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Tropical climate change and its effect on milk production of dairy cattle in Thailand

Thirarat Sae-tiao, Thawee Laodim, Skorn Koonawootrittriron, Thanathip Suwanasopee and Mauricio A Elzo1

Department of Animal Science, Kasetsart University, Bangkok 10900, Thailand
agrskk@ku.ac.th
1 Department of Animal Sciences, University of Florida, Gainesville, FL 32611-0910, USA

Abstract

This research aimed to characterize changes in average temperature (AT), relative humidity (RH), diurnal temperature variation (DTV), and temperature-humidity index (THI), and to determine the effects of stress levels (SL) on milk yield (MY) in Thai multibreed dairy cattle. The AT and RH records (n = 85,824) measured by 17 meteorological stations across Thailand were used to calculate DTV and THI. Climate variables were analyzed using a linear model. The effect of SL on MY was estimated by using milk records (n = 46,442) from 5,080 first-lactation cows raised in 456 farms with a model that included calving herd-year-season, breed group (BG), days in milk, SL, calving age, and interaction between BG and SL as fixed effects, and residual as random effect. All fixed effects were important for all climate variables (p < 0.01). The highest percentages of THI were in the moderate stress level (67%) for all regions. The SL, BG and interaction between SL and BG were important factors for MY (p < 0.01). Cows in BG4, BG5, and BG6 tended to have higher MY than other breed groups including purebred H in the comfort zone and mild stress level, and also had higher MY than BG1, BG2, and BG3 under a moderate stress level. Cows from all breed groups had higher MY than under mild and moderate stress levels. Thus, to increase MY per cow under increasingly stressful climate conditions, farmers would need to enlarge their investment in active cooling solutions to reduce temperature and humidity

Keywords: climate change, temperature-humidity index, stress, dairy cattle, tropics


Introduction

Global climate is changing, and it is manifesting itself through various kinds of environmental changes. Extreme droughts, high ambient temperatures, heat waves, floods, and freak storms occurred across the globe and affected agriculture and productivity of livestock systems (IPCC 2007), especially in tropical areas. The tropical land mass covers over 20% of the earth’s total land surface, and as many as 62 countries are in this region (Oliver and Hidore 1984). Most agriculture and livestock production are located in tropical regions characterized by hot and humid weather conditions (Zhao et al 2005; Key et al 2014). Thailand considered a tropical country with consistently high ambient temperatures and high relative humidity throughout the year (OEPP 2000), has two monsoons every year (TMD 2014): a northeast monsoon between October and February and a southwest monsoon between May and October. High temperature and humidity could create environmental stress and affect dairy cattle productivity, especially in open-house operations which are the predominant dairy cattle housing system in Thailand.

Commercial dairy cattle farming in Thailand began in 1957. To increase milk production, Holstein and other European dairy cattle breeds (Jersey, Brown Swiss, and Red Dane) have been used in crossbreeding and upgrading mating schemes. The current Thai dairy population is multibreed (Koonawootrittriron et al 2009) and most animals (91%) are crossbred and have a Holstein fraction higher than 87.5% (Ritsawai et al 2014). High ambient temperature and relative humidity create uncomfortable and stressful conditions that have a negative effect on feed intake, reproduction and production of dairy cattle, especially lactating cows (Bouraoui et al 2002; Kadzere et al 2002).

The Temperature-Humidity Index (THI) is an indicator to assess the level of stress caused by high ambient temperature and humidity, and THI values are examined to determine whether animals are in the comfort or stress zones (de la Casa and Ravelo 2003; Bohmanova et al 2007). Dairy cows are likely to begin experiencing heat stress when THI values exceed 72 units (Armstrong 1994).   Considering proportion of THI by stress level of dairy cows per season would help increase dairy production efficiency and prevent loss of annual income in dairy operations (St-Pierre et al 2003). Thus, the objectives of this research were:

  1. to characterize changes in daily average temperature, relative humidity, diurnal temperature variation (DTV) and temperature-humidity index (THI) from 2002 to 2015 and their association with dairy cattle stress, and
  2. to determine the effects of heat stress level on milk yield per day on Thai multibreed dairy cattle.


