Duration of egg formation in hens selected for increased rate of lay under 23 h and 24 h light-dark cycles

1. The intervals from oviposition to the next ovulation and the times spent by the ovum in various parts of the oviduct were examined, in hens selected for increased rate of lay over 5 generations under a 23 h light-dark cycle (23HS line) and kept in a 22 h light-dark cycle, and in hens selected under a 24 h light-dark cycle (24HS line) and kept in a 24 h light-dark environment. 2. The intervals from oviposition to the next ovulation were 13 min and 25 min in the 23HS and 24HS lines respectively. Times from ovulation to entry of the ovum into the uterus were 4 h 44 min and 4 h 43 min in the 23HS and 24HS lines respectively, and times spent by the ovum in the uterus were 19 h and 19 h 24 min in the 23HS and 24HS lines respectively. 3. It is concluded that the reduced oviposition interval in the 23HS line compared to the 24HS line was caused by the reduction in the interval from oviposition to the next ovulation and the time spent by the ovum in the uterus.     

Constant photoperiods and eggshell quality in broiler breeder pullets

Broiler breeder pullets were exposed to constant 10-, 11-, 12-, 13-, 14- or 16-h photoperiods from 3 d of age. Egg weight, eggshell weight and shell thickness index were determined at 52 weeks of age. Egg weight increased by 0.31 g, shell weight decreased by 30 mg and shell thickness index decreased by 0.57 mg/cm2 for each one-hour increase in photoperiod. Whilst the changes in egg weight and eggshell thickness index might be overstated because eggs were collected at the same chronological time, the effect of time of egg-laying within the day was minimal in comparison, and did not negate the conclusion that egg weight increases, and shell weight and thickness index decrease with lengthening photoperiods. The effect of photoperiod on eggshell quality was not due to differences in the rate of lay between treatments. Shell weight was unaffected by time of lay.     

Correlated responses in maternal performance following divergent selection for heat loss in mice

Divergent selection in mice was applied in 3 independent replicates for high (maintenance high; MH) and low (maintenance low; ML) heat loss for 16 generations. An unselected control (maintenance control; MC) was also maintained in all replicates. Selection ceased for 26 generations; heat-loss measurement and selection resumed at generation 42. Lactation performance, dam weight, dam feed intake, and efficiency of production of pup weight were recorded or calculated for MH and ML dams in all 3 replicates at generation 46 or 47 with the objective of determining whether selection for heat loss has created correlated responses in maternal performance. One-half of the dams reared their own litters, and one-half reared cross-fostered (across lines) litters. Between 10 and 12 litters were used from each replicate-line-rearing class. Litter size was recorded, and litters were standardized to 8 pups within 24 h of birth. For cross fostering, MH litters were matched to ML litters born within 24 h of each other, and MH-ML litter pairs were cross-fostered at 3 d of age. A weigh-suckle-weigh protocol was used to obtain milk production estimates over a 2-h suckling period at 6, 9, 12, and 15 d. Dam (plus litter) feed intake was also recorded at these times and was calculated as the disappearance of feed over 3-d intervals. Dams of the MH selection tended (P < 0.11) to have greater litter size than those of the ML selection; litter size of MC dams was intermediate. Line of dam affected milk production (P = 0.04) and dam feed intake (P < 0.03) as MH dams produced more milk and consumed more feed than ML dams. Average milk production for the 2-h measurement period was 1.70 +/- 0.07 and 1.41 +/- 0.07 g, and average 3-d feed consumption was 50.8 +/- 1.2 and 45.2 +/- 1.2 g for MH and ML dams, respectively. Cross-fostering had no effect (P > 0.86) on milk production. Line of dam tended to affect 21-d litter weight (P = 0.15) with litters reared by MH dams weighing more than those reared by ML dams, but there was no difference (P > 0.86) in 21-d dam weights. Efficiency of producing litter weight (litter 15-d weight: dam plus litter feed intake from d 6 to 15) was greater (0.49 vs. 0.46, SE = 0.009; P = 0.03) for ML than for MH dams. Selection for reduced heat loss (lower maintenance feed intake in the ML line) resulted in reduced milk production and feed intake in dams and greater efficiency of litter weight production.     

