Effects of corn grain processing method (ground versus steam-flaked) with rumen undegradable to degradable protein ratio on growth performance, ruminal fermentation, and microbial protein yield in Holstein dairy calves

The hypothesis of the current study was that steam-flaking corn grain will increase ruminal available starch, but reduce undegradable protein reaching the small intestine and hence formulating the starter diet with higher undegradable protein content may influence dairy calf performance. The effects of corn processing method (ground corn grain; GC vs. steam-flaked corn grain; SFC) with rumen undegradable to degradable protein ratios [low ratio (LR) = 28:72; high ratio (HR) = 37:63 based on %CP] on growth performance, feeding behavior, nutrients digestibility, ruminal fermentation, urinary purine derivatives and blood metabolites of Holstein dairy calves were evaluated. Forty-eight 3-day-old calves (24 females and 24 males) with a starting BW of 39.5 kg were used in a completely randomized block design with a 2 x 2 factorial arrangement of treatments. Experimental treatments were: (1) ground corn with low RUP:RDP (GC-LR); (2) ground grain with high RUP:RDP (GC-HR); (3) steam-flaked corn with low RUP:RDP (SFC-LR); and (4) steam-flaked corn with high RUP:RDP (SFC-HR). All calves were weaned on d 63 of age and, remained in the study until d 83 to take final measurements. Starter intake was not influenced by the grain processing method nor by dietary RUP:RDP ratio; however, the average daily gain and feed efficiency were improved and final body weight was higher in SFC fed calves. Feeding SFC diet improved the faecal score, increased the time spent on eating and slightly increased ruminating time. The LR diet improved neutral detergent fiber digestibility. Greater ruminal concentrations for total short-chain fatty acids, propionate, and butyrate were obtained when calves fed on SFC diet in pre-weaning period. The greatest heights for both wither and hip among experimental treatments were obtained in SFC-HR treatment. The higher urinary allantoin excretion and microbial protein yield, and lower urinary nitrogen excretion on the other hand, reflected an improved nitrogen efficiency in the SFC diet compared to the GC diet. Blood concentrations for glucose, beta-hydroxybutyrate and insulin were higher, and blood urea nitrogen concentration was lower in calves fed on SFC diet. In conclusion, considering our experimental condition, feeding steam-flaked corn in starter diet of dairy calves is favourable compared to ground corn grain, but RUP:RDP ratio did not influence animal performance per se. Skeletal growth was improved when SFC was fed with greater RUP:RDP ratio in starter diet which may be recommendable in replacement heifer rearing programs.