Cooling dry cows: What is the Value? Sha Tao, Ph.D. Department of Animal Sciences, University of Florida

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1 Introduction Cooling dry cows: What is the Value? Sha Tao, Ph.D. Department of Animal Sciences, University of Florida Elevated ambient temperature is a well-recognized environmental factor limiting production of dairy cattle. It is well studied that, in lactating dairy cows, thermal stress is related to decreased feed intake, altered metabolism, compromised lactation performance, increased disease incidences and impaired reproductive performance (Fuquay, Kadzere, et al., 2002; West; 2003). Compared with lactating cows, dry cows generate less metabolic heat (West; 2003) and have a higher upper critical temperature (Hahn; 1997). Thus, heat stress abatement in the management of dry cows is very often overlooked in the summer but substantially influences future performance of the cow and calf. Evaluation of Heat Stress for Dry Cows Temperature-humidity index (THI) is the most common measure of heat stress in the dairy industry (Armstrong, 1994). It combines the impacts of dry bulb temperature and relative humidity but does not include solar radiation or wind speed. Thus, THI may be a good indicator of heat stress in housing structures but not open lot or pasture based facilities (Collier et al., 2006). In most of the dairy operation, dry cows stay in the pasture until 2 or 3 weeks prior to expected calving. Thus, THI has limitations in measuring heat stress of dry cows in the pasture. In addition, in the confined facilities in subtropical area, data from Florida (Dikmen and Hansen, 2009) suggests that ambient dry bulb temperature is as good as THI to predict heat stress. Thus, the ambient temperature may be used as one criterion to measure environmental heat stress of dry cows in the southeast. Similar to lactating dairy cows, it is suggested that whenever the ambient temperature exceeds 70 F, extensive cooling such as evaporative cooling and supplemental Air flow should be utilized for dry cows. The more accurate measure for heat stress in dairy cows is the body temperature and respiration rate (Hansen et al., 2012). Under thermoneutral conditions, cows maintain their body temperature at F. Thus, whenever cow s body temperature exceeds F (rectal temperature) cooling methods should be considered. In addition to rectal temperature, the other way to identify heat stress is the increase in respiration rate, which is a key hallmark of heat stress and occurs even before the elevation of body temperature. Respiration rate is measured by counting the flank movements in one minute. 45 breath/min or above denotes heat stress. It is almost impossible to completely abate heat stress during the summer. However, successful decrease in rectal temperature and respiration rate of dry cows by cooling can result in huge economic returns. Table 1 summarizes the physiological responses of cooled and noncooled heat-stressed cows during the dry period. For example, as shown in recent studies conducted in the University of Florida (do Amaral et al., 2009; 2012; Tao et al., 2011; 2012b),

2 successful decrease in rectal temperature ~0.7 F and ~25 breath/min reduction in respiration rate of heat-stressed dry cows dramatically enhance subsequent milk production (Figure 1) and improve the immune function during the transition period. Table 1. Summary of studies on effects of supplemental cooling (CL) on late gestation heatstress (HT) cows on physiological parameters. Rectal Temperature, F Respiration Rate, Breath/min Location Reference HT CL Diff. HT CL Diff * * Florida Collier et al., * Israel Wolfenson et al., * * 67 7 Mexico Avendaño-Reyes et al., * * Israel Adin et al., * Florida do Amaral et al., * * Florida do Amaral et al., * * Florida Tao et al., * * Florida Tao et al., 2012b *P < All measures were taken from 1400 to 1500h. Dry Period Heat Stress Affects Feed Intake and Body Weight Similar to lactating dairy cows, heat stress also decreases dry matter intake (DMI) of dry cows. As shown in the Table 3, extensive cooling during the dry period results in ~15% increase in DMI compared with those without cooling during summer. As a result, cooled cows gained more body weight during the prepartum period (~3%, Table 2) and at least part of the increase in body weight gain is due to the increased fetal growth (Tao et al., 2011). Table 2. Summary of studies on effects of supplemental cooling (CL) on late gestation heatstress (HT) cows on DMI and BW during the prepartum period. DMI, kg/d BW, kg Location Reference HT CL Diff. HT CL Diff /2% Florida Collier et al., /8% Israel Adin et al., /18% /10% Florida do Amaral et al., /17% Florida do Amaral et al., /19% /2% Florida Tao et al., /9% /3% Florida Tao et al., 2012b /22% /4% Florida Thompson et al., 2012 In early lactation (first 2-3 weeks postpartum), prepartum heat stress abated cows consume a similar amount of DMI but produce more milk than heat-stressed cows. In order to support higher milk production, prepartum cooled cows have higher feed efficiency (do Amaral et al., 2009; 2011; Tao et al., 2012b) relative to non-cooled cows in early lactation and develop higher peripheral tissue insulin resistance and stronger ability to mobilize adipose tissue which are