Effects of selection for reduced oviposition interval on plasma concentrations of luteinising hormone during the ovulatory cycle in hens on a 24 h lighting cycle

The effects of selection under continuous light for reduced oviposition interval within a sequence of eggs on plasma luteinising hormone (LH) concentrations during the ovulatory cycle were investigated in lines of Australorps and White Leghorns maintained on a 24-h light:dark cycle. Selection did not significantly alter LH concentrations during mid-sequence cycles in either breed. In the control lines, concentrations were higher in the Australorps than in the White Leghorns before and at peak in mid-sequence cycles. The increase in egg production resulting from selection was associated with an advance in the mean time of lay of mid-sequence eggs in both breeds and, in the Australorps, with more pre-ovulatory LH peaks being initiated at the beginning of the open period of the ovulatory cycle. Selection reduced the time an egg spends in the oviduct and, in the Australorps, significantly reduced the interval between a pre-ovulatory LH peak and the oviposition of the egg currently in the shell gland. We suggest that selection under continuous light for reduced oviposition interval increased the rate of ovarian follicular maturation by a mechanism which did not involve an increase in pre-ovulatory concentration of plasma LH in a 24-h light-dark cycle.     

Avian leukosis virus and selection on oviposition interval in Australorp lines.

1. Shedding of group-specific antigen of avian leukosis virus (ALV) into egg albumen was determined in three Australorp lines: AS line that had been selected primarily for short oviposition interval, ASS line that had been derived from the AS line and developed as a commercial dam line for egg laying, and AC line that had been kept as a randombred control. 2. The proportion of shedders was 13.1 to 16.7% in the AS line in 1984-88, 16.3% in the ASS line in 1984 (before culling of the shedders), and 6.1% and 6.6% in the AC line in 1984 and 1988, respectively. 3. In the AS line, shedders were 1.8% lower in rate of lay to 300 d of age, 1.3 g lower in average egg weight at 34 weeks of age, 5.6% lower in hatchability of fertile eggs and 0.24 h shorter in oviposition interval than non-shedders. In the ASS line (1984 only), the differences between shedders and non-shedders were in the same direction, but in magnitude greater for rate of lay and smaller for oviposition interval. 4. The shedders were favoured by the artificial selection because of their shorter oviposition interval and this appeared to be responsible for the higher levels of ALV shedding in the selection lines.     

The time factor in egg formation for hens exposed to ahemeral light-dark cycles

Three hundred and two White Leghorn pullets were killed at intervals 5 min to 7 h following oviposition. The reproductive tract was then examined and, from the position of the yolk, estimates were made of the mean time spent by the ovum in different parts of the oviduct. Half the birds examined had been kept under 24‐h cycles (14 h light : 10 h dark) and half under 27‐h cycles (14 h light : 13 h dark). Mean intervals from oviposition to ovulation were 24 min and 36 min for birds under 24‐h and 27‐h cycles respectively. The difference between these values can be associated with the different rates of lay of birds under the two treatments. Mean times spent in the upper oviduct and the shell gland were estimated as 5·15 h and 19·76 h for the 24‐h cycles and 5·41 h and 20–70 h for the 27‐h cycles. The increase in albumen weight which has been reported to follow from the use of 27‐h cycles can thus be associated with extra time spent in the magnum. The reported increase in shell weight of 10% is more than would be expected from a 5% increase in time spent in the shell gland.     

