Responses in vegetative selection and diet quality for dissimilar sheep breeds under targeted grazing of yellow sweetclover

Abstract

Objective: Sheep are advantageous for targeting invasive plants; however, nutritional consequences of such projects are poorly understood. Genetically dissimilar sheep breeds, or pronghorn (Antilocapra americana) browsing, were assessed to determine selectivity of sweetclover (Melilotus officinalis) and sheep dietary quality. Materials and Methods: In 2015 and 2016, 24 ewes and lambs and 21 ewes and lambs (per breed group annually; Ovis aries; Rambouillet or Hampshire breeds) were grazed in four 3.2-ha paddocks for 16.5-d (±8 d) grazing bouts. Vegetation and sheep diet quality (using near-infrared reflectance spectroscopy of fecal material) were analyzed relative to sheep breed and timing, or pronghorn only. Results and Discussion: Vegetation responses were never different by sheep breed (P ≤ 0.05); meat and wool breeds similarly reduced sweetclover abundance, proportion of aerial stems and flowering stems, and height more than pronghorn only (all P < 0.05). For sheep dietary CP, fecal N, and fecal P, the interactive effect of breed × days since rotation was significant, except for days since rotation singularly for digestible OM (all P < 0.05). Hampshire dietary CP earlier in rotations was higher (ranging from 2.4 to 3.4% higher). Available forage CP and digestibility did not explain dietary differences. Fecal N was significant and correlated with sheep dietary CP for Rambouillets but not Hampshires. Implications and Applications: Both meat and wool breeds may be effective for targeted grazing, but different breeds may have different diet quality due to differential grazing behaviors and N synthesis and retention.