Cooling cows in summer improves annual productivity and fertility, enhances comfort and welfare, increases longevity and reduces greenhouse gas emissions through better feed efficiency and higher milk yield. Heat stress causes immense economical losses to the dairy sector. High-yielding cows in hot climates suffer severely from summer heat, but cows are affected by heat stress in almost all regions. This leads to a decrease in milk production and reduced feed efficiency. Fertility rate is reduced - thus increasing the calving interval and culling rate due to low productive and reproductive performances. All the cows in the herd, including late pregnancy cows, dry cows and heifers, require cooling in summer.
Keywords: cooling heat stress milk production ventilation
Take home messages
1. Summer stressful condition cause large economical losses to dairy sectors all over the world, especially with high yielding herds in warm climates.
2. Cooling the cows by combining wetting and forced ventilation was found to be the cheapest and most effective cooling system for dairy cows in all kind of climates.
3. All the cows in the herd, including late pregnancy cows and heifers, require cooling in summer.
4. Cooling intensity requirements (hours of cooling per day) are proportional to level of production and heat-stress. It ranges between 7 and 3 cumulative hours per day for high and low or dry cows, respectively.
5. Cooling the cows consist sequences of continuous ventilation and short wetting sessions (20-30 seconds), provided every 5 minutes, for 30-45 minutes every 2-3 hours during the day.
6. Large droplets and low pressure sprinklers are required to reach quick and effective wetting of the cow's surface.
7. Cows show stress signals by increasing respiration rate (above 60 breaths /min) and rectal temperature (above 39 C). Monitoring these parameters frequently in the summer days will indicate the farmer about when to start cooling the cows.
8. Heat stressed cows reduce feed consumption and cooled cows will increase it back. Make sure that cows have sufficient fresh food all day long.
9. Heat stressed cows drink more water. Therefore, there is a need to provide sufficient "water trough space" and avoid crowding, when cows are back from milking or feeding.
10. The "summer to winter ratio" is a god tool to evaluate cooling effectiveness. It is recommended to use this index and take corrective measures, as to the proper installation and operation of cooling means in the farm, accordingly.
Global Warming – You, Me and the Cow
On a less scientific note, before we get down to technicalities – let’s try and empathize with the heat stress of our cows. Actually, when we look back a few months to Spring 2013 and the unprecedented amount of snow and cold temperatures that hit the Northern Hemisphere, we can’t help but ask: “Hey – is this Global Warming?”. But whatever the cause, the summer months in most places are going to be HOT. And in desert and tropical areas – very, very hot for much longer periods of time! So what happens to us humans when the heat waves hit? We run for the air-conditioning and can’t wait to jump into a cool shower. Without those “luxuries” we become uncomfortable, apathetic, and stressed. We are not able to function at our optimum levels. It is no different for cows. And they have the added discomfort of wearing a thick leather coat that they can’t take off ... How can we expect to maintain their “top performance” if we don’t offer them the same release from the effects of over-heating that we afford ourselves? To not implement methods for COOLING them is not just inhumane, but adversely affects the bottom line for Dairy Farmers and Milk Producers – PROFIT.
A Look at the Facts and Studies:
The constant rise in the desired production level of dairy herds together with the effects of global warming, highly aggravates the decrease in cows’ performance – even more so in intensively producing dairy farms located in warm regions. A great number of studies have been carried out over the last five decades, aimed at quantifying the negative effect of summer on cows’ performance, and efficient cooling systems have been developed which enable farmers in warm regions to overcome this negative summer impact and reach high per cow yields as well as acceptable fertility and health traits. These cooling systems have been rapidly adopted by farmers all over the world. For optimum effect the systems need to be properly installed and operated, as well as specifically adapted to each farm's region and special management conditions.
There are two cooling methods. Direct Cooling - by cooling the cow’s body surface without changing the ambient temperature, and Indirect Cooling – achieved by cooling the air. To date, the majority of cows in the world are cooled by the direct cooling system, which has proved to be effective in all kinds of climate (both dry and humid) and is the cheapest method of operation. Cows are directly cooled by evaporating water from their surface, usually by a combination of wetting and intensive forced ventilation. This form of cooling system was developed and first implemented in Israel almost 25 years ago (1). Cooling the cows a few times per day allows them to maintain normal body temperature (below 390 C) for the entire day, during a typical Israeli summer day – in which the external ambient temperature can easily reach 300C and above.
