Interactions between barley grain processing and source of supplemental dietary fat on nitrogen metabolism and urea-nitrogen recycling in dairy cows.
The objective of this study was to determine the effects of methods of barley grain processing and source of supplemental fat on urea-N transfer to the gastrointestinal tract (GIT) and the utilization of this recycled urea-N in lactating dairy cows. Four ruminally cannulated Holstein cows (656.3 +/- 27.7 kg of BW; 79.8 +/- 12.3 d in milk) were used in a 4 x 4 Latin square design with 28-d periods and a 2 x 2 factorial arrangement of dietary treatments. Experimental diets contained dry-rolled barley or pelleted barley in combination with whole canola or whole flaxseed as supplemental fat sources. Nitrogen balance was measured from d 15 to 19, with concurrent measurements of urea-N kinetics using continuous intrajugular infusions of [15N 15N]-urea. Dry matter intake and N intake were higher in cows fed dry-rolled barley compared with those fed pelleted barley. Nitrogen retention was not affected by diet, but fecal N excretion was higher in cows fed dry-rolled barley than in those fed pelleted barley. Actual and energy-corrected milk yield were not affected by diet. Milk fat content and milk fat yield were higher in cows fed dry-rolled barley compared with those fed pelleted barley. Source of supplemental fat did not affect urea-N kinetics. Urea-N production was higher (442.2 vs. 334.3 g of N/d), and urea-N entering the GIT tended to be higher (272.9 vs. 202.0 g of N/d), in cows fed dry-rolled barley compared with those fed pelleted barley. The amount of urea-N entry into the GIT that was returned to the ornithine cycle was higher (204.1 vs. 159.5 g of N/d) in cows fed dry-rolled barley than in pelleted barley-fed cows. The amount of urea-N recycled to the GIT and used for anabolic purposes, and the amounts lost in the urine or feces were not affected by dietary treatment. Microbial nonammonia N supply, estimated using total urinary excretion of purine derivatives, was not affected by diet. These results show that even though barley grain processing altered urea-N entry into the GIT, the utilization of this recycled urea-N for microbial production was unaffected as the additional urea-N, which entered the GIT was returned to ureagenesis.
Gozho
G N
GN
Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Canada S7N 5A8.
Hobin
M R
MR
Mutsvangwa
T
T
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D029741:Brassica rapa / Q000378:metabolism; D002417:Cattle / Q000097:blood / Q000378:metabolism* / Q000652:urine; D004042:Dietary Fats, Unsaturated / Q000008:administration & dosage / Q000378:metabolism*; D005243:Feces / Q000737:chemistry; D005260:Female; D019597:Flax / Q000378:metabolism; D001467:Hordeum / Q000378:metabolism*; D007774:Lactation; D008892:Milk / Q000378:metabolism; D011687:Purines / Q000652:urine; D012417:Rumen / Q000737:chemistry; D014508:Urea / Q000097:blood / Q000378:metabolism*
D004042:Dietary Fats, Unsaturated; D011687:Purines; D014508:Urea