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Genomic selection can be implemented based on the genomic relationship matrix (GBLUP) and can be combined with phenotypes from nongenotyped animals through the use of best linear unbiased prediction (BLUP). A common method to combine both sources of information involves multiple steps, but is difficult to use with complicated models and is nonoptimal. A simpler method, termed single-step GBLUP, or ssGBLUP, integrates the genomically derived relationships (G) with population-based pedigree relationships (A) into a combined relationship matrix (H) and allows for genomic selection in a single step. The ssGBLUP method is easy to implement and uses standard BLUP-based programs. Experiences with field data in chickens, pigs, and dairy indicate that ssGBLUP is more accurate yet much simpler than multi-step methods. The current limits of ssGBLUP are approximately 100,000 genotypes and 18 traits. Models involving 10 million animals have been run successfully. The inverse of H can also be used in existing programs for parameter estimationm, but a properly scaled G is needed for unbiased estimation. Also, as genomic predictions can be converted to SNP effects, ssGBLUP is useful for genomic-wide association studies. The single-step method for genomic selection translates the use of genomic information into standard BLUP, and variance-component estimation programs become a routine.

This paper reviews the possibilities of adapting laying hens to cages by means of genetic selection. By selecting separately for rate of lay and longevity using a kin selection method, a strain of laying hen has been developed that shows much less feather pecking and cannibalism than a control strain, and with no decrease in productivity. This experimental strain enjoys a higher level of welfare in cages because it does not require beak trimming.

Four selection strategies aimed at maximizing egg production in laying hens were compared with respect to expected annual genetic gain (GA). The selection strategies were: 1) (S1P) Traditional single-stage selection based on a single-house production system using partial records for both the individual and its ancestors, 2) Single-stage selection based on a single-house production system using full records for both the individual and its ancestors (S1F), 3) Single-stage selection based on a two-house production system using partial records for the individual and full records for its ancestors (S2P), and 4) Multistage selection based on a two-house production system using partial records for the individual and all available ancestral records (M2P). Strategy M2P resulted in the shortest generation interval (0.538 yr) and was the most efficient (deltaGA4 = 3.620 eggs per year), whereas strategy S1F generated the longest generation interval (2 yr) and was the least efficient (deltaGA2 = 1.334 eggs per year). Strategies S1P and S2P resulted in generation intervals of 1 yr, and were intermediate in efficiency (deltaGA1 = 2.232 eggs per year, deltaGA3 = 2.593 eggs per year). It was concluded that a two-house production system utilizing multistage selection was the most effective selection methodology. Further, selection based on M2P is expected to improve persistency of lay, whereas selection on S1P will not.

A selected line of White Leghorns that has shown improved survivability and productivity and reduced feather loss in multiple-hen cages was evaluated for production traits under both stressed and unstressed conditions. It was hypothesized that hens selected for adaptation to multiple-bird cages would react less intensely to stressors and therefore lay more eggs and have lower mortality under stressed conditions. Three lines of chickens (selected, control, and commercial) were housed in either single-hen (1 hen) or multiple-hen cages (12 hens, social competition) at 16.7 or 17.1 wk of age. They were subsequently subjected to cold exposure at 33 wk of age and heat exposure at 44 wk of age. The selected line of chickens in multiple-hen cages showed an increased resistance to heat exposure, as indicated by lower mortality, when compared to the control and commercial lines housed in multiple-hen cages. Egg production 8 d prior to, during, and 8 d following either cold or heat exposures indicated that the selected line of chickens withstood social, handling, and environmental stressors better than the control line and, in some cases, the commercial line of chickens. It was concluded that the selected line of Leghorns showed evidence of stress resistance through lowered mortality and improved production.

A selected line of White Leghorns that has shown improved survivability and productivity and reduced feather loss in multiple-hen cages was evaluated for hematological and adrenal responses under both stressed and unstressed conditions. It was hypothesized that hens selected for adaptation to multiple-bird cages would react less intensely to stressors. Three lines of chickens (selected, control, and commercial) were housed in either single-hen (1 hen) or multiple-hen cages (12 hens, social competition) at 16.7 or 17.1 wk of age. They were subsequently subjected to cold exposure at 33 wk of age and heat exposure at 44 wk of age. Genetic stock as a main effect, and the interaction of genetic stock with either a cold or heated environment or with cage size, had no effect on plasma levels of cholesterol and corticosterone. At the time of transfer to laying cages, the selected line of pullets, as indicated by a decrease in packed cell volume, appeared to adapt more quickly to the new waterer system of multiple-hen cages than did the control and commercial lines. At 33 wk of age, the control and commercial lines in multiple-hen cages experienced heterophilia and increased heterophil to lymphocyte ratios, whereas the selected line did not, when compared with these same lines in single-hen cages. This leucocytic response could be interpreted to mean that the selected line of chickens adapted better to social competition than either the control or commercial lines; however, a similar leucocytic response was not observed at 18 or 44 wk of age. In conclusion, the physiological characterization of the selected line of Leghorns showed evidence of improved adaptation to multiple-hen cages when compared to the other stocks. In some cases, the selected line responded less intensely to stress; however, trends were not always consistent.

