Effects of bovine somatotropin and evaporative cooling plus shade on lactation performance of cows during summer heat stress

Cooling ameliorates decreased milk protein metrics in heat-stressed lactating Holstein cows

Cooling can alleviate the negative consequences of heat stress on multiple milk production metrics in dairy cows. However, it is still controversial whether cooling can increase milk protein content compared with heat-stressed cows. The objective of the present study was to evaluate the relief effect of cooling on the decrease in milk protein concentration during heat stress and elucidate the potential metabolic mechanisms. Thirty lactating multiparous Holstein cows (days in milk = 175 ± 25 d, milk yield = 27.5 ± 2.5 kg/d; mean ± SD) were assigned to 1 of 3 treatments: heat stress (HS; n = 10), cooling (CL; n = 10), and cooling with pair-feeding (PFCL; n = 10). The barns for PFCL and CL cows were equipped with sprinklers and fans, whereas the barn for HS cows were not. The average temperature-humidity index during the experiment ranged from 74 to 83. The spraying was activated automatically 2 times per day (1130-1330 h and 1500-1600 h) with 3 min on and 6 min off during the first 2 wk, and 1.5 min on and 3 min off during the last 2 wk, whereas the fans operated 24 h/d. The experiment lasted for 4 wk in total. Milk, urine, feces, total mixed ration, blood, and rumen fluid samples were collected weekly. Compared with HS, feed efficiency (1.24 and 1.49), milk protein yield (0.82 and 0.94 kg/d), and milk fat yield (0.98 and 1.26 kg/d) were increased in PFCL, whereas the differences between CL and HS were not significant. Compared with HS cows, PFCL and CL cows had a lower respiratory rate (70.6, 59.1, and 60.3 breaths per minute, respectively), rectal temperature (38.95, 38.61, and 38.51°C), and shoulder skin temperature (33.95, 33.25, 33.40°C), and had greater milk protein content (3.41, 3.72, and 3.69%) and milk fat percent (4.08, 4.97, 4.65%). Both the blood activity of catalase (increased by 12.8 and 41.0%) and glutathione peroxidase (12.6 and 40.4%) of PFCL and CL cows were greater than the HS cows. Compared with HS, cooling increased the blood content of glucose, methionine, threonine, and cystathionine by 10.7% and 10.3%, 19.0% and 9.5%, 15.8% and 12.0%, and 9.5% and 23.8% in PFCL and CL, respectively. In conclusion, the results indicated that cooling partially rescued milk protein synthesis induced by heat stress, and the potential mechanism may have been due to increased antioxidant ability, blood glucose, and key AA. Consequently, in addition to modifying the environment, nutritional and physiological strategies designed to influence carbohydrate, AA, and oxidative homeostasis may be an opportunity to maintain or correct low milk protein content during the warm summer months.

Genetic parameters for rectal temperature, respiration rate, and drooling score in Holstein cattle and their relationships with various fertility, production, body conformation, and health traits

Genetic selection for improved climatic resilience is paramount to increase the long-term sustainability of high-producing dairy cattle, especially in face of climate change. Various physiological indicators, such as rectal temperature (RT), respiration rate score (RR), and drooling score (DS), can be used to genetically identify animals with more effective coping mechanisms in response to heat stress events. In this study, we investigated genetic parameters for RT, RR (score from 1-3), and DS (score from 1-3). Furthermore, we assessed the genetic relationship among these indicators and other economically important traits for the dairy cattle industry. After data editing, 59,265 (RT), 30,290 (RR), and 30,421 (DS) records from 13,592 lactating Holstein cows were used for the analyses. Variance components were estimated based on a multiple-trait repeatability animal model. The heritability ± standard error estimate for RT, RR, and DS was 0.06 ± 0.01, 0.04 ± 0.01, and 0.02 ± 0.01, respectively, whereas their repeatability was 0.19, 0.14, and 0.14, respectively. Moderate genetic correlations of RR with RT and DS (0.26 ± 0.11 and 0.25 ± 0.16) and nonsignificant correlation between RT and DS (-0.11 ± 0.14) were observed. Furthermore, the approximate genetic correlations between RT, RR, and DS with 12 production, 29 conformation, 5 fertility and reproduction, 5 health, and 9 longevity-indicator traits were assessed. In general, the approximate genetic correlations calculated were low to moderate. In summary, 3 physiological indicators of heat stress response were measured in a large number of animals and shown to be lowly heritable. There is a value in developing a selection index including all the 3 indicators to improve heat tolerance in dairy cattle. All the unfavorable genetic relationships observed between heat tolerance and other economically important traits can be accounted for in a selection index to enable improved climatic resilience while also maintaining or increasing productivity in Holstein cattle.

