Rates of ovulation and oviposition in growth selected lines of chickens

Targeted differential illumination improves reproductive traits of broiler breeder males

Artificial targeted illumination has a pivotal role in reproductive processes of poultry. The light-absorption mechanism in birds consists of 2 main components: the eye (retinal photoreceptors) and extraretinal photoreceptors located in the brain. Previous studies conducted on hens have shown that photostimulation of brain extraretinal photoreceptors elevates reproductive activity, whereas retinal photostimulation suppresses it. We tested the effect of targeted differential photostimulation (TDP) on reproductive activities of broiler breeder males. Fifty broiler breeder roosters (Ross), 21 wk of age, were divided into 5 environmentally controlled light-treatment rooms (n = 10) equipped with individual cages. Rooms 1 and 2 had 2 parallel lighting systems consisting of red light (630 nm) and green light (514 nm), and rooms 3 and 4 had parallel red and blue (456 nm) lighting systems. Room 5, illuminated with white light, served as the control. Birds of all groups were kept under short day (6L:18D) for 2 wk with both lighting systems in each treatment room turned on. At 23 wk of age, birds were photostimulated by gradually increasing one of the lighting systems to 14 h of light in each room, while the other lighting system was left on short day (6L:18D). Weekly semen samples were collected until 65 wk of age and analyzed for volume, motility, concentration and vitality. Monthly blood samples were drawn for plasma hormone assays. At 65 wk of age, roosters were euthanized and hypothalamus, pituitary gland, retina and testes samples were taken for mRNA expression analysis. TDP using long-day red light and short-day green light significantly increased reproductive performance, manifested by higher semen volume, motility and concentration, and testis weight; furthermore, this group had higher plasma testosterone levels, higher GnRH mRNA expression in the hypothalamus, lower levels of aromatase in the testes, and lower mRNA expression of hypothalamic serotonin transporter, and of pituitary prolactin and its receptors in the testes. This is the first study showing a positive effect of TDP on reproduction of broiler breeder roosters.

Ovarian morphology and internal vis-à-vis non internal laying in relation to triacylglycerol, hormones and their receptors concentration around the age of sexual maturity in broiler breeder hens

1. Ovarian morphology, serum hormone concentrations of 17-β-estradiol, progesterone, testosterone, tri-iodothyronine (T3), thyroxine (T4) and triacylglycerol (TAG) were investigated at 23 and 26 weeks of age in broiler breeder hens provided with ad libitum access to feed. Progesterone, oestrogen-β, thyroid-α and -β receptor mRNAs were also quantified in the infundibulum at the same ages. 2. A large variation in the ovarian morphology was observed at 23 weeks of age including hens with undeveloped ovaries, non-laying hens with post ovulatory follicles (POF) and a predominance of non-laying hens without a POF. 3. Serum concentrations of triglyceride, 17-β-estradiol and progesterone at 23 weeks of age were lower in hens with an undeveloped ovary compared with other groups of hens, whereas testosterone, triiodothyronine and thyroxin were higher. 4. At 26 weeks of age, the average number of hierarchical yellow follicles in normal layers was 7.64 ± 0·41 whereas in internal layers, the follicular numbers were significantly greater at 8.66 ± 0·53. The higher follicular numbers in internal layers were associated with higher serum triglyceride and progesterone concentrations. 5. Oestrogen receptor-β and thyroid receptor-β mRNA was up regulated in the infundibulum of internal layers compared with normal laying hens at 26 weeks of age.

Feeding motivation on the incidence of floor eggs and extraneously calcified eggs laid by broiler breeder hens

