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چکیده
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The hypothesis was to evaluate whether young calf’s response to high-starch grains is more related to particle size (physical factor) or availability rate of starch (chemical factor) in starter diets with no forage inclusion during early weeks of life. For this purpose, feeding starters contained two kinds of high-starch grains (corn grain, CG vs. barley grain, BG) at two different delivery methods (whole grain vs. steam-flaked grains) on growth performance, nutrients digestibility, and microbial protein synthesis (MPS), the latter estimated from urinary purine derivatives (PD). Forty-eight female Holstein calves (3 d of age and averaging initial body weight of 40.5 ± 1.9 kg) were assigned randomly to the following treatments: whole corn grain (WCG), steam-flaked corn grain (SFC), whole barley grain (WBG), steam-flaked barley grain (SFB) (n = 12, each). Milk feeding schedule was identical among treatments until weaning (d 53), but experiment lasted at d 73. Regardless the grain source, steam-flaking the grains improved starter intake compared to whole grain feeding during pre-weaning period (P = 0.041). Calves fed SFB had the greater average daily gain (ADG) compared to other treatments during pre-weaning period (P = 0.039) and accordingly had the greatest FE (P = 0.048) and withers height (P = 0.049) during the pre-weaning period. No respect to processing method, calves fed BG showed to have greater ruminal butyrate concentration (P = 0.009) and lower ruminal acetate concentration (P = 0.029) compared to calves fed CG. The concentration of total volatile fatty acids (VFA) was greater when calves fed steam flaked grain compared to whole grains (P < 0.05). The greatest allantoin and PD excretions through urine were observed when calves fed SFB compared to other diets (P < 0.05). Whole barley grain fed calves had the greatest urinary urea nitrogen concentration indicating the lowest nitrogen efficiency (P = 0.037). Feeding whole grains reduced blood glucose and beta-hydroxybutyrate (BHB) concentrations, but increased blood urea nitrogen (BUN) concentration compared to steam-flaked grains (P < 0.05). Results indicated that feeding BG to young calves as steam-flaked grain can have positive impact on growth performance. However, WBG reduced intake during early weeks of life and thus negatively impacted growth performance of young calves. Not similar extensive difference was found between calves fed WCG and SFC grains. In conclusion, based on the current study condition, greater fermentation rate of grains can improve growth performance of animals and adequate fiber provision in starter diet is necessary to having more favorable response of young calves to inclusion the high fermentable grain in starter diet.
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