Predicting dairy cattle heat stress using machine learning techniques

The objectives of the study were to use a heat stress scoring system to evaluate the severity of heat stress on dairy cows using different heat abatement techniques. The scoring system ranged from 1 to 4, where 1 = no heat stress; 2 = mild heat stress; 3 = severe heat stress; and 4 = moribund. The accuracy of the scoring system was then predicted using 3 machine learning techniques: logistic regression, Gaussian naïve Bayes, and random forest. To predict the accuracy of the scoring system, these techniques used factors including temperature-humidity index, respiration rate, lying time, lying bouts, total steps, drooling, open-mouth breathing, panting, location in shade or sprinklers, somatic cell score, reticulorumen temperature, hygiene body condition score, milk yield, and milk fat and protein percent. Three different treatments, namely, portable shade structure, portable polyvinyl chloride pipe sprinkler system, or control with no heat abatement, were considered, where each treatment was replicated 3 times with 3 second-trimester lactating cows. Results indicate that random forest outperformed the other 2 methods, with respect to both accuracy and precision, in predicting the sprinkler group's score. Both logistic regression and random forest were consistent in predicting scores for control, shade, and combined groups. The mean probability of predicting non-heat-stressed cows was highest for cows in the sprinkler group. Finally, the logistic regression method worked best for predicting heat-stressed cows in control, shade, and combined. The insights gained from these results could aid dairy producers to detect heat stress before it becomes severe, which could decrease the negative effects of heat stress, such as milk loss.

Short communication: Effect of supplemental zinc source with and without evaporative cooling on systemic and mammary metabolism of lactating dairy cows during summer

The negative effects of heat stress partly result from disturbed systemic metabolic responses and possibly altered mammary gland metabolism of lactating dairy cows. Our previous research reported that supplemental dietary Zn sources may affect milk fat synthesis of lactating cows during summer. Thus, our objective was to evaluate the systemic and mammary metabolism of cows fed 2 supplemental Zn sources under 2 environmental conditions. Multiparous lactating Holstein cows (n = 72; days in milk: 99.7 ± 13.4 d; parity: 2.9 ± 0.3) were randomly assigned to 4 treatments in a 2 × 2 factorial arrangement. Treatments included 2 different environments: cooled (CL) using fans and misters or noncooled (NC), and 2 supplemental Zn sources: 75 mg of Zn hydroxychloride/kg of DM (IOZ) or 35 mg of Zn hydroxychloride/kg of DM + 40 mg of Zn-Met complex/kg of DM (ZMC). The 168-d experiment was divided into baseline and environmental challenge phases, 84 d each. During the baseline phase, all cows were cooled and fed respective dietary treatments, and during the environmental challenge phase cows continued receiving the same diets but NC cows were deprived of cooling. Temperature-humidity index averaged 77.6 ± 3.8 and 77.8 ± 3.8 for CL and NC pens, respectively, during the environmental challenge phase. Plasma was collected before the baseline phase and at 1, 3, 5, 12, 22, 26, 41, 54, 61, 68, 75, and 81 d of the environmental challenge phase for metabolites and insulin analyses. Mammary biopsies were collected before the baseline phase and at 7 and 56 d of the environmental challenge phase to measure mRNA abundance of proteins related to mammary metabolism. Compared with CL, NC reduced plasma glucose, nonesterified fatty acids, β-hydroxybutyrate, and triglyceride concentrations, but increased insulin concentration. Cows fed ZMC had greater plasma triglyceride concentration than IOZ. Treatments had no effect on mRNA abundance of protein related to mammary fatty acid and glucose metabolism except that NC cows had greater mammary mRNA abundance of 6-phosphogluconate dehydrogenase and ATP-dependent 6-phosphofructokinase than CL cows. In conclusion, deprivation of evaporative cooling influenced the metabolism of lactating dairy cows but dietary Zn source had no apparent effect.

