Milk production, body weight, body condition score, activity and rumination of organic dairy cattle grazing two different pasture systems incorporating cool- and warm season-forages

Organic dairy cows (n = 90) of Holstein and crossbred genetics were used to evaluate the effect of two pasture production systems (cool season perennial and warm season annual grass species) across two grazing seasons (May to October of 2014 and 2015) on milk production, milk components (fat, protein, MUN, SCS), body weight, body condition score (BCS), and activity and rumination (min/d). Cows were assigned to 1 of 2 replicated pasture systems: 1) System 1 was a diverse-mixture of cool season grasses and legumes [perennial ryegrass (Lolium perenne), white clover (Trifolium repens), red clover (Trifolium pretense), chicory (Cichorium intybus), orchardgrass (Dactylis glomerata), meadow bromegrass (Bromus biebersteinii), alfalfa (Medicago sativa), meadow fescue (Festuca pratensis)] or 2) System 2 was the same combination of perennial grasses and warm season annual grasses (BMR sorghum-sudangrass (Sorghum × drummondii; BMRSS) and teff (Eragrostis tef) grass). There were three replicates of each system; therefore, six total cow groups. Cows rotationally grazed pasture and moved to a new paddock every 2 d, were provided free-choice mineral, and were supplemented with corn (2.27kg/d) to manage MUN levels. Weekly milk production, and bi-weekly milk components, body weight and BCS were recorded for each of the six replicate groups. Activity and rumination time (daily) were monitored electronically using HR-LD Tags (SCR Engineers Ltd., Netanya, Israel) during the grazing season. The PROC MIXED of SAS was used for statistical analysis, and independent variables were fixed effects of system (1 or 2), forage (perennial grass, BMRSS or teff) nested within system, year (2014 or 2015), system nested within year, and week nested within system, with replicate group nested within system as a random effect with repeated measures. System 1 and System 2 cows had similar milk production (14.7 and 14.8 kg/d), fat percentage (3.92% vs. 3.80%), protein percentage (3.21% vs. 3.17%), MUN (12.5 and 11.5 mg/dl), and SCS (4.05 and 4.07), respectively. For yearly effects, milk production was greater in 2015 compared to 2014 (15.6 vs 13.9 kg/d). The BW (485 and 497 kg) and BCS (3.10 and 3.06) were similar for system 1 and 2, respectively. Cows in System 1 had greater daily rumination (530 min/d) compared to cows in System 2 (470 min/d). In summary, warm season annual forages may be incorporated into grazing systems for organic dairy cattle while maintaining milk production and quality.