Search

This work studied the effect of age at photostimulation on reproductive performance of Beijing-You Chicken (BYC) breeders. A total of 384 fourteen-week-old BYC breeder hens were randomly allocated to 4 treatments of 96 birds each, with 2 replicates per treatment. The treatments represent photostimulation at 16, 18, 20, and 22 wk of age, respectively (PS16, PS18, PS20, and PS22) by incrementally increasing day length from 8L:16D to 14L:10D and by increasing lighting intensity from 10 to 80 lx. Egg production was recorded for each replicate until 51 wk. Four birds randomly selected from each treatment were sacrificed to characterize sexual organ development at 4 time points: 1 D before photostimulation and 2, 4, and 6 wk after photostimulation. Eggshell quality at peak laying was measured. The results showed that the changes in ovary and oviduct weight in PS22 were 8.68- and 4.27-fold higher than in PS16 at 6 wk after photostimulation. PS16 had an earlier age at 5% egg production than PS20 and PS22 (P = 0.003). The interval from photostimulation to age at 5% egg production in PS20 and PS22 was shorter than in other treatments (P = 0.005). Later peak egg production was seen in PS20 (211.0 D) and PS22 (218.0 D) than in PS16 (183.0 D) and PS18 (190.0 D, P = 0.020), but the laying rate of PS20 decreased slowly after peak laying. PS20 and PS22 had higher egg weights than PS16 and PS18 at peak laying (P = 0.018). Age at photostimulation had no effect on egg number, defective egg number, or hatchability (P > 0.05). In summary, the onset of lay can be advanced by photostimulation at early ages, but there is no difference on egg production until 51 wk. Photostimulation at 20 wk improves peak of laying and laying uniformity.

The impact of graded levels of day length on turkey health and behavior was determined in hens and toms raised to 18 wk of age. Birds were allocated to one of 4 lighting treatments (trt) providing 14 (14L), 17 (17L), 20 (20L), and 23 (23L) h of day length. Two time-replicated trials were completed with each, providing 2 rooms per lighting trt and each room having 3 hen (n = 720) and 3 tom (n = 480) pens. Data collection included gait score (GS), the incidence of footpad dermatitis (FPD), breast buttons and blisters, ocular size and pressure (males only), and behavioral observations (males only). Data were analyzed using SAS 9.3 based on a completely randomized design nested within 4 lighting trt. Regression analysis established relationships between response criteria and day length. Differences were considered significant at P ≤ 0.05 and trends noted at P ≤ 0.10. Gait score, FPD, and the incidence of breast buttons and blisters were assessed on 5 birds per pen at 11 and 17 wk of age. Average GS increased linearly with day length at 11 and 17 wk for both hens and toms, but the effect was larger in toms. Day length did not affect FPD, but more lesions and severe scores were found for hens than toms. The presence of breast buttons and blisters increased linearly with day length (11 wk) with the effect on blisters predominately seen in toms. Eye weight and size increased with increasing day length at 12 and 18 wk. Ocular pressure was not affected by day length. Infrared cameras recorded tom behavior over a 24 h period, and behaviors were classified over 10-min intervals using a scan sampling technique at 11 and 17 wk. Alterations in behavioral repertoire were observed with a linear increase in inactive resting and a linear decrease in standing, walking, preening, and environmental and feather pecking behaviors with increased day length. To conclude, day length affected bird mobility and incidence of breast blisters in an age- and gender-specific manner, and time spent inactive increased with longer day length.

An experiment was conducted to study the effect of day length, sex, and genotype (Ross × Ross 308 and 708) on mortality causes, bird mobility, footpad health, and ocular size, with 4 trials within the experiment. Four graded day lengths were chosen to allow the study of relationship between day length and health parameters, including 14L:10D, 17L:7D, 20L:4D, and 23L:1D. The primary statistical tools used to assess the day length relationships were regression analysis (Proc Reg and RSReg of SAS). Data were also analyzed as a 4 (lighting program) × 2 (sex) × 2 (genotype) factorial arrangement. Total mortality, as well as mortality due to metabolic and skeletal disease, decreased linearly with increasing inclusion of darkness (7- to 32-, 7- to 38-, and 7- to 48-d periods). Infectious disorders were quadratically related to day length (7- to 48-d period only), with birds under 20L having the highest level. Day length was linearly or quadratically related to average gait score in a positive fashion, and the incidence of birds falling in painful gait score categories increased linearly with increasing day length. Average footpad lesion scores increased with increasing day length (28 and 35 d). The 23L photoperiod resulted in heavier eye weights than other lighting programs. Males had a higher mortality and morbidity rate and a higher average gait score than females. Average footpad score was lower for males than females (28 and 35 d). Overall mortality was higher for 308 than 708 broilers; hence, levels of specific mortality causes were higher. Average gait scores were lower for 308 than 708 birds in 2 of the 3 time periods measured and footpad lesions were higher. To conclude, many aspects of broiler health improve with decreasing day length.

