The fact that fewer birds from each replicate will be used for sampling leaving more than half from each experiment unused is the problem, which in effect is related to cost.
DR. Kan asked for more datails about the study. (please see below).
Experimental Procedure Experiment 1.
Effects of dietary supplementation of a phytobiotic or synbiotic on the growth performance, immune status, and cecal microbiota of pasture-based broilers. A total of 180 one-day-old, male Cornish Cross broiler chicks will be purchased from a local commercial hatchery. All birds will be fed a corn-soy meal starter diet containing 23% CP. After two weeks, the birds will be blocked by weight and randomly allocated in triplicate (20 birds per replicate) to one of three dietary treatments. For six weeks, birds will be fed the control diet (CON), the control diet supplemented with thymol and carvadiol or the control diet supplemented with symbiotic. All birds will have free access to pasture from sunrise to sunset.
On 28 and 42 days of age, six birds from each treatment (two birds from each replicated pen) will be randomly selected, individually weighed and samples taken.
Objective 2:
Effects of dietary supplementation of thymol or synbiotic on laying performance, egg quality, and cecal microbial diversity of pasture-based laying hens. A total of 90 Rhode Island Red hens at point-of-lay will be used in this study. The birds will be randomly allocated in triplicate (10 birds per replicate) to one of three dietary treatments. For 12 weeks, the birds will be fed control diet (CON), the control diet supplemented with thymol and carvadiol or the control diet supplemented with symbiotic. Birds will be placed on commercial layer diet (16% CP) with free access to pasture from sunrise to sunset.
On week 10, samples will be collected from one bird from each replicate.
Statistical Analysis:
Data will be analyzed using the GLIMMIX procedure of SAS. Each replicate will be considered the experimental unit and the model will include the fixed effect of treatment. Effects will be declared significant at P ≤ 0.05 and tendencies will be considered when 0.05 < P ≤ 0.10.
NOTE: In Expt. 1, 36 birds will be sampled out of a total of 180 (144 birds will not be used)
In Expt. 2, 9 birds will be sampled out of a total of 90 (81 birds will not be used)
Still some more questions:
Do the animals survive the sampling or not? What samples are taken and what measurements ?
A rethorical question: why not sampling all animals? Most likely answer: too expensive!
Zootechnical data to be collected is always a balance between accuracy and costs. The same is true for physiological ones.
Dear Frederick
From a statistical point of view, there are two factors that will determine sample size. One: the variability in the parameter that you are interested in; Two: the difference in response between treatments that you want to be able to detect.
All statistical handbooks will tell you that and guide you through the procedures. Often you will have to conclude that you have to compromise due to budget or practical constraints.
Measurements include hematological, antioxidant and metabolomic cprofiling of the ecal microbial population. The selected (sampled) animals will not survived.
Thanks!
Dear Frederick
Stille some (more) questions/comments. (be aware that one fool can ask more that what ten wise men can answer)
Still the same remark to begin with: What is the variation between animals in the things that you are measuring? If that is large you need to sample more animals to have a fair chance to get a significant difference.
If the costs per sample are a limiting factor, you might consider to sample more animals and work with pooled samples of 2 or 3 animals. This will probably reduce variability is results within pens/treatments
For the broiler trial: I am not sure whether blocking by weight is necessary. In our broiler trials (See attachment) we (always) aimed at starting with a similar weight and weight distribution within pens at the start. That worked fine for us.
If I understand the description correctly the trial will last till day 56. Why not sample then?
For the laying hen trial; make sure that all hens are really at point of lay. If just one out of ten, does not lay eggs (that might well happen) that is a 10 % difference in lay and also its physiology might be quite different from the ones that do lay eggs.
I consider (as above) sampling 1 out of 10 a very low number. So once again, sample more birds and if necessary and possible, analyse pooled samples.
Good luck with your trials
I think in poultry trials sampling of at least 20-30% of birds per experimental unit can give a reasonable results, although the @more samples give the better results.
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