This study examines the growth physiology of Naeini sheep in response to different levels of zinc-methionine supplement. Examine how effective these supplements through direct injection into the duodenum was not done due to lack of access to appropriate facilities in this section. At the second part, 16 Naeini ewes about two years old with 45±5 kg weight were fed with 1) without Zinc-Methionine supplement 2) 0.4 gr Zinc-Methionine supplement 3) 0.8 gr Zinc-Methionine supplement and 4) 1.2 gr Zinc-Methionine e supplement in a completely randomized design test with 4 ewes per group and 4 replicates. Blood samples were collected by 6 days interval and were analysed for GH, IGF-I, Insulin, Testosteron, Cortisol and VFA parameters. Results showed significant difference for GH (p 0.05), IGF-I (p 0.02) and Testosteron (p 0.02). But, there was no difference for Insulin, Cortisol, glucose and VFA among the groups. Regarding the results of the second stage and in order to investigate the effect of this supplement on gastrointestinal development during the weaning, the third part was designed for lamb growth of Naeini sheep. Sixteen 30 days old male lamb were allocated to 4 groups. Fourteen days for weaning and getting used to eating dry rations Was considered. Lambs were fed with 1) without Zinc-Methionine supplement 2) 0.4 gr Zinc-Methionine supplement 3) 0.8 gr Zinc-Methionine e supplement and 4) 1.2 gr Zinc-Methionine supplement in a completely randomized design test with 4 replicate per each group. Lambs monthly weight gain were strongly influenced by the use of these supplements (p 0.03). After 1 month, 3 lambs of each treatment were killed and intestinal tissue, liver and rumen samples were conducted. Examining tissue samples showed that the levels of 0.8 and 1.2 g of zinc–Methionine had significant effect on villi height and crypt depth in intestinal tissue. But, there was no difference for villi density and thickness of the muscle in this part of Gastrointestinal tract. Also there was significant difference for liver glycogen storage in Levels of 0.8 and especially 1.2 grams of the zinc–Methionine supplement (p 0.02). It might be concluded that Zinc-Methionine affects the physiological response of the ewes and the growth parameters of their lambs and use of Zinc-Methionine supplement in Elementary ages can be influential on growth by effect on gastrointestinal development. Key words: Zinc–Methionine supplement, growth, gastrointestinal development