1. Commercial broiler breeder hens lay many eggs on the floor rather than in nest boxes provided. A study was conducted to determine whether feeding feed-restricted broiler breeder hens during the sitting phase of nesting results in a higher incidence of floor eggs and/or retained eggs. 2. Sixty broiler breeder females (Ross 308) were randomly assigned to 6 deep litter pens containing 10 nest-boxes. At 35 weeks of age and for 9 weeks, feed was distributed to all pens at lights-on every second day (fed normally, FN). On alternate days (feeding delay, FD), feed was distributed when 2-3 hens/pen were sitting in a nest box. Behaviour was sampled at 41 weeks of age, for 26 d. Eggs and egg location data were collected daily, and eggs were scored for extra-cuticular calcium. 3. Of 81 instances in which the hen was sitting firmly in a nest box at the time of feeding, on 80 instances the hen left the nest-box to feed, and on one instance the hen laid her egg then exited to the feeder. Of these 80 instances, on 58 occasions the hen returned to a nest-box to lay her egg; on 12 the hen returned to the nest-box but laid no egg; on 7 the hen did not return to the nest box and laid no egg; and on three the hen laid her egg on the floor. 4. Mean floor egg percentage was 13·3 ± 3·2% on FN and 13·3 ± 4·7% on FD days; these did not differ significantly. 5. The mean extra-cuticular calcium score over all pens was 0·9 ± 0·06 on FN days and 1·2 ± 0·06 on FD days; these differed significantly. 6. In conclusion, feeding broiler breeder hens during nesting results in a conflict between feeding and nesting motivation and higher numbers of extraneously calcified eggs, but does not result in a significant increase in floor eggs even though nesting hens will leave the nest box for food.

Stochastic modelling of optimum initial body weight, daily weight gain and effect of genetic changes in ovulation rate and age at sexual maturity on total egg production of broiler breeders

1. A model that simulates the total production of eggs (TEP) in broiler breeders was used to predict the optimum initial (20 week) body weight (IBWexp), daily weight gains from 20 to 30 (DWGexp(20-30)) and 31 to 62 weeks of age (DWGexp(31-62)), age at photostimulation (affecting age at first egg, AFEexp), coefficients of variation of initial body weight (CV-IBWexp) and age at first egg (CV-AFEexp), and the effect of genetically increasing the numbers of yellow follicles at the onset of lay. 2. The results suggest that TEP in broiler breeders is very sensitive to changes in body weight gain during the first 10 weeks of the production period and body weight at the start of egg production, whereas changes in body weight gain after peak rate of lay showed only minor effects on TEP. Increasing CV-IBWexp was associated with a linear decrease in the mean and increased variability of TEP. 3. Decreasing AFEexp was negatively associated with TEP, whereas higher CV-AFEexp increased variability of TEP and had a trivial affect on the mean. 4. Results of the simulation suggested that reducing ovarian yellow follicle numbers by means of genetic selection could reduce the degree of feed restriction currently used in broiler breeder commercial stocks while maintaining total egg production. Higher numbers of yellow follicles associated with selection for higher growth rate would not result in lower egg production if the body weight target was maintained at the currently recommended commercial level and the effect on TEP of increasing the target in proportion to potential body weight may be relatively small.

Reproductive Efficiency and Metabolism of Female Broiler Breeders as Affected by Genotype, Feed Allocation, and Age at Photostimulation. 2. Sexual Maturation

A 3 x 4 x 2 factorial design trial was conducted to determine the effect of 3 broiler breeder strains, 4 target BW profiles, and 2 photostimulation ages on sexual maturation traits. A total of 560 pullets from each strain (Hubbard Hi-Y, Ross 508, and Ross 708) were housed in 24 pens. The BW profiles diverged at 4 wk and subsequently converged at 32 wk of age as follows: standard (approximate mean target BW profile of the 3 strains), low (12-wk BW target = 25% lower than standard followed by rapid gain to 32 wk), moderate (12-wk BW target = 150% of standard followed by lower rate of gain to 32 wk), and high (12-wk BW target = 200% of standard followed by minimal growth to 32 wk). Birds were photostimulated at 18 (18WK) or 22 (22WK) wk. Eight birds per interaction (n = 192) were killed and dissected at sexual maturity (first oviposition). Body weight profile affected timing of sexual maturity with the 18WK but not the 22WK treatment. There was no effect of BW profile on initial egg weight. Mean BW at sexual maturity was 3.40, 3.21, 3.01, and 2.84 kg for high, moderate, standard, and low birds, respectively. This affected shank and keel length, indicating differences in frame size. Ovary weight at sexual maturity was 6 g heavier in the low treatment (55 g) compared with other BW profiles. This was related to recent feeding level, which was highest at sexual maturity in the low treatment. Arrangement of ovarian large yellow follicles (LYF) changed with photostimulation age. Birds that were photostimulated at 18WK had 1.33 LYF hierarchies, compared with 1.22 in 22WK birds. The 18WK-high birds had increased excess LYF production (55% paired) compared with other BW profiles, whereas both small yellow follicle number and atresia were increased. Feeding profiles affected growth and conformational traits, with little effect on reproductive morphology at sexual maturity.

