately normally distributed and gave the best fit for the model. Variance components and selection response were estimated using Bayesian analysis with Gibbs sampling technique. The total variation was rather large for the investigated traits in both the low feather-pecking line (LP) and the high feather-pecking line (HP). Based on the mean of marginal posterior distribution, in the Box-Cox transformed scale, heritability for number of feather pecking bouts (FP bouts) was 0.174 in line LP and 0.139 in line HP. For number of feather-pecking pecks (FP pecks), heritability was 0.139 in line LP and 0.105 in line HP. No full-sib group effect and observation pen effect were found in the 2 traits. After 4 generations of selection, the total response for number of FP bouts in the transformed scale was 58 and 74% of the mean of the first generation in line LP and line HP, respectively. The total response for number of FP pecks was 47 and 46% of the mean of the first generation in line LP and line HP, respectively. The variance components and the realized selection response together suggest that genetic selection can be effective in minimizing FP behavior. This would be expected to reduce one of the major welfare problems in laying hens.

Animals↗

PubMed2004

Effects of stocking density and group size on the condition of the skin and feathers of pheasant chicks.

Twenty-two flocks of pheasants were reared from day-old to approximately six weeks of age without the use of beak trimming or other measures against feather pecking. The pheasants were housed in aviaries in groups of 80 or 240 chicks at stocking densities of 0.7, 1.3 or 4.0 birds per m2. The quality of the pheasants' plumage was poorer at the highest stocking density than at the two lower densities. Higher stocking densities resulted in higher proportions of birds with injuries to their skin (7.2 per cent, 13 per cent and 34 per cent). The group size had no significant effect on the quality of the birds' plumage, but at the largest group size there were significantly more beak-inflicted skin injuries (21 per cent v 12 per cent). In the period between 35 and 42 days of age, the quality of the birds' plumage decreased significantly.

Animals↗

PubMed2003

Strain and age differences in behaviour, fear response and pecking tendency in laying hens.

1. Behaviours associated with a high or low tendency to feather peck could be used as predictors of feather pecking behaviour in selective breeding programmes. This study investigated how strain and age at testing influenced responses in behavioural tests. 2. Four layer-type strains (ISA Brown, Columbian Blacktail, Ixworth and a high feather pecking (HP) and a low feather pecking (LP) line of White Leghorn) were reared in 6 same-strain/line pens of 8 birds from one day old. Birds in half the pens were given an open field test, a novel object test and a test with loose feather bundles between 4 and 12 weeks of age and a tonic immobility (TI) test at 13 weeks of age. All pens were tested with fixed feather bundles at 26 weeks, and undisturbed behaviour in the home pens was videoed at 1 and 27 weeks of age. Daily records of plumage damage were used as an indicator of feather pecking activity in the home pens. 3. Strain did not influence novel object test, open field test or loose feather test behaviour, although age effects in all three tests indicated a reduction in fearfulness and/or an increase in exploratory behaviour with increasing age. 4. White Leghorns showed longer TI durations than the other strains but less pecking at fixed feather bundles than ISA Browns and Columbian Blacktails. 5. There were few associations between behaviour in the 5 different tests, indicating that birds did not have overall behavioural traits that were consistent across different contexts. This suggests hens cannot easily be categorised into different behavioural 'types', based on their test responses and casts doubt on the usefulness of tests as predictors of feather pecking.

Age Factors↗

PubMed1997

Feather pecking behaviour in White Leghorns, a genetic study.

1. Genetic variables of feather pecking (FP) behaviour in a 1993 commercial pure line of White Leghorns were estimated at the age of 6, 38 and 69 weeks. 2. Heritability estimates of performing FP were 0.05 +/- 0.06, 0.14* +/- 0.07 and 0.38** +/- 0.12 for 6, 38 and 69 weeks respectively for sum of pecks (PECKS) and 0.13* +/- 0.07, 0.13* +/- 0.07 and 0.35** +/- 0.12 for sum of bouts (BOUTS). 3. Heritability estimates of receiving FP were not significantly different from 0 except at 6 weeks (0.15* +/- 0.07 and the average of the 3 age classes (AVG) (0.22** +/- 0.09) for PECKS and at 6 weeks (0.15* +/- 0.07) using BOUTS. 4. Genetic correlations of performing FP among age classes were in general high and significant. This was not the case with receiving FP. 5. Plumage cover at 51 weeks had a negative genetic correlation with performing FP at 69 weeks and AVG, but not with receiving FP. No phenotypic correlations were significant between plumage and FP. 6. Body weight at 51 weeks had a negative genetic correlation with performing FP at AVG. 7. Heritability estimates for performing and receiving FP at 6 weeks correspond to those in the literature. No estimates have previously been reported on feather pecking at 38 weeks or 69 weeks. 8. Selection of birds with no or a very low tendency to perform feather pecking should, on the basis of our results, be feasible.

Aggression↗