Graduate Student Literature Review: Heat abatement strategies used to reduce negative effects of heat stress in dairy cows

The southeastern United States experiences an extended hot season with a high environmental temperature and relative humidity. With increasing global temperatures, managing dairy cattle in regions with tropical, subtropical, and Mediterranean climates is becoming an increasing challenge. Heat-stressed cows will decrease feed intake, decrease productivity, and increase respiration rate in an attempt to maintain internal body temperature. Temperature-humidity index (THI) is a unitless value that has been used to measure the magnitude of heat stress on dairy cows. Many researchers have studied the THI threshold at which dairy cattle begin to experience heat stress. When housing cows in a confinement setting, a pasture-based setting, or a combination of the two, the appropriate heat abatement should be implemented to allow cows to perform to their potential and to improve overall animal welfare. This review summarizes heat abatement strategies that have been studied to reduce the negative effects of heat stress.

Shade access in combination with sprinkling and ventilation effects performance of Holstein cows in early and late lactation

The negative effect of heat stress on dairy cows, with a temperature humidity index (THI) over 72, has been extensively studied. However, there are few studies on THI values under 72 that compare the effect of heat stress in different lactation stages. The objective of this study was to determine the heat stress effect on two lactation stages with a THI below the threshold 72. Thirty-nine multiparous, non-pregnant Holstein cows with more than 30 kg/cow.day of solid-corrected milk were used in a randomised complete block design to evaluate six treatments. The experimental design had a 3 by 2 factorial arrangement with three heat stress mitigation strategies: No shade (CON), access to shade only, and access to shade combined with sprinkling and ventilation, and two stages of lactation: early (S1) and late (S2), 12 ± 10.3 and 201 ± 45.8 days in milk respectively, for a duration of 81 consecutive days. All treatments, except CON had access to artificial shade from 0900 hours to 0500 hours next day. From 0500 hours to 0900 hours all cows were managed together in a grazing session. Additionally, sprinkling and ventilation cows had two 30-min sessions of ventilation and spray (0900 hours, 1530 hours). The average THI was 70.1 ± 4.46 (minimum THI: 60.4; maximum THI: 81.7) and the average hours above 72 were 7.8 ± 5.98. Animals in S1 presented higher solids-corrected milk reduction (P < 0.0001; 5.4 and 1.9 kg/cow.day), and protein yield (<0.0001; 0.13 and 0.54 kg/cow.day) than animals in S2 when shade was not allowed (CON). It was concluded that under these conditions, animal productivity is more negatively affected in early lactation animals. The use of shade with or without spray and ventilation mitigates heat stress effects on both stages of lactation.

Effects of heat stress and dietary zinc source on performance and mammary epithelial integrity of lactating dairy cows

Dietary Zn and heat stress alter gut integrity in monogastric animals. However, effects of Zn on mammary epithelial integrity in heat-stressed lactating dairy cows have not been studied. Multiparous lactating Holstein cows (n = 72) were randomly assigned to 1 of 4 treatments with a 2 × 2 factorial arrangement to study the effects of environment and Zn source on performance and mammary epithelial integrity. Treatments included 2 environments [cooled (CL) or not cooled (NC)] and 2 Zn sources [75 mg/kg of supplemental Zn as Zn hydroxychloride (IOZ) or 35 mg/kg of Zn hydroxychloride + 40 mg/kg of Zn-Met complex (ZMC)]. The experiment was divided into baseline and environmental challenge phases of 84 d each. All cows were cooled during the baseline phase (temperature-humidity index = 72.5), whereas NC cows were not cooled during environmental challenge (temperature-humidity index = 77.7). Mammary biopsies were collected on d 7 and 56 relative to the onset of environmental challenge to analyze gene expression of claudin 1, 4, and 8, zonula occludens 1, 2, and 3, occludin, and E-cadherin and protein expression of occludin and E-cadherin. Deprivation of cooling increased respiration rate (64.8 vs. 73.9 breaths/min) and vaginal temperature (39.03 vs. 39.94°C) and decreased dry matter intake (26.7 vs. 21.6 kg/d). Energy-corrected milk yield decreased for NC cows relative to CL cows (24.5 vs. 34.1 kg/d). An interaction between environment and Zn source occurred for milk fat content as CL cows fed ZMC had lower milk fat percentage than other groups. Relative to CL cows, NC cows had lower concentrations of lactose (4.69 vs. 4.56%) and solids-not-fat (8.46 vs. 8.32%) but a higher concentration of milk urea nitrogen (9.07 vs. 11.02 mg/mL). Compared with IOZ, cows fed ZMC had lower plasma lactose concentration during baseline and tended to have lower plasma lactose concentration during environmental challenge. Plasma lactose concentration tended to increase at 3, 5, and 41 d after the onset of environmental challenge in NC cows relative to CL cows. Treatment had no effect on milk BSA concentration. Cows fed ZMC tended to have higher gene expression of E-cadherin relative to IOZ. Compared with CL, NC cows had increased gene expression of occludin and E-cadherin and tended to have increased claudin 1 and zonula occludens 1 and 2 gene expression in the mammary gland. Protein expression of occludin and E-cadherin was unchanged. In conclusion, removing active cooling impairs lactation performance and affects gene expression of proteins involved in the mammary epithelial barrier, and feeding a portion of dietary zinc as ZMC improves the integrity of the mammary epithelium.

