Document Detail

Grazing cows are more efficient than zero-grazed and grass silage-fed cows in milk rumenic acid production.
MedLine Citation:
PMID:  19620671     Owner:  NLM     Status:  MEDLINE    
Six rumen-cannulated Holstein cows in early lactation were assigned to 3 treatments: grazing (G), zero-grazing (ZG), and grass silage (GS) harvested from the same perennial rye grass sward in a 3 x 3 Latin square design with three 21-d periods. The objectives of this study were to investigate the underlying mechanisms for the reported elevation in milk rumenic acid (RA) concentration associated with G compared with ZG and GS, and to identify the important variables contributing to the milk RA response. Grazing animals were offered 20 kg of dry matter/cow per day; indoor animals were offered ad libitum grass or silage. A concentrate at a rate of 3 kg/d was also offered to all cows. Rumen, plasma, and milk samples were collected in the third week of each period. Data were analyzed by the MIXED procedure of SAS. Dry matter intakes were less for GS with no difference between G and ZG. Milk yield was greater for G than for ZG or GS. Milk fat and protein contents were less for GS with no difference between G and ZG. The combined intake (g/d) of linoleic and linolenic (18:3n-3) acids was different across the treatments (G: 433; ZG: 327; and GS: 164). Rumen pH was less for G with no difference between ZG and GS. Concentrations of volatile fatty acids and ammonia nitrogen in rumens were not different across the treatments. Wet rumen fill was less for G with no difference between ZG and GS. Vaccenic acid concentrations were different across the treatments in rumen (G: 12.30%, ZG: 9.31%, and GS: 4.21%); plasma (G: 2.18%, ZG: 1.47%, and GS: 0.66%) and milk (G: 4.73%, ZG: 3.49%, and GS: 0.99%). Milk RA concentrations were greater for G (2.07%) than for ZG (1.38%) and GS (0.54%). Milk desaturase index based on the ratio cis-9-14:1/14:0 was not different across the treatments. Milk RA yield per 100 g of linoleic acid and linolenic acid intake (efficiency) was 2.23, 1.50, and 0.62 g in G, ZG, and GS, respectively, suggesting that G cows were more efficient than ZG and GS cows in milk RA production. Stepwise regression analysis of a group of variables revealed that plasma vaccenic acid accounted for 95% of the variation in milk RA production. Milk desaturase index did not enter into the model. Overall findings suggest that substrate intake influenced milk RA production but it was not the only factor involved. There were differences in efficiency of milk RA production, which appears to depend on the factors regulating ruminal vaccenic acid production and its supply to the mammary tissue.
R Mohammed; C S Stanton; J J Kennelly; J K G Kramer; J F Mee; D R Glimm; M O'Donovan; J J Murphy
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of dairy science     Volume:  92     ISSN:  1525-3198     ISO Abbreviation:  J. Dairy Sci.     Publication Date:  2009 Aug 
Date Detail:
Created Date:  2009-07-21     Completed Date:  2009-10-19     Revised Date:  2009-11-19    
Medline Journal Info:
Nlm Unique ID:  2985126R     Medline TA:  J Dairy Sci     Country:  United States    
Other Details:
Languages:  eng     Pagination:  3874-93     Citation Subset:  IM    
Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada.
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MeSH Terms
Animal Feed / analysis
Cattle / metabolism,  physiology*
Diet / veterinary*
Eating / physiology
Fatty Acid Desaturases / metabolism
Fatty Acids / analysis,  blood,  chemistry
Fatty Acids, Volatile / analysis
Gastrointestinal Contents / chemistry,  enzymology
Hydrogen-Ion Concentration
Linoleic Acids, Conjugated / analysis,  metabolism*
Milk / chemistry*,  secretion
Nitrogen / analysis
Random Allocation
Regression Analysis
Rumen / chemistry,  enzymology,  metabolism
Reg. No./Substance:
0/Fatty Acids; 0/Fatty Acids, Volatile; 0/Linoleic Acids, Conjugated; 1839-11-8/9,11-linoleic acid; 7727-37-9/Nitrogen; EC 1.14.19.-/Fatty Acid Desaturases

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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