A selected line of White Leghorns, which has shown improved survivability and reduced feather loss in large multiple-hen cages, was evaluated for humoral immune response to SRBC under both stressed and unstressed conditions. Three lines of chickens (selected, control, and commercial) were housed in either single- (1 hen) or multiple-hen cages (12 hens, social competition) and subjected to a cold ambient temperature (0 C) at 33 wk of age and to two heating episodes (38 C) at 44 wk of age. Each hen was challenged intravenously with 1 mL of a 7% saline suspension of SRBC at the time that cold exposure was initiated. Hens subjected to high ambient temperatures had been exposed previously to a cold temperature, but were not challenged with SRBC until 16 to 18 h following the end of the second heating episode. Exposure to cold caused immunosuppression in single-caged hens, but not in hens in colony cages. Single- vs colony-caged hens of the control environment challenged with SRBC at 33 wk of age had similar primary hemagglutinin responses to SRBC. Hens subjected to heat experienced immunosuppression at 9 and 12 d following challenge to SRBC when compared to the controls. Hens of multiple-bird cages challenged with antigen at 44 wk of age had a significantly lower hemagglutinin response to SRBC than those reared in single-bird cages. The three lines of genetic stock had similar primary hemagglutinin responses to SRBC; the interactions of genetic stock with cage size or environmental temperature were not significant. It was concluded that genetically selecting hens for survival in multiple-hen cages did not affect their humoral immune response to SRBC.

Three stocks of White Leghorns were compared for behavioral traits when kept in single-bird (1H) and 12-hen (12H) layer-house cages. Genetic stocks consisted of a commercial strain (X), a randombred control (C), and a stock derived from C and selected on the basis of kin's group performance information for increased survival and egg production over seven generations (S). Experimental units consisted of four consecutive 1H cages or a single 12H cage. All birds within a unit had intact beaks and were of the same stock. Each stock was represented by hens in 48 units of both 1H and 12H cages, and by 48 males (C and S stocks only) in 1H cages. Birds that died were replaced. Observations involved hens in their home cages except for tonic immobility (TI) and pair contests. Observations carried out soon after birds were placed in layer-house cages indicated that avoidance of the observer was essentially absent after pullets were observed on the 1st and 2nd d. Behavioral profile frequencies differed for nearly all behaviors compared in 1H and 12H environments. Following initially high crouching and low feeding frequencies, apparently normal levels were present by Days 15 and 16 posthousing. During the initial adaptation phase, genetic stock differences were not found within 1H cages and were present in only 2 of 10 categories in 12H cages. Young adult profiles also indicated no differences among stocks in 1H cages, but stock differences were found in 6 of 12 categories in 12H cages. In those cases, X strain hens differed from hens of the C and S stocks, but C and S hens did not differ from each other. Comparisons carried out between hens in 1H and 12H cages revealed that fearfulness was greater in 12H cages. Genetic stock comparisons, involving relative fearfulness and feeding and movement in a frustrating situation indicated that the X stock frequently differed from both C and S, but C and S did not usually differ from each other. However, observations of hens' agonistic activity in the 12H home cage environment revealed that the S stock had fewer agonistic acts than the C stock from which it was derived, and both C and S had less agonistic activity than the X stock. Pair contests carried out within and between C and S stocks in both sexes yielded results inconsistent with those for agonistic activity in 12H cages. The C and S hens did not differ, but S males were more aggressive and, in between-strain contests, were more dominant.

