Effect of fan placement on milk production and dry matter intake of lactating dairy cows housed in a 4-row freestall barn

Heat stress reduces milk production, feed intake, and reproductive efficiency each summer in Kansas. Without heat abatement procedures, milk production may decline 2030% during the summer months. Research has shown that supplemental fan cooling in combination with low pressure feedline sprinklers can reduce the effects of heat stress on milk production and feed intake. One critical issue in heat stress abatement is the location of fans in a 4-row freestall barn. Research conducted during the summer of 2000 on a northeast Kansas dairy found that locating fans over both the feedline and head-to-head freestalls increased milk production 5.8 lb/cow/d and reduced respiration rates in the morning and at night compared to mounting fans only over the feedline. Pen feed intakes also tended to be greater when fans were located in both areas. Economic analysis showed that after accounting for cost associated with ownership, operation, and increased feed intake, net farm income was estimated to be increased by $3,6006,600 for a pen of 84 cows. A 100-cow Kansas dairy could increase farm profits by $8,000 if these heat abatement techniques were utilized. Location of fans over both the feedline and freestalls in combination with a low pressure feedline sprinkling system is an effective heat stress abatement strategy in 4row freestall barns.; Dairy Day, 2001, Kansas State University, Manhattan, KS, 2001;


Introduction
Heat stress abatement in freestall barns should be a major concern for dairy producers and dairy industry advisors.Under modern management systems, lactating dairy cows may spend over 9 0% of the day in the free sta ll barn.Without effective free sta ll cooling systems, significant pro duction and reproduction losses will occur.In terms of cow comfort, the effective temperature is a funct ion of air t emperat ure , humidity, air flow, and solar radiation.Heat dissipation from the dairy cow at temper atur es above 60°F is largely due to evaporative losses from the skin with a much smaller portion lost via lung cooling.Thus, the goal of heat stress abatement in freestall barns should be to provide protection from solar radiation and maximize evaporative losses from the skin.Heat dissipa tio n fro m the skin is increased by increasing air exchange, air flow and the evap oration o f supplementa l water applied to the skin.
Freest all barns that are correctly designed will provide maximum natural ventilation.However, add itio nal cooling eq uipment is necessary to maint ain milk production and reduce its decrease during summer.In addition to maintaining production, heat abatement measures must be cost effective and return a net pro fit to the dairy producer.A study was conducted during the summer of 2000 to evalu ate two differ ent cooling systems in 4-row fre est all bar ns locat ed in northeast Kansas.

Procedures
During the summer of 2000 a study was conducted to determine if fans w ere only needed over the feedline.One hundred midlactation Holstein cows were blocked by milk production and day in milk and assigned randomly to each of four pens of a 4row freestall barn.Two replicates, north and south halves of the barn, contained 2 pens each.Cows in each treatment group averaged 173 days in milk and produced an average of 97.6 lb/cow/day at the st art of the study.Pens contained 85-90 cows.In each pen, 25 wer e study animals.Fan treatments were either a single row of 36-inch fans mounted every 24 ft on the feedline (8, 36inch diameter circulation fans with 0.5 horsepower motors) (feedline fans; F) or a single row of fans (8, 36-inch diameter circulation fans with 0.5 horsepower motors) mounted every 24 ft over the head-to-head free sta lls plus another row of fans (8, 36-inch diameter circulation fans with 0.5 horsepower motors) mounted every 24 ft over t he cow feedline (feedline and stall fans; F+S).Each fan was estimated to provide 10,000 cubic feet /min of airflow when operating.
Each pen was equipped with similar spr inkler systems co nsisting of 2.5 gallon/hr nozzles spaced every 78 inches on-center at a height of 8 ft above the headlocks.Spr inklers were on a 15-min cycle with 3-min on and 12-min off.Sprinklers were activated when the temperature was above 75°F.The designed application rate was 0.04 inches/ft 2 of surface area which consisted of 12 ft 2 /headlock or a 24-inch feeding space.Total application rate was 50 gallons/cycle.Fans of all treatments were activated when the temperature was above 70°F both day and night.A descript ion of fan and sprinkling systems is in Table 1.
Cows were milked 2× and milk production was measured every 2 wk throughout the 10-wk trial.All pens receive d the sa me diet.Amounts of feeds offered and refused were measured and recorded daily.Dry matter content of the diet and refusal of each was determined twice weekly.Cow respiration rates were measured on three separate days during heat stress.Fifteen cows were selected randomly from the 25 stu dy co ws in each pen and respiration rates were measured in the morning (0700-0800 hr), afternoon (1500-1600 hr) and at night (2200-2300 hr) on each of the 3 days.Ambient and pen temperature and relative humidity were recorded ever y 15 min in two locations throughout the study with HOBO® Pro data loggers.Data from each day was averaged by 3-hr blocks of time beginning at midnight each day.
A switch back design with five 2-wk periods was utilized to evalu ate fan p lacement.Cows and treatments were switched at the start of each period within each replicate.Milk and intake data were averaged by treatment within replicate and week prior to statistical analysis.Respiration rates were averaged by treatment within day, period and replicate prior to statistical analysis.