Genetic variation for egg production,egg quality and bone strength in selected and traditional breeds of laying fowl

1. A multi-breed experiment was conducted with 25 commercial and traditional lines of laying fowl to determine the extent of between-breed genetic variation for adult body weight, sexual maturity, rate of lay, egg weight and egg composition to 55 weeks of age. The genetic variability for bone strength and eggshell strength was determined at 55 weeks of age and a comparison of commercially selected and traditional breeds was performed. 2. The proportion of the total variation that was associated with breed or line of origin was high (> 0.8) for body weight, sexual maturity and shell colour; moderately high (0.4 to 0.7) for rate of lay, early and late egg weight, weights of egg yolk, albumen and shell at 55 weeks; and low (< 0.4) for egg weight at 42 to 45 weeks, albumen quality and the number of egg inclusions. 3. There were no detectable differences between breed within category (traditional and commercial lines) for rate of lay, and estimates of breed variation for egg weight and egg components were substantially decreased within category compared with the overall analysis. 4. Commercial lines displayed earlier sexual maturity, greater rates and persistency of lay, and higher egg weights at earlier (32 to 35 weeks) and later (52 to 55 weeks) ages. At 55 weeks, the larger eggs from commercial birds contained more albumen of higher quality and paler yolks of similar weight to those from traditional breeds. The relative weight of the eggshell was similar in both categories. 5. There was considerable genetic variation between commercial lines for bone density and a moderate proportion of genetic variability for bone strength. Commercial lines had very weak bones compared with traditional lines but there was relatively little genetic variation for eggshell strength. The results suggest that eggshell quality is maintained in genetically selected lines at the expense of bone strength and bone radiographic density.     

Limited effect of intense genetic selection for broiler traits on ovarian function and follicular sensitivity in broiler breeders at the onset of lay

Female chicks from 6 pure lines of broiler breeders were obtained from international broiler breeder companies. The lines were from three female and two male lines and a relaxed selection line derived from one of the male lines (M2) and maintained without selection for 25 years (generations). Replicate groups from each line were reared in floor pens and fed ad libitum. An additional group of the M2 male line was feed restricted and housed in similar pens. Twenty birds from each group were photostimulated after housing them in individual cages at 14 weeks of age. Ovarian follicular dynamics and follicular sensitivity were determined after the onset of lay. Female lines had a greater proportion of atretic follicles and more groups of multiple follicles than male lines. Body weights, fatness and age at puberty were similar in male and female lines. The relaxed selection line had more abdominal fat than any of the selected lines and the ovary contained a similar number of normal yellow follicles as the selected male line. Feed restriction decreased body weight, the numbers of yellow follicles, multiple yellow follicles and the proportion of atretic yellow follicles, and increased the age at onset of lay. The response of ovarian follicles of three different sizes to exogenous gonadotrophin stimulation with PMSG was similar in small yellow follicles, 5 to 6 and 2 to 3 mm white follicles in a female line, a male line and its relaxed line fed ad libitum. The results suggest that the original lines from which modern male-line broiler stocks are derived had a relatively large number of yellow follicles and a high propensity for multiple ovulation at the onset of lay. Separate selection for different traits in male and female lines has not had a dramatic effect on ovarian function or sensitivity to gonadotrophin stimulation.     

Growth curve analyses in selected duck lines.

1. Growth patterns of male ducks from 4 lines (lines A, B, C and D) selected for market weight were analysed and compared to growth patterns of ducks in the respective line 7 generations earlier. Growth curves were analysed using procedures derived from the Weibull sigmoidal function and the linear-linear relative growth rate model and simple allometry. 2. The ducks were fed ad libitum under 24-h lighting throughout the experiment. At weekly intervals from the time of hatch through 70 d of age, 16 ducks from each line were killed to determine body, carcase, breast-muscle, leg and thigh-muscle, and abdominal fat weights. 3. Line A was the heaviest line, followed by line B, line C and line D. However, body weight, carcase weight and breast-muscle weight at 49 d of age were not significantly different between lines A and B. After 7 generations of selection, the breast-muscle yield was increased to >19% and the abdominal fat percent was reduced to <1.4% in all lines. 4. The Weibull growth curve analysis of body weight showed an increase in the asymptotes during selection, while the age of the inflection point remained constant in all lines (21.3 to 26.0 d). For breast-muscle growth, ducks reached the inflection point 12.8 to 14.3 d later than for body weight. Between line A and line B, asymptotes for body weight, asymptotes for breast-muscle weight and allometric growth coefficients of breast muscle and leg and thigh muscles from 14 to 49 d were not significantly different. 5. The relative growth rate model discriminated body and breast-muscle growth patterns of line A and line B. The initial decline in the relative body growth rate was less and the time to reach the transition was longer in line A than line B. On the other hand, the initial decline in the relative breast-muscle growth rate was greater in line A than line B.     

