Photoperiod and oviposition time in broiler breeders

Intermittent lighting regime as a tool to enhance egg production and eggshell thickness in Rhode Island Red laying hens

Influences of intermittent light regime as a tool to enhance egg production, egg quality, and blood parameters of laying hens were investigated. A total of 270 hens of Rhode Island Red (during 20 to 36 wk of age) were used to investigate the effects of intermittent light regime in completely randomized design. The birds were divided into 3 equal groups (6 replicates of 15 birds each) and housed in floor pens. The first group was served as non-treated control (C) and was exposed to continuous and constant light for 16 h light/day throughout the experimental period. Whereas, birds of the other groups were exposed to intermittent lights for 20 min/h + 40 min of constant light (T1; FLASH20) and 40 min/h + 20 min of constant light (T2; FLASH40) during the 16 h of light period. Hens of T1 group showed significantly (P ≤ 0.05) the highest concentration of total antioxidant capacity and the lowest one of malondialdehyde in comparison with the other groups. Hens of T1 group had significantly (P ≤ 0.05) the greatest egg laying rate and egg mass in comparison with the other counterparts. Feed consumption was similar in the groups under study. Hens exposed to FLASH20 had the lowest (P ≤ 0.05) FCR when compared with the other treatments. Eggs produced from hens exposed to FLASH20 had the highest value of shell thickness followed by the control and then that of those exposed to FLASH40. There were insignificant differences among the treatments in body weight of hens and all of other egg quality and egg problem traits. In conclusion, intermittent light regime of 20 min/h was the most efficient in comparison with the other ones. Finally, intermittent light regime of 20 min/h during laying period (during 20 to 36 wk of age) is highly recommended.

Analysis of lambing distribution in the Ripollesa sheep breed. I. Development and comparison of circular von Mises models

Circular data originates in a wide range of scientific fields and can be analyzed on the basis of directional statistics and special distributions wrapped around the circumference. However, both propensity to transform non-linear to linear data and complexity of directional statistics limited the generalization of the circular paradigm in the animal breeding framework, among others. Here, we generalized a circular mixed (CM) model within the context of Bayesian inference. Three different parametrizations with different hierarchical structures were developed on basis of the von Mises distribution; moreover, both goodness of fit and predictive ability from each parametrization were compared through the analyses of 110 116 lambing distribution records collected from Ripollesa sheep herds between 1976 and 2017. The naive circular (NC) model only accounted for population mean and homogeneous circular variance, and reached the lowest goodness-of-fit and predictive ability. The CM model assumed a hierarchical structure for the population mean by accounting for systematic (ewe age and lambing interval) and permanent environmental sources of variation (flock-year-season and ewe). This improved goodness of fit by reducing both the deviance information criterion (DIC; -2520 units) and the mean square error (MSE; -12.4%) between simulated and predicted lambing data when compared against the NC model. Finally, the last parametrization expanded CM model by also assuming a hierarchical structure with systematic and permanent environmental factors for the variance parameter of the von Mises distribution (i.e. circular canalization (CC) model). This last model reached the best goodness of fit to lambing distribution data with a DIC estimate 5425 units lower than the one for NC model (MSE reduced 13.2%). The same pattern revealed when models were compared in terms of predictive ability. The superiority revealed by CC model emphasized the relevance of heteroskedasticity for the analysis of lambing distribution in the Ripollesa breed, and suggested potential applications for the sheep industry, even genetic selection for canalization. The development of CM models on the basis of the von Mises distribution has allowed to integrate flexible hierarchical structures accounting for different sources of variation and affecting both mean and dispersion terms. This must be viewed as a useful statistical tool with multiple applications in a wide range of research fields, as well as the livestock industry. The next mandatory step should be the inclusion of genetic terms in the hierarchical structure of the models in order to evaluate their potential contribution to current selection programs.

