PSIV-2 - Dry Matter Intake in Beef Cows Is Influenced by Weather Variables

Abstract: Models that can predict dry matter intake (DMI) of cows will help in efficient allocation and management of feed resources. A study was undertaken to understand the relationship between weather variables and DMI of beef cows in the Northern Great Plains of North America. Data from 155 beef cows with 2,161 observations (cow - weeks) was utilized. The variables utilized for this study were BW (455 to 875 kg), DMI (9.03 to 27.69 kg/d), NEm intake (9.16 to 46.12 Mcal/d), ambient temperature (-18.9 to 23.9°C), range of temperature (4.54 to 13.82 °C), wind speed (2.29 to 5.39 m/s), solar radiation (30.97 to 292.61 W/m²) dew point (-21.4 to 19.2 °C), and two-week lag (average of previous two weeks values) and monthly lag (average of previous four weeks values) of each weather variable. Residuals of DMI fitting week of the year (fixed), and treatment (random), were used to generate scatter plots to identify if linear relationships existed. BW and weather variables had a linear relationship with DMI, while NEm intake had both linear and quadratic relationships with DMI. For the model, MIXED linear regression of SAS was used using stepwise regression. Model fits were determined using P-values, AIC, and BIC values. Absolute ambient temperature and range of temperature were important (P < 0.05) weather predictors of DMI. Wind speed interacted (P < 0.05) with ambient temperature and range of temperature, and this accounted for additional variation in DMI of beef cows. These results improved our understanding of the relationship between weather variables and DMI in beef cows like what was previously reported in beef steers.