Material and methods

Climate variables and regions

Climate variables consisted of 85,824 daily records of average temperature (AT; C), diurnal temperature variation (DTV; C), relative humidity (RH; %), and temperature-humidity index (THI) obtained from January 1, 2002 to December 31, 2015 at 17 meteorological stations of the Thai Meteorological Department (TMD). The DTV were calculated as differences between maximum and minimum daily temperatures (MNT; C). The THI was calculated for all pairs of AT and RH records using the expression (NOAA 1976): THI = (1.8 AT + 32) – (0.55 – 0.0055 RH) (1.8 AT – 26), where AT is the dry-bulb average temperature in C, and RH is the relative humidity from a hygrometer (%). The meteorological stations, located in five regions of Thailand (latitudes 5 37’ N to 20 27’ N and longitudes 97 22’ E to 105 37’ E), were chosen because they were in high-density dairy population areas. The characteristics of each region are as follows (OEPP 2000):

  1. The central region (CT; 4 stations including Nakhon Pathom, Lop Buri, Kanchanaburi and Ratchaburi; 21.2 to 36.2 C for AT and 69 to 79% for RH; 2 to 8 m above mean sea level (msl)). Low-level plains.
  2. Eastern region (ET; 3 stations including Chanthaburi and Sa Kaeo and Aranyaprathet district; 22.3 to 36.2 C for AT and 71 to 81% for RH; 50 to 150 msl). Mostly plains and valleys.
  3. Northeastern region (NE; 5 stations including Khon Kaen, Nakhon Ratchasima, Pak Chong district, Sakon Nakhon and Udon Thani; 18.7 to 35.2 C for AT and 66 to 80% for RH; 140 to 250 msl). High level plains in the west that slope down towards the east.
  4. Northern region (NT; 3 stations including Chiang Mai, Lampang and Lamphun; 17.5 to 36.1 C for AT and 64 to 81% for RH; 250 to 400 msl). Mostly hilly and mountainous.
  5. Southern region (ST; 2 stations including Phetchaburi and Prachuap Khiri Khan; 22.8 to 34.1 C for AT and 48 to 97% for RH; 50 to 80 msl). A long ridge of western mountains.

The CT, ET, NE, and NT are classified as tropical savanna (AW), whereas the ST is classified as tropical rainforest (AF) in the Kppen climate classification system. Thailand has three seasons: winter (November to February), summer (March to June), and rainy (July to October).

Animals, management, and production trait

Animals utilized in this research were 5,080 first-lactation cows. Cows were from 456 dairy farms in Central (61 farms), Northeastern (226 farms), Northern (79 farms), and Southern Thailand (90 farms). Cows were daughters of 771 sires and 4,385 dams. The main breed represented in an individual cow was Holstein (H), and most cows (94%) were crossbred (75% H and above). The other breeds represented in an individual animal were various Bos indicus (Brahman, Sahiwal, Red Sindhi, Sahiwal, and Thai Native) and Bos taurus breeds (Jersey, Brown Swiss, and Red Dane).

Cows were housed in open barns with access to roughage, concentrate, and mineral supplement. Available fresh grasses were Guinea (Penicum maximum), Ruzi (Brachiaria ruziziensis), Napier (Pennisetum parpureum), and Para (Brachiaria mutica). Concentrate (14 to 22% of crude protein and 63 to 83% of nitrogen-free extract) was provided to cows twice a day during milking (4:30 a.m. to 7:00 a.m. in the morning, and 2:30 p.m. to 4:30 p.m. in the afternoon). Additionally, cows were given silage and agro-industrial by-products (rice straw, pineapple peel, and sweet corn husk) when fresh grass was insufficient in winter and summer. The production trait was test-day milk yield (MY) from first-lactation cows. The MY were collected monthly from 2002 to 2015 (n = 46,442). The mean for MY per cow was 13.9 kg/d (SD = 4.83 kg/d).

Statistical analysis

The statistical model used to analyze the four climate variables (AT, RH, DTV, and THI) included the main effects of region, year, season, and year-region, year-season, region-season, and region-year-season interactions as fixed effects, and residual as a random effect. Least squares means (LSM) of fixed effects were computed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC, USA).

