| 1. |
- Alm, Malin, et al.
(författare)
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Corticosterone metabolites in laying hen droppings-Effects of fiber enrichment, genotype, and daily variations
- 2014
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Ingår i: Poultry Science. - : Elsevier BV. - 0032-5791 .- 1525-3171. ; 93, s. 2615-2621
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Tidskriftsartikel (refereegranskat)abstract
- There is growing interest and concern for animal welfare in commercial poultry production. To evaluate stress and welfare in an objective and noninvasive way, fecal corticosterone metabolites (FCM) in droppings can be analyzed. However, the influence of diet, genotype, and daily variations in FCM and production of droppings in laying hens has been poorly investigated. This study examined the effect of insoluble fiber by adding 3% ground straw pellets to the feed to Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB) hens housed in furnished cages between 20 and 40 wk of age. In total, 960 hens were included in the study. Droppings were collected 4 times per day for 3 consecutive days and analyzed by corticosterone immunoassay. Biological validation confirmed the ability of the assay to detect changes in FCM levels. Inclusion of straw pellets in the feed increased FCM concentration in both hen genotypes and increased excretion rate of FCM in LB hens. The LB hens also produced greater amounts of droppings than LSL hens. Both FCM levels and production of droppings varied during the day, although no distinct diurnal rhythm was found. These findings demonstrate that when using FCM to evaluate stress and welfare in laying hens, many factors (e.g., diet, genotype used, and so on) need to be taken into account to allow accurate interpretation of the results. In addition, under certain conditions, excretion rate of FCM might be more appropriate to use compared with FCM concentration.
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| 2. |
- Alm, Malin, et al.
(författare)
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Short term deprivation of the litter area after transfer to the layer facility - effects on welfare and production in pullets
- 2013
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Ingår i: World's Poultry Science Journal. - 0043-9339. ; , s. 38-38
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In order to enable hens to find feed and water and to reduce the number of floor-laid eggs in floor systems, producers sometimes exclude pullets from the litter area for some time when they are moved into the production system. This could have negative consequences since litter is an important resource for layers and the procedure is not allowed in Sweden. The aim of the present study was to investigate how bird welfare and production are affected by deprivation of access to litter and space at introduction of pullets to the laying facility. The study comprised 600 floor reared Bovans Robust layers obtained at 16 weeks of age (wks) and housed in 6 groups of 100 in a single-tier floor laying system. Three groups had full access to the litter area during the whole study (OPEN) and three groups were excluded from the litter during the first two weeks (CLOSED) and then received full access throughout the rest of the study. The experiment will run a full production cycle (75 wks) and figures presented below show the results obtained until 51 wks as it is still in progress. Feather cover (6-24 points), pecking wounds, cleanliness, foot condition and keel bone deviations (all 1-4 points) were assessed by integument scoring at 40 wks. Fearfulness was assessed by testing novel object (NO) and tonic immobility (TI). Based on group means, the data were analyzed by analysis of variance (ANOVA) using the MIXED procedure of the statistical system (SAS 9.2). The feather cover score was higher in treatment CLOSED (17.9 points) compared to OPEN (12.3 points) (P=0.019). No difference was found between treatments in any of the other integument score parameters. Fearfulness was higher in groups in the OPEN treatment as compared to CLOSED, indicated by less approaches in the NO test (21.5 vs 48.0) (P<0.001) and longer duration of TI (11.3 min vs 6.4 min) (P=0.018). Rate of lay, number of mislaid eggs, proportion of cracked or dirty eggs and mortality were recorded regularly but no significant differences between treatments were shown. Thus, excluding hens from the litter area during the first two weeks in this type of production system did not decrease the number of floor laid eggs, but had a positive impact on feather cover and resulted in less fearful birds. Additional welfare parameters will be analyzed later on which may explain these results further.
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| 3. |
- Andersson, Annica, et al.
