The relationship between parental yolk cholesterol and yolk fat concentration to abdominal fat content and feed conversion ratio of their respective offspring.

The correlation of yolk cholesterol and yolk fat concentrations of egg from the pedigreed Athens-Canadian Randombred control population with the percentage of abdominal fat (AF) and feed conversion ratio (FCR) of their progeny were studied. The average yolk cholesterol, yolk fat, and AF were 20.3 mg/g yolk, 244 mg/g yolk, and 1.64%, respectively. The phenotypic correlation of both yolk cholesterol and yolk fat content of eggs from the parental population with AF or FCR of their progeny were low and nonsignificant.

Effects of genetic variation on total plasma protein, body weight gains, and body temperature responses to heat stress.

The effects of heat stress (HS) on total plasma protein (PP) concentrations, body weight gains (BWG), and body temperature (BT) were studied in an Athens-Canadian Randombred (ACRB) population and commercial broilers (BR). The populations were maintained at environmental temperatures of 21, 32, and 38 C from 3 to 6 wk of age. The PP, BWG, and mortality (M) were measured at 3, 4, 5, and 6 wk and BT at 6 wk. After 2 wk of HS, the PP of the birds grown at 38 C was lower than that of birds in the 21 and 32 C environment, but differences for the 21 and 32 C groups were not consistent. The ACRB had significantly lower PP than the BR at 4, 5, and 6 wk. There were no phenotypic correlations between PP and BWG within temperature, line, and sex. The decreased BWG of the BR in response to the HS was much more severe than that of the ACRB. The BT of the ACRB (41.5 C) was significantly lower than that of the BR (41.9 C). Birds grown at 38 and 32 C had a higher BT (42.0 and 41.8 C) than at 21 C (41.3 C). The BR showed an increase in M in both the 38 and 32 C environments, but the M for the ACRB was not affected by environmental temperatures.

The relationships of body temperature to weight gain, feed consumption, and feed utilization in broilers under heat stress.

Commercial broiler males were used to evaluate body temperature response to heat stress and its relationship to gain, feed consumption, and feed conversion ratio. Individual gain, feed consumption, and feed conversion ratio were obtained from 28 to 49 d in a heat stress environment (32 C) and compared to a 21 C environment. Body temperatures were measured at 28, 35, and 42 d, then daily from 43 to 48 d, and correlated with 28 to 49 d gain, feed consumption, and feed conversion ratio. Feather cover was measured at 51 d of age as a percentage of BW. Initial 28-d body temperature was not significantly different between 21 and 32 C. Body temperature was significantly higher in the 32 C environment after 7 d of heat stress and was significantly higher than at 21 C at all points through 21 d of heat stress, with mean differences ranging from 0.5 to 1.0 C. Feather weight as a percentage of BW was significantly greater in the 21 C environment (6.22%) than the 32 C environment (5.03%). Mortality was not affected by the heat stress environment. Correlations between body temperature and gain, feed consumption, and feed conversion ratio were low and nonsignificant for most periods in the 21 C environment. In the 32 C environment, body temperature was significantly correlated with gain, feed consumption, and feed conversion ratio after 7 d of heat stress, with mean correlations of -0.40 for gain, -0.31 for feed consumption, and 0.24 for feed conversion ratio in Replicate 1 and -0.44 for gain, -0.40 for feed consumption, and 0.43 for feed conversion ratio in Replicate 2.

Genetic variation in body temperature and its response to short-term acute heat stress in broilers.

Genetic variation in body temperature of broilers and its response to short-term acute (43.5 C for 45 min) heat stress was studied. Body temperatures before (T0) and after (T45) heat exposure were recorded and the changes in body temperature (T delta) were calculated for 5-wk-old chicks from 32 broiler sire families. The T0 data were utilized to rank the families as to their relative body temperature and used to conduct a one-generation divergent family selection program for high basal body temperature (H-BT) and low basal body temperature (L-BT). A control (C) line was established by random selection from the nonselected birds. There was little genetic variation in the base broiler population for body temperature, and one generation of selection for divergence in T0 did not result in differences. There were also no differences among lines in T45. Low realized heritability estimates of .09 and .17 were obtained for T0 in the L-BT and H-BT lines. Phenotypic correlations between body temperature and body weight were very low for all groups. Highly significant negative correlations were observed between T0 and T delta after heat exposure. The T0 fluctuated during the course of each day and between days. The adjustment of the data to eliminate this variation did not result in increased heritability estimates.

