Stocking density impacts on key pullet performance indicators

Studies looking at caged pullet stocking densities have been conducted to assess the effects on live production parameters and welfare in differing spaces allotted per pullet. Previous studies that have explored cage density effects on pullet performance in large agree that higher stocking densities decrease feed intake (Carey, 1987; Leeson & Summers, 1984; Patterson & Siegel, 1998). Although these higher stocking density pullets consumed less feed compared to their low stocking density counterparts, they found no significant impacts on pullet body weights associated with cage density (Carey, 1987; Patterson & Siegel, 1998). In contrast some studies found that along with the decreased feed intake, the pullets in higher cage densities (222 cm2) also had reduced body weights compared to the lower stocking density pullets (311 cm2) (Carey, 1987). Furthermore, one study found no differences between differing densities (221, 249, 277, and 304 cm2) pertaining to pullet body weights and feed intake ( Anderson and Adams, 1992). The differences between white laying hen pullets need to be explored further in order to determine the effects of cage density on pullet performance. The heterophil to lymphocyte ratio (H:L) has been used as a accepted measure of chronic stress responses in poultry (Davis et al., 2000; Gross and Siegel, 1983; Siegel, 1980). Previous research has concluded that the decrease of lymphocytes and an increase in heterophil counts happens in response to stress (Lentfer et al., 2015). Meaning that a higher H:L ratio can lead to conclusions that the bird is more stressed compared to lower H:L ratios. Researchers (Gross and Siegel, 1983) also stated that H:L ratios are a more reliable measure of chronic stress in poultry, compared to corticosterone measurements, as it detects physiological changes in the body whereas corticosterone in the blood measures before that physiological change can happen. Tonic Immobility (TI) is characterized by motor inhibition, low responsiveness to stimuli, and suppression of the righting response (Jones, 1986). TI is generally regarded as a fear response, where fear inducing procedures prolong the TI period, while fear reducing tactics tend to reduce TI periods (Jones, 1986). Tonic immobility responses have long been regarded as an anti-predator response, as cessation of movement or crouching can reduce detection by a predator, where flight can lead to escape measures if a predator approaches (Jones, 1986). The interplay between production demands and bird welfare concerns continues due to consumer apprehensions, as these two sides seem to be inverses of each other. Continued research into these systems and into welfare needs to be done in order for the middle ground to be achieved. Furthermore, consumer awareness of how agriculture as a whole, and more specifically how animal production occurs, need to be elucidated. The aim of this study is to assess if manipulation of pullet cage density, to be less dense than industry standards, will present with better growth parameters of the pullet.