To assess the effect of stress level (SL) on MY, SL were classified into three categories using THI values (Armstrong 1994):

  1. comfort zone when THI values were below 72 units;
  2. mild stress when THI values were from 72 to 77 units; and
  3. moderate stress level when THI values were from 78 to 88 units.

Percentages of this SL were determined for each region, month, season, and year. Then, the THI values from the closest meteorological stations to each dairy farm (based on postal code) were used to calculate an average of daily THI three days before each MY. Lastly, these average THI values were used to classify the stress level of dairy cows for each MY at each farm.

The statistical model used to analyze MY included the fixed effects of contemporary group (herd-year-season), breed group (BG; BG1 = H < 0.50, BG2 = 0.50 ≤ H < 0.75, BG3 = 0.75 ≤ H < 0.875, BG4 = 0.875 ≤ H < 0.9375, BG5 = 0.9375 ≤ H < 0.9687, BG6 = 0.9687 ≤ H < 1.0, and BG7 = Holstein), days in milk, stress level (SL; comfort zone, mild stress, and moderate stress), calving age, and BG-SL interaction. The random effect was residual. LSM of fixed effects were computed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC, USA). Significant differences were considered at α = 0.05. LSM of fixed effects were compared using adjusted Bonferroni t-tests.


Results and discussion

Climatic conditions in Thailand

The distributions of AT, RH, DTV, and THI data during the entire period of the study (January 1, 2002, to December 31, 2015) are shown in Figure 1. Values ranged from 14.6 to 35.5 C for AT (Figure 1a), from 29 to 99 % for RH (Figure 1b), from 0.3 to 19 C for DTV (Figure 1c), and from 58.3 to 88.8 units for THI (Figure 1d). Means were 27.9 C (SD = 2.56 C) for AT, 73.6 % (SD = 9.65 %) for RH, 9.9 C (SD = 2.94 C) for DTV, and 78.7 units (SD = 4.03 units) for THI. The mean of LSM for THI was within the range of values previously estimated in Thailand (73 units to 80 units from January 1990 to December 2008; Boonkum et al 2011). However, all of them were higher than THI estimated under temperate climate conditions in Europe (40.8 units to 79.9 units in May 2010 to October 2012; Schller et al 2014).

Figure 1. Distribution of average temperature (a), relative humidity (b), diurnal temperature
variation (c) and temperature-humidity index (d) from 2002 to 2015

Variation in all climate variables (AT, RH, DTV, and THI) in Thailand was affected by differences among regions, years, seasons, and year-region, year-season, region-season, and region-year-season interactions (p < 0.01). Significant interactions among main effects (region, year, and season) indicated that each of them influenced the value of the other two in this population, and none of them could be estimated unbiasedly. The LSM estimates of climate variables for within region-year-season subclasses and their standard errors ranged from 23.4 0.07 C (Northeastern-2008-winter) to 31.2 0.08 C (Central-2010-summer) for AT, from 58.2 0.41 % (Northern-2010-summer) to 86.6 0.71 % (Eastern-2013-rainy) for RH, from 7.1 0.16 C (Southern-2007-rainy) to 15.5 0.13 C (Northern-2004-winter) for DTV, and from 71.2 0.11 units (Northeastern-2008-winter) to 83.4 0.24 units (Eastern-2013-summer) for THI.

Trends for year-region LSM for AT, RH, DTV, and THI are shown in Figure 2 for the summer season, Figure 3 for the rainy season, and Figure 4 for the winter season. In the summer and winter seasons, all climate variables (AT; Figures. 2a and 4a, RH; Figures. 2b and 4b, DTV; Figure 2c, and THI; Figures. 2d and 4d) tended to have wider fluctuations in the last seven years (2009 to 2015) than during the first seven years of the study (2002 to 2008), except for DTV in the winter season that had wider fluctuations during the first seven years (2002 to 2008; Figure 4c). Conversely, in the rainy season, all climate variables tended to have small fluctuations during the entire period of the study. The expansion of variability in climate variables was widespread between 1981 and 2010, and it was more evident in Asia probably due to the unusually strong El Nio Southern Oscillation (ENSO) in 1997 to 1998 (Hansen et al 2012). Although increasing trends in THI did not occur during the years of the study, variability in THI increased since 2009. This variability was likely associated with ENSO, which was a primary factor for temperature fluctuations in large areas of Southeast Asia. Moreover, ENSO affected many countries in temperate and tropical Asia causing frequent severe droughts and floods in the 20th century. El Nio Southern Oscillation is associated with high temperatures and droughts whereas another Southern Oscillation, called La Nia, is associated with heavy precipitation and flooding. The combined ENSO phenomena of El Nio and La Nia are the main factors leading to climate changes generating uncertain temperature and rainfall patterns (Daz et al 2002). Further, Segnalini et al (2011) indicated that THI changes in the Mediterranean basin caused extreme climate events between 1998 and 2007. Dairy industry losses in the United States due to climate change amounted to more than $1 billion (Collier and Zimbelman 2007). To help decrease the negative effects of El Nio and La Nia Southern Oscillations, farmers should implement selection and management strategies suitable for unpredictable climate changes.