A selection experiment was initiated with a synthetic line of White Leghorns in 1982 to improve adaptability and well-being of layers in large multiple-bird cages by use of a selection procedure termed "group selection". With this procedure, each sire family was housed as a group in a multiple-bird cage and selected or rejected as a group. An unselected control, with approximately the same number of breeders as the selected line, was maintained for comparison and housed in one-third cages. Annual percentage mortality of the selected line in multiple-bird cages decreased from 68% in Generation (G)2 to 8.8% in G6. Percentage mortality in G6 of the selected line in multiple-bird cages was similar to that of the unselected control in one-bird cages (9.1%). Annual days survival improved from 169 to 348 d, eggs per hen per day (EHD) from 52 to 68%, eggs per hen housed from 91 to 237 eggs, and egg mass (EM) from 5.1 to 13.4 kg, whereas annual egg weight remained unchanged. The dramatic improvement in livability demonstrates that adaptability and well-being of these birds were improved by group selection. The similar survival of the selected line in multiple-bird cages and the control in one-bird cages suggests that break-trimming of the selected line would not further reduce mortalities, which implies that group selection may have eliminated the need to beak-trim. Corresponding improvements in EHD and EM demonstrate that such changes can also be profitable. The most surprising finding was the rate of which such improvement took place, with the majority of change in survival occurring by the third generation. However, EHD continued to improve at the rate of 4% per generation.

Selection of hens with intact beaks for high performance in multiple-bird cages has produced a stock that clearly exceeds its unselected control when hens have intact beaks but shows less advantage when comparisons involve effectively beak-trimmed birds. The selected stock performed at about the same level as a stock recently derived from a commercial source (but with two generations of relaxed selection) when birds had intact beaks but at a lower level when birds had their beaks trimmed. Relative incidences of deaths from cannibalistic pecking were partially responsible for the results obtained.

Pullets of stocks derived from the North Central Randombred White Leghorn population without selection (C) or selected (S) on family performance when kept with beaks intact in multiple-hen cages were compared. Pullets had intact, one-fourth, or one-half of the beak removed (IN, 1/4R, and 1/2R, respectively). No stock differences were detected for behavior traits or other measures during the rearing period. However, beak-trimmed pullets were more inactive and feeding behavior was depressed in 1/2R pullets 1 wk after beak trimming. At 16 wk, 1/4R pullets' beaks had regrown but 1/2R pullets' beaks continued to be shorter than IN pullets' beaks. No differences in fearfulness were found between genetic stocks or among beak length treatments early in the laying period. Deaths from beak-inflicted injuries accumulated steadily from 18 wk until the study was ended at 40 wk. Cannibalistic deaths occurred less frequently in S as compared with C pullets within each beak treatment. As the amount of beak removal increased, beak-inflicted mortality decreased. The S pullets had earlier sexual maturity, lighter egg weights, and greater hen-housed egg production and egg mass than C pullets, and 1/2R pullets had greater egg production than 1/4R and IN pullets. Genetic stock by age and beak treatment by age interactions were present for hen-housed production and egg mass, and the interactions appeared to result primarily from increased mortality from cannibalistic pecking with increased age.

The performance of dwarf and normal White Leghorn laying hens with similar genotypes other than for the dwarf gene (dw) was observed over thirteen 28-day periods in a factorial arrangement involving four protein levels (20.0, 18.1, 16.4 or 14.3% protein plus supplemental methionine) and two densities (two or three birds per standard 10 X 16 in cage). The normal birds had significantly higher overall hen-day egg production, egg weight, and body weight, but the dwarf birds excelled for feed efficiency and adult viability. Significant genotype X ration interactions were observed for egg lay, egg weight, body weight, and feed efficiency, primarily due to the relatively poor performance of the dwarf birds on the 14% protein. A significant genotype X density interaction resulted for feed efficiency, due to a higher efficiency in 3-bird than in 2-bird cages for dwarf birds, while the reverse was true for normal birds. These results suggest that the potential of the dwarf gene for increasing the efficiency of commercial egg layers can be enhanced by further study as to optimal nutrition and management regimens.

Three trials, each with 24 hens, were conducted to determine the effects of dietary cholesterol, caloric intake, and genotype on the synthesis, storage, and excretion of cholesterol in the laying hen. The two genotypes of birds used in this experiment had been divergently selected for high and low oxygen consumption and had been shown to differ significantly (P less than .01) in body weight gain and carcass lipid deposition from 0 to 4 weeks of age. The dietary treatment, administered for a 2-week period to birds in each genotype, consisted of two levels of dietary cholesterol (0 and 1% added) and two energy intakes (ad libitum and 75% ad libitum). The experimental design was a 2 X 2 X 2 factorial. One percent added cholesterol versus none supplemented produced a significant (P less than .01) decrease in available metabolizable energy and uptake of acetate into liver cholesterol while causing significant (P less than .01) increases in egg and liver cholesterol but not in plasma cholesterol. Restricting caloric intake, as compared to ad libitum feeding, resulted in significantly (P less than .01) decreased egg production and total amount of cholesterol excreted via the egg with significantly (P less than .05) increased plasma and liver cholesterol levels but no change in egg cholesterol concentration. Differences were significant (P less than .05) between the two genotypes in feed intake and hepatic cholesterol and lipid synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Two experiments were conducted to investigate the response of two populations of chickens, divergently selected for high and low oxygen consumption, to varying protein levels. Protein levels used for Experiments 1 and 2 were 16, 18, 20, and 22% and 20, 22, 24, and 26%, respectively. The birds were weighed initially and weekly to 4 weeks of age. Feed consumption was ad libitum with amounts consumed recorded weekly. Gross feed efficiency was computed per pen as the difference between initial and weight at 4 weeks divided by feed consumed adjusted for spillage. The results from these experiments indicate that at low protein levels both lines were equally efficient, but, as the level of protein was increased, the low line was increasingly more efficient while the high line became less efficient. Gain for the low O2 birds was greater than the high O2 birds in all cases with both lines increasing in gains equally with increased protein levels.