Day length and intensity are commonly manipulated aspects of the light environment in commercial broiler production. Both influence circadian rhythms, but it is unclear if they do this independently or synergistically. The effect of light:dark (20L:4D, 16L:8D) and intensity contrasts (1 lx:0.5 lx, 200 lx:0.5 lx) on broiler behavior and health (n=1,004, 4 replicates/treatment) was evaluated. Activity was measured using passive infrared detection, and feeding activity was measured by the amount of feed consumed/h over one 24-h period each week. Broilers were gait scored and weighed at 6 wk of age. Following euthanasia, eyes were dissected from 30 birds/treatment. Behavior and performance were analyzed using the GLM, gait score using the Kruskal-Wallis test, and eye measures using a MANOVA. The 200 lx birds were more active (P=0.03) and fed more (P=0.001) during the photophase but were less active (P=0.02) and fed less (P

It is frequently recommended that commercial laying pullets are reared on step-down lighting regimens, rather than on constant short photoperiods, to help achieve BW targets during rear and optimal performance in lay. To evaluate the effectiveness of this strategy, Shaver White pullets were maintained on 8-h day lengths or given a step-down lighting regimen from 23 to 8 h over periods of between 1 and 15 wk. Other pullets, which were initially maintained on 8 h of light, were given an abrupt increase in day length prior to transfer to step-down lighting at various ages between 1 and 13 wk. All birds were given abrupt increments to 14 h at 18 wk and to 16 h at 20 wk to stimulate appetite and optimize uniformity of sexual development. Body weights at 6 and 12 wk were generally heavier and cumulative feed intakes to 6 wk were greater for birds given step-down lighting from 1 wk of age than for constant 8-h controls or birds given an initial period on 8-h day lengths prior to step-down lighting. Sexual maturity for birds on step-down lighting from 1 wk and for those on < or =5 wk of 8-h day lengths before transfer to step-down lighting was delayed by about a week compared with the constant 8-h controls or birds on 9 wk or more of 8-h day lengths before step-down lighting. These delays in sexual maturity resulted in a lower BW at 18 wk. Body weight uniformity at 18 wk was improved by step-down lighting, whether it was given from 1 wk or after a period of 8-h day lengths. Despite step-down lighting resulting in larger initial feed intakes and improved early growth, there was no significant improvement in egg numbers, egg weight, egg mass, feed intake, shell deformation, or albumen height compared with constant 8-h controls. Differences in egg output were generally the consequence of photoperiodically induced changes in sexual maturity.

In a prior study, we reported that a high proportion of hens in a winter-laying flock became relatively photorefractory (rPR) early in the reproductive cyand that successive short-term reductions in photoperiod in such hens each initially depressed egg production but then caused a rebound in rate of lay to briefly exceed that of hens that did not exhibit rPR. The present study was conducted to assess rPR in a summer-laying flock and to determine whether a single short-term reduction in day length early in the reproductive cycle might enhance egg production and delay the onset of absolute photorefractoriness (aPR). Control hens received a photoperiod of 16L:8D throughout the experiment. Experimental hens were photostimulated with 16L:8D, received a reduced (but still stimulatory) photoperiod of 11.5L:12.5D for 2 wk beginning 8 wk after photostimulation, and then were returned to 16L:8D for the remainder of the 23-wk test period. Results showed that a single 2-wk reduction in day length shortly after the hens reached peak egg production did not significantly reduce overall flock egg production, but it also did not improve late-season egg production or retard the onset or incidence of aPR. The incidence of rPR was substantially less in this study than we had observed with a winter-laying flock (32.9 vs. 67.1%), but similar proportions of treated hens exhibited the most severe rPR response (a brief but complete cessation of egg production) in both studies (21.1 vs. 24.0%), and all treated hens that subsequently became aPR had shown this severe rPR response to the test photoperiod. We concluded that a core proportion of hens (approximately one-fifth) exhibited a strong rPR response when presented with a reduced photoperiod early in the reproductive cycle, regardless of season of the year, and that such hens were more likely to subsequently exhibit poor egg production or become aPR than flockmates that did not exhibit rPR. Therefore, some indication of the incidence of rPR early in the lay period may have a predictive value for the overall egg production of the flock.

The effects of strain, age at photostimulation, and dietary CP intake during the early lay period on sexual maturation and egg production parameters in broiler breeder hens were determined. Three Arbor Acres strains, Classic, Feather Sexable Yield (FSY), and an experimental line (EXP), were reared in floor pens. At 19 wk of age, pullets were moved into individual cages. At 20 wk of age one-half of the birds were photostimulated by increasing the day length from 8L:16D to 15L:9D. The remaining birds were photostimulated at 23 wk of age. The birds were fed 16 or 18% CP diets from 19 to 32 wk of age. The Classic hens achieved sexual maturity 4 d before the EXP hens. Delaying photostimulation to 23 wk of age delayed sexual maturity but the rate of sexual maturation was accelerated after photostimulation occurred. Egg weight at sexual maturity was higher for the later photostimulated birds. The FSY and EXP hens, selected for more white-meat yield than the Classic hens, were heavier in BW but had lower settable egg production than the latter. Feeding 18% CP resulted in a higher BW throughout the trial, as compared to the 16% CP diet. There was a response to dietary CP and photostimulation age on initial egg weight and the number of double-yolked eggs. Early photostimulation was not advantageous because egg production parameters were not affected. Both Classic and FSY strains performed well when fed 18% CP; however, EXP hens benefited from 16% CP intake.

