1. Radioimmunoassays were validated for oestradiol and testosterone in faecal and plasma samples from domestic fowls. Faecal samples were prepared in phosphate buffer. A delay of up to 24 h between defaecation and the freezing of a dropping did not affect faecal steroid concentrations. 2. Differences in plasma concentrations of testosterone and oestradiol between cockerels and hens were clearly reflected in faecal hormone concentrations. Faecal concentrations of oestradiol were low in males and did not overlap with much higher concentrations in females, whereas there was some overlap between the sexes in faecal concentrations of testosterone. 3. The correlation coefficients (r2) between plasma and faecal steroid concentrations were 0.464 for testosterone and 0.852 for oestradiol (log-transformed data). The coefficients did not increase when the mean hormone concentrations for several droppings produced by each bird during a collection period were used. 4. Faecal steroid concentrations can be used as a measure of plasma steroid concentrations and hence of gonadal activity in chickens. The resolution of the faecal steroid method is less than if plasma measurements were used, but it offers a practical alternative to blood sampling that is non-invasive and does not require birds to be handled.

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The galactopoietic effect of growth hormone (GH) in lactating ruminants is well established; however the mechanisms that mediate these effects are not well understood. The first objective of this study was to determine the effect of GH on the synthesis of the major casein and whey proteins. The second objective was to identify the genes and pathways that may be involved in mediating the effect of GH on milk synthesis. A single subcutaneous injection of a commercially available slow release formulation of GH (Lactatropin ® ), or physiological saline solution (control) was administered to non-pregnant dairy cows (n = 4/group) in mid-late lactation. Milk samples were collected for composition analysis and mammary lobulo-alveolar tissue was collected postmortem 6 days post injection. Gene expression profiles were evaluated using either a 22 000 bovine complementary DNA microarray or quantitative PCR (qPCR), and microarrays were validated by qPCR. The yield of all the major casein and whey proteins was increased 32% to 41% in GH-treated cows, with the exception of α-lactalbumin yield which was elevated by 70% relative to controls. Treatment with GH treatment tended to increase the concentration of α-lactalbumin but had no effect on the concentration of any of the major milk proteins. Messenger RNA (mRNA) abundance of the major whey and casein genes, with the exception of α-s2-casein, was increased in response to GH compared with controls, which is consistent with the positive effect of GH on milk production. Treatment with GH treatment influenced the mRNA abundance of genes involved in cell growth and proliferation, transcriptional and translational regulation, actin cytoskeleton signalling, lipid metabolism and cell death. This study has provided new insights into the cell signalling that may be involved in mediating the effect of GH on milk production in the mammary gland of lactating dairy cows.

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