PSVIII-17 - A comparison of a monoculture barley crop to a barley-based complex mixture on forage yield, quality, dry matter intake, enteric methane emissions and growth performance of pregnant yearling heifers.

Abstract: The objective of the study was to compare forage yield and composition, dry matter intake (DMI), growth, and enteric methane emissions for heifers grazing a barley monoculture (MON) or a barley-based complex forage blend (COM). The 2-year study was conducted near Saint Brieux (SK, Canada) and evaluated 2 treatments with 4 paddocks/treatment/year. Treatments included MON (CDC Rosser) seeded at 123 kg/ha or a COM which contained barley seeded at 61.5 kg/ha and a mixture of species seeded at 12.3 kg/ha. The COM mixture included 54% millet (Proso and Japanese), 14% Italian ryegrass, 13.5% clover (Berseem, Persian, Crimson), 4.5% hairy vetch, 4.5% black oil sunflower, 3% forage collards, 3% turnips, 2% phacelia, and 1% chicory. Forages were seeded in alternating strips (0.4 ha) to create individual paddocks. Pregnant yearling heifers (n= 80/year) were weighed on 2 consecutive days at the start and end of the study, randomly allocated based on BW to each treatment, and assigned to a paddock (10 heifers/paddock). Heifers were provided fresh forage daily. Grazing was initiated at the late milk stage for MON and continued until the hard dough stage of maturity. Paddocks were then swathed, and grazing continued resulting in 84 and 77 d in yr 1 and 2, respectively. Forage samples and residual forage were collected weekly to estimate forage yield, composition, and intake. Rib and rump fat measurements were taken at the start and end of the study. Methane emissions were measured using the sulfur hexafluoride (SF6) tracer gas technique over a 4-d period while grazing both standing and swathed crops in each year. Forage yield (DM basis) did not differ among treatments (P=0.59) during the growing season averaging 5.6 t/ha and did not differ (P=0.57) once swathed averaging 5.7 t/ha. Treatment and date of sampling affected (P< 0.01) the proportion of barley, with barley representing 95% of the DM for MON and 81% for COM. Chemical composition did not differ among treatments for OM, CP, NDF, lignin, and starch; however, DM tended (P=0.08) to be less for COM, and ADF and WSC were greater (P=0.01 and P=0.02) for COM than MON. DMI was not affected while grazing standing (P=0.98) or swathed (P=0.50) forages with mean values of 8.8 and 10.2 kg/d, respectively. Rib and rump fat did not differ, but ADG was 0.1 kg/d greater (P< 0.01) for COM than MON. As a result, gain:feed was 0.08 kg/kg greater for heifers grazing COM (P< 0.01) than MON. Enteric methane emissions did not differ for treatment when heifers were grazing standing (P=0.77) or swathed (P≥0.99) forages. Growing an annual complex forage mixture rather than a monoculture crop may improve growth of yearling heifers, but does not affect forage yield, DMI, or enteric methane production.