城口山地鸡两个品系主要性状选育效果分析

试验采用家系选择与个体选择法,对组建的城口山地鸡基础群分别进行生长性能和产蛋性能的选择,并结合体型外貌羽色和胫色的选择,建立城口山地鸡CR1和CK1两个品系。结果显示:经过5个世代的选育,CR1系L5世代17周龄和43周龄公、母鸡体重较L1世代分别提高了166.5 g、193.3 g、182.4 g和127.3 g,且体重性状差异均显著(P<0.05);而CK1系L5世代各阶段体重较L1世代均有所提高(P>0.05)。CR1系和CK1系L5世代开产日龄较L1世代分别提前了13.5 d(P<0.05)和13.1 d(P<0.05),L5世代43周龄产蛋量较L1世代分别提高了3.9个(P<0.05)和9.8个(P<0.01)。同时,两个品系L5世代黑羽率、青胫率、受精率和受精蛋孵化率较L1世代均有不同程度的提高。研究表明:城口山地鸡两个品系主要性状选育效果突出,生长性能和产蛋性能明显改善提高,该品系的培育可为地方鸡品种内的品系培育提供参考。     

Plasma concentrations of luteinising hormone and body weights during somatic maturation in intact and castrated Australorp cockerels from a line of hens selected for increased ovulation rate

1. Plasma concentrations of luteinising hormone (LH), comb size and body weight were measured between 46 and 208 d of age in intact and castrated cockerels from lines of selected and control Australorp domestic chickens. The selected line had been selected for increased rate of lay by reducing oviposition intervals within sequences. The cockerels were reared and maintained on 15.25 h light/d. 2. Concentrations of plasma LH in the intact control cockerels were low in the 'immature' phase (less than 100 d old) and increased during the 'mature' phase (older than 175 d) with a peak occurring when the testes are beginning to grow at the onset of the 'mature' phase. In comparison with the control line of cockerels, the selected line had significantly higher plasma LH concentrations at the onset of the 'mature' phase. Selection had no effect on the mean concentration of plasma LH in either the immature phase or a few weeks after the onset of the mature phase. 3. There was no effect of selection in sibling females for higher rates of lay on changes in comb size or body weight during sexual maturation in the intact cockerels. 4. Castration at 45-46 d of age resulted in increased plasma LH concentrations and no comb growth. Plasma LH concentration increased progressively between 40-208 d. There was no difference between the two lines of cockerels in plasma LH concentration or rate of body growth after castration. 5. It is concluded that selection of females for a change in the rate of egg production has resulted in increased plasma LH concentrations in sibling males around the onset of sexual maturation. Selection appears to have caused this effect by altering an unidentified component of the inhibitory feedback mechanism which controls the tonic secretion of LH.     

Photoperiod and oviposition time in broiler breeders

1. Oviposition times were recorded for broiler breeder hens under 8-, 10-, 11-, 12-, 13-, 14- and 16-h photoperiods. 2. Mean oviposition time (MOT) was delayed relative to dawn by approximately 0.5 h for each 1-h increase in photoperiod up to 14 h, but was similar for 14- and 16-h photoperiods. However, the 0.5 h/h regression for the time when half the eggs were laid continued through to 16 h. 3. The rate of change in MOT for each 1-h increase in < or = 14-h photoperiod was similar to that reported for early and modern egg-type hybrids, but, compared with modern genotypes, time of lay itself was 1 h later than white-egg and 2.5 h later than brown-egg hybrids. 4. At photoperiods < or = 12.25 h, the number of eggs laid before dawn increased by 4-5% for each 1-h reduction in daylength.     

