HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Boutton, T. W. Articles by Klein, P. D. Search for Related Content PubMed PubMed Citation Articles by Boutton, T. W. Articles by Klein, P. D.

Carbon Kinetics of Milk Formation in Holstein Cows in Late Lactation^1,2,

Abstract

Carbon transfer to milk in Holstein cows in late lactation was measured by introducing changes in the natural stable carbon isotope composition of the feed. Six Holstein cows in mid-lactation were placed on a diet naturally low in ¹³C (–25.0 vs Pee Dee belemnite [PDB] an international carbon isotope standard), based on alfalfa-barley, and six others were placed on a diet naturally enriched in ¹³C (–11.5 vs PDB), based on corn. After a 7-wk equilibration period on these diets, three cows were switched from alfalfa-barley to corn, and three were switched from corn to alfalfa-barley. The three other cows in each group served as controls. ¹³C/¹²C ratios were measured in daily morning milk samples during the week before and for 6 wk after the changes in diet. After the diets had been switched, milk isotope ratios rapidly approached the isotopic composition of the new diet, indicating rapid transfer of dietary carbon into milk. The data were consistent with a model whereby milk was synthesized from a single precursor pool that responded rapidly to dietary perturbation. The milk precursor pool had a half-life of approximately .9 d and had a mass of approximately 7 kg of carbon, which was renewed daily by the entry of 5 kg of digestible dietary carbon.

¹ We thank Mary Nelson and Patti Marcus for technical assistance, the Animal Operations Support Staff for care and supervision of the animals, Rosalind Lewis and Mercedes E. Lewis for assistance with manuscript preparation and E. Roseland Klein for editorial assistance. D. L. Hachey and P. J. Reeds provided helpful criticism of the manuscript and C. S. Irving assisted with model development.

² This work is a publication of the USDA/ARS Children's Nutr. Res. Center, Dept. of Pediatrics, Baylor College of Medicine and Texas Children's Hospital, Houston. This project has been funded in part with federal funds from the USDA/ARS, under Cooperative Agreement number 58-7MNI-6-100. The contents of this publication do not necessarily reflect the views or policies of the USDA, nor does mention of trade names, commercial products or organizations imply endorsement by the U.S. Government.

³ USDA/ARS Children's Nutr. Res. Center, Dept. of Pediatrics, Baylor College of Medicine and Texas Children's Hospital, Houston 77030.

⁴ Present Address: Dept. of Range Sci., Texas A&M Univ., College Station 77843-2126.

⁵ USDA/ARS Ruminant Nutr. Lab., Anim. Sci. Inst., Beltsville, MD 20705.

⁶ Present Address: Dept. of Anim. Sci., Pennsylvania State Univ., University Park 16802.