A survey evaluating the effect of cooling cows on milk production and reproduction was carried out in 15 large scale dairy farms in Israel (2). The ratios between summer and winter daily average milk production was 98% in intensively cooled cows, as compared to only 91% in those who were only lightly cooled. These results indicate that intensively cooling cows during summer has the potential to almost eliminate summer-decline in cows’ milk production and to reduce by half the decline in summer conception rate.
In another survey we attempted to determine if intensive cooling in summer can prevent summer decline in milk production even in extremely high yielding herds (3). Winter and summer daily production per cow averaged 41.5 and 40.7 kg/d respectively in cooled cows - less than 1 kg/d drop - as compared to a drop of more than 5 kg/d in non-cooled cows, indicating that intensive cooling can be effective even in extremely high producing cows.
A computerized report, called the Summer to Winter (S:W) performance ratio, was recently developed by extension services in Israel. This annual report aids farmers in monitoring the effectiveness of the type of cooling system installed in their farms (4). The report is based on information from each farm’s monthly electronically recorded data for milk production and fertility traits per cow . Ratios close to 1.0 represent the farms which are dealing with summer heat-stress the best. S:W milk ratios of > 0.96, 0.90 - 0.96 and < 0.90, were recorded respectively in 34%, 44% and 22% of the dairy farms in Israel. These results indicate that most of the farms in Israel have nearly "closed the gap" between summer and winter performance ratios, but that there are still close to 20% of farms who need to improve their cooling methods.
The rate of improvement in the way Israeli dairy herds deal with summer heat stress – the S:W ratio - was calculated and compared through the years 1994 to 2008. Results presented in Table 1 below indicate that, during the tested period, average daily milk production was increased by 2.3 kg/d (6%) in winter, as compared to an increase of 7.3 kg/d in the summer (23%), and S:W ratio was increased from 0.82 in 1994 to 0.96 in 2008 - a significant improvement achieved mostly through better implementation of cooling methods in the Israeli dairy farms.
TABLE 1 – AVERAGE MILK PRODUCTION (KG/D) IN THE SUMMER AND THE WINTER AND ITS RATE OF INCREASE, IN LARGE SCALE COOPERATIVE DAIRY FARMS IN ISRAEL FROM 1994 – 2008
Based on the S:W ratio data, we were recently able to quantify the effect of intensive cooling on cows’ annual milk production (5). Average 305 d production in the 24 highest S:W ratio farms was compared to that of the lower 24 S:W ratio farms. The assumption is that the difference between them is significantly related to better implementation of cooling methods in summer – see Table 2.
TABLE 2 - SUMMER AND WINTER AVERAGES OF MILK PRODUCTION AND S:W RATIOS IN HIGH RATIO (INTENSIVELY COOLED) AND LOW RATIO (ALMOST NON- COOLED) HERDS
As indicated in Table 2, average S:W annual production ratio for the top 24 farms was 0.98 as compared to a ratio of 0.87 in the lower ones. Comparison of annual average 305d production between the two groups of farms is presented in Table 3, where we discovered that cows in high S:W ratio farms produced nearly 730 kg/year more than cows in the low S:W ratio farms (6.5%).
TABLE 3 - AVERAGE PRODUCTION (305 DAYS) FOR MILK, MILK FAT AND MILK PROTEIN, FOR HERDS WITH HIGH AND LOW S:W RATIO
Although much information has been published describing the negative effect of summer heat stress on milk production, very limited information is available regarding its effect on "feed efficiency" (feed to milk ratio). Researchers from the University of Arizona recently published a study carried out in the new climatic chambers located in Tucson (6), in which high yielding cows, subjected to normal climatic conditions and whose feed intake was restricted to that of heat stressed cows, dropped by only half the drop in milk recorded in heat stressed cows - 30% and 15% respectively, in heat stressed and feed restricted cows maintained in cool chambers.
The researchers therefore assumed that the need to canalize feed energy for activation of body mechanisms to dissipate heat, as well as changes in metabolic pathways are the 2 main causes for decline in cows’ feed efficiency.