Critical day lengths (CDL) for ovarian growth, egg production, and photorefractoriness were estimated in turkey hens during winter and summer seasons. In two experiments, one in each season, fixed day length treatments ranging from 10.5 to 16 h/d were applied to photosensitive hens at 30 wk of age. Daily egg production was used to estimate CDL for the induction of egg production as well as optimal egg production. After 24 wk on light treatments, hens used during the winter season were exposed to 20 h light:4 h dark and subsequent changes in egg production were used to evaluate photorefractoriness. In two additional experiments, a night-interruption design was used to evaluate CDL and ovarian photoresponsiveness during winter and summer. The CDL for inducing egg production varied by season and was estimated to be 10.5 h or less during winter and about 11 h during summer. Likewise, the CDL for optimal egg production varied by season, being 11 to 11.5 h during winter and >14 h during summer. The CDL for photorefractoriness in winter photostimulated hens was between 12 and 12.5 h. It was concluded that CDL vary by season and are not fixed, but are dynamic characteristics of photoperiodic processes. Thus, photoresponsiveness of turkey hens changes by season. In addition, CDL for initiating egg production, stimulating egg production, and inducing photorefractoriness are all different, with the CDL for photorefractoriness being longest.

Manipulation of light intensity is an important management tool affecting broiler production and well being. Despite considerable research on light intensity, there is still a debate on the optimum level to be used for intensively housed broilers. Two trials were conducted with the objective of investigating the effect of light intensity, within the practical levels at confinement barns (1, 10, 20, and 40 lx), on production, processing characteristics, and welfare of broilers raised to 35 d of age. Each light intensity treatment was replicated in 2 environmentally controlled rooms in each trial with 950 Ross × Ross 308 chicks per room. Data were analyzed as a randomized complete block design with trial serving as a block. All chicks were exposed to 40 lx of light intensity and 23 h of light for the first 7 d followed by treatment light intensity and 17 h of day length thereafter. Body weight and feed consumption were determined at 7, 14, and 35 d of age. At the end of each trial, 60 birds per treatment were processed to determine the detailed meat yield. Skeletal and footpad and ocular health were monitored at 31 and 32 d of age, respectively. Body weight, feed consumption, feed:gain ratio, and mortality were unaffected by light intensity. Carcass, thigh, and drum yield as a percentage of live weight decreased linearly with increasing light intensity. The 1 lx treatment resulted in heavier wings as a percentage of live weight. Light intensity had no effect on skeletal health, but ulcerative footpad lesions decreased linearly with increasing light intensity. Birds exposed to the 1 lx treatment had heavier and larger eyes. In conclusion, light intensity did not affect broiler production and mortality but did affect carcass characteristics. The 1 lx light intensity treatment had a negative effect on broiler welfare as demonstrated by increased ulcerative footpad lesions and eye size.

Studies were conducted to compare the effects of two ahemeral (AH) light-dark cycles of 26 and 28 h (AH26 and AH28) with a 24-h hemeral (H) cycle early in the lay cycle on egg production and size. Nine rooms, three per treatment, each holding 264 hens, were maintained with identical photoperiods. The scotoperiod was increased to provide (he desired AH “day length” at 20 wk of age. Later decreases of the AH cycles back to the H cycle were accomplished by decreasing the scotoperiod only. There were no significant differences in egg production in Experiment 1 for both AH26 and AH28 compared with the H control. However, egg size as percentage of large (56 g) and above was significantly improved at 28 wk of age for both AH treatments. In Experiment 2, egg size was again significantly higher for AH28. This was accompanied by a significant increase in egg production for 28-day Periods 1 and 2 and a decrease in Periods 3, 7, and 10 versus H. A new AH26 lighting program was then tested in Experiments 3 and 4. This resulted in significant increases in egg production for Periods 2 (Experiment 3) and 1 (Experiment 4). Within experiment, annual egg production was similar for H and AH26 birds. Egg size, as percentage of large and above, was also significantly increased for AH26 at 25, 26, 27, and 29 wk of age (Experiment 3) and 26 wk (Experiment 4). A tested AH26 lighting program leading to increased pullet egg size with no loss in egg numbers for 20-wk-old pullets is outlined.