3 reflected by lower plasma glucose concentration and higher NEFA concentration compared with non-cooled cows. Thus, although the higher milk production, prepartum cooled cows may need extra attention on the metabolic diseases such as ketosis and fatty liver in early lactation. As the lactation advances, prepartum cooled cows will consume more feed relative to non-cooled cows in order to meet the nutrient demand of higher milk production. Dry Period Heat Stress Affects Subsequent Milk Production Late gestation heat stress has profound effects on milk production in the subsequent lactation in dairy cattle (Figure 1). Several factors influence the effect of cooling dry cows on the milk production in the next lactation. Duration of cooling during the dry period has substantial impact on subsequent lactational performance. Cooling during the close-up period (last 3-4 wks of the gestation) only improves 1.4 kg/d more milk in the next lactation relative to those who don t receive cooling (Urdaz et al., 2006). In contrast, cows are cooled during the whole dry period produce ~5 kg/d more milk during the next lactation compared with those without prepartum cooling (Tao et al., 2011, 2012b; Thompson et al., 2012; Figure 1). Dry period length seems not to have any influence on the effects of prepartum cooling with respect to future milk production. For cows with short dry period (<40 d), prepartum cooling during the whole dry period still significantly improves the subsequent milk production (5.2 kg/d, Thompson et al., 2012). Figure 1. Summary of studies on effects of supplemental cooling (solid bars) on late gestation heat-stress (open bars) cows on subsequent milk production. The cooling method influences the effectiveness of heat stress abatement on subsequent milk production. With limited cooling, such as shade (Collier et al., 1982) or short interval soaking in

4 the middle of the day (Avendaño-Reyes, et al., 2006), only modest increases (1.1-2 kg/d) in subsequent milk production were observed and the difference was not statistically significant. However, when more extensive cooling (shade, fans and sprinklers) was provided to dry cows, milk production in the subsequent lactation was significantly improved (Wolfenson et al., 1988; do Amaral et al., 2011; Tao et al., 2011; 2012b; Thompson et al., 2012). Although the higher milk production, prepartum cooling doesn t affect concentrations of milk components in the subsequent lactation. It has been reported that milk fat percentage is increased in the next lactation (Avendaño-Reyes et al., 2006; do Amaral et al., 2009; 2011) by heat stress abatement during the dry period, but this observation only occurs in the early lactation. In other words, when the whole lactation is considered, no difference is observed regarding milk fat concentration between prepartum cooled and non-cooled cows (Tao et al., 2011, 2012b). Dry Period Heat Stress Affects Immune Function and Health In addition to milk production, heat stress during the dry period also affects the immune function of the animals during the transition period. The immune system includes the nonspecific innate immune function that is the first line of defense to pathogens in the body and the specific adaptive immune function that generates memory of pathogen exposure. Both arms of immune function are affected by the thermal status of the animals during the dry period. Recent studies from University of Florida provide evidence that cooling during the dry period enhances the proliferation of peripheral blood lymphocyte when encounter with mitogen in vitro and the ability of neutrophils to phagocytize and destroy pathogens via oxidative burst in early lactation (do Amaral et al., 2009; 2010; 2011). These studies are of importance because the enhanced immunity, especially for neutrophil function, plays an important role in the combat of pathogens involved in mastitis and metritis. Thus, it is expected that cooling heat-stressed dry cows enhances the health of the animals and decrease disease incidence. However, there is no study which explores the relationship between heat stress during the whole dry period and the incidence of disease in the postpartum period. In a larger scale study that included more than 2600 calving records over three consecutive years on a commercial dairy located in Florida, Thompson et al. (2012) studied seasonal effects during the dry period on the occurrence of health disorders in the first 60 DIM and found that cows dried off in hot months (June, July and August) had higher incidences of mastitis, respiratory problems and retained fetal membranes in early lactation compared with those dried in cool months (December, January and February). Although these results are confounded with the seasonal effects during early lactation and photoperiod during the dry period, the compromised immune function during the transition period due to late gestation heat stress may partly result in the observation of an increased occurrence of health disorders in early lactation of cows dried off in hot weather. Dry Period Heat Stress Effects on Reproduction Studies related to the impact of dry period heat stress on reproduction in the next lactation are limited and the existing data are inconsistent. Studies conducted in Mississippi suggest that there is no correlation between late gestation heat stress and reproductive performance in the next