Practices for Alleviating Heat Stress of Dairy Cows in Humid Continental Climates: A Literature Review

Simple Summary

The severity of heat stress issues on dairy cows will increase as global warming progresses. Fortunately, major advances in environmental management, including fans, misters, sprinklers, and cooled waterbeds, can attenuate the effects of thermal stress on cow health, production, and reproduction. These cooling systems were, however, tested in subtropical areas and their efficiency in northern regions is uncertain. This article assesses the potential of existing technologies to cool cows in humid continental climates through calculation of heat stress indices.

Abstract

Heat stress negatively affects the health and performance of dairy cows, resulting in considerable economic losses for the industry. In future years, climate change will exacerbate these losses by making the climate warmer. Physical modification of the environment is considered to be the primary means of reducing adverse effects of hot weather conditions. At present, to reduce stressful heat exposure and to cool cows, dairy farms rely on shade screens and various forms of forced convection and evaporative cooling that may include fans and misters, feed-line sprinklers, and tunnel- or cross-ventilated buildings. However, these systems have been mainly tested in subtropical areas and thus their efficiency in humid continental climates, such as in the province of Québec, Canada, is unclear. Therefore, this study reviewed the available cooling applications and assessed their potential for northern regions. Thermal stress indices such as the temperature-humidity index (THI) were used to evaluate the different cooling strategies.

Postgraze assessment of toxicosis symptoms for steers grazed on toxic endophyte-infected tall fescue pasture

A 2-yr pen experiment was conducted using 12 different crossbred Angus steers each year to determine if short-term changes in prolactin concentrations, body temperature, and vasoconstriction reflect recovery from fescue toxicosis after steers that previously grazed toxic endophyte (Neotyphodium coenophialum)-infected Kentucky 31 tall fescue [Lolium arundinaceum (Schreb.) Darbysh] are placed on nontoxic feed. Groups of 6 steers from toxic endophyte-infected and endophyte-free tall fescue grazing treatments were blocked by BW for assignment to pens as a randomized complete block design with 2 replications. Two environments were implemented by initiating the experiment on 18 August in yr 1 and on 8 September in yr 2 for durations of 30 and 21 d, respectively. Rectal temperatures were recorded, jugular blood was collected for assaying serum prolactin, and cross sections of the caudal artery were ultrasonically imaged at selected time points to evaluate temporal changes in the response variables. Rectal temperatures in steers on the toxic endophyte pasture treatment declined (P < 0.05) linearly over time in yr 1 and 2 and were similar (P > 0.10) to those on endophyte-free treatment on d 30 in yr 1 and by d 15 in yr 2. Prolactin concentrations in steers on the toxic endophyte pasture treatment showed curvilinear increases (P < 0.05) over time and were similar (P > 0.10) to steers on the endophyte-free treatment by d 15 in yr 1 and by d 10 in yr 2. Luminal areas of the caudal artery in toxic endophyte steers were less (P < 0.05) than those in endophyte-free steers across all dates in both years. Results indicated that rectal temperatures in steers after they are removed from toxic fescue may decrease over time, but temporal changes in rectal temperatures could be affected more by prevailing ambient temperatures than by actual mitigation of fescue toxicosis. Prolactin concentrations in steers after they are removed from toxic endophyte tall fescue can increase and stabilize in less than 2 wk, but alkaloid-induced vasoconstriction that causes a vulnerability to severe heat stress is not alleviated within 30 d.