In addition to inducing egg production, exposure to long days concomitantly activates processes that eventually result in photorefractoriness (PR) and cessation of egg production. Experiments were conducted to evaluate the duration of exposure to long days that result in these processes. In each of 3 experiments, we subjected Large White turkey breeder hens to long days (16 or 18 h per day) for differing lengths of time from initial photostimulation and then returned them to a photoperiod (12L:12D) that provided sufficient, but decreased, photoperiodic drive to support egg production but not induce PR. Photoresponsiveness was then evaluated by egg production after a return to a longer day length (20 h per day) late in the lay period and beyond the mean onset of PR typical for these turkey hens. Hens that have undergone any reduction in photoresponsiveness should not increase egg production in response to the increased photoperiod. From experiments 1 and 2, exposure to long days for as little as 1 d and as much as 9 wk from initial photostimulation did not result in an alteration in subsequent photoresponsiveness. This was based on an increased egg production response to a change in photoperiod from 12L:12D to 20L:4D after 20 wk of photostimulation that was similar to controls held continuously on 12L:12D and opposite to the response of controls held continuously on 18L:6D. It was clear that PR had been fully programmed by 20 wk of exposure to long days. Exposure to long days for 12 wk (experiment 3) resulted in a partial alteration of subsequent photoresponsiveness. It was concluded that programming of PR during late spring-summer season occurs after 9 wk of long day exposure, is not fully expressed by 12 wk of long days, and can be fully expressed by 20 wk of photostimulation.

This experiment tested the hypothesis that typical poor egg production during the summer is a consequence of insufficient lighting and reduced photoperiodic drive. Large White turkey breeder hens were photostimulated at 30 wk of age with incandescent light on May 12 for summer (off-season) egg production and continued for 28 wk. The lighting treatments were given in a 2 x 2 factorial arrangement with day length and light intensity as main effects. Day lengths used were 15L:9D and 18L:6D, whereas the intensities were 567 +/- 67 and 22 +/- 2 lx. All the treatments were within a light-controlled building, and there were 8 replicate pens of 4 hens for each treatment. Data were collected, by pen, for onset and the rate of lay; BW and feed consumption at 4-wk intervals; and egg weight (EW) at 4-wk intervals including the weight of the first 14 eggs laid, livability, and plasma thyroid hormones for 8 wk postlighting. The rate of egg production through 28 wk of photostimulation was better in the hens receiving 18 than 15 h of light per day (14 eggs/hen difference) but was similar between the 2 intensity treatments. The lower number of eggs in the 15-h group was associated with a greater number of photorefractory hens than in the 18 h of light per day group (39 vs. 14%, respectively). Egg weights were similar between the 18 and 15 h of light/day treatment groups but was significantly greater in the low intensity treatment as compared with the high intensity treatment. We may conclude that by increasing photoperiodic drive by increased day length, but not light intensity, there results an improved summer egg production by turkeys and reduced incidence of photorefractoriness. Egg weight was best at a reduced light intensity.

Broiler breeder pullets were grown on 8-h photoperiods to 2.23 or 2.42 kg of BW at 20 wk, and then transferred abruptly to 11- or 16-h photoperiods. Subsequently, some of the 11-h photoperiod birds were given 15-min increases in day length weekly or a 1-h increase every 4 wk to reach 16 h of light at 54 wk. The birds transferred abruptly to a 16-h photoperiod at 20 wk matured 4 d earlier than 11-h photoperiod birds, required 500 g less feed to reach 50% lay, but, because of a 3% lower rate of lay after peak, produced 5 fewer eggs to 60 wk. However, the number of settable eggs was similar for the 2 groups because the 11-h photoperiod birds laid more eggs on the floor, resulting in more cracked and dirty eggs. The 11-h photoperiod birds converted feed into egg more efficiently, and were 100 g heavier at end of lay. Increasing the photoperiod in 15-min or 1-h increments from 11 to 16 h during the laying cycle depressed egg production. Mean egg weight and mortality were similar for all lighting groups. The heavier BW birds at 20 wk reached maturity 1 d earlier, but used 1 kg more feed to reach maturity, laid 5 fewer total eggs (because of a 3% lower rate of lay after peak), produced 7 more unsettable eggs (because more eggs were laid on the floor), and converted feed into egg less efficiently than did the lighter BW birds. Mean egg weight, BW at 57 wk, and mortality were similar for both groups. There was no significant light x growth interaction for any performance parameter. It is concluded that there is no benefit to egg production from extending the photoperiod to 16 h when broiler breeders are kept in light-proofed housing, especially if they have access to illuminated nest boxes.