Entrainment of oviposition in the fowl using light-dark cycles

1. Fourteen experiments were performed to determine the minimum photoperiod and minimum scotoperiod needed for entrainment of oviposition in hens exposed to 21-h, 24-h and 30-h cycles. Entrainment was measured by the proportion of total eggs laid in a modal 8-h segment of each cycle. 2. In a 24-h light and dark cycle, a 15-min photoperiod or a 5-h scotoperiod produced essentially the same degree of entrainment as 6 h light, 18 h darkness (6L : 18D) or 14L : 10D, which were used as control treatments. Under 21-h light and dark cycles a minimum 3-h photoperiod or a minimum 9-h scotoperiod was needed to achieve full phase setting. When the cycle length was increased to 30 h a minimum 8-h photoperiod or a minimum 12-h scotoperiod was required for full entrainment. 3. This study demonstrates that photoperiod is a stronger signal than scotoperiod for the purpose of phase setting oviposition. It also shows that a stronger signal is required to achieve entrainment when the length of the light-dark cycle is several hours shorter or longer than the natural period of 24 h.     

Classical and mixed-model analysis of an index selection experiment for fecundity in Drosophila melanogaster.

A comparison of three family indices to increase number of pupas from 3-d lay in Drosophila melanogaster is reported. The three indices were Id, based exclusively on dam's information; Ihd, based additionally on dam's full-sibs' and half-sibs' information; and Ihs, which also included the sire's full-sibs' and half-sibs' records. Three lines, D, HD, and HS, were selected, each according to one of the three indices: Id, Ihd, or Ihs. Each line consisted of 10 sires and 60 dams. Each dam contributed one male offspring and three female offspring. Seven generations of selection were performed in a two-replicate experiment. The expected advance of Ihs and Ihd over Id in the seventh generation was .38 and .15 phenotypic standard deviations, respectively. The experiment was analyzed in terms of both classical ordinary least squares (OLS) and mixed-model methodology (MMM). The phenotypic trends in the first replicate were 4.06 +/- 1.74, 1.42 +/- 1.76, and .26 +/- 1.94 pupas per generation for Lines D, HD, and HS, respectively, and in the second replicate 8.52 +/- 2.40, 6.16 +/- 3.21, and 4.21 +/- 2.60, respectively. The genetic trends in the first replicate were 2.18 +/- .61, 1.08 +/- .67, and .24 +/- .68 pupas per generation and, in the second replicate, 2.51 +/- .60, .16 +/- .61, and .05 +/- .64 for Lines D, HD, and HS, respectively. Despite theoretical expectations, the Id index was consistently better than the more complex indices. Several explanations for these results are possible: 1) smaller than expected selection differential, 2) inbreeding depression, and 3) incorrect heritability used to construct the indices.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of light,vitamin d and dietary phosphorus on egg‐shell quality late in the pullet laying year

1. Eighteen diets supplying all combinations of three phosphorus contents (3.1, 4.0 and 4.8 g non‐phytate P/kg) and six vitamin D supplements (37.5 or 150 μg cholecalciferol/kg; or 16 or 24 μg 25‐hydroxy‐cholecalciferol/kg; or 37.5 μg cholecalciferol/kg with either 16 or 24 μg 25‐hydroxycholecalciferol/kg) were fed to 2 880 pullets of two stocks from 64 to 74 weeks of age. The birds were housed in eight light‐proof rooms, four of which had 24‐h light‐dark cycles (16L : 8D) and four had 28‐h cycles (20L : 8D).

2. The dietary treatments had no significant effect upon food intake, egg output, shell thickness, shell deformation or specific gravity of the eggs.