(författare)
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Paths to a sustainable food sector guided by LCA – exemplified by pork production
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- To describe a more sustainable food sector, a supply chain approach is needed. Changing supply chains inevitably means that a range of attributes of the product and its system will change. This project will take on this challenge and deliver detailed descriptions of supply chains of six commodities from a Swedish region in 2012; Milk, cheese, beef, pork, chicken and bread. The set-up of the project was that experts on production along the supply chain design environmentally improved systems. The next step was to challenge the improvements considering their possible consequences on products and systems from different perspectives: food safety, sensory qualities, animal welfare, and consumer appreciation and (only for primary production) costs. The final supply chains were quantified by life cycle assessment (LCA), and they were again assessed from the perspectives mentioned above. Results will be generated during August 2014 and comprise both single-product LCA and region-wide impacts of the future scenarios.
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| 4. |
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| 5. |
- Eriksson, Maria, et al.
(författare)
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Hemp seed cake in organic broiler diets
- 2012
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Ingår i: Animal Feed Science and Technology. - : Elsevier BV. - 0377-8401 .- 1873-2216. ; 171, s. 205-213
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to examine production and health of fast-growing broilers fed diets with and without hemp seed cake (HSC) in organic broiler production. Two diets, a control diet (C) and a diet including HSC (H), were fed to 1200 Ross 308 chickens which were divided over 8 pens. Birds were housed indoors until 21 d, and thereafter kept in the same groups in two chicken houses with access to outdoor pasture up to slaughter at 70 d. Production performance was registered weekly. The number of Clostridium perfringens (C. perfringens) in caeca, as well as leg and foot health and carcass quality was registered during the study period or at slaughter. Total mortality was high regardless of diet due to a short heat wave extreme for Swedish conditions which predominantly affected the heavy male broilers. The inclusion of HSC did not affect total production performance or mortality. Furthermore, no effect of HSC inclusion in the feed was seen on the number of C. perfringens in the caeca. There were differences in litter condition and foot health of birds, which may have been related to the high crude fibre (CF) content of the H diet. (C) 2011 Elsevier B.V. All rights reserved.
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| 6. |
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| 7. |
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| 8. |
- Ivarsson, Emma, et al.
(författare)
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Slutrapport: ökat utnyttjande av raps och åkerböna i slaktkycklingfoder
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Sojaanvändningen inom animalieproduktionen är kraftigt ifrågasatt, och att ersätta sojan med inhemska proteinfodermedel är en av de viktigaste förändringar för att minska miljöpåverkan och stärka svensk kycklings varumärke. Raps och åkerbönor är två av de proteingrödor som är odlingsbara i Sverige och det finns stora möjlighetet att öka användningen av dessa i kycklingfoder. Ett litet gissel med i stort sett alla inhemska proteingrödor är att de innehåller en del ämnen s.k. antinutritionella substanser (ANS) som kan störa näringsupptaget hos fjäderfän. I raps är det framförallt glukosinolater och dess nedbrytningsprodukter som utgör ett problem. Nedbrytning av glukosinolater aktiveras av enzymet myrosinas. Begränsningen hos åkerböna är för växande djur framförallt tanniner och trypsininhibitorer, där vitblommiga åkerbönorna är i princip fria från tanniner. Såväl myrosinas som trypsininhibitorer är värmeinstabila och det finns därmed möjligheter att genom förbehandling med värme, förstöra dessa oönskade substanser i råvaran innan den blandas in i fodret. Dock saknas information om optimal tid och temperatur på värmebehandlingen och hur denna påverkar möjlig inblandningsnivå i slaktkycklingfoder. Risken med en för kraftig värmebehandling är att proteinkvaliteten blir negativt påverkad. För att undersöka detta genomfördes fyra delförsök, ett labförsök och ett slaktkycklingförsök med rapsfrö och ett labförsök och ett slaktkycklingförsök med vitblommig åkerböna. Labförsöken utfördes på Kungsängens forskningscentrum, SLU och raps respektive åkerböna torr-rostades i ugn i olika tider och temperaturer. För raps var enzymet myrosinas helt inaktiverat vid rostning 120 °C, 15 min samtidigt som proteinets kvalité var bibehållen. För åkerböna sågs en sänkning av trypsininhibitoraktivitet och bibehållen proteinkvalitet vid rostning 140 °C, 5,5 min, och dessa temperaturer bedöms som optimala vid torr- rostning. Slaktkycklingförsöken utfödes på Lövsta forskningscentrum, och i rapsförsöket testades 4 inblandningsnivåer, 0, 8, 16, 24 % raps, samt effekt av värmebehandling i form av ångpelletering. För de pelleterade fodren var 16 % inblandning möjlig