The addition of two 3-h periods of very dim light, one before and one after a normal 8-h photoperiod, advances sexual maturity in pullets by about a week. This trial tested the hypothesis that dim light given before a short day of normal intensity is linked to form a more stimulatory day length and that dim light given after it is photosexually ignored. Pullets were reared from 2 d of age on 8-h photoperiods. From 10 wk, they were continued on 8-h photoperiods, transferred to 16 h, or given an 8-h period of dim light (0.09 lx) immediately before or after the main 8-h photoperiod. The bright/dim and dim/ bright groups matured at the same age, thus disproving the hypothesis tested. Both groups matured 1 wk earlier than the 8-h controls but 5 wk later than birds transferred to 16-h photoperiod. Oviposition time was similar for 8-h controls and bright/dim hens and delayed by 3 h for 16-h birds, but phase advanced by 2.4 h for dim/bright hens. Plasma melatonin rhythm was phase-advanced by about 5 h in the dim/bright hens and retarded by about 5 h in the bright/dim hens, suggesting a 13-h subjective day. However, these treatments were not regarded as fully stimulatory, as a transfer to a normal 13-h photoperiod at this age advances maturity by 5 to 6 wk. These findings show that the addition of a period of dim light to a normal nonstimulatory photoperiod differentially affects the clocks that control sexual maturation, plasma melatonin concentration, and oviposition time.

The time course of comb development and estrogen levels were compared in broiler (BX) and layer (LX) females that consumed feed ad libitum (A) or were subjected to quantitative feed restriction (R). The chicks were reared under short photoperiod [(6 h light (L):18 h dark (D)] until 22 wk of age. At this time, photoperiod was increased in one step to 8L:16 D, and then gradually increased until 14L:10D at 34 wk. There was a significant interaction between genetic type and feeding treatment, such that entry into lay of the LX-R and BX-R females was delayed by 1 and 4 wk, respectively, relative to the LX-A and BX-A birds. Mean comb size of LX-A birds began to increase while still under 6L:18D photoperiod; that of the other treatment groups did not begin to increase until photoperiod was shifted to 8L:16D. Comb size of individual LX-A, LX-R, and BX-A birds began to increase about 8 wk prior to individual onset of lay; that of BX-R birds about 11 wk prior to onset of lay. In all groups, estrogen levels remained low until 3 to 4 wk prior to onset of lay, when they showed a sharp increase. Following onset of lay, estrogen levels of all groups remained high. Critical day length of LX-A birds appears to be lower than that of BX-A birds. In addition, feed restriction per se appears to decrease photoperiod responsiveness of BX birds.

Two experiments were conducted to determine whether the critical day length (CDL) for photorefractoriness remained stable or varied by season of the year. The first experiment was done in the fall with photosensitive hens that were exposed to fixed day length treatments ranging from 12 to 16 h/d for 24 wk. At 24 wk of treatment, all hens were given 20 h light (L):4 h dark (D) and subsequent changes in egg production were used to evaluate photorefractoriness. This experimental approach was the same as that used by Siopes (1994) to estimate the CDL for photorefractoriness in winter-photostimulated hens. It was determined that the CDL for photorefractoriness in fall-photostimulated hens was 12 to 12.5 h, the same as that obtained in the earlier report for winter-photostimulated hens. A second experiment was done to further test the possibility that the CDL for photorefractoriness was static during the year. A gradually increasing photoperiod was started in winter at 12L:12D, just under the CDL for photorefractoriness but just over the CDL for egg production. Subsequent egg production and expression of photorefractoriness were compared to controls to estimate the dynamics of the CDL for photorefractoriness. Results supported a static CDL for photorefractoriness and suggest that any daily photoperiod exceeding 12 h will activate processes leading to photorefractoriness, independent of season.

A series of four experiments was conducted to determine the response of meat-type breeder pullets to various light and feed management systems during the rearing, developing, and laying periods. Pullets reared under a short-day (8 h) lighting regimen entered lay at a significantly younger age and lighter body weight than did pullets reared under natural day length. When reared under short days, pullets subjected to light and feed stimulation earlier than 18 wk of age entered lay at a slightly younger age and significantly heavier body weight and produced fewer eggs through 45 wk of age. When pullets were reared under natural day length and photostimulated at 14 wk of age, incremental reductions in age (from 24 to 15 wk of age) at which feed stimulation was initiated resulted in proportionate reductions in age at first egg but had no effect on body weight at first egg. Results suggest that egg production by commercial meat-type females is optimum when managed to begin lay at 24 wk of age. Pullets reared under short days will enter lay at 24 wk if photostimulation is begun at 18 wk and feed stimulation is initiated not later than 24 wk. Pullets reared under natural day length will enter lay at 24 wk if photostimulation is begun at 14 wk and feed stimulation is initiated at 15 wk.