Effects of environment on growth, efficiency of feed utilization, carcass fatness, and their association.

The effects of environmental factors (house type, temperature, and type of watering system) on gain (G), feed consumption (FC), feed conversion (FCR), accumulation of abdominal fat (AF), and the association between FCR and AF of broilers were studied in a series of seven experiments. In addition, the adjustment of broilers to new housing environments and the factors affecting this adjustment were evaluated. The 4- to 7-wk G and FC were greater in groups raised at 21.1 C than 26.7 C. There were no consistent effects of environmental temperature on FCR (significantly reduced in 21.1 C groups compared with the 26.7 C groups in two of four trials) or in AF (significantly greater in 21.1 C groups than in 26.7 C groups in one of four trials). Environmental temperatures had no consistent effect on the relationship between FCR and AF. Both waterer types and environmental temperature affected the adjustment of broilers to placement in individual cages. Adjustment was better (less mortality and shorter periods of reduced FC) in the 21.1 C environment and when cup instead of trough waterers were provided. The 4- to 6-wk G and FC were reduced in the caged birds compared with the floor pen birds, but the FCR and AF were not consistently different. The initial (4-wk) BW significantly affected the 6-wk BW, G, FC, and FCR, but was not correlated with AF.

Assessing the effects of the naked neck gene on chronic heat stress resistance in two genetic populations.

The effect of the naked neck (Na) gene on resistance to chronic heat stress was studied in the F2 generation of two populations of chickens genetically differing in growth. The Na gene was introduced into the Athens-Canadian randombred (ACRB), a small BW population, and into a large BW commercial broiler population. Naked neck and normally feathered birds were maintained in either a chronic heat stress (32 C) environment or a control (21 C) environment from 4 to 8 wk of age. Body weight, BW gain, feed consumption, and feed efficiency were calculated at 4, 6, and 8 wk. The 32 C environment significantly reduced gain and feed consumption at all age intervals in both populations. Feed conversion ratio (FCR) was lower in the 32 C environment in the ACRB population, but in the broiler population FCR either was the same or increased when compared with the 21 C environment. In the F2 generation of both populations the naked neck birds were significantly larger than the normally feathered birds although the two types segregated from the same parents. In the ACRB population the relative growth response was not significantly different between naked neck and normal feathered birds, indicating that the Na gene did not confer resistance to chronic heat stress in the small BW population. In the broiler population, an assessment of the relative growth response in the 32 C environment showed that the naked neck birds had a smaller reduction in BW gain and better feed efficiency than the normally feathered birds, indicating that in the large BW broiler population the Na gene did confer resistance to chronic heat stress.

Body, abdominal fat, and testes weights, and line by sex interactions in Japanese quail divergently selected for plasma cholesterol response to adrenocorticotropin.

Line by sex interactions of BW, abdominal fat, testes weight, and plasma cholesterol were investigated in two Japanese quail lines. High (H-PCHOL) and low (L-PCHOL) quail lines had been developed by 18 generations of divergent selection for plasma cholesterol response to adrenocorticotropin (ACTH). Quail were from Generation 28 breeders maintained under a normal environment with no exposure to exogenous ACTH after Generation 18. Quail from growth-selected lines were also used to examine relationships between BW and plasma cholesterol. Body weights of H-PCHOL quail were significantly (P less than or equal to .05) heavier than BW of L-PCHOL quail at 2 and 4 wk of age. However, at 8, 16, and 28 wk BW were similar. Quail from long-term, growth-selected lines were observed to have plasma cholesterol levels similar to those of control lines. Therefore, early BW changes in H-PCHOL and L-PCHOL lines may not be related to plasma cholesterol changes. At 2 and 4 wk, male and female plasma cholesterol values were similar in the H-PCHOL and L-PCHOL lines, however, at 8 and 16 wk males had higher values than females in the H-PCHOL line, and females had higher values than males in the L-PCHOL line. Because interactions were present only after sexual maturity was reached, sex hormones may be involved in the expression of these interactions. Quail in the L-PCHOL line were observed to have significantly (P less than or equal to .05) more abdominal fat and significantly (P less than or equal to .05) smaller testes than quail in the H-PCHOL line.