5 lactation (Moore et al., 1992; Avendaño-Reyes et al., 2010). In controlled studies, Avendaño- Reyes et al. (2006) reported that compared with those provided with cooling during the dry period, heat-stressed cows had more days open and increased services per conception in the subsequent lactation. In contrast, Adin et al. (2009) reported no differences with regard to reproductive traits between cows non-cooled or cooled prepartum. Lewis et al. (1984) studied the residual effects of prepartum heat stress on uterine and ovarian development and function in early lactation and found that late gestation heat stress was related to increased systemic 13,14- dihydro-15-keto-prostaglandin F2α concentrations, accelerated uterine involution and smaller corpora lutea, but there were no differences for days open and services per conception between treatments. Therefore, the impact of dry period heat stress on subsequent reproductive outcomes remains unclear and large scale studies are warranted. Dry Period Heat Stress Affects Gestation Length and Performance of Offspring Late gestation heat stress also shortens cow s gestation length. As shown in Table 3., in most of the studies, relative to heat stress abatement, heat-stressed cows during the dry period have ~4 days shorter gestation length. In addition, the calves born from the heat-stressed cows are smaller and prepartum cooling increases calf birth weight (Table 3, ~5kg, 13%). The biology behind this maternal heat stress related fetal growth retardation is still unclear, but it is suggested that the shorter gestation length of heat-stressed cows account 33% of the reduction of fetal growth and the other 67% is due to the compromised placental development and direct effect by fetal hyperthermia (Tao et al., 2012a). Table 3. Summary of studies on effects of supplemental cooling (CL) on late gestation heatstress (HT) cows on gestation length and calf birth weight. Gestation Length, d Birth Weight, kg Reference HT CL HT CL Diff * /8% Collier et al., 1982a * /8% Wolfenson et al., /12% Avendaño-Reyes et al., * /7% Adin et al., * /42% do Amaral et al., * /13% do Amaral et al., * /12% Tao et al., * /16% Tao et al., 2012b * /13% Monteiro et al., 2012 *P < 0.05; P < 0.10 Additionally, maternal heat stress also compromises the immune function of the offspring. Passive immunity is of particular importance to neonatal survival of farm animals and is altered by maternal heat stress. After ingestion of same amount colostrum from respective dams, calves from heat-stressed cows during the dry period had lower serum IgG concentration and apparent efficiency of absorption relative to those from cooled dams (Tao et al., 2012a). Colostrum

6 quality is also of importance in the passive immunity of the offspring. Early studies (Nardone et al., 1997; Adin et al., 2009) indicate that colostral IgG content is reduced by the maternal heat stress. However, recent studies in Florida suggest that colostral IgG concentration is not related to the thermal status of the dams. In addition to the passive immunity, prepartum cooling also improves the cell-mediated immune function of the calves during the preweaning period (Tao et al., 2012a). Therefore, with the improved immune function, cooling during the dry period may decrease morbidity and enhance calf survival in the preweaning period. But the relevant study is still lacking Take Home Messages Dry cows also suffer from heat stress, and cooling dry cows improves production and health of the cows and calves. Provide cooling for dry cows in the summer as for lactating dairy cows. Cool the whole dry period. Acknowledgement Author thanks Dr. Geoffrey E. Dahl and Dave Bray for the valuable suggestions. References Adin, G., A. Gelman, R. Solomon, I. Flamenbaum, M. Nikbachat, E. Yosef, A. Zenou, A. Shamay, Y. Feuermann, S. J. Mabjeesh, and J. Miron Effects of cooling dry cows under heat load conditions on mammary gland enzymatic activity, intake of food water, and performance during the dry period and after parturition. Livest Sci. 124: Armstrong, D. V Heat stress interaction with shade and cooling. J. Dairy Sci. 77: Avendaño-Reyes, L., J. W. Fuquay, R. B. Moore, Z. Liu, B. L. Clark and C. Vierhout Relationship between accumulated heat stress during the dry period, body condition score, and reproduction parameters of Holstein cows in tropical condition. Trop Anim Health Prod. 42: Avendaño-Reyes, L., F. D. Alvarez-Valenzuela, A. Correa-Calderón, J. S. Saucedo-Quintero, P. H. Robinson, and J. G. Fadel Effect of cooling Holstein cows during the dry period on postpartum performance under heat stress conditions. Livest Sci. 281: Collier, R. J., G. E. Dahl, and M. J. Vanbaale Major advances associated with environmental effects on dairy cattle. J. Dairy Sci. 89: Collier, R. J., S. G. Doelger, H. H. Head, W. W. Thatcher, and C. J. Wilcox Effects of heat stress during pregnancy on maternal hormone concentrations, calf birth weight and postpartum milk yield of Holstein cows. J. Anim. Sci. 54: Dikmen, S., and P. J. Hansen Is the temperature-humidity index the best indicator of heat stress in lactating dairy cows in a subtropical environment? J. Dairy Sci. 92:

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8 Thompson, I. M., S. Tao, K. C. Jeong, W. W. Thatcher, and G. E. Dahl Effect of cooling during the dry period on neutrophil gene expression after Streptococcus uberis infection. J. Anim. Sci. 90(Suppl.3):188. (Abstr.) Urdaz, J. H., M. W. Overton, D. A. Moore, and J. E. P. Santos Technical note: Effects of adding shade and fans to a feedbunk sprinkler system for preparturient cows on health and performance. J. Dairy Sci. 89: West, J. W Effects of heat-stress on production in dairy cattle. J. Dairy Sci. 86: Wolfenson, D., I. Flamenbaum, and A. Berman Dry period heat stress relief effects on prepartum progesterone, calf birth weight, and milk production. J. Dairy Sci. 71: