Modelling cumulative egg production in laying hens and parent stocks of broiler chickens using classical growth functions

ABSTRACT

1. The objective of the present study is to introduce fresh insight into modelling of egg production by applying classical growth functions to egg production records reported by Aviagen Management Guide to laying hens and the parent stock of broiler chickens.

2. The functions (monomolecular, logistic, Gompertz, Richards and Morgan) were fitted using nonlinear regression procedures of SAS software, and their performance was assessed using goodness-of-fit statistics (coefficient of determination, residual mean squares, Akaike information criterion and Bayesian information criterion).

3. Overall, except for the logistic and Gompertz, the growth functions evaluated gave an acceptable fit to the cumulative egg production curves, with the Morgan equation ranking first followed by the Richards equation. The Morgan and Richards equations provided satisfactory predictions of weekly egg yield at different egg production stages, from early to late production, whereas the least accurate estimates were obtained with the logistic equation.

4. In conclusion, classical growth functions proved feasible alternatives to fit cumulative egg production curves of laying hens and parent stock of broiler chickens, resulting in suitable statistical performance and accurate estimates of production.     

Temperature control of the distributional range of five C3 grass species in the uKhahlamba-Drakensberg Park,KwaZulu-Natal,South Africa

Global climate change is expected to influence the distribution of global biodiversity. C₄ and C₃ perennial grasses co-occur in the fire-prone KwaZulu-Natal uKhahlamba-Drakensberg grasslands, with C₃ grass species occurring at cooler locations in the mountain range and C₄ grass species at warmer locations. If a warming climate is expected to cause a contraction in the ranges of C₃ grasses, evidence of temperature controlling current distributions is required. This study modelled the distribution of five C₃ grass species, namely Tenaxia stricta, Tenaxia disticha, Festuca costata, Merxmuellera drakensbergensis and Merxmuellera stereophylla, to temperature-related surrogate variables using presence–absence data collected across the environmental heterogeneity of the mountain range. Distributions of each species, and of all species combined, were modelled using generalised additive models. These temperature-related variables accounted for the distribution of all five species, least so for F. costata. Four species could therefore contract in range in response to climate change, whereas F. costata is least likely to have a range contraction directly related to a warming climate and could experience a range expansion owing to the fertilising effect of increased [CO₂].     

Social resilience as a controlling influence on desertification in Senegal

While ecological resilience may explain why apparent symptoms of desertification are often temporary, social resilience can prevent degradation resulting from overexploitation of land in response to drought and other constraints. This paper describes a Social Resilience Model in which actors switch from performance strategies to survival strategies when the perceived severity of constraints exceeds a critical performance–survival threshold (PST). This is determined in comparison with a reference mode that depends on a learning facility developed by repeated exposure to cycles of constraint, search and feedback. Actors select particular strategies by comparing welfare gains with their aspiration levels—a concept that allows more flexible decision making than profit maximizing or satisficing alone. The model is tested in the silvopastoral zone of Senegal, where desertification is not as widespread as commonly assumed, despite severe constraints. The two major ethnic groups, the Wolof (mainly croppers) and the Peul (mainly pastoralists) anticipate and respond to environmental and socio‐economic constraints differently, and have different performance and survival strategies. The Peul have the higher social resilience, with more flexible decision‐making objectives, greater mobility, a more extensive action space, a learning facility supporting efficient search and feedback processes, a reference mode attuned to high anticipation and recognition of stress, and a high PST. They also exhibit more continuous performance–survival switching than the Wolof, who make a radical change from cropping to labour migration and reliance on external support. Copyright © 2004 John Wiley & Sons, Ltd.     

