The current study examined the effects of probiotics (Pronifer and More-yeast) supplementation to growing lambs. 25 crossbred (Osimi×Rahmani) growing lambs of about 6-8 months age and an average initial live body weight of 25 kg were used. Lambs divided into five groups (5 lambs for each group) and the experimental period lasted for 169 days. The control group T 1 received concentrate feed mixture (CFM), group T 2 and T 3 received 1.5 and 3 kg Pronifer/Mg (megagram) CFM and group T 4 and T 5 received 2.5 and 5 kg More-yeast/ Mg CFM, respectively. Rumen liquor and blood samples were taken and digestibility trial was conducted at the end of the experiment. Results showed higher digestibility values for crude protein (P<0.05) in T 3 and T 4 when compared to control. Nutritive ratio was lower (P<0.05) in groups T 3 and T 4 than in group T 2 . More-yeast supplementation improved dry matter intake (P<0.001), while a reverse trend was observed with Pronifer supplementation. All treatments had little effect on ruminal liquor except ruminal ammonia concentration in T 5 was lower (P<0.05) than other treatments. The differences in most blood plasma parameters due to treatment effect were not significant, except plasma urea and globulin concentrations increased (P<0.05) with T 5 treatment. The obtained results appear to indicate that Moreyeast supplementation improved lambs performance and digestibility, whereas, Pronifer supplementation enhanced digestibility.Keywords: probiotics, performance, rumen activity, blood constituents and growing lambs Tierzucht 54 (2011) 6, 607-617, ISSN 0003-9438 © Leibniz Institute for Farm Animal Biology, Dummerstorf, Germany Hillal et al.: Effect of growth promoters (probiotics) supplementation on performance in growing

Nutrient partitioning was investigated in cows with different genetic merits for milk production by measuring (13)C/(12)C ratios (reported by delta values δ(13)C) in milk components in response to C3 (grass silage) and C4 diets (corn silage). We hypothesised that changes of δ(13)C in milk differ between Holstein (HOL; high milk production) and Charolais × Holstein cows with medium (CHM) and low (CHL) milk production. Changes of δ(13)C (Δδ(13)C) in milk components were estimated by calculating differences of δ(13)C due to switch from C3 to C4 feeding. After switch to C4 feeding, Δδ(13)C of lactose was greater in HOL than in CHL. Immediate Δδ(13)C of milk fat was the lowest in CHL. The maximal Δδ(13)C of casein was the lowest in HOL. The proportion of carbon in milk derived from diet increased with milk yield, indicating the main impact of the milk production level, but minor impact of breed, on nutrient partitioning towards the mammary gland.