Evaluation of solar photovoltaic systems to shade cows in a pasture-based dairy herd.

Discipline: cow comfort; Keywords: dairy, heat stress, pasture-based, solar photovoltaic.   

Heat stress has been estimated to cost the dairy industry in the United States more than $900 million annually due to production losses. The main contributors to heat stress are temperature, humidity, and the temperature-humidity index (THI). A THI of 68 to 72 has been reported to induce heat stress in cows and decrease milk production. Prior research has been conducted on heat abatement measures in free stall barns with sprinklers, evaporative cooling, and fan design. However, pasture-based research efforts on heat abatement are limited and have investigated fabric and trees for shade and sprinklers.

Agrivoltaics is the combined use of solar photovoltaic (PV) and agricultural systems to provide mutual benefits for both the agricultural and energy industries. It has been determined that agrivoltaic systems have the potential to increase land productivity and efficiency by 60 to 70%. No research as yet has investigated the use of shade from a ground-mounted solar PV system and the effects on dairy cows. The current study of Dr K.T. Sharpe and colleagues used a solar PV system for shade that was a permanent structure in the pasture, and the solar panels were not translucent compared with shade cloth, which may not be permanent in pasture and may allow some light through the cloth. The permanent solar system is expected to be in the same location in the pasture for 25 to 30 years with low or no maintenance. The solar photovoltaic system would also provide benefits of solar energy for the farm, whereas shade cloth would provide no energy generation. The hypothesis of the authors was that shade from solar panels for dairy cows would reduce the intensity of heat stress as indicated by reduced respiration rates, internal body temperatures, and drinking events. Therefore, the objective of their study was to investigate the effects of shade from solar PV on the production, health, and behaviour of pastured dairy cows. The results were published in The Journal of Dairy Science, Volume 104 of 2021, page 2794 to 2806. The title of the paper is: Evaluation of solar photovoltaic systems to shade cows in a pasture-based dairy herd.

Twenty-four crossbred cows were randomly assigned to two treatment groups (shade or no shade) from June to September (northern summer). The replicated (n = 4) treatment groups of six cows each were provided shade from a 30-kW photovoltaic system. Two groups of cows had access to shade in paddocks, and 2 groups of cows had no shade in paddocks. All cows were located in the same pasture during summer. Behaviour observations and milk production were evaluated for cows during four periods of summer. Boluses and an ear tag sensor monitored internal body temperature, activity, and rumination on all cows, respectively. Independent variables were the fixed effects of breed, treatment group, coat colour, period, and parity, and random effects were replicate group, date, and cow.

No differences in fly prevalence, milk production, fat and protein production, or drinking bouts were observed between the treatment groups. Shade cows had more ear flicks (11.4 ear flicks per 30 seconds) than no-shade cows (8.6 ear flicks per 30 seconds) and had dirtier bellies and lower legs (2.2 and 3.2, respectively) than no-shade cows (1.9 and 2.9, respectively). During the afternoon hours, shade cows had lower respiration rates (66.4 breaths per minute) than no-shade cows (78.3 breaths per minute). From 1200 to 1800 hours and 1800 to 0000 hours, shade cows had lower body temperature (39.0 and 39.2°C, respectively) than no-shade cows (39.3 and 39.4°C, respectively). Furthermore, between milking times (0800 and 1600 hours), the shade cows had lower body temperature (38.9°C) than no-shade cows (39.1°C). The results suggest that Agrivoltaics incorporated into pasture dairy systems may reduce the intensity of heats stress in dairy cows and increase well-being of cows and the efficiency of land use.                                                                                                                                  

It was recommended that future research should be conducted on the effect of climate change on heat stress in pastured dairy cows as well as heat abatement techniques, especially within pasture-based systems and in different locations. Furthermore, research should investigate whether shade use during the hottest hours of the day is more or less beneficial to the cow than grazing. Complete pasture coverage by PV systems may allow for simultaneous grazing and cooling of cows. Although Agrivoltaics may provide an acceptable method of heat abatement to pastured dairy cows, more long-term studies should be conducted to gain a clearer picture of the effects of solar shade on dairy cows. Future research on solar systems in a pasture dairy system should explore the economic effects of the solar system as well as long-term effects on milk production, reproductive performance, body weight etc.