Results
Milk production (Figure 1) was greater (P<0.01) for cows exposed to F+S the treatment than for tho se exposed to the F treatment.Dry matter intake (Figure 2) tended (P=0.11) to follow a similar pattern as milk production with pen feed intakes (54.0 vs 52.7 lb/cow/d) great er w hen F+ S wa s ut ilized rather tha n F. M ilk production (Figure 3) was more consistent during the study for the F+S treatment compared to the F treatment.Milk produc tio n in periods 3 and 4 dropped 7 and 10 lb, respectively, for the F treatment, wher eas milk in the F+S treat ment did not drop greatly until period 4. Average ambient temper atur e (Figure 4) increased about 4.5°F during period 4 compared to period 3.If milk pr oduct ion by p erio d is compared to period ambient t emperat ure , it appears that the F+S maintained milk production over a longer period of the summer than did F.However, when ambient temperatures were the greatest, even F+S cat tle experienced a significant drop in milk production, but no t to the extent of cattle cooled with F. Based on the average pen temperature (Figure 5), no differences were observed between the treatments.It was possible that the F+S treat ment allowed cattle to exchange greater amounts of heat while lying in the freestalls due to the increased airflow.Increased airflo w likely wou ld have increased evaporation rates of sweat and supplemental water from the skin surface.
Respiration rates (Figure 6) showed that the cattle exposed to F+S had reduced (P<0.06)respir ation r ates in the morning (71.7 vs 79.3 breat hs/cow/min), at night (76.0 vs 80. 1), and d aily (79 .4vs 83.2) compared to those under F. Afternoon respiration rates were unaffected by treatment.Respiration data indicate t hat the cat tle treated with F+S were mo re c omfo rtable than those cooled with F.
An economic analysis (Table 2) suggested that production losses due to heat stress were reduced from an estimated 20% with no heat abatement system (no fans or sprinklers) to 12% (F) and 5.6% (F+S).The cooling response of F was 7.3 lb of milk and that of F+S was 13.1 lb of milk relative to no heat stress abatement practice.Total cost to install cooling equipment was $3,536 (F) or $7,072 (F+S) per pen of 84 cows.Estimated increased milk income for and 85-day coo l-ing season was $6,730 (F) or $12,114 (F+S) per pen.Estimated net income after accounting for ownership, operation, and additional feed expenses was either $3,656 (F) or $6,693 (F+S) for a pen of 84 cows.On a cow per day basis, net returns were either $0.51 (F) or $0.94 (F+S) for the 85-day cooling season.A 100-cow Kansas dairy could expect to r eceive an additional $4,335 (F) or $7,990 (F+S) by utilizing these heat abatement techniques.Additional net income would pay for the complete syst em in a single year.
This study clearly demonstrated that cows in a 4-row free sta ll barn produced more milk and had lower respiration rat es by locating fans on both the feedline and over the freestalls.Based on lower respiration rates in the mor ning and at night, t he duration of heat stress was reduced by the F+S treat ment.Appro pria te fan locat ion in combination with feedline sprinklers reduced heat stress in lactat ing dairy cattle housed in a 4-row freestall building.In addition, heat abatement measures can be effect ive and profit generating.Dimensions: width-100 ft, length-420 ft, sidewall height-14 ft, roof slope-4 /12; Configu ratio n: 4 pens with 84 stalls per pen and 100 headlocks per pen. 2 F=one row of fans over feedline and F + S=one row of fans over the feedline and one row of fans over the head-to-head freestalls.-----------$---------- Ex tra in co me du e to c oo ling syst em , p en/yr 3,656 6,693 1 Assumptions of Economic Model -84 cows per pen -85 days of heat stress -$13/cwt milk price -$1.60/1,000 gal of water -20% reduction in milk production without cooling system 2 F=one row of fans over feedline and F + S=one row of fans over the feedline and one row of fans over the head-to-head freestalls.

Figure 1 .
Figure 1.Average Milk Production of Lactating Holstein Cows Exposed to Either Fans over the Feedline (F) or Fans over Both the Feedline and Freestalls (F+S).

Figure 2 .
Figure 2. Average Pen Dry Matter Intakes of Lactating Holstein Cows Exposed to Either Fans over the Feedline (F) or Fans over Both the Feedline and Freestalls (F+S).

Figure 3 .
Figure 3. Average Milk Production by Period of Study of Lactating Holstein Co ws Exposed to Either Fans over the Feedline (F) or Fans over Both the Feedline and Freestalls (F+S).

Figure 4 .
Figure 4. Avera ge Daily Ambient Temperature During Study.

Figure 5 .
Figure 5. Average Temperature of Pens Coo led with Either Fans over the Feedline (F) or Fans over Both the Feedline and Freestalls (F+S) at Different 3-Hour Periods of the Day.

Figure 6 .
Figure 6.Average Respiration Rates of Cows Exposed to Either Fans over the Feedline (F) or Fans over Both the Feedline and Freestalls (F+S).

Table 2 . Economic Analysis of Using Either Fans over the Feedline (F) or Fans over Both the Feedline and Freestalls (F+S) 1
An nu al f ixe d s pr ink ler co st, pe n/yr 100 100 To tal sp rin kle r w ater us age, gal /p en/yr 189,567 186,428 Co st o f wa ter fo r spr ink ler s, pe n/yr 303 298 To tal co st o f el ec tricity fo r fa ns, pe n/yr 445 890