Figure 2. Least squares means trends per regions; Central region (CT), Eastern region (ET), Northern region (NT), Northeastern
region (NE) and Southern region (ST) during the year 2002 to 2015 for average temperature (a), relative humidity (b),
diurnal temperature variation (c), and temperature-humidity index (d) that occurred in the summer season


Figure 3. Least squares means trends per regions; Central region (CT), Eastern region (ET), Northern region (NT), Northeastern
region (NE) and Southern region (ST) during the year 2002 to 2015 for average temperature (a), relative humidity (b),
diurnal temperature variation (c), and temperature-humidity index (d) that occurred in the rainy season


Figure 4. Least squares means trends per regions; Central region (CT), Eastern region (ET), Northern region (NT), Northeastern
region (NE) and Southern region (ST) during the year 2002 to 2015 for average temperature (a), relative humidity (b),
diurnal temperature variation (c), and temperature-humidity index (d) that occurred in the winter season

Trends for year-season LSM for AT, RH, DTV, and THI in each region (Figures 2 to 4) indicated that the highest AT (Figure 2a) and THI (Figure 2d) occurred in the summer season, the highest RH (Figure 3b) in rainy season, and the highest DTV (Figure 4c) in the winter season. Further, most of the highest LSM for AT, RH, and THI estimated within seasons were from the Eastern region, except for the winter season in the Southern region where LSM for RH was higher than in other Thai regions. However, the highest LSM for DTV was from the Northern region in all three seasons. Interestingly, all regions in Thailand had THI LSM values higher than 72 units indicating that the weather in all regions of the country created stressful conditions to dairy cows. Ravagnolo et al (2000) found that MY decreased by 0.2 kg per unit of increase in THI when THI exceeded 72 units. Moreover, the negative impact of increases in temperature not only includes milk production, but also the availability of food, water, and the spread of infectious diseases. Nearly all dairy farms in Thailand kept lactating cows in open barns; thus, both ambient temperature and relative humidity directly affect the stress level of dairy cows. Utilization of THI information should indicate farmers when to provide cows with appropriate cooling solutions to mitigate climate stress.

Percentages of THI by stress level of dairy cows

Percentages of THI by stress level and region during the entire period of the study are shown in Figure 5. The overall percentage of moderate stress level (67.4 %) was higher than the one for mild stress level (24.3 %) and comfort zone (8.3 %). Further, the percentage of THI in moderate stress level was higher than for other levels in all regions. Percentages of THI in the moderate stress level by region ranged from 52.2 % in the Northeastern region to 81.2 % in the Eastern region. The percentages of THI in the mild stress level in the Northeastern region (34 %) was higher than in the Northern (29.2 %), Southern (17.9 %), Central (17.7 %), and Eastern (16 %) regions. The percentage of THI in the comfort zone ranged from 2.1 % in the Southern region to 13.8 % in the Northeastern region. The lower percentages of THI for the moderate stress level in the Northern and Northeastern regions indicated that these regions were more favorable to dairy farming than the Central, Eastern and Southern regions. The Northern and Northeastern regions are higher than other regions and are more influenced by cold weather from the northeastern monsoon than the other regions in Thailand. These results pointed out that the need for more comprehensive strategies to reduce heat stress of dairy cattle in the Central, Eastern, and Southern regions is more significant than in the Northern and Northeastern regions.

