title: Nitrogen supplementation of corn silages. 2. Assessing rumen function using fatty acid profiles of bovine milk.
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 x 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 rumen-degradable 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 dietary N and 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), delta9-desaturase activity (monoenoic fatty acids), direct absorption from the blood stream (long-chain 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.
authors.affiliation: Centro de Estudos de Ciência Animal do Instituto de Ciências e Tecnologias Agrárias e Agro-Alimentares, Vairão VC, Portugal. rita.cabrita@mail.icav.up.pt
authors.forename: A R J
authors.initials: AR
authors.lastname: Cabrita
authors.forename: A J M
authors.initials: AJ
authors.lastname: Fonseca
authors.forename: R J
authors.initials: RJ
authors.lastname: Dewhurst
authors.forename: E
authors.initials: E
authors.lastname: Gomes
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D004043:Dietary Fiber / Q000008:administration & dosage; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism; D019587:Dietary Supplements; D005227:Fatty Acids / Q000032:analysis* / Q000096:biosynthesis; D005260:Female; D008321:Mammary Glands, Animal / Q000378:metabolism; D008892:Milk / Q000737:chemistry*; D009584:Nitrogen / Q000008:administration & dosage*; D012417:Rumen / Q000382:microbiology / Q000502:physiology*; D012820:Silage; D013025:Glycine max; D013230:Stearoyl-CoA Desaturase / Q000378:metabolism; D014508:Urea / Q000008:administration & dosage; D003313:Zea mays; D017962:alpha-Linolenic Acid / Q000032:analysis
chemical_list: D004040:Dietary Carbohydrates; D004043:Dietary Fiber; D004044:Dietary Proteins; D005227:Fatty Acids; D017962:alpha-Linolenic Acid; D014508:Urea; D013230:Stearoyl-CoA Desaturase; D009584:Nitrogen