Effects of supplemental recombinant bovine somatotropin and mist-fan cooling on the renal tubular handling of sodium in different stages of lactation in crossbred Holstein cattle

The effect of supplementary administration of recombinant bovine somatotrophin (rbST) on the renal tubular handling of sodium in crossbred 87.5% Holstein cattle housed in normal shade (NS) or mist-fan cooled (MF) barns was evaluated. The cows were injected with 500 mg rbST at three different stages of lactation. The MF barn housed cows showed a slightly decreased ambient temperature and temperature humidity index, but an increased relative humidity. Rectal temperature and respiration rates were significantly lower in cooled cows. The rbST treated cows, housed in NS or MF barns, showed markedly increased milk yields, total body water, extracellular fluid and plasma volume levels, along with a reduced rate of urine flow and urinary excretion of sodium, potassium and chloride ions and osmolar clearance, in all three stages of lactation. Renal tubular sodium and water reabsorption were increased after rbST administration without any alteration in the renal hemodynamics. Lithium clearance data suggested that the site of response is in the proximal nephron segment, which may be mediated via increases in the plasma levels of aldosterone and IGF-1, but not vasopressin, during rbST administration.

Effects of misty-fan cooling and supplemental rbST on rumen function and milk production of crossbred Holstein cattle during early, mid and late lactation in a tropical environment

Two groups of five crossbred 87.5% Holstein cattle were housed in normal shade only (NS) as non-cooled cows and in shaded housing with misty-fan cooling (MF) as cooled cows. The cows were treated with recombinant bovine somatotropin (rbST) in early, mid and late lactation with three consecutive injections of rbST in every 14 days. Ambient temperatures and the temperature humidity index in the NS barn were significantly higher than those of the MF barn, whereas relative humidity in MF was higher than that of NS barn. The DMI of cooled cows were higher than those of non-cooled cows, and cooled cows exhibited more response to rbST treatment. Exogenous rbST significantly increased milk yield throughout lactation. The rbST-treated cows had higher total ruminal fermentation products as volatile fatty acid and ammonia nitrogen than the non-rbST treated cows and associated changes were greater in cooled animals in all stages of lactation. Exogenous rbST increased the concentrations of milk urea nitrogen in both groups. These results suggest that the changes in ruminal fermentation with greater production of total VFA and NH(3)N in response to rbST in crossbred cows whether under misty-fan cooling or not, is in part through an increase in feed intake, thereby making more substrate available to the mammary gland for milk synthesis.

Effect of sprinkling on feedlot microclimate and cattle behavior

Experiments were conducted to evaluate strategies designed to reduce heat stress of cattle. In the first experiment, cattle were sprinkled for 20 min every 1.5 h between 1000 hours and 1750 hours (WET) versus not sprinkled (DRY). In a second experiment, treatments consisted of: (1) control, no water application; (2) water applied to the pen surfaces between 1000 hours and 1200 hours (AM); and (3) water applied to pen surfaces between 1400 hours and 1600 hours (PM). In both experiments, sprinkling lowered (P < 0.05) mid-afternoon temperatures. In the first experiment, relative humidity (RH) of WET versus DRY pens differed (P < 0.05) and averaged 72.4 and 68.9%, respectively. The average temperature-humidity index (THI) in WET pens was 0.5 units lower (P < 0.05), than the THI in DRY pens. In the second experiment, RH in sprinkled pens was also greater (P < 0.05) than RH in control (CON) pens However, THI differed (P < 0.05) among treatments, being 81.5, 80.9, and 80.3, respectively for CON, AM, and PM. Pens with sprinklers had a larger percentage of steers in areas where sprinkling took place, even on days when sprinkling had not occurred. Based on differences in percentage of cattle panting in sprinkled and non-sprinkled treatments, sprinkling was found to have a positive effect on cattle feeding area microclimate and to reduce the susceptibility of cattle to hyperthermia. However, cattle acclimatization to being sprinkled can result in slight hyperthermia even during cooler days when sprinkling would normally not be utilized.

