Short-term reduction in egg production in laying hens treated with an agonist of GnRH.

1. In two experiments laying hens were treated with an agonist of gonadotrophin releasing hormone (GnRH) to induce a reduction in the secretion of luteinising hormone (LH) and a pause in egg production. 2. In experiment 1, 70-week-old laying hens were either given daily subcutaneous injections of saline for 7 d, offered whole oats for 7 d (nutrient restriction), given daily injections of the GnRH agonist D-Trp6-Pro9 N-ethyl amide]GnRH for 7 d at 50 micrograms/kg or 100 micrograms/kg or administered 4 biocompatible implants each containing 120 micrograms of the GnRH agonist. 3. Weekly egg production was monitored for 7 weeks and blood samples were taken at weekly intervals and assayed for plasma LH and oestradiol. Egg production was reduced in the birds treated with the agonist (28 to 46% reduction) but not to the same extent as in the birds offered whole oats (92.3% reduction). 4. The treatments also reduced plasma LH and oestradiol in treated hens but again to a greater extent in the birds offered whole oats than the birds treated with the agonist. Egg production and plasma LH and oestradiol increased following the termination of the treatments. 5. The birds fed whole oats suffered a reduction in weight of 16.7% over the treatment period whereas there were increases in the weights of the birds treated with saline, 50 micrograms of GnRH agonist and the implants of GnRH agonist, but no change in birds treated with 100 micrograms of GnRH agonist. 6. The birds fed oats lost feathers over the treatment period but the birds in the other treatment groups suffered no loss. 7. In experiment 2 laying hens were either injected daily with saline or 200 micrograms GnRH agonist and weekly egg production and plasma LH and oestradiol were measured. As egg production was reduced by almost 60% in the birds treated with the agonist but did not completely cease. Reductions in plasma LH and oestradiol were also observed. All variables increased to pretreatment levels once treatment ceased. 8. These data confirm the effects of severely depriving hens of nutrients on egg production and the secretion of LH and oestradiol.(ABSTRACT TRUNCATED AT 400 WORDS)