287 Comparison of diet selection by Raramuri Criollo and Angus crossbreeds in the Chihuahuan Desert

Abstract

Flowers contained the highest CT concentration followed by leaf and stem tissues. As the plant matured, CT concentration decreased in stem tissue but remained relatively constant in leaf and flower tissues. Regardless of plant tissue or maturity, PPC CT consisted mostly of epicatechin (EC; 70-80%) and epigallocatechin (EGC; 20-30%), with minor amounts of cat-echin and gallocatechin. Leaf CT consisted of more EC (P < 0.01) but less EGC units (P < 0.01) than CT from stem and flowers at both EF and LF stages. The procyanidin:prodel-phinidin (PC:PD) ratio was greater (P < 0.05) for leaf CT than for stem and flower CT. The mean degree of polymerization (mDP) was highest for stem CT and lowest for leaf CT. The PC:PD ratio of stem CT decreased and the mDP increased as the plant matured. Leaf CT had higher BSA-precipitating capacity than stem and flower CT (P < 0.001), with EF leaf CT exhibiting the highest capacity (P < 0.001). Leaf and flower CT had a greater ability to precipitate RuBisCO protein than stem CT (P < 0.05). These results demonstrated that PPC CT were predominantly of the procyanidin type and that the concentration and chemical structure varied with different plant tissues and growth periods. Condensed tannins in PPC at the early flower stage exhibited the greatest protein-precipitation capacity. Raramuri Criollo (RC) is a cattle biotype that has undergone natural selection for the past 500 yr in northern Mexico. No information exists on diet selection for this biotype. The objective of this study was to compare diet selection of RC and Angus × Hereford crossbreeds (AH) typically found in the arid southwestern United States. We examined dietary composition of RC and AH cattle using DNA metabarcoding of fecal samples. Ten mature cows of each breed grazed 2 adjacent pastures (1,190 and 1,165 ha) for 28 d in July through August 2015 and January through February 2016 in a crossover design. Each breed grazed each pasture 14 d per period, and cows were then switched to the reciprocal pasture. Fecal samples were collected on d 14 in each pasture in both seasons. Dominant species present in fecal samples included black grama (Boute-loua eriopoda), tobosa (Pleuraphis mutica), plains bristlegrass (Setaria leucopila), hog potato (Hoffmannseggia glauca), and four-wing saltbush (Atriplex canescens). Black grama was present in higher concentration in AH than RC fecal samples (P < 0.0001) and was greater during winter dormancy than during the summer growing season (P < 0.0001). Hog potato was not affected by breed (P = 0.137) but was greater in fecal samples during the growing season than during winter dormancy (P < 0.001). Four-wing saltbush was marginally greater in AH than in RC fecal samples (P = 0.053) and greater during dormancy than in the growing season (P < 0.0001). These results suggest that RC cattle select diets that differ from AH cows and that differences are affected by plant growth phenology.