Don't forget about dry cows in cooling efforts

Don't forget about dry cows in cooling efforts

Studies show economic and welfare advantages to controlling heat stress in the dry cow pen, too.

*Dr. Bruno do Amaral is a dairy nutritionist consultant based in Jacksonville, Fla., with Purina Animal Nutrition.

GROWING awareness about the detrimental effects of heat stress on cow health and performance has led to tremendous advancements in heat stress abatement efforts throughout the U.S. dairy industry.

Today's lactating dairy cows benefit, more than ever before, throughout the hottest months of the year from fans, sprinklers, misters, shade and dietary adjustments to help them cope with heat stress. The benefits: reducing the negative impact on milk production and fertility.

However, what about dry cows in those same herds? Current statistics indicate that they are not faring as well.

According to the National Animal Health Monitoring System's Dairy 2007 report, 74.3% of U.S. dairy operations provide fans for the lactating herd, but only 36% of operations provide fans for dry cows. Evaporative cooling via sprinklers was utilized by 20.3% of operations for their lactating cows, but only 4.6% of operations reported using sprinklers for dry cows.

Results of a series of studies recently conducted at the University of Florida indicate that heat stress abatement efforts for dry cows might — and should — be changing soon.

 

Prepartum heat stress

It is interesting to note the correlation between quarterly U.S. milk production statistics and heat stress on pre-fresh cows.

According to the National Agricultural Statistics Service's 2003-07 "Milk Cows & Production" report, milk production nationwide was consistently lowest in the fourth quarter (October to December) and highest in the second quarter (April to June).

During the fourth quarter, the cows reaching peak lactation are those that were in their last trimester of pregnancy during the peak heat stress months. The second quarter, on the other hand, is populated with cows peaking after completing gestation and freshening during the coolest winter months.

Researchers at the University of Florida have evaluated the effects of heat stress on late-gestation dry cows and found influences on milk production that further support this correlation.

In each of three consecutive studies, cows were dried off 46 days before expected calving and assigned to one of two treatment groups. One group was exposed to heat stress with no heat abatement other than shade, while the other received cooling via fans and sprinklers and had shade as well. After calving, both groups were housed together in a free-stall barn, where all animals received the cooling treatment (do Amaral et al., 2009; do Amaral et al., 2010; Tao et al., 2011).

Milk production was measured for all animals for the first 30 weeks of lactation. The cows that received heat stress abatement during the dry period consistently produced more milk in their subsequent lactations, as well as component yield (Table). For the three respective studies, these cows had an average of 20.5 lb., 10.3 lb. and 11.02 lb. more fat-corrected milk per day, for an overall average of approximately 14 lb. more milk per day.

The researchers attributed some of the difference in milk production to their findings that heat stress abatement increased mammary epithelial cell proliferation during the close-up dry period (Tao, 2011).

Heat stress during the dry period also impaired cows' immune systems. When immune function was evaluated at 20 days postpartum, the Florida researchers found that both neutrophil phagocytosis and neutrophil oxidative burst were reduced in the heat-stressed cows compared to the cooled cows. Lymphocyte proliferation also was three times higher in the cooled group versus the heat-stressed animals, indicating more active postpartum immunity in the cows that had received the heat stress abatement treatment prepartum (do Amaral et al., 2010; do Amaral et al., 2011).

This is an important finding, given the fact that the transition period has been identified as a time of immunosuppression, leaving fresh cows vulnerable to a host of early-lactation disease challenges. It is apparent from this research that the fresh cow disease complex could be influenced by the occurrence of heat stress in the pre-fresh period.

Finally, cows that were heat stressed in the dry period had higher rectal temperatures, reduced dry matter intake, higher respiration rates and consumed significantly more water than the cows that were cooled with fans and sprinklers.

 

Offspring

At birth, calves from cooled cows weighed an average of 28.7 lb., 12.0 lb. and 10.7 lb. more, for a total average of approximately 17 lb. more (do Amaral et al., 2009; do Amaral et al., 2010; Tao et al., 2011).

The difference in calf weights is likely due, at least in part, to the fact that heat-stressed cows calved earlier than their cooled counterparts. The result: earlier-term calves born with greater susceptibility to health and performance issues.

The researchers studied the immunity of calves born to the two groups of dams and found that calves born to heat-stressed dams had significantly lower serum immunoglobulin-G (IgG) levels from birth through 28 days of age (Figure 1) compared to calves from cooled dams (Tao et al., 2012).

Also, like their dams, calves exposed to heat stress in utero had suppressed lymphocyte proliferation compared to the cooled group (Tao et al., 2012a).

Finally, the research showed that the effects of heat stress in utero affected offspring all the way into adulthood. Heifer calves born in the study were followed through their first 30 weeks of lactation. The researchers found that calves from heat-stressed dams produced an average of 10 lb. less milk per day (Figure 2) than their cohorts born to cooled dams (Monteiro et al., 2013).

The collective results of recent research on the impact of providing heat stress abatement to dry cows suggest that this management practice could have important implications for animal welfare, postpartum milk production, transition cow health and offspring health and productivity.

 

References

Do Amaral, B.C., E.E. Connor, S. Tao, J. Hayen, J. Bubolz and G.E. Dahl. 2009. Heat-stress abatement during the dry period: Does cooling improve transition into lactation? J. Dairy Sci. 92:5988-5999.

Do Amaral, B.C., E.E. Connor, S. Tao, J. Hayen, J. Bubolz and G.E. Dahl. 2010. Heat stress abatement during the dry period influences prolactin signaling in lymphocytes. Domestic Animal Endocrinology. 38:38-45

Do Amaral, B.C., E.E. Connor, S. Tao, J. Hayen, J. Bubolz and G.E. Dahl. 2011. Heat stress abatement during the dry period influences metabolic gene expression and improves immune status in the transition period of dairy cows. J. Dairy Sci. 94:86-96.

Monteiro, A.P.A., S. Tao, I.M. Thompson and G.E. Dahl. 2013. Effect of heat stress in utero on calf performance and health through the first lactation. J. Anim. Sci. 91(suppl. 2):184(abstr.).

Tao, S., J.W. Bubolz, B.C. do Amaral, I.M. Thompson, M.J. Hayen, S.E. Johnson and G.E. Dahl. 2011. Effect of heat stress during the dry period on mammary gland development. J. Dairy Sci. 94:5976-5986.

Tao, S., A.P. Monteiro, I.M. Thompson, M.J. Hayen and G.E. Dahl. 2012. Effects of late gestation heat stress on growth and immune function of dairy calves. J. Dairy Sci. 95:7128-7136.

 

Comparison of fat-corrected milk production between groups of cows based on heat abatement treatment in the dry period versus no treatment over three studies

Variable

Heat stress

Cooling

P-value

Fat, %

3.58

3.52

0.57

Protein, %

3.01

2.87

0.01

Fat yield, lb./day

2.25

2.56

0.06

Protein yield, lb./day

1.92

2.11

0.17

Data from do Amaral et al. (2009 and 2010), Tao et al. (2011).

 

 

Don't forget about dry cows in cooling efforts

 

Volume:86 Issue:15

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