Efficiency of feed utilization and rate of feed passage through the digestive system.

The relationship of efficiency of feed utilization determined by the feed conversion ratio (FCR) to the rate of feed passage through the digestive system of juvenile chickens was studied and three different methods of measuring feed passage rate (FPR) were evaluated. The FPR did not differ between sexes that had different FCR, nor did it differ between commercial broiler strains that differed in FCR. Feed restriction did not affect FPR. There was little correlation between FCR and FPR in any of the groups evaluated and the FPR was similar for high- and low-FCR groups. There was some evidence for increased FPR in birds grown at 32.2 C compared with those grown at 26.7 C. Similar results were obtained for FPR whether the tracer dye was given in the feed, or in a gelatin capsule, or no tracer dye was used. Repeatability of FPR obtained on the same individuals at different ages was very low.

Plasma and yolk cholesterol levels in Japanese quail divergently selected for plasma cholesterol response to adrenocorticotropin.

Studies were conducted to determine the effect of divergent selection for plasma cholesterol response to adrenocorticotropin (ACTH) on the levels and relationships between plasma and yolk cholesterol in Japanese quail. Cholesterol data were obtained in Generation 25, following seven generations of relaxed selection, from birds maintained under a normal environment with no exposure to exogenous ACTH. Levels of plasma and yolk cholesterol were determined at 22 and 28 wk. Plasma cholesterol levels of quail in the low cholesterol line were significantly (P less than .01) lower than levels in the high line at both ages (224 versus 383 and 209 versus 326 mg/100 mL, respectively). In contrast, yolk cholesterol levels were significantly (P less than .01) higher in the low line than in the high line (24.1 versus 21.5 and 21.1 versus 16.9 mg cholesterol/g yolk at 22 and 28 wk, respectively). A significant line by sex interaction was present at both ages for plasma cholesterol with females having higher cholesterol values than males in the low line and males having higher values than females in the high line. A negative relationship was observed between changes in plasma and yolk cholesterol in the selected lines. Greater deposition of cholesterol in the yolk of the line with lower plasma cholesterol indicates that excretion rate may play a role in explaining genetic differences in plasma cholesterol.

Variation in the three-week body temperature of broilers and Athens-Canadian randombred chickens.

The body temperatures of commercial broilers and an Athens-Canadian randombred population (ACRB), correlations of body temperature with BW, and a sire family heritability (h2) estimate in the ACRB population were obtained. The body temperature of the broilers was significantly lower than that of the ACRB chicks (41.44 versus 41.77 C). Correlations between BW and body temperature were very low for both the broiler and ACRB chicks (.04 and .06). A sire-component h2 estimate of .19 was calculated for 3-wk body temperature in the ACRB population.

Genetic variation of plasma growth hormone and its genetic association with growth traits in young chickens.

A pedigreed, randomly mated population of 25 sire families was assessed for genetic variation in body weight, gain, and plasma growth hormone (GH) under conditions of reduced temperature brooding (26.7 C) from day of hatch to 7 days of age. Heritability estimates (h2) for 7-day body weight and gain were moderate to high. The calculated h2 for GH was moderate. Plasma levels of GH were not phenotypically or genotypically correlated with body weight or gain.

Use of a fat probe to assess variation in abdominal fat in broilers.