utan att påverka foderintag, tillväxt eller foderomvandlingsförmåga (FCR) negativt. För de icke-pelleterade - müslifodern var FCR bibehållen vid 8 % inblandning, men vikt och foderintag var sämre än kontrollfodret och sänktes sedan linjärt med ökad inblandningsnivå. I slaktkycklingförsöket med åkerböna testades också 4 inblandningsnivåer, 0, 10, 20 och 30 %, dessa foder ångpelleterades. För nivån 20 % åkerböna testades även effekten av värmebehandling och foderstruktur genom att två müslifoder tillverkades, i det ena var åkerbönorna förrostade i 140 °C, 5,5 min i det andra var de obehandlade. Resultaten visade att foderintag, vikt och FCR var bibehållen vid 20 % inblandning, vid 30 % inblandning var FCR bibehållen, men foderintag och vikt var sänkta. I båda müslifodern sågs ett väldigt lågt foderintag och därmed låga vikter, men bibehållen FCR. Som slutsats konsterades att värmebehandling i form av pelletering möjliggör inblandning av 16 % rapsfrö och 20 % vitblommig åkerböna i slaktkycklingfoder.
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| 9. |
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| 10. |
- Jönsson, Lotta, et al.
(författare)
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Production and egg quality in layers fed organic diets with mussel meal
- 2011
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Ingår i: Animal. - 1751-7311 .- 1751-732X. ; 5, s. 387-393
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Tidskriftsartikel (refereegranskat)abstract
- The first limiting nutrients in typical laying hen diets are the sulphur-containing amino acids and, in particular, methionine. To fulfil the birds' recommended requirement, conventional diets are supplemented with synthetic methionine. As this is not allowed in organic production it becomes very important to have access to alternative high-quality protein feed ingredients. An experiment was performed to evaluate the possibility to compose a diet with 100% organically approved feed ingredients using mussel meal as a major source of methionine. The experiment included 678 Lohman Selected Leghorn (LSL) and 678 Hyline White, W-98, layers during 20 to 72 weeks of age. There were 12 aviary pens with 113 birds in each. The birds were fed one of the two experimental diets containing either 3.5% or 7% dried mussel meat meal or a commercial organic diet from a Swedish feed manufacturer for comparison. Production and mortality were recorded daily per group, and egg weight was recorded once weekly. At 33, 55 and 70 weeks, 10 eggs from each treatment group were collected and analysed for internal egg quality. Diets had no significant effect on laying percentage, egg mass, feed intake, feed conversion ratio, mortality, bird live weight or proportion misplaced, cracked or dirty eggs. Egg quality, that is, shell deformation, shell breaking strength, albumen height, shell percentage and proportion of blood and meat spots were also unaffected. There was a significant difference in egg yolk pigmentation, that is, the egg yolk was more coloured when feeding 7% mussel meal compared with the other diets. Hyline hens had lower feed intake and laying percentage, and higher egg weight, but lower egg mass production than LSL birds. The age of the birds influenced all egg quality traits except for meat and blood spots. The dry matter of the excreta was significantly lower for both genotypes fed the 7% mussel meal diet. These results indicate that mussels may be a high-quality protein source and may replace fishmeal in organic diets for layers.
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| 11. |
- Kalmendal, Robin, et al.
(författare)
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Effects of fiber supply in furnished cages on performance, egg quality, and feather cover in 2 egg-laying hybrids
- 2013
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Ingår i: Journal of Applied Poultry Research. - : Elsevier BV. - 1056-6171 .- 1537-0437. ; 22, s. 109-117
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Tidskriftsartikel (refereegranskat)abstract
- Poultry may obtain fiber from the feed or from the ingestion of, e. g., fibrous litter materials. In earlier studies, it was shown that insoluble fiber may stimulate digestion and exert a calming effect on laying hens. Fiber may also influence the metabolism of minerals and fat, which might affect egg quality. In this paper, we describe the effects of 2 means of fiber supply on production performance, feather cover, and egg quality in Lohmann Brown (LB) and Lohmann Selected Leghorn (LSL) hens housed in furnished cages between 20 and 60 wk of age. Insoluble fiber was supplied by either including 3% ground straw pellets in the feed or by substituting the saw dust in the litter bath with crumbled straw pellets. Overall, hens were frequently pecking the litter, but litter bath occupation, litter pecking, and litter intake was higher in LB than in LSL. In LB, more crumbled straw pellets were consumed from the litter bath compared with saw dust. Compared with the control, adding straw pellets to the feed reduced egg shell thickness in LB but not in LSL. Otherwise, treatments had no significant effects on production performance, egg quality, or feather cover. Therefore, litter may constitute a significant source of insoluble fiber to laying hens, but notable hybrid differences in the interaction with litter were observed.