Interaction of hen production type, age, and temperature on laying pattern and egg quality

The effect of production type (layer vs. broiler breeder), age (onset and end of laying cycle), and temperature (20 and 28°C) on various aspects of the egg production process and quality was evaluated. Highly significant differences were detected between laying hens and broiler breeders (P ≤ 0.001) in all production parameters. Similarly, age significantly affected rate of lay (P ≤ 0.001; 75.4% for young vs. 62.6% for old), mean sequence length (P ≤ 0.001; 7.7 d for young vs. 2.6 d for old), and time of oviposition (P ≤ 0.001). However, there was no effect of temperature on rate of lay, sequence length, or feed intake. Significant interactions between hen type and age were apparent in rate of lay (P ≤ 0.001), sequence length (P ≤ 0.001), and time of oviposition (P ≤ 0.001). A significant interaction between production type and age (P ≤ 0.015) was evident in egg weight, but egg component proportions were dependent only on hen type. Egg shape index was significantly affected by age (P ≤ 0.004), by temperature (P ≤ 0.028), and an interaction between type and age (P ≤ 0.001). Specific gravity declined with age (P ≤ 0.035) and increasing temperature (P ≤ 0.013).

Photoperiods for broiler breeder females during the laying period

Ross 308 broiler breeder females, maintained in litter-floor pens, were reared from 2 d of age on 8-h photoperiods and transferred abruptly to an 11-, 12-, 13-, or 14-h photoperiod at 20 wk of age and at a mean BW of 2.09 kg. Four qualitative dietary treatments were superimposed upon each photoperiodic treatment, but, in the absence of any significant interactions of photoperiod with diet, only photoperiodic means are reported. Age at 50% egg production (ASM) was progressively advanced as photoperiod increased from 11 to 13 h but was similar for 13-h and 14-h birds. Egg production was significantly related to ASM, with peak egg numbers being stimulated by a transfer to 13-h photoperiods. Rate of lay after 48 wk of age declined more rapidly in the 14-h birds than in any of the other groups, suggestive of an earlier onset of adult photorefractoriness. More eggs were laid outside the nest box and more cracked and dirty eggs were produced by birds on 11- and 12-h photoperiods than on 13- or 14-h photoperiods. Mean egg weight was positively correlated with ASM but negatively related to photoperiod; the number of eggs thought to be double-yolked was not significantly affected by photoperiod. Total egg mass output was not significantly affected by photoperiod. Birds exposed to 11-h and 12-h photoperiods were heavier at 60 wk than birds transferred to 13- or 14-h photoperiods. These findings show that a transfer from 8 to 13 h at 20 wk optimizes egg-laying performance in broiler breeder females, especially when they are kept beyond 60 wk of age.

Choice of nest types by hens of three lines of broiler breeders

1. Choice of three different nest types by hens of broiler breeder lines was investigated: metal nests (26 x 29 x 33-45 cm, w x d x h) with inclined rubber mats, metal nests of the same size with litter, and larger wooden nests (30 x 40 x 38) with litter. Three lines were studied: line B (324 females + 36 males), line P (315 + 36), and line WM (306 + 32). Each line was housed in a pen 23.3 x 3.9 m (90.7 m2); half the area was concrete floor with litter, and the other half raised plastic slats, on which stood 84 nests, 28 of each type, in two-tier blocks. 2. Ninety-five per cent of eggs were laid in nests, with significant variation between types: 63% metal littered, 30% wooden littered, and 2.3% metal with inclined rubber mats. Choice between types was similar in the three lines. Hens of line B laid 66% of nest eggs in lower nests, P laid 57% and WM laid 64%. 3. The other 5.1% of eggs were laid on the floor: 1.2% on the litter and 3.9% on the slats in front of the nests. It is suggested that some subordinate hens were excluded from nests, and therefore laid on the floor.

