Interaction effect of corn grain physical form and monensin level on performance of Holstein dairy calves

Introduction: Improving growth and reducing mortality in dairy calves and heifers can affect the long-term production and reproductive performance and profitability of dairy cattle enterprise. The most important factors affecting mortality, survival, growth and performance of dairy calves include nutrition, vaccination schedule and housing conditions of dam, management programs at the time of calving, care of the newborn calf and management of rearing from birth to weaning (nutrition, hygiene and housing). Cereal grains are the most important components of the starter feed of growing calves and, compared to other feed ingredients in the starter diet, have a greater effect on the development of the rumen epithelium because their fermentation by rumen microorganisms produce greater amount of volatile fatty acids. The absorption and metabolism of nutrients enhance the growth and development of the rumen epithelium, which affects the amount of starter feed consumed and the appropriate time of weaning. Corn grain is the most important cereal for providing starch in the composition of the starter feed of growing calves. Corn starch is degraded in the rumen at a slower rate than barley and wheat grains. One of the important methods of processing cereal grains is steam flaking. The use of whole grains increases feed particle size and possibly improves rumen health, resulting in improved performance in dairy calves. The positive effects of monensin in ruminant nutrition include increased feed utilization efficiency, increased milk production, reduced methane production, reduced digestive (rumen acidosis, bloating) and metabolic (ketosis) disorders, improved energy balance, enhanced immune system, reduced degradation of proteins and amino acids in the rumen, reduced lipid hydrolysis, and reduced biohydrogenation of unsaturated fatty acids in the rumen. In this experiment, the interaction effect of corn grain physical form (whole vs. steam flaked) and monensin level (0 vs. 40 mg/kg of DM) in starter diet were evaluated on growth performance, skeletal growth indices, ruminal fermentation parameters, urinary purine derivatives, microbial protein synthesis and plasma metabolites in Holstein dairy calves.
Materials and methods: Forty-eight newborn Holstein female calves (3-d-old; average BW = 41.4±1.6 kg) were devided to 4 groups (n=12 calves/group) and randomly assigned to one of four experimental diets: 1) starter diet contained whole corn grain (WCG) without monensin (WCG-NM); 2) starter diet contained WCG with 40 mg monensin/kg of DM (WCG-M); 3) starter diet contained steam flaked corn (SFC) grain without monensin (SFC-NM) and 4) starter diet contained SFB with 40 mg monensin/kg of DM (SFB-M). Calves fed a constant amount of milk (d 1 to 63) and had ad-libitum access to water and starters (d 1 to d 83). Starter feed intake was measured daily on an individual basis throughout the study, by subtracting refusals from the amounts offered. Rumen fluid (approximately 13 ml) was collected (2-3 h after morning feeding) on d 45 (pre-weaning) and d 80 (post-weaning) of the experiment using a stomach tube fitted to a vacuum pump. Urine spot samples (approximately 5 mL) were collected in the mornings (between 09:30 and 11:30 h) and afternoons (between 14:30 and 16:30 h) of four consecutive days (d 79 - 82) during the post-weaning period when calves urinated spontaneously. The blood samples were collected on d 46 (pre-weaning) and 82 (post-weaning) 3 h after morning feeding (at 12:00 h) from the jugular vein into 10 mL tubes, placed on ice, and centrifuged at 3,000 × g for 20 min at 4°C. Serum glucose, total protein and urea nitrogen concentrations were measured using kits from Pars Azmoun Company and spectrophotometric method. Serum beta-hydroxybutyrate concentration was also measured using a commercial kit. Insulin concentration was measured using a corresponding kit and an ELISA reader. The pH of the rumen fluid was measured immediately using a pH meter. Then, the samples were filtered using 4 layers of clean cloth and 6 mL of them mixed with 1.5 mL of 25% metaphosphoric acid and stored at -20°C. After thawing the frozen samples, the total volatile fatty acid concentration and the molar concentrations of propionate and butyrate were measured using a gas chromatography according to the recommended method. Then, the ratio of acetate to propionate in the rumen fluid was calculated based on the molar concentrations of acetate and propionate. To measure ammonia nitrogen, rumen fluid was thawed at 4°C and centrifuged at 15,000 rpm for 20 minutes, and then its concentration was measured using spectrophotometry.
Results and discussion: Starter dry matter intake (DMI) (pre- and post-weaning), milk DMI, total DMI did not influence by experimental diets (P > 0.05). Experimental diets had no effect on average daily gain (ADG) and feed efficiency (FE) during pre- and post-weaning and entire period (P > 0.05). Calves fed SFC-M had higher body weight (BW) at weaning compared to other groups (P < 0.05). Experimental diets had no effect on body length, heart girth and hip width of calves at weaning and at the end of study (P > 0.05). Wither height and hip height at weaning and at the end of study were higher in calves received SFC-M starter diet compared to other groups (P < 0.05). Ruminal pH and ammonia and butyrate concentrations (pre- and post-weaning) did not influence by experimental diets (P > 0.05). The SFC-M starter diet increased ruminal total volatile fatty avids (pre- and post-weaning) and propionate (pre-weaning) concentrations and decresed ruminal acetate concentration (pre-weaning) and acetate to propionate ration (pre-weaning) compared to other diets (P < 0.05). Urinary excretion of creatinine, allantoin and uric acid and microbial protein synthesis did not influence by interaction effect of corn grain physical form and monensin (P > 0.05). Plasma concentrations of glucose, beta-hydroxybutyrate, urea nitrogen and total protein (pre- and post-weaning) did not influence by experimental diets (P > 0.05). The highest plasma insulin concentration was observed in calved fed SFC-M startet dist than other diets (P < 0.05).
Conclusions: Based on the conditions of the present study, it can be concluded that feeding starter diet containing SFC with M improved growth performance of Holstein dairy claves.