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| 12. |
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| 13. |
- Rubene, Diana, et al.
(författare)
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The presence of UV wavelengths improves the temporal resolution of the avian visual system
- 2010
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 0022-0949 .- 1477-9145. ; 213:19, s. 3357-3363
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Tidskriftsartikel (refereegranskat)abstract
- The ability to perceive rapid movement is an essential adaptation in birds, which are involved in rapid flight, pursuing prey and escaping predators. Nevertheless, the temporal resolution of the avian visual systems has been less well explored than spectral sensitivity. There are indications that birds are superior to humans in their ability to detect movement, as suggested by higher critical flicker frequencies (CFFs). It has also been implied, but not properly tested, that properties of CFF, as a function of light intensity, are affected by the spectral composition of light. This study measured CFF in the chicken, Gallus gallus L., using four different light stimuli - white, full-spectrum (white with addition of UV), yellow (590 nm) and UV (400 nm) - and four light intensity levels, adjusted to relative cone sensitivity. The results showed significantly higher CFF values for full-spectrum compared with white light, as well as a steeper rate of increase with intensity. The presence of UV wavelengths, previously demonstrated to affect mate choice and foraging, appears to be important also for detection of rapid movement. The yellow and UV light stimuli yielded rather similar CFFs, indicating no special role for the double cone in flicker detection.
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| 14. |
- Wall, Helena, et al.
(författare)
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Effects of a high oil and fibre diet and supplementary roughage on performance, injurious pecking and foraging activities in two layer hybrids
- 2012
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Ingår i: British Poultry Science. - : Informa UK Limited. - 0007-1668 .- 1466-1799. ; 53, s. 153-161
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Tidskriftsartikel (refereegranskat)abstract
- 1. The study investigated the feeding of a high oil and fibre diet containing 260 g/kg organically produced cold pressed sunflower cake or supplemental roughage to aviary-housed Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB) layers between 20 and 74 weeks of age with outdoor access during summer. 2. Feeding roughage was associated with reduced vent injuries, a tendency to improve plumage condition, and was accompanied by improved FCR compared with controls. Feeding the high oil and fibre diet tended to improve FCR compared with the control diet. 3. The dry matter of faeces was reduced in both treatments compared with controls. Foot pad cleanliness and the proportion of dirty eggs were negatively affected by the high oil and fibre diet. Foot health was superior in LB compared to LSL. 4. LB used the outdoor hen-runs more than LSL, but LSL consumed more litter indoors. Fewer LB hens fed on the control feed were recorded in the outdoor hen-runs. Supplemental roughage tended to decrease litter consumption. 5. In conclusion, supplemental roughage reduced vent injuries and was correlated with foraging activities. Feeding 260 g/kg sunflower cake negatively affected hygiene in aviary hens. Sunflower cake is nevertheless a promising alternative feedstuff to fulfil the protein requirement in organic layers.
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| 15. |
- Wall, Helena, et al.