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.

Heterosis of growth and reproductive traits in fowl

Long-term divergent selection for high (HH) and low (LL) BW at 56 d of age in White Plymouth Rock chickens resulted in deviations from a typical chronological timeline for reproductive development. Line HH chickens of the 42nd generation of selection (S(42)) were heavier at 28, 56, 168, and 266 d of age, as well as at sexual maturity than those from line LL of the same generation, and commenced egg production at a younger age (188 d vs. 217 d). Once the LL chickens reached sexual maturity, 99.5% of their ovulations resulted in normal oviposits, in contrast to 94.6% for HH females. Heterosis, as measured by differences of F(1) progeny from the parental lines, can have a positive or negative sign. Although negative heterosis does not imply inferiority, results may be confusing because, depending on the trait, positive or negative can biologically be the phenotype that is preferred. Heterosis was calculated using coefficients of variation and means for reciprocal crosses from S(41) parents of the selected lines. Growth and reproductive traits were measured in this experiment. In almost all cases, heterosis calculated using coefficients of variation had a narrower range of magnitudes.

Ovarian follicular dynamics in selected and control (relaxed selection) male- and female-lines of broiler breeders fed ad libitum or on restricted allocations of food

1. The reproductive structures of 4 broiler breeder lines fed ad libitum or restricted were compared at 1st egg. The lines were contemporary male- and female-lines and their respective progenitor lines maintained without selection for 20 years. 2. The selected lines were larger and had more hierarchical yellow follicles than the relaxed lines. The numbers of positions in the hierarchy were greater in the selected lines. The number of atretic follicles and the proportion of multiple follicles were relatively high in the selected male-line. 3. There were more white follicles in the range 1.8 to 5.0 mm diameter in the selected male-line than in the relaxed line, whereas selection did not change white follicle numbers in the female-line. 4. Food restriction decreased the numbers of normal and atretic yellow follicles and the proportion of multiples but had no effect on the number of positions in the hierarchy. Restricted feeding decreased the number of white follicles 1.4 to 2.4 mm and increased follicles 2.4 to 5.0 mm diameter. 5. There was little change in age at 1st egg among lines fed ad libitum. Restricted feeding increased age at 1st egg and the difference was greater in female- than in male-lines and in relaxed compared with selected birds. 6. Abdominal fatness was similar among the lines fed ad libitum and was decreased by restricted feeding. 7. Oviduct weights were greater in selected than in relaxed lines and were decreased by restricted feeding only in the selected male-line. 8. The weight of the largest follicle was higher in the selected lines and in restricted compared with ad libitum-fed birds. Plasma triglyceride concentrations were lower in restricted birds from the selected and relaxed female-lines compared with the other groups. Differences in plasma oestrogen concentrations could not be detected.

Long-term divergent selection for eight-week body weight in white Plymouth rock chickens

This paper provides an overview of results from a long-term (38 generations) selection experiment. Lines were developed from individual phenotypic selection for high or low body weight at 8 wk of age. Included are data for the selected lines, sublines in which selection was relaxed, crosses of the selected lines, and sublines in which the sex-linked dw gene was introduced. Periodically (and in some cases every generation) data were obtained for unselected traits. These unselected traits included feed consumption and intake behavior, reproduction, allomorphic relationships, and metabolic, immunological, endocrine, and molecular factors. These responses have been integrated into a resource allocation paradigm.

Effect of feed allowance during rearing and breeding on female broiler breeders. 2. Ovarian morphology and production

