Short communication: Relationship between the efficiency of utilization of feed nitrogen and N-15 enrichment in casein from lactating dairy cows

• Type: Article in International Scientific Journal
• Date: 2014

Authors

A. Cabrita (Author) FCUP; Antonio J M Fonseca (Author) ICBAS; Dewhurstt, RJ (Author) Other

Journal

Title: Journal of Dairy Science

Vol. 97

Pages: 7225-7229

ISSN: 0022-0302

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 11 Citations

Scopus - 10 Citations

Scientific classification

CORDIS: Natural sciences > Agrarian Sciences > Zootechnics

FOS: Agrarian Sciences > Animal and Dairy science

Other information

Authenticus ID: P-009-WWT

DOI: 10.3168/jds.2014-8297

Abstract (EN): The objective of the present study was to evaluate the relationship between the efficiency of conversion of feed N into milk N [N-use efficiency (NUE)] and N-15 enrichment of milk casein from lactating cows fed corn silage-based diets. Samples of feeds and milk were obtained from 3 experiments with lactating dairy cows. All diets were based on corn silage and were designed to evaluate the effects of (1) diets with different ratios of effective rumen-degradable protein to fermentable metabolizable energy (experiment 1), (2) different proportions of quickly and slowly rumen-degradable protein (experiment 2), and (3) synchronizing the availability of fermentable metabolizable energy and effective rumen-degradable protein in the rumen (experiment 3). Although no significant effect of diet on casein delta N-15 values was detected, casein was more enriched than the diet in each of the experiments. Nitrogen-use efficiency was negatively related to adjusted Delta N-15 (casein ON diet delta N-15) for experiments 1 and 2 individually and when combining data from all 3 experiments. The relatively low values for Delta N-15 suggest that these productive animals were using dietary N efficiently, with a high proportion of N going to milk protein and less to urea. The weak, although significant, relationship between NUE and adjusted Delta N-15, is consistent with relatively little variation in hepatic deamination and transamination, with variation in rumen efficiency having the predominant effect on NUE. The present study confirms the lower N-15 enrichment in protein when NUE is high and the potential to use N-isotope fractionation as a marker of NUE.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 5