Transmission from Seed to Seedling and Secondary Spread of Xanthomonas campestris pv. Campestris in Brassica Transplants: Effects of Dose and Watering Regime

The effects of inoculum load and watering regime on the transmission of Xanthomonas campestris pv. campestris from seed to seedlings of cauliflower were investigated. Seed, inoculated with different concentrations of bacteria, was sown in commercial module trays and subjected to four different watering regimes: high frequency overhead spray, low frequency overhead spray, high frequency capillary and low frequency capillary. Visible symptoms were recorded and leaf washings were carried out to detect the pathogen on symptomless plants. The effects of treatments on symptoms and on the proportion of contaminated but symptomless plants was similar. Initially, they were influenced only by the dose of bacteria with little difference between the watering regimes, but later the proportion of plants with symptoms was greater for plants subjected to overhead watering, due to spread and secondary infection. Generalised linear models were fitted to the data relating the proportion of symptomless contaminated plants or the proportion of plants with symptoms, p, to the mean dose of bacteria per seed, d, and the number of overhead waterings, noh. The equations were: p=1–exp(–0.014·d ^0.32·noh ^0.045) for symptomless contaminated/infected plants and p=1–exp(–0.0056·d ^0.44·noh ^0.014) for plants with symptoms. These models indicated that the one-hit probability for transmission of the pathogen (i.e. with/without visible symptoms) was 0.014 and for infection (i.e. with visible symptoms) was 0.0056.     

Do boating and basking mix? The effect of basking disturbances by motorboats on the body temperature and energy budget of the northern map turtle

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Assessing vulnerability of New Zealand lakes to loss of conservation value from invasive fish impacts

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Finding suitable growth models for turbot (Scophthalmus maximus L.) in aquaculture 1 (length application)

Growth data of two different commercial turbot (Scophthalmus maximus) strains reared in recirculating aquaculture systems were analysed with the aim to determine the most suitable model for turbot. To assess the model performance three different criteria were used: (1) The mean percentage deviation between the estimated length and actual length; (2) the residual standard error with corresponding degrees of freedom and (3) the Akaike information criterion. The analyses were carried out for each strain separately, for sexes within strains and for a pooled data set containing both strains and sexes. We tested a pre‐selection of six models, containing three to four parameters. Models were of monomolecular shape or sigmoid shape with a flexible point of inflection including the special case of monomolecular shape in defined cases of their parameters. The 4‐parametric Schnute model achieved best fit in 62% of all cases and criteria tested, followed by the also 4‐parametric generalized Michaelis–Menten equation in 48% and the 4‐parametric Janoschek model (38%). The von Bertalanffy growth function achieved only 29%, Brody 24% and a new flexible function 19% best fit. In a 1–1000 day growth‐simulation sigmoid shaped curves were produced by the Schnute model in 71% of cases. The Janoschek and the Michaelis–Menten model each produced sigmoid curves in 57% of all cases. This indicates that a flexible 4‐parametric function reflects the growth curve of turbot the best and that this curve is rather sigmoid than monomolecular shaped.     

Determination of growth,colour and other traits in F1 hybrid of Amphiprion percula (male) × A. ocellaris (female)

This study reported the traits values such as colour, feed conversion ratio (FCR), specific growth rate (SGR) and fluorescence capacity of F₁ hybrids of Amphiprion percula (male) and A. ocellaris (female). The hybrids exhibited significant variation in FCR (3.63 ± 0.56) and SGR (3.63% ± 0.44) compared with the pure breeds, A. percula (3.12 ± 0.42; 2.80% ± 0.42) and A. ocellaris (3.17 ± 0.43; 3.02% ± 0.19). An exponential relationship was found between FCR and SGR in both the breeds. Image analysis displayed a better colour performance of hybrid than the pure breeds. Individual body parts of the hybrid and pure breeds showed significant colour variation between each other. However, colour contrast of whole body of hybrid was found closer to A. ocellaris in hue cone and towards A. percula in saturation and brightness values. Hence, hybrid displays combination colour reflexion of both the parents. The total pigment content of hybrid (65.71 μg g^?1 ± 2.81) was found higher than A. ocellaris (62.01 μg g^?1 ± 2.29) and A. percula (56.71 μg g^?1 ± 2.56). Further, the spectroflurometric analysis revealed that the both hybrid and pure breeds having poor fluorescence on skin pigmentation. A direct positive heterosis was observed on the SGR, FCR, total pigment and spawning frequency, while negative effect was noted on total length of newly hatched larvae (TL), fertilization rate (FrR), hatching rate (HR), deformation rate (DFR) and survival rate (SR). Hence, multiple cross‐breeding programmes will help in developing high‐quality traits in successive generations.