Three experiments were conducted to examine the impact of changing photoperiod length on the performance of chicken broilers. Effect of long, constant (23-h) photoperiod length (23H) was compared with treatments where photoperiod increased from 6 to 23 h abruptly after 21 days (6H) or gradually during the experiment (INC). The 6H program was used in all three experiments, whereas the INC treatment was included only in Experiment 3. Differences between total body weight gains of birds in the 6H and 23H treatments were inconsistent and small in the three experiments. In Experiment 3, there were no differences between total body weight gains for INC, 6H, and 23H treatments. Feed-to-gain ratios for 6H broilers were significantly superior to those for birds on the 23H treatment for Days 0 to 21 (all experiments), Days 21 to 42 and Days 0 to 42 (Experiment 2), and inferior for Days 21 to 42 (Experiment 3). The INC treatment was significantly superior to the 23H program for all time periods and to 6H birds for Days 21 to 42 and Days 0 to 42. The 6H treatment significantly reduced the incidence of leg abnormalities in comparison with the 23H program in all experiments; the INC and 6H treatments were equal in incidence in Experiment 3. When data from the three experiments were combined, mortality due to sudden death syndrome and other causes for the 6H treatment was significantly lower than that of the 23H program; values for the 6H and INC treatments were not different in Experiment 3. Results indicate that changing the photoperiod length from short to long during broiler growth improves bird health while maintaining equal or slightly superior performance characteristics compared with effects of a long constant day length.

MORE losses occur in duck eggs (Horton, 1932) than in chicken eggs (Hafez and Kamar, 1955), during the incubation period, either due to low fertility (Fronda, Zialcita and Dalisay, 1940; Pozo Lora, 1959), or low hatchability (Pritsker, 1941). Ducks, in general, have a restricted breeding season and lay relatively few eggs. Accordingly, it is important to reduce these losses to a minimum to use the reduced number of eggs to produce the highest number of ducklings possible. Seasonal variation occurs in fertility of Khaki Campbell duck eggs. An increase in atmospheric temperature causes the decrease in fertility, while an increase in normal day length causes a rise in fertility when the atmospheric temperature is relatively low (Pozo Lora, 1959). The normally low fertility in Khaki Campbell could be improved by supplemental artificial light summing up to 14 hours of light daily when the atmospheric temperature was relatively low (Pozo Lora …

INTRODUCTION IT IS well established that the external environment influences sexual maturity in birds. Light is the most important environmental factor as shown by the work of Rowan (1925) with juncos (Junco hyemalis), Bissonnette (1930) with starlings (Sturnus vulgaris), Scott and Payne (1937) with turkeys. Experiments at the Nebraska station reported in 1930 had demonstrated that lighted turkeys could be induced to start laying earlier than those not subjected to artificial light, and this was confirmed by Albright and Thompson (1933) and the later work of Scott and Payne (1937). The hypophysis has been shown by Hill and Parkes (1937) to control gonad activity in birds. Benoit (1935) has obtained evidence that light acts on receptive organs which transmit stimuli to the hypophysis which in turn produces hormones that act on the gonads. Presumably there are inherited differences in the response of different individuals to a given length of day . . .

USE of artificial light is known to bring turkey hens into egg production earlier than if the birds are exposed only to normal daylight (Albright and Thompson, 1933). Moreover, blue light was found to be ineffective by Scott and Payne, 1937, presumably because the light intensity was reduced below the required level. Turkey hens require a light intensity of about 2 foot candles (Asmundson, Lorenz, and Moses, 1946). Data on the optimum length of day are not available for turkeys, hence further tests were started. MATERIALS AND METHODS Bronze hens were used. They were selected in such a way that, for example, the first bird banded in one pen was of similar ancestry (usually a full or half sister) to the first bird banded in any of the other pens; they weighed about the same at the time the tests were started. Thus the ten birds in one pen could . . .

CONFINEMENT rearing is the general procedure for the production of young turkey fryer-roasters. Consequently, artificial light is supplied, particularly during the “off season” when the natural day lengths are short. Often the light is continuous as producers have felt that this lighting program reduced certain management problems. The diurnal light-dark sequence is an important environmental factor which conditons, synchronizes, and stimulates various physiological processes in the avian species, including the turkey. Alterations of the light-dark sequence at an early age is of interest in at least two phases of turkey management. One of these is the effect on subsequent management for reproductive purposes and the other is the effect on market quality characteristics such as growth and feathering. Previous investigations bearing on the latter phase by Mueller et al. (1951), Moultrie et al. (1955) and McCartney (1956) indicated that body weights were somewhat larger in groups receiving the longer light …

AS the level of egg production increases in flocks bred for high fecundity, more environmental and hereditary factors influencing annual egg production are being reported. This study includes three sections each concerned with different phases of the problem in a closed flock for Rhode Island Reds that has been bred for high fecundity for many years. The first section includes a study of the decline in egg production from first to second laying year in five generations of birds. The second section has to do with some possible new factors that may affect production. The third section includes a study of the two environmental factors, house temperature and length of day in relation to egg production over a three year period. 1. DECLINE IN EGG PRODUCTION FROM FIRST TO SECOND LAYING YEAR IN RHODE ISLAND REDS Birds bred for high fecundity normally exhibit a significant decline the second year in . . .