(författare)
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Effects on egg quality traits of genotype and diets with mussel meal or wheat-distillers dried grains with solubles
- 2010
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Ingår i: Poultry Science. - : Elsevier BV. - 0032-5791 .- 1525-3171. ; 89, s. 745-751
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the study was to evaluate effects on exterior and interior egg quality and sensory characteristics of eggs from hens fed diets with admixtures of 3.5 or 7.0% of mussel meal or 20% wheat-distillers dried grains with solubles (DDGS). The mussel meal diets followed organic standards, whereas the DDGS diet was formulated for hens in conventional production. Standard diets, one organic and one conventional from a Swedish feed manufacturer, were included for comparison. The study used 164 Hy-Line White W-98 and 164 Hy-Line Brown layers housed in small-group furnished cages. Egg flavor or odor was not affected by genotype. Egg flavor intensity was stronger in eggs from hens fed either of the mussel diets or the standard organic diet compared with the conventional diet. There were no differences between any of the diets in egg odor intensity, off-flavor, or off-odor. The mussel diets and the standard organic diet gave stronger yolk pigmentation than the conventional and DDGS diet, respectively. Manure DM was lower with the admixture of 7.0% mussel meal than 3.5%. There was a tendency (P < 0.10) toward a difference between diets in dirty eggs, and the percentage was highest with 7.0% mussel meal. Diet or genotype had no effect on egg weight, albumen height, shell deformation, shell breaking strength, or proportion of cracked eggs. Genotype differences were found in weight percentage of albumen, yolk, and shell and in the presence of blood and meat spots and in percentage of dirty eggs. In conclusion, the majority of egg quality traits were unaffected by the diets studied. With the admixture of DDGS used in the present study, the characteristics of eggs were similar to those of eggs produced on the conventional standard diet. There was no indication of impaired egg odor or flavor with the used fractions of DDGS or mussel meal.
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| 16. |
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| 17. |
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| 18. |
- Wall, Helena, et al.
(författare)
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Nest lining in small-group furnished cages for laying hens
- 2013
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Ingår i: Journal of Applied Poultry Research. - : Elsevier BV. - 1056-6171 .- 1537-0437. ; 22, s. 474-484
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Tidskriftsartikel (refereegranskat)abstract
- In small-group furnished cages with nests lined with artificial turf, a high use of nest and acceptable egg quality are generally achieved. However, artificial turf has drawbacks, such as not letting manure through and not being cleanable in position. Therefore, a more perforated nest-lining material would be preferable given that nest acceptance and egg quality are not impaired. The main aim of the present study, comprising 2 trials, was to evaluate layers' use of nests, egg quality, and bird exterior appearance in furnished cages with nests lined with artificial turf, plastic netting, or with the cage floor left bare. The furnished cages used in this study housed 8 or 10 layers; the hybrids included were Hy-line White and Hy-line Brown in trial 1 and lohmann selected Leghorn and lohmann Brown in trial 2. In this study, plastic netting was as good as the artificial turf for all the aspects compared, whereas the bare cage floor as a nest bottom resulted in lower use of the nest and tendencies for inferior egg quality. Hybrid differences were found in most of the traits studied.
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| 19. |
- Wall, Helena
(författare)
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Production performance and proportion of nest eggs in layer hybrids housed in different designs of furnished cages
- 2011
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Ingår i: Poultry Science. - : Elsevier BV. - 0032-5791 .- 1525-3171. ; 90, s. 2153-2161
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the study was to compare use of nests, production performance, and egg quality in 4 designs of furnished cages (FC) housing 8 (T8), 10 (T10), 20 (T20), or 40 (T40) layers. The FC housing 8 and 10 hens were commonly used in commercial egg production in Sweden, whereas the cages housing 20 and 40 hens constituted new designs, at present not allowed in Sweden. The FC also differed in design and location of litter facilities. The study comprised 2 full production cycles (20-72 wk of age). Trial 1 included 588 Hy-Line White W98 and 460 Hy-Line Brown layers, and trial 2 used 572 Lohmann Selected Leghorn and 588 Lohmann Brown layers. In accordance with Swedish prohibition, beak treatment was not conducted. In both trials production parameters and mortality were considered normal and levels were unaffected by cage design. Deaths attributable to cannibalistic pecking were rare. Overall, exterior egg quality was superior in T8 compared with T20 and T40, whereas T10 generated intermediate results. Genotype differences were found in production performance, exterior egg quality, and use of nests. In T8 and T10 at least 95% of the eggs were laid in nest whereas in T20 and T40 a considerable percentage of eggs were laid on the litter mat, constituting the litter facility in those cage models. Additional lighting of litter mats (trial 2) had no effect on layers' choice of site for egg laying. Dividing T40 cages in 2 identical cage halves by a rear partition with pop holes had no effect on any of the traits measured. In conclusion, housing larger groups of non-beak-treated hens together in FC is possible, with acceptable levels of production and mortality, provided that cannibalism does not develop. The inferior egg quality in T20 and T40, likely caused by the large proportions of misplaced eggs, needs to be considered in the further development of those cage designs.