Sprinklers and Shade Cool Cows and Reduce Insect-Avoidance Behavior in Pasture-Based Dairy Systems

The body temperature of dairy cows in pastoral systems during summer reaches a peak during and following the p.m. milking. Shade and sprinklers can be used separately or in combination at the milking parlor to reduce heat load. Farmers anecdotally report that the use of sprinklers reduces irritation from insects that occurs while cows are waiting for milking. Once daily, we assessed the effectiveness of short-term exposure to shade and sprinklers for cooling cows [via respiration rate and body (vaginal) temperature] and reducing insect-avoidance behaviors before the p.m. milking in a pasture-based dairy system. Head position was measured as an indicator of whether cattle were avoiding water from the sprinklers. Forty-eight Holstein-Friesian dairy cows were divided into 12 groups (4 cows per group, n = 3 groups/treatment) and were exposed to 1 of 4 treatments for 90 min before the p.m. milking: 1) shade, 2) sprinklers, 3) shade and sprinklers, or 4) uncooled control. Respiration rate was reduced by 30% with shade alone compared with controls [54 vs. 78 +/- 2.3 ( +/- SED) breaths/min, respectively]. Sprinklers alone (30 +/- 2.3 breaths/min) and the combined effects of shade and sprinklers (24 +/- 2.3 breaths/min) reduced the respiration rate by 60 and 67%, respectively, compared with controls. Shaded cows had lower body temperatures during the 90-min treatment period compared with controls (shade: 38.6 degrees C; shade and sprinklers: 38.6 degrees C; control: 38.9 +/- 0.09 degrees C). The decrease in body temperature of cows under sprinklers was more marked than for shade alone and remained lower for at least 4 h after milking (sprinklers: 38.7 degrees C; shade and sprinklers: 38.6 degrees C; shade: 38.9 degrees C; control: 39.2 +/- 0.10 degrees C). The sprinkler treatment reduced the number of tail flicks (control: 12.6 vs. sprinklers: 6.6 +/- 2.4 flicks/min) and hoof stamps (control: 4.4 vs. sprinkler: 2.2 +/- 0.5 stamps/min). Cows exposed to sprinklers spent more time with their heads lowered compared with cows in the shaded and control treatments. The reductions in body temperature and respiration rate attributable to shade and sprinklers were greatest when the temperature-humidity index and heat-load index were > or = 69 and 77, respectively, and cows benefited from cooling when these levels were exceeded.

Fertility of Lactating Dairy Cows Administered Recombinant Bovine Somatotropin During Heat Stress

Administration of recombinant bovine somatotropin (bST) to lactating dairy cows during heat stress increases milk yield, but it also can increase body temperature and may therefore compromise fertility. However, it is possible that bST treatment could increase fertility during heat stress because it has been reported to increase fertility in lactating cows. In addition, bST increases secretion of insulin-like growth factor-I (IGF-I) that promotes embryo survival. The purpose of this study was to determine effects of bST on reproductive function in lactating dairy cows during heat stress. The experiment was conducted in southern Georgia from July to November 2005 using lactating Holstein cows (n = 276 for reproductive traits). For first service timed artificial insemination (TAI), cows were presynchronized with 2 injections of PGF(2alpha) given 14 d apart followed by a modified Ovsynch protocol (GnRH and insemination at 72 h following PGF(2alpha) ). Pregnancy was diagnosed by using ultrasonography on d 29 and reconfirmed by palpation between d 45 and 80 post-TAI. Nonpregnant cows were resynchronized with the modified Ovsynch protocol and received a second TAI. Treatment with bST started 1 wk before the start of Ovsynch and continued at 2-wk intervals. Blood samples were collected from a subset of cows to determine IGF-I profiles immediately before the first bST injection, 1 wk later, and at d 35 of bST treatment. Rectal temperatures were assessed on d 29 of bST treatment. Pregnancy rates (d 45 to 80 post-TAI) did not differ between bST and control cows for first- (16.7 vs. 15.2%) or second-service TAI (14.8 vs. 17.2%). Plasma concentrations of IGF-I and milk yield were greater for bST-treated cows following the initiation of bST treatment and bST increased rectal and vaginal temperatures. Body condition score was less for bST-treated cows. In conclusion, treatment with bST during heat stress increased IGF-I concentrations, milk yield over time, and rectal and vaginal temperatures without affecting first- or second-service pregnancy rates. Thus, at least under certain housing conditions, bST can be used to improve milk yield during heat stress without compromising fertility.

