The Effects of Harvest Maturity of Eragrostis tef ‘Moxie’ Hay and Supplemental Energy Source on Forage Utilization in Beef Heifers

Simple Summary Due to several factors including persistent drought conditions and the increased occurrence and severity of fire on rangeland, there is an increased need for the use of alternative forages to meet the nutrient requirements of ruminants raised in extensive grazing systems. However, information on the nutritive value of alternative forages like Eragrostis teff as influenced by harvest maturity, and the best supplementation strategies that complement and improve utilization of those forages, is still lacking. Therefore, the present study evaluated the effects of harvest maturity of teff hay (early- compared to late-heading stage of maturity) and supplemental energy sources (corn grain compared to beet pulp at 0.5% of body weight) on nutrient intake and digestibility and nitrogen utilization in beef heifers. Delaying the harvest of teff hay resulted in a decrease in nutrient supply, which was not attenuated by feeding either supplemental corn grain or beet pulp. Nitrogen retention was also negative regardless of harvest maturity, and this potentially indicates that there might be a need to provide both energy and protein supplements to improve nutrient supply and, thus, growth performance when feeding teff hay to beef cattle. Abstract The phenological stage of maturity of grasses and supplementation program can impact forage utilization in grazing beef cattle. However, the potential interaction between harvest maturity of Eragrostis tef (teff) hay and energy supplement source was yet to be fully evaluated. Therefore, our objective was to determine the effects of harvest maturity of teff hay and supplemental energy sources on nutrient intake, apparent total-tract nutrient digestion, nitrogen (N) utilization, and ruminal fermentation characteristics in beef heifers. A split-plot design with teff hay harvest maturity as the whole plot and supplemental energy source as the subplot was administered in a three-period (21 d), three × three Latin square design. Six crossbred beef heifers (804 ± 53.6 kg of body weight; BW) were allocated to two harvest maturities (early- (EH]) or late-heading (LH)) and to two supplemental energy sources (no supplement (CON), or rolled corn grain or beet pulp pellet fed at 0.5% of BW). Data were analyzed using SAS. There was no harvest maturity × energy supplement interaction. Although harvest maturity had no impact on total dry matter intake (DMI), crude protein (CP) intake was greater (p < 0.01) for EH than LH heifers. Total intakes of dry (DM) and organic matter (OM) were also greater (p < 0.01) for supplemented than CON heifers, whereas acid detergent fiber (ADF) intake was greater for beet pulp heifers compared to heifers fed the CON diet and supplemental corn grain. Harvest maturity had no impact on ruminal pH. However, mean ruminal pH was lower (p = 0.04), duration pH < 6.2, and molar proportions of butyrate and branched-chain fatty acids were greater (p ≤ 0.049) for heifers fed corn grain compared to CON and beet pulp diets. Heifers fed EH hay had greater (p ≤ 0.02) apparent total-tract DM, OM, CP, NDF, and ADF digestibility than heifers fed LH hay. Although there was no supplemental energy effect on microbial nitrogen (N) flow, it was greater (p < 0.01) for EH than LH heifers. Apparent N retention, which did not differ, was negative across all diets. In summary, delaying the harvest of teff hay from the EH to LH stage of maturity compromised nutrient supply, which was not attenuated by feeding supplemental corn grain and beet pulp at 0.5% of diet DM. Because N retention was negative across harvest maturity, there might be a need to provide both energy and protein supplements to improve growth performance when feeding teff hay to beef cattle.