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| 20. |
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| 21. |
- Wistedt, Anna, et al.
(författare)
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Effects of phytoestrogen supplementation in the feed on the shell gland of laying hens at the end of the laying period
- 2012
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Ingår i: Animal Reproduction Science. - : Elsevier BV. - 0378-4320 .- 1873-2232. ; 133, s. 205-213
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Tidskriftsartikel (refereegranskat)abstract
- Shell quality decreases as laying hens age and the aim of present study was to investigate how a supplement of daidzein, a natural phytoestrogen in soya, affects key factors in the shell gland and eggshell quality in late-stage laying hens. Hybrids of Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB), received either a daidzein diet (50 mg/kg feed) or a control diet from 60 to 72 weeks of age. Both the total number of capillaries and capillaries with carbonic anhydrase (CA) activity were higher in the LSL hybrid than in the LB. After daidzein supplementation the number of CA positive capillaries was unaffected in the LSL but increased in the LB hybrid indicating a higher sensitivity to daidzein in this hybrid. Estrogen receptor alpha and beta (ER alpha, ER beta) were localized and the complete picture of the two ERs can now be described in shell gland of domestic hens. Nuclear and cytoplasmic staining was generally stronger for ER beta, while membrane associated staining was present only for ER alpha. Interestingly, capillary endothelium contained only ER beta and since estrogen regulation of CA is well documented, the presence of an endothelial ER provides one possible route for the increase in CA positive capillaries found in LB hybrids. Eggshell quality or egg production was not affected by daidzein supplementation. The hybrids used in this study showed anatomical differences and reacted differently to daidzein supplementation, but if this can be explained by the divergences in ER beta localization noted between the hybrids remains to be clarified. (C) 2012 Elsevier B.V. All rights reserved.
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| 22. |
- Wistedt, Anna, et al.
(författare)
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Exogenous estradiol improves shell strength in laying hens at the end of the laying period
- 2014
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Ingår i: Acta Veterinaria Scandinavica. - : Springer Science and Business Media LLC. - 0044-605X .- 1751-0147. ; 56
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Tidskriftsartikel (refereegranskat)abstract
- Background: Cracked shells, due to age related reduction of shell quality, are a costly problem for the industry. Parallel to reduced shell quality the skeleton becomes brittle resulting in bone fractures. Calcium, a main prerequisite for both eggshell and bone, is regulated by estrogen in a complex manner. The effects of estrogen, given in a low continuous dose, were studied regarding factors involved in age related changes in shell quality and bone strength of laying hens. A pellet containing 0.385 mg estradiol 3-benzoate (21-day-release) or placebo was inserted subcutaneously in 20 birds each of Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB) at 70 weeks of age. Eggs were collected before and during the experiment for shell quality measurements. Blood samples for analysis of total calcium were taken three days after the insertion and at sacrifice (72 weeks). Right femur was used for bone strength measurements and tissue samples from duodenum and shell gland were processed for morphology, immunohistochemical localization of estrogen receptors (ER alpha, ER beta), plasma membrane calcium ATPase (PMCA) and histochemical localization of carbonic anhydrase (CA). Results: Estrogen treatment increased shell thickness of both hybrids. In addition, shell weight and shell deformation improved in eggs from the brown hybrids. The more pronounced effect on eggs from the brown hybrid may be due to a change in sensitivity to estrogen, especially in surface epithelial cells of the shell gland, shown as an altered ratio between ER alpha and ER beta. A regulatory effect of estrogen on CA activity, but not PMCA, was seen in both duodenum and shell gland, and a possible connection to shell quality is discussed. Bone strength was unaffected by treatment, but femur was stronger in LSL birds suggesting that the hybrids differ in calcium allocation between shell and bone at the end of the laying period. Plasma calcium concentrations and egg production were unaffected. Conclusions: A low continuous dose of estrogen improves shell strength but not bone strength in laying hens at the end of the laying period.
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| 23. |
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| 24. |
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