Four trials were conducted to compare the fat probe measure of abdominal fat with that of actual abdominal fat weights and percentage abdominal fat. Various ages, diets, and genetic groups were used to provide experimental chickens with a wide range in body weights and abdominal fat percentages. Mean values obtained by two operators using the probe on the same bird were similar (correlations of .70 to .79). Considering all comparisons, the arithmetic mean of the correlations between fat probe values and percentage abdominal fat was .24; values ranged from .01 to .44. In five comparisons of groups differing significantly in percentage abdominal fat, there were no significant differences in probe values, and correlations between fat and probe values were low. In three other comparisons of groups differing significantly in percentage abdominal fat, differences between probe values were significant and correlations between fat and probe values were moderate. In the comparison groups in which there was an association between probe and fat values, the magnitude of the differences in fat values was about four times as great as that of differences in probe values and the correlations were moderate (.28 to .44). In the comparisons in which higher abdominal fat. In comparisons where higher probe values were not associated with higher abdominal fat, higher body weights were not associated with higher percentage fat.

Genetic variation of neonatal stress response to reduced temperature brooding in a randombred population of chickens.

Chicks from a randombred population were assessed for genetic variation in 1-day body weight and serum corticosterone under two brooding temperatures (26.7 and 32.2 C). Brooding at 26.7 C resulted in lower 1-day body weights and higher corticosterone levels. Heritability estimates (h2) for 1-day body weight were moderately high in both temperature groups but were low for gain in both temperatures. The h2 for corticosterone level from chicks brooded at 26.7 C was moderate, whereas estimates for those brooded at 32.2 were very low. Statistically significant (but low) negative phenotypic correlations were obtained for corticosterone with body weight and gain in both temperature groups. A significant negative genotypic correlation was observed between corticosterone and body weight for chicks brooded at 26.7 C but not for those brooded at 32.2 C. Corticosterone data from the highest and lowest responding sire families revealed a significant response group by temperature interaction. Chicks from the first of two additional hatches showed significant response group differences in serum corticosterone to the reduced brooding temperature. The neonatal serum corticosterone response to cold stress has a genetic basis; however, because there was a negative genotypic correlation between serum corticosterone and body weight, selection for increased corticosterone levels under reduced temperature brooding would likely result in decreased body size.

Evaluation of growth, hormonal, and hematological responses of neonatal chickens to reduced temperature brooding.

A series of experiments was conducted to examine the response of neonatal, male broiler chicks to brooding at a reduced temperature. In Trials 1 and 2, chicks brooded at 26.7 C generally had lower body weights and higher serum corticosterone levels during the first week after hatch than those brooded at 32.2 C. However, significant differences in body weight were observed only on Day 6 in Trial 1 and on Days 1 and 5 in Trial 2. Serum corticosterone levels, likewise, were not significantly different on all days in Trials 1 and 2. These hormone levels were statistically different on Days 1 and 5 in Trial 1 and on Days 1 and 3 in Trial 2. Brooding neonates at 26.7 C for 3 days in Trials 3 and 4 resulted in consistently lower body weights and gain and higher serum corticosterone, thyroxine, total protein, albumin, and globulin. Serum growth hormone levels in chicks brooded at 26.7 C were initially depressed the first day but were elevated on the 2 subsequent days, compared with chicks brooded at 32.2 C. Considering the physiological importance of corticosterone and thyroxine in the adaptation of chickens to cold environmental temperatures, it would be useful to evaluate the genetic variation associated with the responsiveness of these hormones in a randombred population and to improve tolerance of neonatal chickens to reduced temperature brooding through selection.

Genetic variability in growth response of chicks to cold brooding temperature.

Genetic variability in adaptation to brooding at a reduced temperature was examined by comparing 1 to 14-day body weight gains of progeny from 28 sire families of the Athens-Canadian randombred population brooded at 32.2 C and at 26.7 C. The 1 to 7-day gain of the chicks brooded at 26.7 C was significantly depressed, but 7 to 14-day gain was not significantly depressed by brooding at the reduced temperature. Heritability estimates averaged over the two trials were .31, .23, and .35 for the 1 to 7-, 7 to 14-, and 1 to 14-day weight gains of groups brooded at 32.2 C and .55, .59, and .67 for the gain of groups brooded at 26.7 C. The heritability estimates for the difference in weight gain of families brooded at the two temperatures was .78.