Figure 5. Percentages of daily temperature-humidity indexes by heat stress level and
region (Central region (CT), Eastern region (ET), Northern region (NT),
Northeastern region (NE) and Southern region (ST)) of Thailand


Figure 6. Percentages of daily temperature-humidity indexes by
heat stress level and month and season of Thailand

Figure 6 shows the percentages of THI by stress level, month, and season in Thailand. The percentages of THI in the stress levels by month ranged from 12.7 % (January) to 95.2 % (June) for moderate stress level, from 4.8 % (June) to 48.8 % (January) for mild stress level, and from 0 % (June, July, and August) to 38.5 % (January) for comfort zone. Trends for the percentage of THI by stress level and month (Figure 6) indicated that the frequency of THI in the moderate stress level increased after January until the June and then decreased after June until the December, which was contrary to the frequency of THI in the mild stress level and comfort zone. In addition, most of the months with high percentages of THI in the comfort zone and mild stress level were associated with the winter season. Thus, the winter season in Thailand has the highest frequency of THI in the comfort zone (23.7 %) and mild stress level (47.5 %) and the lowest frequency of THI in the moderate stress level (28.7 %; Figure 6). In the summer season, the percentage of THI in the comfort zone (1.2 %) and moderate stress level (87.1 %) are higher than in the rainy season. Conversely, the percentage of THI in the mild stress level (11.7 %) is lower than in the rainy season (0.2 % for comfort zone, 14.1 % for mild stress level and 85.7 % for moderate level). Variation of monthly percentages of THI in the three stress levels may have been associated with differences in MY per month of dairy cows in Thailand reported by Boonkum et al (2011) who found that more dairy cows with high MY occurred in the winter than in the summer season. However, trends for yearly percentages of THI by stress level within regions (Figure 7) indicated that all regions in Thailand had a higher frequency of THI values in the moderate stress level than in other stress levels. This result supported that the weather in all regions of the country created stressful conditions for dairy cows. Consequently, dairy farmers in all regions need to implement management strategies to mitigate the impact of high THI, such as the use of fans to reduce relative humidity and shades to reduce ambient temperatures.

Figure 7. The trend for percentages of daily temperature-humidity indexes by heat
stress level occurred in each region of Thailand (2002 to 2015)
Effect of stress levels on milk yield of dairy cow

The correlation between MY and THI was close to zero (r = 0.008) indicating that there was no correspondence between MY of animals and their stress to a unit increase in THI. However, the stress level of dairy cows based on THI values influenced MY in the Thai multibreed dairy population (p < 0.01). Cows in the comfort zone (14.2 0.08 kg per day) and mild stress level (14.1 0.05 kg per day) had higher LSM for MY than cows in the moderate stress level (13.9 0.05 kg per day; p < 0.05). The lower MY of dairy cows in the are stress level (78 to 88 units for THI) may be due to heat stress which directly reduces dry matter intake, creating a negative energy balance that reduces milk synthesis (West 2003; Rhoads et al 2009; Wheelock et al 2010). In addition, heat stress can affect the rumen function and udder health of dairy cows resulting in lower milk production (Pragna et al 2016). Even though MY of Thai dairy cows trended to increase with decreased levels of stress, it was a little bit of amount of increased MY from moderate stress level to comfort zone (0.3 kg per day). The small difference in MY between cows from moderate stress level and comfort zone was consistent with previous findings in this population (Boonkum et al 2010) Holstein-Frisian in Serbia (Knyves et al 2017) and Holstein in Turkey (Duru 2018), who reported that MY declined 0.002 - 0.07 kg per unit increase in THI. Further, Boonkum et al (2011) indicated that first-lactation Thai multibreed dairy cows with H ≥ 93.6% had higher reductions in MY due to heat stress than cows with H percentages lower than 93.6%. Nearly all dairy cattle in Thailand have high Holstein percentages (Koonawootrittriron et al 2009), making them susceptible to high THI conditions. Thus, Thai dairy farmers need to utilize appropriate management practices to reduce dairy cow stress during high THI periods. In addition, Thai dairy farmers need to select dairy animals for both adaptability and productivity under high THI conditions.

