Steam-flaked corn or finely ground corn with different protein levels? What is best to feed high producing dairy cows? Researchers put several corn processing methods to the test.
High-producing dairy cows require greater amounts of energy and protein in order to meet their nutrient requirements. The high performing diets often contain more corn grains, as this increases the energy density of diets because of its high starch content. However, the whole corn grain is almost completely resistant to microbial digestion in the rumen. This is why different methods of grinding or steam flaking have been used to enhance ruminal carbohydrate availability for improved performance and feed efficiency in dairy cattle. Steam flaking of corn can increase ruminal digestion of starch and boost the microbial protein synthesis, provided the level of physically effective fiber is sufficient to prevent acidosis.
In a new paper, researchers from Iran and Russia delved deeper into the effects of different corn processing methods and corn with different levels of protein on the performance of dairy cows. This was done by looking at the effects of corn processing and dietary protein level and their interaction on intake, digestibility, and feeding behaviour. Eating and ruminating behaviours were monitored visually for a 24-h period on day 19 of each period using sheet scale scoring. In this method, individuals (3 people) are instructed before recording on detection of various behaviours such as eating and ruminating. Then, a specific sign is assigned for each behaviour. For the study, 8 multiparous Holstein dairy cows in mid-lactation (105 ± 9 days in milk and 47.2 ± 3 kg/day milk production at the start of the experiment) were used. Experimental diets contained either finely ground corn (FGC) or steam-flaked corn (SFC) based on either low protein (LP, 14.8%) or high protein (HP, 16.2%) content. The way of processing is explained in the box below. Diets contained 40% corn either finely ground or steam-flaked. The forage to concentrate ratio was 40:60 on a DM basis. Corn silage and chopped alfalfa were the forage components.
The researchers showed that dry matter intake did not differ between HP and LP diets. In contrast, cows fed LP had greater total tract digestibility compared with that for HP-fed cows. Cows fed LP had greater chewing time and lower chewing rate (g of DM/min) compared to those for cows fed HP. Cows receiving SFC had a lower intake of nutrients and tended to have greater ADF and starch digestibility than cows fed FGC. There was an interaction between corn processing and level of protein with respect to the apparent total tract digestibility with cows fed FGC with HP resulted in the lowest digestibility. Steam-flaked corn had lower density and greater moisture and mean particle size than the FGC. In comparison with FGC, SFC did not pass through the 8-mm sieve and caused significant increase in physical effectiveness factor (pef) and physically effective fibre (peNDF) in SFC diets compared to that for FGC diets. Cows fed SFC sorted against longer particles (P = 0.04) to a greater extent than cows fed FGC. Dietary protein level had no detectable effect on sorting index. Chewing time did not differ for cows fed SFC or FGC; however, cows fed SFC had lower chewing and rumination rate (g of DM/min). Chewing time per kg of DM and CP were greater and per kg of peNDF were lower in cows fed SFC rather than cows fed FGC.
Corn processing techniques
Corn grain (40% of diet as DM basis) from one source (Chavdane Co., Isfahan, Iran) was used throughout the experiment. Finely ground corn was processed through a conventional on-farm hammer mill with 3-mm screen (Isfahan Dasht, model 5543 GEN, Isfahan, Iran). Optimal flake density of steam-flaked corn grain appears to be approximately 360 g/L (Theurer et al., 1999), and this study used this density. Corn flaking followed method described by Plascencia and Zinn (1996) at a commercial feed processing complex (Chavdane Co., Isfahan, Iran). Corn grains were screened and steamed (boiler pressure: 80 psi) for 30 min at 99 °C in a stainless steel chamber and subsequently rolled between preheated, corrugated rollers (46 cm × 90 cm). The gap between the two rollers was adjusted to produce the flake density of about 360 g/L, and grains flaked during the adjustment period were discarded. Density (kg per liter) was determined after rolling and before cooling. The steamed corn was dried immediately in a horizontal drier. Flake thickness (mm) and processing index (PI, %) were determined according to the method of Zinn and Barajas (1997) and Yang et al. (2000), respectively. Particle size of each processed corn type was determined by dry sieving with a Ro-Tap sieve shaker equipped with sieves (W. S. Tyler, Inc., Mentor, OH) arranged in the descending mesh size (4.75, 2.36, 1.18, 0.85, 0.60, 0.30, 0.15,0.075 mm, and pan). Duplicate samples of ground and steam-flaked corns (100 g) were placed on the top screen and shaken for 10 min. The amount of grain held on each screen was weighed and used to calculate mean particle size. Geometric mean diameter and standard deviation of steam-flaked and ground corns were determined according to the procedure of the American Society of Agricultural Engineers (2006).
Results indicated that corn processing and dietary protein level may interact to affect nutrient digestibility, but did not affect the feeding and chewing behaviour of lactating cows under our experimental conditions. Results also showed that dietary peNDF content and chewing activity can be effectively manipulated by steam flaking of corn, and cows fed SFC had greater peNDF and energy intake despite lower DMI.
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