Effect of moving dawn, dusk, or both on oviposition time in domestic laying hens

1. Lohmann Brown pullets were reared on 8-h photoperiods and transferred to 12 h at 15 weeks by either advancing dawn or delaying dusk by 4 h. At 25 weeks, half of each group was transferred to 16 h by advancing dawn or delaying dusk and, 10 d later, each photoperiod-group was advanced or delayed 4 h by moving both dawn and dusk. Individual oviposition times were recorded over 48 h at 25 weeks and 8-10 d after each lighting change. 2. At 25 weeks, there were no differences in mean time of oviposition, eggs laid in the modal 8 h, or in the proportion of eggs laid before dawn between pullets that had been given a 4-h increase in daylength at 15 weeks by advancing dawn and those photostimulated by delaying dusk. 3. Extensions of the daylength from 12 to 16 h at 25 weeks, whether by advancing dawn or by delaying dusk, delayed mean oviposition time by 2 h and virtually eliminated egg-laying before dawn. All groups laid > or = 94% of eggs in the modal 8 h. 4. Moving the complete 12- or 16-h photoperiod forwards by 4 h delayed egg-laying by 0.5 h (relative to dawn), whilst moving them backwards advanced it by 0.7 h. Pullets given 16 h of light laid very few eggs before lights-on, but the divergent movements in oviposition time, relative to dawn, resulted in more eggs being laid before lights-on when the 12-h photoperiod was moved backwards and fewer eggs when it was moved forwards. However, a slower adjustment to the new times of dawn and dusk by the pullets whose day had been moved forward, as indicated by fewer eggs being laid in the modal 8 h and poorer rates of lay compared with pullets that had their photoperiod moved backwards, may explain these differences. It is doubtful that the differences would have persisted after all birds had adjusted their ovulatory cycle, and so any reduction in pre-dawn egg-laying is likely to have been transitory. 5. The only permanent way to minimise pre-dawn egg-laying in brown-egg hybrids is to provide a photoperiod of at least 16 h, though 14-15 h may be long enough for white-egg hybrids and 12-13 h sufficient for broiler breeders.

Effect of final photoperiod and twenty-week body weight on sexual maturity and early egg production in broiler breeders

Cobb broiler breeder pullets, grown to achieve 2.19 kg (normal growth) or 2.41 kg (faster growth) BW at 20 wk, were given continuous light during the first 2 d posthatch, were reared on 8-h photoperiods between 2 d and 20 wk of age, and were then transferred abruptly to 10-, 11-, 12-, 14-, 16-, or 18-h photoperiods at 20 wk. Controls remained on 8 h at 20 wk. The birds were reared on a litter-floor from 1 d and transferred at 15 wk to individual cages. Mean age at first egg (AFE) was advanced by 12 d, compared with controls, for the transfer to 10 h, and progressively earlier for longer photoperiods until a 25-d advance for 14 h; AFE was similar for pullets transferred to 14, 16, and 18 h. A quadratic regression indicated that a transfer to 15 h would induce the earliest maturity. On average, accelerating growth by about 10 d advanced AFE by 4 d, but the difference was larger for transfers to a more stimulatory photoperiod. Body weight at first egg increased by about 20 g for each 1-d delay in first egg and was 110 g heavier for the faster growth pullets than for controls. Egg numbers to 39 wk increased by 0.75 for each 1-d earlier AFE. Mean egg weight was negatively related to photoperiod, decreasing by 0.3 g per 1-h, but positively linked to AFE, increasing by 0.1 g for each 1-d delay in AFE. Faster growth did not significantly increase egg numbers or mean egg weight, but it did increase egg output to 39 wk by 150 g. The data suggest that broiler breeders reared on 8-h daylengths do not need more than a 14-h photoperiod in the laying period to optimize sexual development or egg production. Typically recommended BW targets for broiler breeders (2.1 to 2.2 kg) appear to be optimal for egg production. Responses to the lighting treatments were independent of those to 20-wk BW.

Constant and changing photoperiods in the laying period for broiler breeders allowed [corrected] normal or accelerated growth during the rearing period

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.

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.