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

Abstract Text:

Organic dairy cows (n=90) of Holstein and crossbred genetics were used to evaluate the effect of two pasture production systems (perennial versus perennial/annual systems) over two grazing seasons (May to October of 2014 and 2015) on milk production, milk components (fat, protein, MUN, SCS), rumination (min/d), body condition score (BCS), and body weight (BW). Cows were assigned to one of two pasture systems, 1) system 1 was a diverse-mixture of cool season grasses and legumes (perennial ryegrass, white clover, red clover, chicory, orchardgrass, meadow bromegrass, alfalfa, meadow fescue) or 2) system 2 was the same combination of perennial polycultures and annual warm season grasses (brown midrib sorghum-sudangrass (BMRSS) and teff grass). Cows rotationally grazed pasture and moved to a new paddock every two days, and were supplemented corn (2.27kg/day) and provided free-choice mineral on pasture. Weekly milk production, monthly milk components, and bi-weekly BW 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) for 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 nested within system as a random effect with repeated measures. System 1 and system 2 cows had similar (P>0.05) 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.  There was a significant yearly effect (P<0.05) for milk production, MUN, and SCS for both systems. Milk production was higher (P<0.05) in 2015 compared to 2014 (15.6 vs 13.9kg/d). There was no effect (P>0.05) of forage type on milk production, fat, protein, MUN, or SCS. Cows in system 1 had greater (P < 0.05) daily rumination (530 min/d) compared to cows in system 2 (470 min/d). The BW (485 and 497 kg) and BCS (3.10 and 3.06) were similar (P>0.05) for system 1 and 2, respectively. In summary, warm season annual forages may be incorporated into grazing systems for organic dairy cattle while maintaining milk production and quality.

Keywords: grazing, BMR sorghum-sudangrass, teff