3. The 28‐h cycle reduced mean rate of lay by 4.5%, increased egg weight by 5.8% and increased shell thickness by 9.4%. The proportion of eggs with shell faults revealed on candling was reduced from 4.1 % to 2.8%.

4. It is concluded from this and other sources that decreasing dietary phosphorus or modifying vitamin D supplements may sometimes lead to increases in shell thickness of the order of 1 to 2%, but that these changes are unlikely to result in a measurable reduction in the proportion of cracked eggs late in the laying year.

5. A 28‐h light‐dark cycle results in a longer and more uniform interval between consecutive ovipositions and thus gives reliable increases in shell thickness which are large enough to reduce the proportion of cracked eggs in many practical situations. Whether it is profitable to use an ahemeral cycle will depend upon the relative prices paid for eggs of different sizes.     

Effect of age and physiological status on sperm storage 24 hours after artificial insemination in broiler breeder hens

1. Uterovaginal junction (UVJ) tissues were collected 24 h after artificial insemination (AI) from 85- and 125-week-old broiler breeder hens in three physiological states: laying hard shell eggs (HS), laying shell-less eggs (SL) and non-laying (NL). This was confirmed by egg production records and visual appraisal of the oviduct at the time of necropsy. 2. Three longitudinal sections of each UVJ were evaluated microscopically and sperm host glands (SHG) were scored in 5 categories: glandular morphology evident but not lumen present, basophilic stained epithelium and no spermatoza present, glands that contained one to five spermatozoa; glands that contained 6 to 20 spermatozoa and glands that contained more than 20 spermatozoa. 3. Laying hens (HS and SL) at 85 weeks of age had significantly more sperm host glands (SHG) containing spermatozoa than NL hens. At 125 weeks of age HS and SL hens had significantly more unscorable glands. 4. The only category that showed no difference between age and physiological status group was the empty category. No significant differences were observed for any gland category in 82- and 125-week-old NL hens. 5. A greater proportion of the 85-week-old group of HS and SL hens had more SHG containing spermatozoa and fewer unscorable glands that the 125-week-old birds. The only category that showed any difference within the SL group was the low category.     

Changes in ovarian function and egg production in commercial broiler breeders through 40 weeks of lay

1. Egg production, body weight, feed intake and mortality were recorded in over 78?000 broiler breeder hens in 4 commercial flocks housed in 16 houses from early lay though 40 weeks of lay. A total of 420 hens were sampled at regular intervals throughout the laying period to determine the changes in body weight and the numbers of yellow follicles, paired follicles and hierarchical positions with time in the ovary throughout lay to relate ovarian function to productivity. Average egg weight was recorded weekly from one flock.

2. A quadratic equation fitted the changes in time for the number of yellow follicles, body weight, feed intake and mortality; a linear equation described the decline in the number positions in the hierarchy and there was a linear decline in the logistic scale of the proportions of yellow follicles developing as pairs of similar weight. Egg production was described by a cubic equation and egg weight by a line plus exponential model.

3. The average number of yellow follicles declined from 7·2 to 5·4 and the number of hierarchical positions from 6 to 5 from 4 to 40 weeks after photostimulation. The proportion of follicles developing as pairs of similar weight was over 25% at the onset of lay and declined to less than 10% from 20 weeks after photostimulation, representing a substantial loss of potential productivity.

4. Body weight and egg production were similar to the breeder's targets whereas average egg weight and mortality were higher than expected.

5. The relationship defining ovarian function will facilitate the development of an improved model of egg production in broiler breeder hens.     

Correlated responses in reproductive and carcass traits to selection for 70-day weight in Landrace swine.