Parabiosis between avian embryos resistant and susceptible to Rous sarcoma virus.

Parabiosis of chicken embryos was used to determine if resistance or susceptibility to Rous sarcoma virus (RSV) tumors could be transferred between RSV-resistant (R) and RSV-susceptible (S) embryos. Eggs from RSV-R and RSV-S lines were parabiosed at 12 days of incubation. One week after hatching the chicks were inoculated in the wing web with RSV. Birds were examined for tumor lesions through 9 weeks of age. Lesion scores of the nonparabiosed RSV-S line were significantly higher than nonparabiosed RSV-R lines. Lesion scores of RSV-R chicks that had been parabiosed to RSV-S chicks were higher than nonparabiosed RSV-R chicks. Lesion scores of RSV-S chicks parabiosed to RSV-R chicks were not different from nonparabiosed RSV-S chicks. These results suggest that the resistance to RSV was not transferred between parabionts but that there was significant transfer of susceptibility from the RSV-S embryos to the RSV-R embryos.

Thyroid and adrenal response to heat stress in chickens and quail differing in heat tolerance.

Three experiments were conducted to evaluate the thyroid and adrenal response in groups of birds with altered heat tolerance. Groups of chickens that had been handled on each of 4 days and a nonhandled control group were bled on the 5th day with or without heating for 1 hr at 50 C. Handling did not affect the thyroid response as indicated by thyroxine (T4) or triiodothyronine (T3) levels. Corticosterone levels were lower in handled birds than nonhandled birds after heating. In a second experiment, groups of broilers were fed a diet containing .2% thiouracil or a control diet. After 2 weeks they were bled either with or without 1 hr of heating at 50 C. The T3 and T4 levels were reduced by thiouracil feeding both with and without heating, but adrenal function was not affected. In Experiment 3, T3 and T4 levels were compared for four lines of Japanese quail. The nongrowth-selected line had higher T3 and T4 levels than growth-selected lines but did not have elevated levels of T3 or T4 in response to heat stress. The growth-selected lines (T, S, and P) responded to heating with increased T3 and T4 levels. Levels of T4 in Line T (selected on a thiouracil diet) after heating were significantly higher than all other lines.

Effect of initial size on subsequent growth and carcass characteristics of divergently selected channel catfish.

Two experiments were conducted simultaneously to determine (1) if fast-growing fingerlings of channel catfish, Ictalurus punctatus, could be identified by simple visual selection of body size and (2) if initial size advantages influenced subsequent growth and carcass traits of divergently selected channel catfish. Exp. 1 included large (L), medium (M), and small (S) fingerling sizes from each of the control (C), selected upward (+) and selected downward (-) lines for body weight. Exp. 2 included all fmgerlings of the same size (25±5 g) from the 3 lines. Catfish from the L size-class, within each full-sib family in each line, were consistently heavier and longer than M and S size-classes throughout the 53-week experimental period. Fingerlings from the M size-class were also superior in growth to those from the S size-class. Catfish from the + line exceeded those from the C and -lines in body weight and total length at the conclusion of Exp. 1 but not in Exp. 2. This was attributed to the selection of equal size fmgerlings in Exp. 2 which may have excluded fingerlings with the best growth potential from the + body weight line. Results of the two experiments combined indicated that one generation of divergent selection has created genetic differences among lines of channel catfish.

Preconditioning to heat stress by a nontemperature stressor.

Three experiments were conducted in which 3-week-old chickens were subjected to a handling procedure for 4 days (21 to 24 days of age) and subjected to heat stress on either the 5th or 7th day (25 or 27 days of age). The heat stress episode consisted of exposure to 50 C for up to 240 min in a forced-draft chamber. In two experiments in which broiler chickens were studied, the heat stress survival time, determined at 25 days of age, was increased by the handling procedure. The same phenomenon did not occur in Leghorn chicks or broiler chickens heat stressed after a 3-day adjustment period.