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Research review: Sorghum silage and cow cooling options

Pedro Nogueira for Progressive Dairy Published on 30 June 2020

“Graduate student literature review: Current perspectives on whole-plant sorghum silage production and utilization by lactating dairy cows.” Journal of Dairy Science Vol. 103 No. 6, 2020. This article, originating from the University of Florida, reviews whole-plant sorghum silage production and utilization by dairy cows.

The authors refer that as challenges like the need to increase efficiency of production and reduced water availability become more prevalent, greater reliance on sorghum can be expected because of its ability to produce high dry matter (DM) yields while maintaining nutritive value, even under less-than-ideal growing conditions. They indicate advancements in sorghum genetics and mechanical processing have the potential to alleviate common challenges associated with whole-plant sorghum silage supplementation, such as increased neutral detergent fibre and decreased neutral detergent fibre digestibility, starch concentration and starch digestibility.

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As background information, the article refers that in 2018, there were approximately 2.5 million hectares of whole-plant corn silage (WPCS) harvested in the U.S., whereas there were over 100,000 hectares of whole-plant sorghum silage (WPSS).

The article indicates degradability of sorghum grain starch is generally accepted as being less than other grain sources, such as corn, barley and wheat. Studies around this area underscore that sorghum grain must be broken to disrupt barriers, such as the pericarp and the starch-protein matrix, which inhibit DM degradation. However, mechanical processing of sorghum grain contained within WPSS is often difficult under field conditions.

Few published studies have evaluated the effects of varying theoretical length of cut or roll gap settings on WPSS grain breakage and starch digestibility. The few existing ones have shown that as processing score increased (roll gap spacing from not processed, 1.5, 1.0 and 0.5 mm), the digestibility of starch after seven hours increased substantially. Further research should focus on designing experiments that quantify the relationships among grain breakage, starch digestibility and lactation performance of dairy cows.

A widespread critique of WPSS is that it contains greater fibre concentrations compared with WPCS, as well as reduced digestibility of NDF (NDFD). However, improvements of NDFD in WPSS have been made through genetic selection for the brown midrib (BMR) trait.

The authors conclude by saying that although great progress has been made to improve the NDFD of WPSS through the BMR trait, careful replacement of WPCS with WPSS is still recommended. Starch concentration and starch digestibility have consistently been lower for WPSS than for WPCS. As discussed earlier, harvesting sorghum at later maturity would allow for greater starch deposition; however, digestibility of starch is negatively affected by formation of a more pronounced starch-protein matrix.

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Early harvesting of sorghum increases starch digestibility but does not allow for adequate starch deposition, resulting in reduced concentrations of starch. Perhaps the most feasible solution to improve WPSS starch concentration and digestibility is harvesting at a maturity that allows for greater starch deposition and aggressively mechanically processing the grain fraction. Careful hybrid selection, proper silo management and continued advancement in agronomic and harvesting practices will continue to add value to whole-plant sorghum silage as a forage source to dairy cattle.

“Innovative cooling strategies: Dairy cow responses and water and energy use.” Journal of Dairy Science Vol. 103 No. 6, 2020. To mitigate heat stress, producers normally install fans in the barn or a combination of fans and water sprinklers. Although these methods can be effective, the authors of this study, from the University of California – Davis, evaluated the effectiveness and resource efficiency of four cooling treatments on behavioural and physiological responses in dairy cows housed in a freestall barn:

1. Conductive cooling in which mats with recirculating evaporatively cooled water were buried under sand bedding (Mat; the system was activated at 18.9ºC [66ºF])

2. Targeted convective cooling in which evaporatively cooled air was directed toward the cows through fabric ducts with nozzles at both the feedbunk and lying areas (similar to a positive-pressure tube we see in calf barns) (Targeted air; activated at 22ºC [71.6ºF])

3. Evaporative cooling with spray water in the feed area and fans over the freestalls (Baseline; activated at 22ºC [71.6ºF]). This served as a control, since it’s the typical system in California.

4. Evaporative cooling with half the amount of spray water used in the baseline and the fan moved to the feedbunk (Optimized baseline; activated at 22ºC [71.6ºF])

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They used eight groups of cows, producing an average of 37.5 plus or minus 4.5 kilograms per day of milk. The study recorded body temperature, posture and location within the pen every three minutes for 24 hours a day and respiration rates every 30 minutes daily from 10h00 to 19h00. Daily air temperature averaged 26.3 plus or minus 7.1ºC during 24 hours and 33.3 plus or minus 4ºC from 10h00 to 19h00.

According to the authors, spray water and fans, in addition to shade, are the most commonly used forms of heat abatement in the U.S. Although these systems can be effective, they also use large quantities of water and electricity, which can affect profitability and sustainability of the dairy industry. In addition, the cost of electricity is continuing to rise, and water availability is decreasing due to changed rainfall patterns, particularly in California. These changes prompt the study of more efficient heat abatement strategies that use less water and energy.

The article refers that the modes by which heat transfer occurs include conduction, convection and radiation. Convective cooling involves heat transfer to cooler air that surrounds the body of the cow, allowing her to dissipate heat. Evaporative cooling is a particularly effective mode of convective heat transfer due to the amount of heat that can be removed by changing the phase of liquid water to vapor, and it is widely used on dairies in the form of spray water and fans. Conductive cooling uses the transfer of heat from the cow to the surrounding media the animal comes in contact with, often while lying down.

These results collectively indicate the mat treatment did not effectively reduce indicators of heat load compared with baseline. In contrast, targeted air and optimized baseline were both effective but differed in aspects of efficiency. Targeted air used the least amount of water but the most energy of all options tested. In conclusion, more efficient heat abatement options were identified, particularly an optimized baseline strategy, which cut water use in half, required the same amount of energy as the baseline and maintained similar physiological and behavioural responses in cows.  end mark

This column brings you information regarding some of the research being done around the world and published in the Journal of Dairy Science. The objective is to bring to light areas of research that may have an immediate practical application on a dairy farm, as well as research that, even though it may not have a practical impact now, could be interesting for its future potential application. The idea is to give a brief overview of select research studies but not go into detail on each topic. Those interested in further in-depth reading can use the citations to find each study.

Pedro Nogueira
  • Pedro Nogueira

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