Influence of stocking rate and steroidal implants on growth rate of steers grazing toxic tall fescue and subsequent physiological responses

An 84-d grazing experiment was conducted in 2 growing seasons to evaluate interactions of stocking rate and steroidal implants with BW gain and symptoms of toxicosis in yearling steers grazing endemic endophyte-infected (E+) tall fescue (Festuca arundinacea Schreb.). A 4 x 2 factoral design was used to evaluate 4 stocking rates (3.0, 4.0, 5.0, and 6.0 steers/ ha) with or without steroidal implants (200 mg of progesterone + 20 mg of estradiol benzoate). Treatment combinations were randomly assigned to eight 1-ha pastures of E+ Kentucky-31 tall fescue (i.e., treatments were not replicated). Treatment effects were analyzed for ADG, total BW gain per hectare, forage availability, and hair coat ratings. At the conclusion of grazing in the second year (22 June), steers were placed on a bermudagrass [Cynodon dactylon (L.) Pers.] pasture, and rectal temperatures and serum prolactin concentrations were monitored for 10 d to assess carryover effects of stocking rate and steroidal implants on recovery from toxicosis-related heat stress. Forage availability differed (P < 0.001) between years, but there were no year x treatment interactions (P > 0.10). There was an implant x stocking rate interaction (P < 0.05) on ADG. Differences between the slopes in the regression equations indicated that ADG responded to implantation when stocking rates were low, but the response diminished as stocking rate increased. Stocking rate did not influence (P = 0.89) postgraze rectal temperature, but the regression intercept for implanted steers was 0.4 degrees C greater (P < 0.05) than for nonimplanted steers, and the difference was consistent across the entire 10-d fescue-free grazing period. Concentrations of prolactin increased during the 10-d fescue-free grazing period, but trends differed due to an implantation x stocking rate interaction (P < 0.05). Results indicate that implantation with progesterone + estradiol benzoate increases ADG with lower stocking rates, but the effect diminishes with increased grazing intensity. Implantation with steroid hormones increased rectal temperatures, but during a fescue-free grazing period rectal temperatures and serum prolactins for implanted and nonimplanted steers returned to values indicative of a stable and healthy status in a 192- to 240-h (i.e., an 8- to 10-d) period. However, because the treatments used in this study were not replicated, these observations need to be confirmed with replicated studies.

Diet and cooling interactions on physiological responses of grazing dairy cows, milk production and composition

The objective of this trial was to evaluate the effects of diet and cooling in the holding pen before milking on rectal temperature, respiration rate and milk production and composition. Fifty-eight lactating Holstein cows were used in a factorial split-plot design, at Rafaela Experimental Station from 12 January to 3 March 2003. The treatments were combinations of two diets: control (CD) and balanced (BD) with two levels of cooling before milking: none (NSF) and a sprinkler and fans (SF). Forage:concentrate ratios for CD and BD were 81:19 and 68:32, respectively. Cows were milked twice daily. Milk production was recorded daily, and milk composition (fat, protein, lactose and urea) was analysed twice a week. The physiological data were recorded once a week, before the cattle entered the holding pen and after milking, in the afternoon. Average maximum weekly temperature humidity index was 75.4 and ranged from 61.4 to 83. There were highly significant effects of cooling on physiological responses. Milk production was affected by diet and cooling, with no interaction; the highest and lowest production of milk was 22.42 and 20.07 l/cow per day, for BD+SF and CD+NSF, respectively. Protein was affected by diet, and was higher for BD (3.17 vs. 3.08%). There were interaction effects on milk fat at the 8% level, the highest concentration being 3.65% for BD+NFS. It was concluded that under grazing conditions, cooling by sprinkler and fans before milking improves the comfort of dairy cows, and that the effects on milk production and composition are enhanced when diets are specially formulated for heat-stress periods.

Comparison of three estrus detection systems during summer in a large commercial dairy herd

The objective of the study was to compare three systems for estrus detection and combinations of these systems on a large commercial dairy (1075 lactating cows) during stress of summer heat. At 37-45 days in milk (DIM), 255 cows were fitted with a HeatWatch device (HW; DDx Inc., Denver, CO), an activity sensor ALPRO (ALPRO; DeLaval Inc., Kansas City, MO), and visually observed (VO) three times daily. Pregnancy status was determined by uterine palpation per rectum 35-49 days following artificial insemination (AI). Effects of DIM, parity, standing events, inseminator, and interval between onset of estrus and AI on conception rates were determined using logistic regression. Efficiencies for detection of estrus, determined by comparing detected periods of estrus with a theoretical total of 570 periods, were 49.3% (VO), 37.2% (ALPRO), 48.0% (HW), and 80.2% for all three systems simultaneously. Conception rates (LSM+/-S.E.) for cows detected by one or more of the three systems were 6.2+/-3.9 for VO, 19.8+/-5.6 for ALPRO, 17.3+/-5.0 for HW, 22.8+/-7.0 for VO+ALPRO, 26.9+/-4.6 for VO+HW, 23.2+/-5.2 for ALPRO+HW, and 18.4+/-4.7 for VO+ALPRO+HW. Inseminations performed during no and mild heat stress (temperature-humidity index; THI< or =76) had greater conception rate (P<0.05; 38.8%) compared to AI performed during moderated heat stress conditions (THI>76; 17.6%). Number of mounts were higher for primiparous versus multiparous cows (P<0.05). Cows over 80 DIM during estrus exhibited fewer (P<0.05) standing events. The highest conception rate occurred with the combination of VO+HW, which confirms the premise that combination of multiple systems enhances both the efficiency and accuracy of estrus detection.

