Splanchnic and mammary nitrogen metabolism by dairy cows fed steam-rolled or steam-flaked corn.
Objectives were to determine net release or uptake of a-amino N, ammonia N, and urea N across portal-drained viscera, liver, splanchnic, and mammary tissues of lactating Holstein cows (n = 6; 109 +/- 9 d in milk) fed alfalfa hay-based total mixed rations (TMR) containing 40% steam-rolled or steam-flaked corn grain. The TMR were offered at 12-h intervals in a crossover design. Blood samples were obtained from indwelling catheters in portal, hepatic, and mammary veins and mesenteric or costo abdominal arteries, every 2 h for each cow and diet. Steam-flaked compared with steam-rolled corn greatly increased in vitro starch hydrolysis (56 vs. 34%). Daily intake of dry matter (18.4 +/- 0.4 kg/d), starch, N, and net energy for lactation by cows were not altered by processing corn; neither were daily yield of milk (29.1 +/- 0.7 kg/d), fat-corrected milk, nor fat-corrected milk per dry matter intake. Steam-flaking tended to increase percent milk protein (2.97 vs. 2.82%; P = 0.07), but not yield, and decrease percent lactose (4.83 vs. 4.94) but not yield. Portal and hepatic blood flows were not affected by diet, nor were net absorption of alpha-amino N and ammonia N. Steam-flaking compared with steam-rolling increased urea N cycling to portal-drained viscera (212 vs. 87 g/d) by 140%, estimated mammary uptake and extraction ratio of alpha-amino N. Flaking versus rolling of corn improved N utilization in dairy cows by increasing urea cycling to the gut and uptake of a-amino N by the mammary gland. Higher mammary uptake of alpha-amino N (78 vs. 50 g/d) by dairy cows fed steam-flaked corn tended to increase milk protein content and may explain the previously observed effects of cows fed steam-flaked versus steam-rolled corn.
Delgado-Elorduy
A
A
Department of Animal Sciences, University of Arizona, Tucson 85721, USA.
Theurer
C B
CB
Huber
J T
JT
Alio
A
A
Lozano
O
O
Sadik
M
M
Cuneot
P
P
De Young
H D
HD
Simas
I J
IJ
Santos
J E P
JE
Nussio
L
L
Nussio
C
C
Webb
K E
KE
Tagari
H
H
D000821:Animal Feed / Q000145:classification*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001806:Blood Urea Nitrogen; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D018592:Cross-Over Studies; D004032:Diet; D005260:Female; D005511:Food Handling / Q000379:methods; D007408:Intestinal Absorption; D007774:Lactation / Q000502:physiology*; D007785:Lactose / Q000032:analysis; D008099:Liver / Q000098:blood supply / Q000378:metabolism; D008892:Milk / Q000737:chemistry; D008894:Milk Proteins / Q000032:analysis; D009584:Nitrogen / Q000378:metabolism*; D011168:Portal System; D011897:Random Allocation; D013152:Splanchnic Circulation; D003313:Zea mays
D008894:Milk Proteins; D007785:Lactose; D009584:Nitrogen