Stress level defined in terms of THI values had nonsignificant effects on MY from dairy cows in BG1, BG2, BG3, and BG6 and purebred H, but it affected MY from cows in BG4 and BG5 (p < 0.05). The highest MY for cows in BG4 (14.6 0.08 kg/day/cow) and BG5 (14.6 0.10 kg/day/cow) occurred in the comfort zone. However, the MY LSM for cows in BG5 under mild stress was not significantly different from the MY LSM of cows in other stress levels. The lack of a significant effect of stress level on MY in crossbred cows with H percentages lower than 87.5% was in agreement with a previous study in the Thai multibreed dairy cattle population, where Holstein crossbred cows (H < 87%) were able to maintain milk production under high heat stress (Boonkum et al 2011).

Table 1 shows the LSM for MY per breed group and stress level of dairy cows. The MY LSM ranged from 13.3 0.26 kg/day/cow (BG7; purebred H) to 14.6 0.10 kg/day/cow (BG5) for comfort zone, from 13.7 0.14 kg/day/cow (BG7; purebred H) to 14.3 0.23 kg/day/cow (BG1) for mild stress level, and from 13.4 0.18 kg/day/cow (BG1) to 14.2 0.04 kg/day/cow (BG4) for moderate stress level. Breed group differences were significant for MY at each stress level (p < 0.01). Cows in BG4, BG5, and BG6 on the comfort zone and mild stress level had higher MY LSM than purebred H (p < 0.05). However, under moderate stress level, MY LSM for purebred H cows was not significantly different from MY LSM for crossbred cows (BG1 to BG6), but cows in BG4 and BG5 had higher MY LSM than cows in other breed groups including purebred H (p < 0.05). As previously reported in this population, crossbred cows in BG4, BG5, and BG6 (0.875 ≤ H< 1.0) tended to have higher MY than cows in other breed groups (Koonawootrittriron et al 2009; Boonkum et al 2011). Although crossbred cows with larger H fractions tended to have higher MY than cows with lower H fractions, they also tended to have lower MY as the stress level increased. Current cooling strategies would need to be improved if crossbred cows under mild and moderate stress are to achieve similar MY to cows in the comfort zone (Table 1). However, Koonawootrittriron et al 2009 and Seangjun et al 2009 indicated that not only farmers in Thailand have to manage for reducing stress due to hot and humid of dairy cows but also they have to provide appropriate nutrition and health care so that their cows can produce higher MY. Thus, to increase the amount of milk produced per cow under increasingly stressful climate conditions in Thailand, farmers would need to increase their investment in active cooling solutions to reduce ambient temperature and relative humidity as well as in nutrition and health care.

Table 1. Least squares means and SE per heat stress level and breed groups (BG) for milk yield per day of the Thai multibreed dairy cattle population
BG Holstein Fraction N Milk yield (kg/d)
Stress level
Comfort zone
(72 < THI)
Mild stress
(72 ≤ THI < 77)
Moderate stress
(77 ≤ THI < 88)
1 H < 0.50 91 13.7 0.37ab 14.3 0.23ab 13.4 0.18b
2 0.50 ≤ H < 0.75 189 14.5 0.29ab 13.8 0.14ab 13.6 0.13b
3 0.75 ≤ H < 0.875 960 14.1 0.12ab 14.0 0.06ab 13.8 0.06b
4 0.875 ≤ H < 0.9375 1,752 14.6 0.08a 14.3 0.05a 14.2 0.04a
5 0.0.9375 ≤ H < 0.9687 1,202 14.6 0.10a 14.3 0.05a 14.2 0.06a
6 0.9687 ≤ H < 1.0 742 14.4 0.12a 14.2 0.07a 14.0 0.08ab
7 Holstein (H) 144 13.3 0.26b 13.7 0.14b 14.1 0.18ab
a,b Least squares means within a column with different superscript letters differ (p<0.05)


Conclusions


Acknowledgments

The authors would like to thank the Graduate School of Kasetsart University and Kasetsart University Research and Development Institute (KURDI; S-K 21.56) for supporting the research scholarship, and Thai Meteorological Department for providing climate records in this research.


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Received 9 August 2019; Accepted 11 November 2019; Published 2 December 2019

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