Examination of Heat Stress and Stage of Lactation (Early versus Late) on Fecal Shedding ofE. coliO157:H7 andSalmonellain Dairy Cattle

Mature, healthy lactating dairy cattle were sampled on two farms in the southwestern United States to examine the effects of heat stress (Experiment I) and stage of lactation (Experiment II) on the fecal shedding of E. coli O157:H7 and Salmonella. To examine the effects of heat stress, fecal samples were collected from 45 cows at 7:00 AM (coolest part of the day) and 5:00 PM (hottest part of the day) in August 2002 on a 250 cow dairy. The study was replicated one month later (n = 170 total samples). A temperature-heat index (THI) was calculated for each sampling time. In Experiment II, stage of lactation was examined by sampling lactating dairy cattle early [< 60 days in milk (DIM)] and late (> 150 DIM) in the lactation cycle in the summer of 2001. The study was replicated the following summer (60 cows/group/replicate; n = 240 total samples). For Experiment I, THI averaged 75 and 82 for the AM and PM samplings, respectively, indicating the cows were beginning to experience heat stress in the morning and by afternoon were in severe heat stress. The shedding of E. coli O157:H7 tended to be higher (p = 0.09) in the afternoon sampling of the first replicate, however was not different in the second replicate or when both replicates were pooled (p > 0.10). Salmonella shedding was not different (p > 0.10) at any sampling time with nearly 100% of the cows positive. Stage of lactation had no effect on the number of cows shedding E. coli O157:H7 (p > 0.10). Salmonella shedding tended to be higher (p = 0.09) in early lactation cows in the first replicate, while in the second replicate more late lactation cows were shedding Salmonella (p < 0.05); however, there were no differences due to stage of lactation when replicates were pooled (p > 0.10). While further research is needed, results of this research highlight the variability in pathogen shedding in healthy dairy cattle and indicate that environmental factors and/or production demands may influence shedding patterns of E. coli O157:H7 and Salmonella.

Antimicrobial susceptibility and factors affecting the shedding of E. coli O157:H7 and Salmonella in dairy cattle

AIMS

To examine factors affecting faecal shedding of the foodborne pathogens Escherichia coli O157:H7 and Salmonella in dairy cattle and evaluate antimicrobial susceptibility of these isolates.

METHODS

Faecal samples were obtained in replicate from lactating (LAC; n = 60) and non-lactating (NLAC; n = 60) Holstein cattle to determine influence of heat stress, parity, lactation status (LAC vs NLAC) and stage of lactation [</=60 or >60 days in milk (DIM)] and cultured for E. coli O157:H7 and Salmonella. A portion of the recovered isolates were examined for antimicrobial susceptibility using the broth microdilution technique.

RESULTS

No effects of heat stress were observed. Lactating cows shed more (P < 0.01) E. coli O157:H7 than NLAC cows (43% vs 32%, respectively). Multiparous LAC cows tended to shed more (P = 0.06) Salmonella than primiparous LAC cows (39% vs 27%, respectively). Parity did not influence (P > 0.10) bacterial shedding in NLAC cows. Cows </=60 DIM shed more (P < 0.05) Salmonella than cows >60 DIM. Seventeen Salmonella serotypes were identified with the most prevalent being Senftenberg (18%), Newport (17%) and Anatum (15%). Seventy-nine of the Salmonella isolates were resistant to at least one of the seven antibiotics. Escherichia coli O157:H7 isolates were resistant to 11 different antibiotics with multiple resistance to nine or more antibiotics observed in five isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated differences in the shedding patterns of foodborne pathogens due to the stage of the milk production cycle and may help identify times when on-farm pathogen control would be the most effective.