IN PRACTICALLY all of the literature, both scientific and popular, the conclusion is reached that restricting nutrient intake of developing pullets results in delayed sexual maturity (Sunde et al., 1954; Milby and Sherwood, 1956; Tomhave, 1958; and MacIntyre and Aitken, 1959). However, the effect of restricted feeding during the developing period on such laying house performance criteria as egg production, body weight, liveability and size of egg have not been consistent from test to test. Many of the experiments reported have been conducted with winter or spring hatched pullets subjected to natural daylight during the developing period. In such instances the birds were exposed to increasing day length as they progressed to sexual maturity. The data to be reported herein indicate that when pullets are raised under conditions of restricted light, from 8 to 21 weeks of age, restricting the feed intake of pullets to 83 percent of normal consumption …

INTRODUCTION OBSERVATIONS by a number of investigators including Pearl and Surface (1911) and Whetham (1933) show that egg production in the hen is influenced by season. Highest egg production tends to be correlated with increasing length of day. Because of the similarity of the hormonic mechanisms governing egg production in the female and spermatozoa formation in the male, it was thought probable that semen production in the domestic cock likewise is related to length of day. Results of previous studies (Parker, McKenzie, and Kempster, 1942) showed that, when semen was intercepted in a semen collector during mating trials, male fowls ejaculated the greatest number of sperms during the spring months. However, since the influence of libido was not eliminated, these results were not necessarily indicative of the rate of spermatozoa formation. The following experiment was conducted to determine whether there are measurable seasonal differences in semen production in the cock.

THE quality of different strains of turkeys at market age varies considerably irrespective of data of hatch. It seems most likely that the expression of this character is conditioned to some degree by environmental factors, such as day-length and temperature. Turkeys hatched in January, February, and March reach market age during the warm summer months when the days are long, while turkeys hatched in May, June and July reach market age during the cooler fall and winter months when the days are short. In general, turkeys hatched during the first three months of the year do not attain as good quality at market age as their full-sibs hatched from May to July, inclusive. The problem of environmental factors affecting growth, feathering and market quality of turkeys has been the subject of a very limited number of investigations. Date of hatch has been found by Margolf (1948) to influence growth and …

THERE is an increased demand for out-of-season poults for the fresh young tom and hen turkey market. The problems in reproducing turkeys are difficult during the normal spring breeding season but are even more difficult for out-of-season poult production. The first obstacle to overcome is that of obtaining egg production levels which at least approach those obtained during the spring. Up to this time such levels of production have rarely been attained. It would appear however, that proper manipulation of artificial lights may provide at least part of the answer to the problem. Once optimum light environment is obtained, the geneticist can then attempt to develop genotypes for higher levels of production during the various seasons of the year, and eventually throughout the year. One common characteristic in all birds is the definite initiation of reproductive cycles as hours of daylight or artificial light increase during the spring. Bissonnette (1931)…

INTRODUCTION DURING the course of an unpublished study to evaluate environmental factors affecting rate of egg production, it was deduced that age at first egg among genetically similar pullets should be closely related to daily hours of illumination. As a corollary, winter hatched pullets should mature earlier than spring hatched pullets. Evaluation of these relationships may enable poultry breeders to correct their genetic selection for early maturity in accordance with date of hatch or persuade them to limit comparisons to groups of pullets hatched during a very limited period. Selection is effective in proportion to the degree with which it reflects genetic variation rather than variation due to environment. Several studies of the effect of date of hatch on age at first eggs are summarized by Lippincott and Card (1939) and Jull (1940). Conclusions as to the effect of date of hatch on age at first egg drawn from these . . .

THE influence of light on reproduction in birds has been reported recently, and reviewed by King (1961), Lanson and Sturkie (1961), Morris and Fox (1960), Fox (1961), Shutze et al. (1961), Bowman and Jones (1961), Lowe and Heywang (1961), and Farner (1961). McClary (1960a, b) reported that he was able to increase egg production and egg size by increasing the day length at hatching time approximately 51/2 hours beyond that which would be available under natural conditions at 22 weeks of age, then gradually decrease the day length 51/2 hours during the rearing period, followed by an abrupt or gradual increase in day length in the laying house. The experiment being reported was designed to determine if a reduction in day length from 22 hours at hatching to 16 hours at 20 weeks of age was comparable in enhancing production to a decrease in day length from 16 to 9 …

CONTRADICTING results appear in the literature as to the effect of thyroprotein on egg production. Turner et al. (1945a, b, 1946a, b, 1947) found that thyroprotein feeding resulted in higher egg production than the controls during summer. On the other hand, Hutt and Gowe (1948), Godfrey (1949), Berg and Bearse (1951) and Oloufa (1953) found that thyroprotein caused a depression in egg production during the hot months of the year. While the results obtained by Turner et al. (1945a), Hoffman and Wheeler (1948), Turner (1948) and Berg and Bearse (1951) indicated that thyroprotein was without effect on egg weight, Blaxter et at. (1949) and Oloufa (1953) found that feeding thyroprotein resulted in a decline in the weight of eggs. There is an ample evidence that increased length of light exposure is the stimulating factor affecting egg production. Nicholas et al. (1944) found that increasing day length stimulated egg production in mature …

SEASONAL variation in the rate of egg production is associated with seasonal variation in length of day. The excellent paper of Whetham (1933) summarized a very large amount of data from a wide range of latitudes, all showing correlated changes in day length and rate of egg production. Kennard and Chamberlin (1931) showed that seasonal variation can be modified by use of supplementary artificial light, confirming the work of several earlier laboratory workers and of many poultrymen. Kennard and Chamberlin also showed the close relationship of body weight and rate of egg production. A good review of the earlier literature is contained in the paper of Callenbach, Nicholas and Murphy (1944). Several analyses of egg production data for the purpose of describing the relation of time in production and rate of production have been made. Harris et al. (1921) reported that annual production within a genetically similar flock maintained under . . .

