¹³C discrimination between diet, faeces, milk and milk components

Abstract

Stable isotope analysis is a fundamental tool in food origin and authenticity testing. Its use in livestock production requires knowledge of isotope discrimination between product and diet. Here, we report (13)C discrimination ((13)Δ) for milk, milk components (fat, casein and lactose) and faeces in eight lactating dairy cows, which grazed pasture or were fed fresh pasture herbage in the stall. Cows were supplemented with grain maize at 1.72 kg d(-1) (dry matter). Feed components were collected daily, and faeces, milk fat, casein, lactose and whole milk 4 times per week during an 8-week-long sampling period. Carbon isotope composition (δ(13)C) of each sample was analysed. δ(13)C was lowest in milk fat (-29.8‰) and highest in casein (-26.4‰). Compared to the diet, whole milk was depleted in (13)C ((13)Δ = 0.4‰) due to a strong (13)C-depletion of fat ((13)Δ = 2.2‰), which was not fully compensated by the (13)C-enrichment of casein ((13)Δ = -1.1‰) and lactose ((13)Δ = -0.7‰). Faeces were also depleted in (13)C ((13)Δ =1.7‰). Influences of feeding environment (stall vs. pasture) and herbage quality were minor (<0.4‰). A review of literature data shows large variation between studies. We consider that the present results are superior, as they are based on a much larger data set regarding the number of cows and milkings (total n = 256) with greater detail in analyses of diet and milk products. Also, the study covered both stall- and pasture-feeding scenarios in realistic settings with long periods of equilibration. This is the first comprehensive analysis of (13)C discrimination between diet and all main milk components (as well as faeces). Thus, the results will improve the use of stable isotope analyses in regard to authenticity testing and proof of origin.

Traceability of ‘Mozzarella di Bufala Campana’ production chain by means of carbon, nitrogen and oxygen stable isotope ratios

“…Different studies have analyzed the link between feeding and produced milk isotopic signals. [22][23][24][25]36 In the case of this work, analyzing the isotopic carbon and nitrogen ratio values calculated from the mixing model (model 1) (that reflects the feed isotopic signal and the proportion given to the buffaloes), a lower value for 15 N with respect to that measured in milk was found. This result was reported also in Cantalapiedra-Hijar et al, 25 where ruminant animal and milk proteins were found enriched with regards to their diet, due to the metabolic pathways of these animals.…”

“…different food digestibility, possible animal preference of one constituent in respect to another, delay between food ingestion and milk production, energy negative balances that may occur when energy spent for milk production exceed that acquired by food. 23 Focusing on the 13 C trend of milk and mozzarella over time, for the farm Ce1 ( Fig. 1(a)) it was possible to note an increasing trend from September 2016 to February 2017, even if the values were inside the standard deviation of the average.…”

“…In order to examine the isotopic ratios in the protein components of whole milk or cheese samples, whose signal could be different from other components (i.e. fats), 22,23,29 the casein (the main milk protein) was extracted from mozzarella and milk. Therefore, the 13 wileyonlinelibrary.com/jsfa to identify possible variations from the whole samples, which could invalidate the investigations.…”

“…10 The relationship between the isotopic carbon ratios of animal diet (composed by C3 and C4 photosynthetic pathway plants) and of milk produced by cows was investigated in Camin et al, 22 who found a correlation between 13 C of casein and the percentage of maize addicted in the diet. Schneider et al 23 investigated the carbon-13 ( 13 C) discrimination between diet and milk, while Cabrita et al 24 and Cantalapiedra-Hijar et al 25 studied nitrogen fractionation processes in ruminants, which determine the nitrogen signal of milk, starting from the nitrogen signal of eaten plants and so, in turn, influenced by agriculture practice, fertilizer used, climate and nearness to the sea. 10 In Bontempo et al, 26 27 on the bases of stable isotopes signal, linked to the cattle diet and local climate conditions.…”

Carbon and nitrogen stable isotopes in U.S. milk: Insight into production process

“…Of the naturally occuring components, the difference in carbon stable isotope composition between the lipid (triacylglycerols/sterols) and lipid‐free (protein/carbohydrate) components (Δ 13 C lipid‐lipid free ) is particularly conspicuous, with lipids possessing lower δ 13 C values due to enzymatic fractionations during formation . Δ 13 C lipid‐lipid free values of −3.3 and −3.5‰ were determined for stall‐ and pasture‐fed cows, respectively, on long‐term, isotopically consistent diets . The similar offset between the Δ 13 C lipid‐lipid free value (−3.76‰) calculated in our study and the values from controlled feeding studies with homogeneous diets suggests that dairy cattle on conventional U.S. dairy farms are close to isotopic equilibrium, i.e., their diets are homogeneous over a long period of time, and that the effect of varying lipid concentrations on the isotopic composition of milk may be predictable.…”