The Number of Chicks Required to Demonstrate the Significance of Growth Differences

Methods of Experimentation in Animal Nutrition

“…Eesults with poultry-feeding experiments on 800 chickens reported from America (44), where groups of the same sex were compared, have been analysed, and from the standard deviation per cent, of the mean for both males and females the figures given in column 4 of Table VI have been calculated. Similar analyses of the results in cattle-feeding experiments, involving 84 animals, conducted at the West of Scotland Agricultural College (39), provide the figures given in column 5 for their paired cattle-feeding trials.…”

Partition of variation for predicting experimental power with a broiler chicken example

“…The important pieces of information needed to predict experimental power for a future experiment are the expected means and standard deviations from past experiments. The terms that need to be added to the Schroedek and Lawrence (1932) analysis of variance ( ANOVA ) are the variances due to the birds within a pen (the genetic variation) and the variances between the physical pens themselves. Pen-to-pen environmental variation can result from differences in ventilation within a house, lack of lighting uniformity, differences in noise, humidity, and arbitrary human disruptions.…”

“…They used paired t tests for individual mean separation between 4 dietary treatments, the same procedure used currently with Proc LSMeans of the Statistical Analysis System (SAS, 2012). Schroedek and Lawrence (1932) emphasized the need to keep birds under identical conditions, presenting pictures of seemingly identical pens with identical sunporches. At that time, physical separation of birds on different treatments, whereas ensuring pen environments were as similar as possible, was considered adequate.…”

Effects of Nutrition on Variability in the Growth of Chickens

“…He worked out and tabulated the smallest differences that would be significant at coefficients of variability of IS, 17.S, and 20 percent for groups of chickens from 10 to 100. Schroeder and Lawrence (1932) used large numbers of chicks in several replicate pens and found that large differences occurred in mean live weight and variability. They found that variability reached a maximum by six weeks but that the occurrence of disease greatly increased variability.…”