Feeding layers of different genotypes in organic feed environments.

1. Two experiments were carried out to evaluate the suitability of an experimental laying hen genotype (SH) in organic egg production. SH had been selected over 25 generations on a low protein diet (130 g/kg) based on home grown feedstuffs. SH hens were compared with LSL (Experiment 1) and Hyline (Experiment 2) hens. The birds were kept in 12 aviary pens with access to outdoor runs. 2. Four diets, which were different in each experiment, were used. A control diet was compared with diets based on feedstuffs supposed to be able to be grown and produced according to organic standards. The diets differed in the content of sulphur amino acids. 3. There were no significant differences in mortality caused by diets or genotypes but an incidence of cannibalism occurred in one Hyline group fed on the diet with the lowest methionine content. 4. Severe feather pecking of LSL birds occurred and was worst on the low protein diet. In Experiment 2, signs of feather pecking of birds on the low protein diet occurred at the end of the experiment, but there was no difference between the genotypes. There was no significant difference in number of eggs produced between diets. Egg weight was influenced by diets in both experiments and by genotype in Experiment 2. Number of misplaced eggs was higher in SH hens in both experiments. There were few significant diet x genotype interactions. 5. The use of the outdoor area was influenced by diets and genotype in both experiments. 6. In conclusion, diets low in methionine content influenced predominantly plumage condition and egg weight, although production of eggs by number was unaffected. The SH hen adapted well to organic conditions, as did the Hyline genotype.

Selection for litter size, body weight, and pelt quality in mink (Mustela vison): correlated responses.

In a five-generation selection experiment, separate lines of standard mink (Mustela vison) were subjected to selection for litter size at 3 wk (F line), body weight in September (BS line), underfur density (P line), or combined selection for litter size and body weight (I line). One unselected line served as a control (C line). The present paper focuses on correlated responses to selection regarding fertility and fitness traits, fur quality, and body size traits. Genetic and environmental parameters were estimated with REML (Restricted Maximum Likelihood) techniques using a multi-trait, reduced animal model in a derivative-free way. Genetic and phenotypic correlations were estimated from four subsets of data consisting of 1) female September weight, litter size, and kit mortality; 2) body size traits; 3) September weight and fur traits graded on live mink; and 4) fur traits graded on live mink and skins. September weight was found to be negatively correlated with fertility and fitness traits as well as with fur traits. Selection for underfur density resulted in an improvement in guard hair quality and in general impression of the fur and almost eliminated the fur defect metallic sheen.

Selection for litter size, body weight, and pelt quality in mink (Mustela vison): experimental design and direct response of each trait.

In a five-generation selection experiment, separate lines of mink (Mustela vison) were subjected to selection for improved litter size at 3 wk (F line), BW in September (BS line), and underfur density (P line), and combined selection for litter size and BW (I line). Underfur density was subjectively judged on live animals. One unselected line served as a control (C line). Significant changes were achieved in each trait: litter size in the last generation was 5.3 in the F line vs 3.7 in the C line; September weight in males was 2,254 g in the BS line vs 1,979 g in the C line, and the underfur density score, graded using a 5-point scale, was 4.1 in the P line vs 2.9 in the C line. In the combined line (I line) litter size was only slightly improved, whereas BW was substantially increased (male mean = 2,194 g). A univariate animal model was used to predict genetic values and to estimate variance components with a REML procedure. Heritability estimates were .14 +/- .09 for litter size, .39 +/- .06 for September weight, and .21 +/- .06 for underfur density. It was confirmed that the reproductive performance of heavy of fat animals was poor. Responses were higher than predicted when selecting for September weight and underfur density. In the last generation the average breeding values, relative to the base generation, were +.8 kits for litter size (F line), +365 g for male September weight (BS line), and +1 point for underfur density (P line). The study suggests that negative maternal effects on litter size may exist in mink.

Effect of selection on digestibility and carcass composition in mink.

In a 5-generation selection experiment, separate lines of mink (Mustela vison) were selected for litter size at 3 weeks (F-line) and body weight in September (BS-line). One unselected line served as a control (C). Nutrient digestibility was studied in a balance experiment with four male kits from each line in the last generation. Carcass composition was determined for four 4th-generation F- and BS-males each that had been killed on September 21. The feed consumption rate was higher in the BS-line animals in the balance experiment than in the F- and C-animals (1687 versus 1532 and 1504 kJ/animal and day). These differences reflected the higher average live weights measured on August 25, of the BS-males (1831 g versus 1728 and 1619). CP and CHO digestibility were similar in all lines, whereas a numerically small but significant difference in apparent fat digestibility was found between the F- and BS-lines (95%) and the C-line (93%). Average body weights of animals in the carcass composition evaluation were 2607 g (BS-line) and 2023 g (F-line). Retained protein, fat, and energy were significantly affected by line. The amount of protein retained per kg metabolic weight (kg0.75) was nearly equal in the two lines, indicating that the animals' genetic capacity for protein retention was similar and probably utilized to its full extent. Retained fat and energy per kg0.75 were higher in the BS-line, indicating that the animals had been selected for fat deposition rather than for body size. Hence, selection for body size in mink should be performed by using a selection criterion with which the negative effects of increased fat deposition on reproductive performance can be avoided.

Profiles of oestradiol-17 beta and progesterone and follicular development during the reproductive season in mink (Mustela vison).

Plasma concentrations of oestradiol-17 beta and progesterone were studied in yearling mink females. The blood samples were collected from 2 March until 13 April in females not subjected to mating and in females mated on two consecutive days, early or late in the breeding season, or with 8-9 days between matings. Peaks in oestradiol-17 beta were recorded on the day of first mating, in relation to the second wave of growing follicles, and in early April, around the time when implantation should have occurred. Significant rises in progesterone were recorded from 17 to 21 March and were slightly later in females mated late in the season. Histological studies of ovaries from unmated females revealed that the number of 'active' follicles exceeded the number of degenerated or luteinized follicles until 7 April, after which the number of degenerated follicles increased rapidly. Degeneration was followed by luteinization. On 15 April, ovaries were collected from two females having 15 luteinized follicles each. These females had increased plasma concentrations of progesterone. These studies indicate that, in female mink, peaks in oestradiol-17 beta coincide with the first mating as a result of the copulatory act and that unmated females appear to experience a luteal phase in the absence of ovulation.