Correlated responses in reproductive and carcass traits were studied in 181 litters and 218 pigs from a line of Landrace pigs selected six generations for increased weight at 70 d of age and a contemporaneous, randomly selected control line. The reproductive and maternal traits studied included litter sizes born, born alive, and alive at 21 d and litter weight at birth and at 21 d. Carcass traits studied were carcass length, longissimus muscle area, average backfat thickness, 10th-rib backfat thickness, specific gravity, weights of closely trimmed ham, loin, and shoulder, belly weight, subjective scoring of the longissimus muscle for color and marbling, estimated percentage of muscle, and lean gain per day. Total weighted cumulative selection differential for 70-d weight was 30.2 kg. The realized heritability for 70-d weight was .13 +/- .06, and the change in 70-d weight was .65 +/- .29 kg per generation. The regression coefficient of litter size at 21 d on generation was .24 +/- .10 (P less than .10) pigs per generation. None of the other regression coefficients for the reproductive traits differed from zero. Carcass length, specific gravity, and ham weight decreased (P less than .10) -.075 +/- .036 cm, -.00054 +/- .00027, and -.102 +/- .048 kg, respectively, per generation. Color score and lean gain per day increased .046 +/- .021 points and .0032 +/- .0013 kg/d, respectively, each generation in response to the selection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selection line x diet interactions for two lines of pigs fed 12 or 24% protein diets

An experiment with crossbred swine was conducted over six generations of selection based on an index (Index) of average daily gain in weight (ADG) in a test period from 56 d of age to 91 kg gross weight and average backfat thickness (ABF) measured from ultrasonic scans at 91 kg. Test pigs of the high protein select (HS) and control (HC) lines were fed a 24% crude protein (CP) diet and pigs of the low protein select (LS) and control (LC) lines were fed a 12% CP diet during the test period. The extent of genetic (selection line) x environmental (dietary) interaction effects was determined based on feeding closely related boars and gilts from both the HS and LS lines on both diets. Tests were conducted in 1986 and 1987 with progeny of the fifth and sixth generations of selection. Records for 472 pigs sired by 37 boars and out of 101 dams were analyzed for effects of selection and diets on AGE of pig at 91 kg, ADG, ABF, LMA (longissimus muscle area at the last rib) and Index. Statistically significant interactions effects of line x diet were noted (P less than .01) for AGE, ADG and Index, traits with low to moderate heritabilities (h2). For ABF and LMA, body composition traits with moderate or higher h2, interaction effects of line x diet were near zero. These results suggest that for best all-around future performance, traits such as AGE and ADG, selection probably should be practiced under dietary conditions under which future populations will be produced. For body composition traits such as ABF and LMA, selection probably would be more effective if pigs were fed a more enriched protein diet. However, as a practical matter, to more rapidly improve the genetic merit of the swine population, both the central station and on-the-farm testing programs should be conducted under standard commercial production systems.     

One-generation divergent selection on large and small yolk proportions in a White Leghorn line

1. A striking change in egg consumption from shell eggs toward egg products is taking place. Consequently, internal egg quality traits must be seen in a different light, as they may affect the profitability of the egg processing industry. In order to study the possibility of using breeding as a means to alter yolk production, a one-generation divergent selection experiment was set up. The trait was yolk proportion. The effect of hen's age on egg composition was also studied. Genetic parameters for yolk proportion, yolk weight, egg weight and albumen weight were estimated, using a multiple trait animal model, and restricted maximum likelihood. 2. Selection response was obtained for yolk proportion and correlated selection responses for yolk weight and albumen weight. In the 'high line' a decrease in egg weight and an increase in yolk weight was established, whereas in the 'low line', egg weight remained more or less the same and yolk weight decreased slightly 3. Yolk proportion, yolk weight, egg weight and albumen weight all increased with increasing age of the hen in both selection lines. The difference between selection lines in yolk proportion, yolk weight and albumen weight persisted throughout the laying period. 4. Estimated heritabilities for yolk proportion, yolk weight, egg weight and albumen weight were 0.38, 0.22, 0.34 and 0.41 respectively. The genetic correlation between yolk proportion and yolk weight was 0.52, whereas the genetic correlations with egg weight and albumen weight were -0.51 and -0.74 respectively. 5. We conclude that selection can be used to alter yolk production. Selection can be at an early age with a sustained effect throughout the laying period.