The influence of feed allowance during rearing (4 to 18 wk) and breeding (18 to 62 wk) on ovarian morphology and egg production was examined. During rearing, beginning at 4 wk of age, 400 Indian River pullets that had been full-fed from 1 day of age either continued to be full-fed (F, n = 200) or were feed restricted (R, n = 200), following commercial practice. At 18 wk of age, 100 birds (within +15% of the mean BW) in each of F and R rearing groups were further assigned to be full-fed (n = 50) or feed restricted (n = 50) during breeding. Thus, based on feed allowance during rearing and breeding, four treatment groups were formed (FF, FR, RF, and RR). Feed restriction during rearing significantly delayed oviduct development and age at sexual maturity (age at first egg). Compared with feed restriction during both rearing and breeding (RR), ad libitum feeding beginning at 18 wk of age (RF) significantly increased the weight of the ovary and the number of large follicles at sexual maturity but did not significantly affect the age at sexual maturity. Feed restriction during rearing, breeding, or both significantly reduced the incidence of erratic ovipositions, defective eggs, and multiple ovulations. The incidence of erratic ovipositions was positively correlated (r = .692, P less than or equal to .001) with the laying of soft-shelled and shell-less eggs and negatively correlated (r = -.508, P less than or equal to .001) with the production of settable eggs to 62 wk of age. Compared with ad libitum feeding, controlled feeding during breeding significantly improved both settable and total egg production. Among the four feeding regimens, Treatment RR resulted in the highest fertility and hatchability.

Ovum formation and multiple ovulation in lines of white Plymouth Rocks and their crosses

The production of double-yolked eggs and the duration of the rapid growth phase of yolks were measured in parental lines of White Plymouth Rock pullets and their crosses over 30 d, commencing with the day of first egg. Significant differences were found between mating combinations in the incidence of multiple-yolked eggs, but not in the period of rapid yolk growth. Heterosis and recombination effects for multiple ovulation were respectively -9% and -66% of the mean, while the corresponding values for the period required for rapid yolk growth were -1% and -5%. Three double-yolked eggs were observed containing yolks which differed by 3 d in their periods of rapid growth. Hypotheses are were presented for the origin of double-yolked eggs.

Ultrastructural observations of the adenohypophyseal gonadotrophs from growth selected lines of chickens

The ultrastructure of adenohypophyseal gonadotrophs (GT-cells) from pullets of lines selected for high (HWS) and low (LWS) body weight was studied at various physiological ages. Increasing the photoperiod beyond 14 hours in a 24-hour cycle did not have a significant effect on the ultrastructure of GT-cells in either line. A qualitative analysis, based on the extent and complexity of the protein synthetic apparatus, suggested that the synthetic activity of gonadotrophs from HWS pullets was greater than that of LWS pullets at each of the ages studied. Although no significant differences were found in the frequency of pullets showing evidence of intracellular digestion of secretory products, the condition was more severe in the HWS than in the LWS females. Crinophagy tended to be positively correlated with cell activity in both lines. These observations suggest that selection for growth rate had a correlated effect on hypophyseal proteinaceous secretions. They also indicate that interactions between fluctuations in gonadotrophic cell activity, secreting mechanisms and neural thresholds for hormone action may be implicated in the manifestation of the erratic ovulation patterns.

Selection for body weight at eight weeks of age. 11. Ovulation and oviposition patterns

Two experiments were conducted to study oviposition patterns and ovarian activity at various physiological ages in S15 and S16 generation pullets from lines selected bidirectionally for high (HWS) and low (LWS) juvenile body weight. The fixed periods of lay for random samples of pullets from the date of first egg were 20, 40, 60, and 80 days in the first experiment and 40, 80, 120, and 160 days in the second experiment. HWS pullets matured significantly earlier than LWS pullets in both generations. The frequency and the percentage hen-day production (%HDP) of defective eggs were significantly greater in the HWS than LWS line in both generations. Delayed sexual maturity did not significantly change the pattern of defective egg production for a fixed period of lay. In the HWS line the %HDP of defective eggs progressively increased until about 40 days of lay and tended to decline thereafter, while in the LWS line the percentage decreased from 20 to 40 days and then stabilized. The frequency of normal unbroken eggs to 80 days of production did not differ among lines either in the S15 or S16 generation. When measurements were extended to 160 days of lay in the S16 generation HWS pullets produced significantly more normal eggs than LWS pullets. Possible effects of ovarian activity on the egg production pattern during the laying cycle are discussed. There was a significantly higher incidence of internal laying and atrecia of the growing follicles in the HWS than in the LWS pullets. Ovarian activity, evidenced by the number of developing and ruptured follicles, was significantly greater in the HWS than the LWS line, as was the incidence of ova developing in pairs. Product moment correlations and multiple regressions among the measurements of ovarian activity were calculated within lines. In the HWS line, 62.5% of the variation in %HDP of defective eggs could be accounted for by the %HDP of normal eggs and the number of developing follicles while in the LWS line these variables accounted for only 7.29% of the variation in %HDP of defective eggs.