We hypothesized that steam-flaking barley grain may improve ruminal fermentation rate and rumen development as well as reduce cecal fermentation rate through reducing starch escape to the lower parts of gastrointestinal trach (GIT) which can modulate inflammatory response of young calves. Therefore, the interaction effect of barley grain processing method (ground barley; GB vs. steam-flaked barley; SFB) and starter protein content (20% vs. 24%, DM basis) on growth performance, skeletal growth indices, ruminal fermentation, urinary purine derivatives and microbial protein synthesis, blood biochemical, and inflammatory indicators in Holstein dairy calves were evaluated. Fifty-two new-born Holstein female calves (3 day-old) were assigned to one of four treatments: 1) GB grain with 20% CP (GB-20CP); 2) GB grain with 24% CP (GB-24CP); 3) SFB grain with 20% CP (SFB-20CP); 4) SFB grain with 24% CP (SFB-24CP). Calves received 4 L/d whole milk from d 3-10, 7 L/d from d 11-45, 2 L/d from d 46-50 of the study followed by 1 L/d from d 51 and 52 of the study and had ad-libitum access to water and starters (d 1 to d 73). The greatest starter intake was observed in SFB-24CP diet during the pre-weaning period. Accordingly, calves fed this diet had higher weaning and final, body weight (BW), greater average daily gain (ADG) during the pre-weaning period and as well as higher weaning and final wither heights compared to other groups. Calves received starters contained SFB-24CP had higher ruminal concentration of short chain fatty acids (pre-weaning) and serum beta-hydroxybutyrate (BHB; pre-weaning; compared to other groups. The highest (428 pg/mL) and the lowest (359 pg/mL) concentrations of tumour necrosis factor-α (TNF-α) was observed in calves fed GB-20CP and SFB-24CP diets, respectively. Same trend was detected for serum amyloid A during pre-weaning period. Calves fed starters containing GB had looser feces, higher ruminal NH3- N concentration, and higher alanine aminotransferase (post-weaning) compared to those received SFB diets. Dairy calves fed 24CP had slight improvement in growth performance, particularly before weaning, compared to those fed 20CP. Based on the conditions of the present study, it can be concluded that feeding SFB grain may reduce starch flow to the lower sections of GIT and consequently reduce inflammatory responses of young claves compared to GB grain. Furthermore, concurrent feeding SFB and 24CP improved ruminal metabolism in calves which can be due to higher starch availability in the rumen. Further researches are needed to evaluate the effect of grains processing methods on ruminal and cecal microbial community.
