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.
Department of Animal Science, University of California, Davis 95616-8521, USA.
L M
LM
Crocker
E J
EJ
DePeters
J G
JG
Fadel
H
H
Perez-Monti
S J
SJ
Taylor
J A
JA
Wyckoff
R A
RA
Zinn
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