Summer losses in milk production are usually related to the negative impact of summer heat stress on the lactating cow. In the last 40 years, some studies realized in different parts of the world showed that also dry cows are negatively affected, when subjected to heat stress conditions. These losses are mainly related to lower milk volume and solids production, as well as fertility traits in early stages of the subsequent lactation. Heat stressed dry cows also suffer from higher incidences of diseases and metabolic disorders post calving (mostly, due to reduce in cow’s immune function). All these changes take place after calving and in early stages of subsequent lactation, although it occurs in autumn and early winter, when heat stress is already over.
In the table below, the list of researches, dealing with heat stress mitigation from dry cows is described. As can be seen, in most of the studies, the positive effect of cooling the dry cows on their milk production is compared to that of cows provided only shade. As can be seen, the studies were conducted in different climatic conditions (dry and humid regions), and by making use of different cooling methods (direct cooling, by combing wetting and forced ventilation) and indirect cooling, by using high and low pressure fogging).
Table - Average milk production (kg/d), in subsequent lactation of dry cows from different climatic regions, cooled by different cooling methods, as compared to cows provided only shade.
Summarizing the studies presented in the table above, we can see that, in an average:
- Body temperature of cooled dry cows was 0.4 C lower, as compared to not cooled cows (38.9 C and 39.2 C), respectively.
- Dry matter intake (DM) was higher by 1.5 kg/day in cooled dry cows, as compared to not cooled cows (11.4 kg/d and 9.8 kg/d), respectively.
- Calves birth weight was 4.4 kg higher in calves born to cooled dry cows, as compared to calves born to not cooled cows (42.4 kg and 38.0 kg), respectively.
- Calves weaning weight was 7.7 kg higher in calves born to cooled dry cows, as compared to calves born to not cooled cows (77.7 kg and 70.0 kg), respectively.
- Milk production in subsequent lactation was 3.5 kg/d higher in cooled dry cows, as compared to not cooled cows (35.8 kg/d and 32.3 Kg/d), respectively.
In a survey carried out in the different parts of the USA, the production losses of milk production in subsequent lactation were related to the number of days in a year, where average daily THI was above 72. The losses in milk production in subsequent lactation averaged 450 kg/year in the average US cow, ranging between 230 kg/year in the “coldest state”, where 12% of the dry cows experience heat stress per year, and 1170 kg/year in the “warmest state”, where 70% of the dry cows in the herd experience heat stress per year. Economic losses due to heat stress in dry cows for the entire US dairy sector was estimated to be 810 million US$ annually (87 US$/cow/year). In an average, subsequent lactation drops in 4.7 kg/d, for each stressful day in the year (average daily THI above 72). Economic annual losses per dry cow ranged between 68 US$ in Wisconsin, and 230 US$ in Florida.
Differently from the lactating cows, very few studies evaluated the economic benefit from cooling the dry cows.
The first study was published by Urdaz et al in 2006. An experiment carried out in a 3,000 cow’s farm, located in central California, where cooling day cows by combining wetting and forced ventilation in shaded feed line was compared to only wetting the cows. Cooling systems operated between 09:00 and 20:00 and was provided to cows in last 3 weeks of pregnancy. Adding fans to the sprinkling system in feed line increased per cow annual profit by almost 10 US$.
Adin et al published in 2009 a study examining the benefit of cooling dry cows by a combination of wetting and forced ventilation carried out in a commercial dairy farm in the south of Israel. The researchers found that additional 80 kg of milk in subsequent lactation were needed, in order to cover the expenses required to cool the cows (cooling equipment and its operation). Subsequent lactation milk production of the cooled dry cows increased by 190 kg over the control cows who were provided shade only, leaving in farmer’s pocket the profit from additional 110 kg of milk for every dry cow receiving the cooling treatment.
The last and most detailed evaluation of the cost effectiveness of cooling dry cows was done by researches from the University of Florida and published it in the American Journal of Dairy Science in 2016. The researchers calculated the cost effectiveness of providing direct cooling system to dry cow, this for the “average US cow”, and for a dry cow in Florida.
In the US there are in an average 96 stressful days per year (26% of year time). Assuming milk price and feed DM prices of 0.54/kg and 0.28/kg US$, respectively, and an increase of 5 kg of milk production in subsequent lactation for every stressful days, direct cooling increase by 62 US$, the annual net income per cooled dry cow. In Florida, with 257 stressful days per year and milk price of 0.44 US$/kg, direct cooling increase by 140 US$, the annual net income per dry cow. Assuming that 70% of Florida cows experience heat stress in their dry period, this means 100 US$ annually, for every cow in Florida herds.
The investment in cooling dry cows start being cost effective when number of stressful days increase 50, under moderate climate conditions and about 10 stressful days, in extremely hot region like Florida and the south of the USA.
In this article, I decided to show Brazilian dairy sector data as an example. In a request and by using my special excel program for calculation of cost-effectiveness of the implementation of cooling means, I will be glad to “run” this study for other countries, once getting their special numbers.
The cost benefit of cooling the dry cows in two 200 cow's dairy farms in Brazil, averaging milk production of 9,000 lit. /cow, which do not cool the dry cows yet. The first farm is located in warm region (250 stressful days per year, where THI average 72 or more). The second farm is located in cooler region (150 stressful days per year).
In warm region, 70% of adult cows (140 cows) spend their entire dry period under heat stress conditions. We assume that cooling these cows during the entire dry period will increase by 15% their subsequent lactation. With milk and feed DM prices of 1.6 R$/kg and 0.9 R$/kg, investment in cooling equipment of 1,150 R$ per dry cow (added cooling in feed line), and 75 R$ of operation cost per dry cow, the expected increase in net annual income per dry cow is of 915 R$ per year and 1280,000 R$ per farm.
In cooler region, 40% of adult cows (80 cows) spend their entire dry period under heat stress conditions. We assume that cooling these cows during the entire dry period will increase by 10% their subsequent lactation. With milk and feed DM prices of 1.6 R$/kg and 0.9 R$/kg, investment in equipment of 1,150 R$ per dry cow stall and 80 R$ of operation cost per dry cow, the expected increase in net annual income per dry cow is of 915 R$, and 73,000 R$ per farm.
It must be clarified that, the calculations presented above, included only cows going to second lactation or more, and do not include the beneficial effect of cooling late pregnant heifers, although recent literature shows that they can benefit from cooling in late pregnancy too. The calculation do not include also the improvements in cow’s health and fertility in early subsequent lactation, expected when dry cows are cooled in the warm season. Including all these benefits to the calculation will obviously increase the economic benefit from cooling the dry cows.
Cooling dry cows and late pregnancy heifers in Brazilian dairy farms have the potential to increase annual milk production of cows calving in late summer and early autumn by 1,000 kg per dry cow in subsequent lactation. This can increase net income between 70,000 R$ per farm per year, in farms located in relatively cool parts of Brazil and by 130,000 R$ per farm per year, in farms located in warm parts of Brazil. The investment in cooling dry cows can be paid back in less than two years.