Splanchnic and mammary nitrogen metabolism by dairy cows fed dry-rolled or steam-flaked sorghum grain.
Objectives were to determine net release or uptake of alpha-amino N, ammonia N, and urea N across portal-drained viscera, liver, splanchnic, and mammary tissues of lactating Holstein cows (n = 8, 86 +/- 8 d in milk) fed alfalfa hay-based total mixed rations containing 40% dry-rolled or steam-flaked sorghum grain. The total mixed rations were offered at 12-h intervals in a crossover design. Blood samples were obtained from indwelling catheters in the portal, hepatic, and mammary veins and mesenteric or costoabdominal arteries, every 2 h for each cow and diet. Steam-flaking increased in vitro rate of starch hydrolysis compared with dry-rolled sorghum (66 vs. 25%). Diet did not alter dry matter intake (18.2 +/- 0.3 kg). Daily milk yield (27.6 +/- 0.8 kg), efficiency of production, and most milk components did not differ between diets, but fat yield was reduced (0.86 vs. 0.91 kg/d) by steam-flaked sorghum, and lactose concentration was increased (4.99 vs. 4.82%). Blood flows in portal and hepatic veins did not differ between diets. Steam-flaking tended to increase urea N cycling to the gut (162 vs. 95 g/d) compared with dry-rolling of sorghum, whereas net absorption of ammonia N and alpha-amino N across portal-drained viscera were decreased. Net mammary uptake of a-amino N increased more than 20% (83 vs. 67 g/d), resulting in a higher mammary extraction ratio (15 vs. 11%) for steam-flaked versus dry-rolled sorghum. Flaking of sorghum improved the efficiency of postabsorptive N metabolism by increasing urea N cycled to the gut and alpha-amino N uptake by the mammary gland.
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
Cuneo
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 / Q000662:veterinary; D004435:Eating / Q000502:physiology; D002523:Edible Grain; D005260:Female; D005511:Food Handling / Q000379:methods; D007408:Intestinal Absorption; D007774:Lactation / Q000378:metabolism / Q000502:physiology*; D007785:Lactose / Q000032:analysis; D008055:Lipids / Q000032:analysis; D008099:Liver / Q000098:blood supply / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000098:blood supply / Q000378:metabolism; D008892:Milk / Q000737:chemistry / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D011168:Portal System / Q000502:physiology; D011897:Random Allocation; D013152:Splanchnic Circulation
D008055:Lipids; D007785:Lactose; D009584:Nitrogen