Diet selection by Raramuri Criollo and Angus crossbreds in the Chihuahuan Desert

The Raramuri Criollo (RC) cattle biotype has undergone natural selection for hundreds of generations in northern Mexico. Little information about diet selection exists for this biotype. The objective of this study was to compare diet selection of RC to Angus x Hereford crossbreds (AH) common in the southwestern United States. Ten mature cows of each breed grazed two adjacent pastures (1190 ha, 1165 ha) in a crossover design for 28 days in summer 2015 (July-August), winter 2015-2016 (January-February), summer 2017 (September), and winter 2016-2017 (February). Each breed grazed each pasture 14 days per period and were then switched to the other pasture. In each period, fecal samples were collected on day 14 in each pasture and analyzed using DNA metabarcoding. Four of the six dominant species present in fecal samples differed between breeds in one or more seasons. Black grama (Bouteloua eriopoda), a grass species of conservation interest, was greater in AH than RC fecal samples (P < 0.0001), with the difference driven largely by winter 2015-2016. Concentration of plains bristlegrass (Setaria leucopila) differed between breeds (P < 0.05), with RC consuming less in summer 2015 and more in winter 2015-2016. Alkali sacaton (Sporobolus airoides) and giant dropseed (Sporobolus giganteus) were greater in RC than AH fecal samples, with differences in dropseed occurring mainly in summer 2015 (P < 0.005) and alkali sacaton in summer 2016 (P < 0.05). These results suggest diets selected by RC and AH cows differ, and that differences are affected by plant phenology.