HATCHING egg producers using supplemental hatches of fall pullets to provide a year around uniform supply of hatching eggs have found that small egg size (under 22 ounces per dozen) is a problem with out-of-season hatched birds. Pullets hatched during October, November and December tend to lay small eggs over a longer period of time than pullets hatched in the spring of the year, and therefore produce a lower ratio of saleable hatching eggs during their year of production. These field observations have been confirmed by research reports pertaining to this problem. Jeffrey and Platt (1941) found that on a yearly basis their April hatched White Leghorn pullets produced 55 percent large eggs; January hatched, 47 percent; November hatched, 43 percent; June hatched, 42 percent; and September hatched, 38 percent. Callenbach et al. (1944) studied the relative effects of normal day length, and continuous 24-hour per day illumination as supplied …

LENGTH of the natural daylight or of imposed periods of artificial light restrict the pattern of lay of most domestic fowls. Egg sequences are usually initiated in the early morning and terminated in mid or late afternoon. Continuous alternating periods of light and dark fail to alter the rhythmic 24-to-26 hour laying pattern of the hen. Thus, the nature of the neurohumoral control of lay with regard to the role of the dark and of the light period of the day can best be tested under periods of unusual or abnormal day lengths and photoperiods. The purpose of these experiments was: (1) to attempt to modify the time interval between intra-sequence eggs by imposing an unnatural day length of 16 hours (8L-8D), and (2) to examine the extent to which darkness and the normal daily activity period influence the initiation and termination of egg sequences. METHODS AND PROCEDURE The hens …

Length of day is a major factor controlling egg production of birds. That egg production can be initiated and/or stimulated in the domestic fowl, duck or turkey by increased exposure to light is too well known to require documentation. Sexually dormant adult birds of these species begin to lay about two weeks after the regimen of increased light is initiated. A further observation of interest, although admittedly not particularly to the point, is the precocious sexual development of immature 10 to 12 week-old broiler pullets in late March and April. Numerous follicles of ovulatory size are commonly seen in broilers processed at Gainesville, Ga. The consistent occurrence of this phenomenon in the springtime during the period of increasing day-length suggests that this too is a response to light. Response to increased exposure to light has also been produced in wild birds such as the starling (Bissonnette, 1933; although in this . . .

Day-old tom poults were exposed to one of the following light treatments: 1) continuous incandescent light (24LL), 2) 23L:1D incandescent light, 3) 12L:12D incandescent light, or 4) natural day lengths only. Mortality was recorded daily. At Weeks 1, 2, 4, 6, and 8, after poult placement, body weights and feed consumption were measured. At each of these times, 10 poults were sacrificed from each treatment group for evaluation of plasma corticosterone. Day lengths utilized in this study had no consistent effect on poult-performance parameters except from 0 to 2 weeks of age. During this time, poults in the 24LL and 23L:1D treatments consumed less feed but were similar in body weight to poults in the other treatments. Adrenal function was also not consistently affected by day length. However, in all treatment groups plasm a corticosterone was lowest during the first 2 weeks posthatching, when compared to hormone levels at 4, 6, and 8 weeks. The lower corticosterone that occurred during the first 2 weeks posthatching may be involved in early poult mortality.

Bobwhites were fed one of several doses (.01 to 1,000 micrograms/day) of estriol (E3), beta-estradiol-3-benzoate (E2B), diethylstilbestrol (DES), or biochanin-A (BA) during two 10-week trials. The initial 2 weeks of each trial were short day length (10L:14D) followed by 8 weeks of long day length (16L:8D). In addition, female bobwhites were given daily injections containing dosages (.01 to 10 micrograms/day) of E2B, E3, and DES while housed on the same light regimen. Reproductive performance as assessed by onset of lay, egg production, and egg fertility was depressed in a dose-dependent manner and was inhibited by dietary dosages of 1,000 micrograms/day of E3, DES, and E2B. No consistent effects on reproductive performance were observed in bobwhites fed up to 1,000 micrograms/day of the phytoestrogen BA. Injected estrogens appeared approximately 100 times more potent than dietary estrogens. It was concluded that both dietary and parenteral estrogen can inhibit reproduction, but in order for phytoestrogen (BA) in natural feedstuffs to impair reproduction in bobwhites it would have to be consumed in excess of 1 mg/day.