Stable isotopes of C and N differ in their ability to reconstruct diets of cattle fed C3–C4 forage diets

Abstract

Stable isotopes are useful for estimating livestock diet selection. The objective was to compare δ13C and δ15N to estimate diet proportion of C3–C4 forages when steers (Bos spp.) were fed quantities of rhizoma peanut (Arachisglabrata; RP; C3) and bahiagrass (Paspalumnotatum; C4).Treatments were proportions of RP with bahiagrass hay: 100% bahiagrass (0%RP); 25% RP + 75% bahiagrass (25%RP); 50% RP + 50% bahiagrass (50%RP); 75% RP + 25% bahiagrass (75%RP); and 100% RP (100% RP). Feces, plasma, red blood cell (RBC), and hair were collected at 8-days intervals, for 32 days. Two-pool mixing model was utilized to back-calculate the proportion of RP based on the sample and forage δ13C or δ15N. Feces showed changes using δ13C by 8 days, and adj. R2 between predicted and observed RP proportion was 0.81 by 8 days. Plasma, hair, and RBC required beyond 32-days to reach equilibrium, therefore were not useful predictors of diet composition during the study. Diets were best represented using fecal δ13C at both 8-days and 32-days. By 32-days, fecal δ15N showed promise (R2 = 0.71) for predicting diet composition in C3–C4 diets. Further studies are warranted to further corroborate fecal δ15N as a predictor of diet composition in cattle.

Tracking Livestock Diets Using Stable Isotopes in Complex Mixed Farming Systems

“…Overall, our results are consistent with previous studies that have found a significant relationship between the isotopic information in hair and feces (Crumsey et al 2019), reflecting isotopic patterns of diet sources. Moreover, our results corroborate with a recent study conducted by Jaramillo et al (2022) on using δ 13 C and δ 15 N in feces, hair, blood, and plasma samples to predict diet composition of cattle fed mixed C 3 -C 4 forages. They concluded that fecal δ 13 C was the best predictor to accurately reconstruct cattle diets.…”

“…As mentioned by Gannes et al (1997) , the 15 N/ 14 N ratio in animal tissue increases as animals are nutritionally stressed. Previous studies stated that 15 N enrichment is a response to a negative energy balance (caused by nutrient deficit) that leads to body mass loss from recycling of muscle tissue causing enrichment of 15 N ( Rysava et al 2016 ;Crumsey et al 2019 ;Funck et al 2020 ;Jaramillo et al 2022 ). Body mass loss due to forage deficit is an issue during potential feed gaps, especially in the arid warm zone on livestock-only farms ( Lamega et al 2021 ).…”

“…The analysis of stable isotopes has become an essential tool for determining an animal's diet origin or composition in ecological studies. The stable isotopes of carbon and nitrogen ( δ 13 C and δ 15 N, respectively), especially, have been extensively used to identify or reconstruct dietary choices of grazing animals in relation to changes in the ecosystems ( Schwertl et al 2005 ;Sponheimer et al 2006 ;Jaramillo et al 2022 ;Silva et al 2022 ). In ecological and agronomic studies, continuously growing tissues such as hair are commonly analyzed since they contain time-series information, incorporated into the tissues through diet consumption ( Schwertl et al 2003 ).…”

“…In ecological and agronomic studies, continuously growing tissues such as hair are commonly analyzed since they contain time-series information, incorporated into the tissues through diet consumption ( Schwertl et al 2003 ). In effect, the isotopic composition of hair tissues informs us about an animal's diet selection, remote movement, nutritional status, and locations ( Lazzerini et al 2019 ;Funck et al 2020 ;Oelze et al 2020 ;Jaramillo et al 2022 ). Though such growing tissues are key in quantifying dietary information over much longer periods of time, fecal samples can also provide a resource to enable documentation of short turnover periods ( Codron et al 2005 ).…”

“…For instance, aridity (or water stress) (Crumsey et al 2019), plant available nutrients (Ma et al 2012), plant nitrogen uptake mechanisms (Wrage et al 2011), the protein content of the consumed diet (Sponheimer et al 2003a,b), or animal's metabolic status (Funck et al 2020) may influence isotopic patterns. This technique has been successfully applied in investigating the response of δ 13 C and δ 15 N to controlled differences in the dietary proportion of C 3 and C 4 plant-based diets (Jaramillo et al 2022; Silva et al 2022). From those studies, it is known that the stable isotope of carbon is particularly useful in estimating the diet proportion of animals or livestock fed C 3 and or C 4 forages.…”