Techniques to increase silage stability and starch availability and the effects of heat stress abatement systems on reducing heat load in dairy cattle

Abstract

Four studies were conducted that focused either on silage quality parameters or heat abatement systems to improve cow comfort. Study 1 evaluated the effects of treating whole-plant corn at harvest with a dual-purpose commercial silage inoculant containing Lactobacillus buchneri and Lactococcus lactis O224 on fermentation and aerobic stability of corn silage through 32 d of ensiling. Inoculating silage to be fed after minimal storage time (≤ 32 d post-harvest) had no effect (P > 0.05) on the chemical composition, fermentation variables, aerobic stability or rise in temperature post-harvest. Study 2 was designed to develop a berry processing score (BPS) for sorghum silage as well as evaluate the change in starch digestibility as the level of berry processing increased. A method to evaluate the level of processing in sorghum silage was successfully developed by measuring the percent of starch passing through a 1.7 mm screen. This provides the industry with a standardized method to measure the level of processing in sorghum silage. As BPS increased from 26.28 to 55.05 ± 0.04%, 7-h in situ starch digestibility increased from 50.54 to 82.07 ± 4.94% for unprocessed and heavily processed sorghum silage, respectively (R² = 0.43). By processing sorghum silage during harvest and measuring the extent of processing, sorghum silage starch digestibility can be enhanced and may serve as a viable alternative to corn silage in the diet of lactating dairy cows in areas of the country where corn silage is a high-risk forage crop due to lack of water. Study 3 evaluated the effects of 2 heat stress abatement systems on barn temperature, micro-environmental temperature, core body temperature (CBT), respiration rate, rear udder temperature, and lying time in lactating dairy cows. The systems evaluated were: direct cooling via feedline soakers and fans, or evaporative cooling via a fan and fog system. The evaporative cooling system was effective (P = 0.04) in reducing respiration rates (52.0 vs. 57.9 ± 2.2 breaths per min; P < 0.01) and rear udder temperatures (33.2 vs. 34.5 ± 0.3ºC; P < 0.01), and increased daily lying time (11.8 vs. 10.8 ± 0.3 h/d; P < 0.01) due to differences in barn THI and airflow. No treatment differences (P = 0.79) were detected for CBT, likely due to cooler ambient conditions during the study. Study 4 assessed the effects of the same evaporative and direct cooling systems as in Study 2 but were applied in the holding area prior to afternoon milking, where effects on CBT and micro-environmental temperature in lactating dairy cows were measured in addition to water usage by each system. No significant differences (P > 0.05) between direct cooling and evaporative cooling were detected for micro-environmental THI. However, the evaporative cooling system reduced the consumption of water in the holding area while maintaining CBT < 39.0ºC. Future research should be conducted under greater ambient THI to determine if an evaporative cooling system is able to maintain CBT < 39.0ºC, while also comparing CBT and water usage to a soaker system in the holding area.