Nitrogen supplementation of corn silages. 2. Assessing rumen function using fatty acid profiles of bovine milk.

A. R. J. Cabrita, Richard J. Dewhurst, A. J. M. Fonseca, E. Gomes

Research output: Contribution to journalArticlepeer-review

Abstract

The effects of N supplementation strategies on milk fatty acid profiles of dairy cows and their use as a noninvasive technique to diagnose rumen function, and to guide protein feeding decisions on-farm were evaluated in three experiments. Each experiment was designed according to three 3 × 3 Latin squares with 9 Holstein cows receiving total mixed rations based on corn silage. Experiment 1 was designed to study effects of diets with different ratios of effective rumendegradable protein (ERDP; g) to fermentable metabolizable energy (FME; j) providing, respectively, a large deficiency, a slight deficiency, and a slight excess in relation to the target level of 11 g of ERDP/MJ FME for lactating cows. Experiment 2 evaluated effects of different proportions of quickly and slowly rumen-degradable protein achieved by replacing soybean meal with urea in the concentrates (0, 0.5, and 1% urea for U0, U5, and U10, respectively). Experiment 3 investigated effects of synchronizing the availability of FME and ERDP in rumen by offering the protein-rich concentrate once or twice per day before the meal (corn silage, ryegrass hay, and energy-rich concentrate), or included in the total mixed ration. Milk fatty acid profiles were significantly affected by dietaryNand carbohydrate supply. Principal component factor analysis provided a reasonable description of the data, clearly discriminating between fatty acids that are synthesized by different metabolic pathways. Several sources/pathways were distinguished: de novo synthesis in the mammary gland (short- and medium-chain fatty acids), 9-desaturase activity (monoenoic fatty acids), direct absorption from the blood stream (longchain fatty acids), and de novo synthesis by the rumen microbial populations (odd-chain fatty acids). Discriminant canonical analysis showed that milk odd-chain fatty acids had a higher ability to discriminate between diets than even-chain fatty acids. The anteiso C15:0 increased in line with increasing sugar supply, and C17:0 appears to be a marker of protein deficiency. Additionally, iso C17:0 and anteiso C17:0 were associated with the NDF and CP contents of diets. The results suggests that milk odd-chain fatty acids have the potential to be used as a noninvasive technique to assess rumen function in terms of microbial populations, substrates and interactions.
Original languageEnglish
Pages (from-to)4020-4032
Number of pages13
JournalJournal of Dairy Science
Volume86
Issue number12
DOIs
Publication statusPublished - 2003

Keywords

  • corn silage
  • dairy cows
  • nitrogen supplementation
  • rumen synchrony

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