Influence of processed corn grain in diets of dairy cows on digestion of nutrients and milk composition.
Five primiparous Holstein cows (55 d in milk) that were fitted with ruminal and duodenal cannulas were used in a 4 x 5 incomplete Latin square to determine the effects of blends of steam-flaked and dry-rolled corn on site and extent of nutrient digestion and milk yield and composition. Diets were fed as total mixed rations and consisted of 45% forage and 55% concentrate; each diet contained 27% corn grain. Dietary treatments were composed of blends of dry-rolled and steam-flaked corn in ratios of 100:0, 67:33, 33:67, and 0:100. Intake of dry matter; digestibilities of dry matter, organic matter, acid detergent fiber, cellulose, neutral detergent fiber, fatty acids, and N; and microbial efficiency were unaffected by diet. Ruminal, postruminal, and total tract digestion of starch increased linearly, and starch passage to the duodenum decreased linearly, as the proportion of dry-rolled corn in the diet decreased. Ruminal propionate and valerate increased linearly, and acetate, butyrate, isovalerate, and the acetate to propionate ratio decreased linearly, as proportions of dry-rolled corn in the diet decreased; however, no changes in total volatile fatty acid concentrations in ruminal fluid were observed. Ruminal fluid pH was similar across diets. A decrease in dry-rolled corn decreased ruminal ammonia N and plasma urea N linearly. Milk yield and composition, as well as milk N fractions, were similar across diets. Although changes in fatty acid composition of milk fat were small, linear decreases in percentages of trans-C16:1 and cis-9- and cis-10-C18:1, as well as a linear increase in the percentage of C18:2 occurred as the proportion of dry-rolled corn in the diet decreased. An increased proportion of dry-rolled corn in the diet decreased digestion of starch in the rumen, and patterns of volatile fatty acid concentrations shifted accordingly. However, no effects on lactational parameters were observed.
Crocker
L M
LM
Department of Animal Science, University of California, Davis 95616-8521, USA.
DePeters
E J
EJ
Fadel
J G
JG
Perez-Monti
H
H
Taylor
S J
SJ
Wyckoff
J A
JA
Zinn
R A
RA
D000641:Ammonia / Q000378:metabolism; D000818:Animals; D002417:Cattle / Q000502:physiology*; D002482:Cellulose / Q000008:administration & dosage / Q000378:metabolism; D004032:Diet; D004043:Dietary Fiber / Q000008:administration & dosage / Q000378:metabolism; D004063:Digestion; D002149:Energy Intake; D005227:Fatty Acids / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism; D005260:Female; D005511:Food Handling; D006863:Hydrogen-Ion Concentration; D007774:Lactation / Q000502:physiology; D008892:Milk / Q000737:chemistry*; D009584:Nitrogen / Q000378:metabolism; D012417:Rumen / Q000378:metabolism; D013213:Starch / Q000008:administration & dosage / Q000378:metabolism; D003313:Zea mays
D004043:Dietary Fiber; D005227:Fatty Acids; D000641:Ammonia; D002482:Cellulose; D013213:Starch; D009584:Nitrogen