Based on the results of this "Arizona Study" and using identical experimental procedures, the effects of heat stress versus intensive cooling of cows on feed efficiency were recently studied in Israel (7). Just as in the Arizona study, milk drop in heat stressed cows was almost double of that obtained from cooled cows whose feed consumption was restricted to the amount consumed by cows in normal climatic conditions. It therefore follows that cooling dairy cows in the summer, not only increases cows’ annual production, but also improves feed efficiency - by reducing feed required for milk production under heat stress conditions by 5 to 10 percentage units.
Cost effectiveness of cooling cows was evaluated by a specially designed program that calculates the increase in net income per cow, after the deduction of cooling expenses. Since this program was developed 5 years ago, it is being used to evaluate cost effectiveness of implementing cooling solutions in different climatic and economical conditions, including Southern USA (8), Northern Mexico (9), Coastal Peru (10), Central Argentina and Uruguay (11) and Central Brazil (12). See Table 4.
TABLE 4 – THE INCREASE IN ANNUAL NET PROFIT (US$) PER COW RESULTING FROM THE PROPER IMPLEMENTATION OF AN INTENSIVE COOLING SYSTEM IN DIFFERENT COUNTRIES OF THE AMERICAN CONTINENT
The data in Table 4 above indicates that despite existing differences in climatic conditions, level of production, management practices, cooling cost and milk prices - the increase in annual profit per cow is directly related to intensively cooling the cows, and ranges between 100 to 300 US$/cow/year, depending on the rate of increase in annual milk production per cow and improved feed efficiency. It is reasonable to assume that by adding the expected benefits which arise from also improving summer fertility and health traits - annual profitability per cow can increase by as much as 30-40% more.
Cooling also improves cows’ fertility and positively influences the cow's lifespan. Intensively cooled cows obtained significantly higher conception rates, as compared to non-cooled cows – 57% and 17% respectively (13). Pregnancy rates calculated for 90, 120 and 150 days after calving, differed significantly between the two groups (44, 59 and 73% versus 5, 11 and 32%), in cooled and non-cooled cows, respectively. Conception rates and pregnancy rates obtained in intensively cooled cows in summer were similar to those obtained from winter inseminations in Israel. The effect of cooling on reproductive traits of high yielding cows (45-50 kg/d) was recently studied in a large scale survey in Israel. The difference between conception rates obtained in the winter and those in summer were 34% in cooled cows and only 17% in non-cooled cows. These results indicate that intensive cooling of cows in summer has the potential to double summer conception rates, even if they don’t quite reach winter levels.
In any case, this improvement in cows’ summer fertility can significantly enhance cows’ longevity due to the improved productivity related to shorter calving intervals, and also reduce the number of cows that need to be culled due to infertility.
The facts leave no doubt that cows need intensive cooling in the summer and that intensive cooling can be highly cost effective under climatic conditions similar to those existing in Israel. The impact on cow's comfort and well being of frequently “moving” them to cooling sites and the length of time they need to spend there, was recently tested at the Israeli
Ministry of Agriculture’s Experimental Dairy Farm (14). Many dairy farmers in hot regions were concerned about the possibility that these cooling procedures could cause cows to “suffer” when obliged to be moved to the cooling site plus the additional time spent standing when treated. In this study, high yielding cows were divided into two types of cooling treatments differing in the time of cooling provided. Cows in both groups were cooled by a combination of wetting and forced ventilation, provided in the waiting yard to the milking parlour. Cows in Group A were cooled for 5 "cooling sessions" per day totalling 3.75 cumulative hours (5T), while cows in Group B were cooled for 8 "cooling sessions" per day totalling 6 cumulative hours (8T).
Sophisticated equipment developed in Israel automatically monitored:
- Feed intake
- Body temperature
- Cows’ resting and rumination time
As anticipated, increased cooling time increased feed consumption by 2.1 kg/d (8.5%) and daily milk production by 3.4 kg/d (9.3%). Body temperature and respiration rate were significantly lower in 8T cows, as compared to 5T (+ 0.8 C and + 30 respirations per minute at noon time, respectively). Surprisingly, the cooled cows, despite being "obliged" to stand for a longer time to be cooled, laid down and their resting time increased by almost 10% (480 and 430 minutes/day, in the 8T and 5T groups, respectively). Rumination time was also increased by 6% in the more intensively cooled group (445 and 415 minutes/ day, in 8T and 5T, respectively).