An experiment, involving 32 roosters, was designed to study the interaction of dietary cholesterol and genotype on cholesterol metabolism in roosters. The two lines of birds used in this study had been divergently selected for high and low oxygen consumption and had been shown to differ significantly (P less than .01) in body weight gain and carcass lipid deposition from hatch to 4 weeks of age. The dietary treatments, administered for a 2-week period, were 0 and 1% dietary cholesterol added to a basal mash diet. Two separate trials were run, each with 16 roosters, resulting in four replicates of each treatment per line for each trial (block). After the trial period, the birds were injected with 1-(14)C-acetate and livers were removed; hepatic cholesterol synthesis was measured by the uptake of labeled acetate into liver digitonin precipitable sterols. Plasma and liver cholesterol levels were also measured. The data were analyzed as a randomized complete block design. Added dietary cholesterol significantly (P less than .01) increased both plasma and liver cholesterol levels over the control while significantly (P less than .01) decreasing the uptake of acetate into hepatic cholesterol in both lines by about 7-fold. Plasma cholesterol was significantly (P less than .05) greater in the high than low oxygen-consuming birds, and liver cholesterol was higher (P less than .10) in the low than high oxygen-consuming line.(ABSTRACT TRUNCATED AT 250 WORDS)

This experiment, involving 320 chicks, was conducted to determine the effects of dietary cholesterol, restricted caloric intake, and genetic lines on cholesterol metabolism in the bird. The two lines of chicks studied had been divergently selected for oxygen consumption and had been shown to differ significantly (P less than .01) in weight gain and carcass lipid deposition. The dietary treatments, administered for a 2-week period, consisted of two levels of dietary cholesterol (none and supplemented) for each of two levels of energy (ad libitum and restricted). At the end of this 2-week period, the birds were injected intravenously with 1-14C-acetate and their livers removed 4 hr later. Hepatic cholesterol and lipid synthesis were measured by the uptake of acetate. Added dietary cholesterol significantly (P less than .01) decreased hepatic cholesterol synthesis, lipid synthesis, and specific activity of hepatic cholesterol but increased plasma and liver cholesterol. However, the elevation in plasma and liver cholesterol represented only .9 and 1.8% respectively, of the increase in total intake of dietary cholesterol. Metabolizable energy of diets fed ad libitum was also significantly (P less than .01) reduced with supplemented dietary cholesterol. A significant (P less than .01) difference in body weight was present between the two lines, with low oxygen consuming (LOC) birds exhibiting heavier body weights than high oxygen consuming (HOC) birds. A significant interaction between line and energy intake (P less than .05) was present for hepatic cholesterol levels; LOC birds exhibited higher levels of hepatic cholesterol than HOC birds when both groups were fed at restricted levels.(ABSTRACT TRUNCATED AT 250 WORDS)

This experiment involving 288 Coturnix quail was conducted to determine the effects of various fiber sources (alfalfa, wheat bran, dried brewer's grain, cellulose, and pectin) on serum, liver and egg yolk cholesterol, and egg production. The fiber sources were added at a rate to provide 6.25% fiber to a corn-soybean meal diet and fed for a 28-day experimental period. Serum, liver, and egg cholesterol levels were measured as pen composite samples at the end of the experimental period. No difference was exhibited in egg yolk cholesterol among any of the groups (P greater than .10). Liver and serum cholesterol levels were elevated in the birds fed the pectin and wheat brain diets as compared with that in birds fed the other fiber source; also, metabolizable energy intakes and eggs per hen day (EHD) were decreased for both groups. When data were adjusted for EHD by covariance analysis, the treatment differences no longer appeared (P greater than .05). These results indicate that 1) there is a basal quantity of cholesterol deposited in the egg on which fiber intake, energy consumed, or egg production have very little effect and that 2) there is an inverse relationship between serum and tissue cholesterol levels and the total quantity of cholesterol excreted via the egg.