From the results of this study we learn that intensive cooling of high yielding cows in summer, not only improves productive, reproductive and health traits, but also improves cows’ comfort and welfare. Heat stressed cows usually tend to stand and crowd. Cooling cows more frequently on extremely hot summer days, facilitates maintaining them in normal thermal conditions for more hours per day. They tend to lay down and ruminate for longer periods and probably feel far more comfortable. Therefore, farmers should understand that, by cooling the cows, they are not depriving them of required rest time, but on the contrary - they are vastly improving their wellbeing, a critical factor during the hot summer months.
Up till now we have only dealt with the benefits and well being of the cow's and the farmers.
So let’s take a look at the impact on the environment!
Does cooling cows in the summer have a positive or negative effect on the environment - especially in reference to the emission of Green House Gases (GHG) and global warming?
It is a well known fact that dairy sectors will be evaluated in the future, not only for their economic efficiency and the way animals are handled and treated, but also for their contribution to the prevention of global warming. New data from recent studies indicates that obtaining higher yields has the potential to reduce GHG emission during the milk synthesis process.
Methane gas emission per cow and per litre of milk produced by high yielding cows producing 11,500 kg milk per year reaches only 40% of that emitted by low producing cows (4000 kg/year), and only 80% of that emitted by 8000 kg/year cows.
We recently calculated the "GHG emission balance” for the cooling process provided to the cows in the summer. We compared the increased CO2 emission to the atmosphere, from the use of electricity for operating the fans, to the expected reduction in CO2 emission to the atmosphere, due to the reduction in number of cows required to produce a certain amount of milk and their maintenance methane (CH4) emission, as well as the improved conversion rate of feed to milk, due to cows being cooled. The results of our study (15) show that improved production efficiency and the reduction in herd size by 5%, as a result of cooling the cows in the summer, reduced CO2 emission by 320 kg/cow/year - more than double of the amount of CO2 emitted by generating the energy required for operating the fans for the cooling process. In the event that the increase in annual milk production due to cooling reaches 10% (a common result in many dairy sectors in hot regions), the decrease in CO2 emission is expected to be four times the amount emitted by the cooling process.
It is therefore quite obvious that cooling cows in summer (in addition to the many benefits to both cow and farmer), is actually more environmentally friendly - as it reduces the contribution of milk production to GHG emission and hence to global warming.
High yielding cows in hot climates suffer severely from summer heat stress for a few months during every year - which leads to a decrease in annual milk production and feed efficiency. Fertility rate is reduced and more post-calving health problems appear - thus increasing the calving interval and culling rate due to low productive and reproductive performances. The goal of cow cooling is to positively impact the modern global Dairy Sector by significantly extending the lifetime of the dairy cow by increasing their productivity while assuring they maintain good health and fertility. Over the last 3 decades efficient cow cooling systems have been developed all over the world and successfully implemented in dairy farms. The most common and efficient system is "Direct Cooling" – which is based on evaporation of water from the cow's skin surface by a combination of short wetting treatments followed by intensive forced ventilation. Intensive cooling of cows in the summer increases annual milk production by 10% and milk fat and protein content by 0.4 and 0.2%, respectively. The conception rate of cooled cows inseminated in the summer is increased, while culling rate caused by poor health and lowered fertility is reduced – all of which leads to a marked improvement in the lifespan of the herd. Furthermore, cooling cows during the summer months increases rumination and resting time in comparison to non-cooled cattle. In short, cooling cows vastly improves their overall welfare.
The increase in milk production achieved by cooling cows enables the same amount of milk to be produced by fewer cows – which reduces the emission of greenhouse gases (GHG) into the atmosphere. The CO2 emitted by the operation of fans for the cooling process has been calculated to be only one third of the amount saved when milk production is increased due to cooling.
Cooling cows in summer improves their annual productivity and fertility, enhances their comfort and welfare, increases longevity and lifetime productivity and reduces the effects of GHG release on global warming.
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12. Hoard’s Dairyman en Espanol, January 2010, p 46
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14. PANVET annual meeting, Lima, Peru
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This article belongs to the proceedings from the Cow Longevity Conference 2013 that took place at Hamra farm, Sweden in August 2013