Assessment of milk yield, physiological responses, and heat tolerance of lactating dairy cows in different agroclimatic in Bogor of West Java, Indonesia

Azhar Amir¹, Afton Atabany², Sutomo Syawal³, Zulkharnaim³, Reny Debora Tambunan¹, Zubir¹ and Ade Syahrul Mubarak¹

¹ Research Center for Animal Husbandry, National Research and Innovation Agency (BRIN), Cibinong 16911, Indonesia
azha001@brin.go.id
² Faculty of Animal Science, IPB University, Bogor 16680, Indonesia
³ Faculty of Animal Science, Hasanuddin University, Makassar 90245, Indonesia

Abstract

This research aimed to study the effect of agroclimatic on milk yield, physiological response, and heat tolerance of lactating dairy cows. The research was conducted in smallholder farms at different altitudes in Kebon Pedes (200 meters above sea level (m asl)), Situ Udik Village (476 m asl), and Cibeurum Village (1100 m asl). 30 Friesian Holstein (FH) cows with a body weight of 420.16±22.3 kg and a lactation period of 2.56±0.62 were used in this study. The study variables were temperature humidity index (THI), dry matter Intake (DMI), milk yield, feed efficiency (FE), physiological responses such as rectal temperature (RT), respiration rate (RR), and heart rate (HR) and heat tolerance ability such as heat tolerance coefficient (HTC), heat tolerance index (HTI), Benezra coefficient of adaptability (BCA) and dairy search index (DSI). The results showed that THI in the lowlands put lactating cows under moderate stress, while in the midlands and highlands, with mild stress. Different altitudes affected DMI, milk yield, RT, RR, HR, HTI, and BCA (p<0.05), while FE, HTC, and DSI values did not differ (p>0.05). It was concluded that lactating cows in the lowlands decreased DMI by 0.985 kg/d, milk yield decreased by 0.46 kg/d with each THI unit increase, each cow experienced enhanced physiological responses, and lactating cows in the highlands showed better heat tolerance.

Keywords: altitudes, coefficient, heat stress, smallholder farms, village

Introduction

The distribution of the dairy cattle population in Indonesia is centred in the provinces of East Java, Central Java and West Java (Priyanto and Rahmayuni 2020, Sembada et al 2020). The 2022 statistics show that these three provinces account for 97.4% of the total population of 507,075 dairy cows. West Java has 21.7% of dairy cows, around 110,005 head (BPS 2023). This number is spread across 18 districts and nine cities in West Java. The largest population is in West Bandung Regency (38,491 heads), Bandung Regency (24,306 heads), Garut Regency (14,419 heads), Kuningan Regency (7,864 heads), and Bogor City-District (6,914 heads).

Smallholder farms dominate the characteristics of dairy cattle farming in Bogor with an ownership scale of 3-10 heads. Milk production of lactating cows is in the range of 7-15 litres/head/day (Asminaya et al 2017). This production varies because cattle rearing in Bogor is in several different agroclimatic zones (Susanty et al 2018). Agroclimatic differences are influenced by altitude. Dairy cattle rearing in the city is in the lowlands, and in the regency, it is in the midlands and highlands. The ambient temperature, air humidity, and temperature-humidity index (THI) also differed at these three altitudes. An increase of 1^oC above in the comfort zone for dairy cows will decrease dry matter intake by 0.85 kg (West et al 2003). In addition, each unit increase beyond THI 72 decreases milk yield by 0.2 kg (Ravagnolo et al 2000), and Bouraoui et al (2002) that if THI is more than 69, it will decrease milk yield by 0.41 kg per cow per day.

THI values are a common approach to detecting heat stress in dairy cattle. However, Amamou et al (2019) stated that a combination of environmental measurements and physiological responses of dairy cows is a more efficient method to detect heat stress, such as rectal temperature (RT) and respiration rate (RR). These physiological parameters can describe the adaptability of livestock to their environment and can be calculated using various methods (Benezra 1954, Gaalaas 1947, Rhoad 1944, Thomas et al 1973). The RT value of the livestock indicates the heat production gain generated by the cows's bodies. The RR number indicates the response of releasing or expelling heat to the surrounding air. The heat release reaction is necessary for the homeostatic condition of cows to maintain average body temperature (Atrian and Shahryar 2012, Fournell et al 2017).

Combining ambient and animal measurements was essential for identifying which metrics more accurately forecast animal performance in heat stress conditions. Production traits declined at elevated THI levels. Conversely, physiological traits increased in response to THI (Habeeb 2020). Studies on the combination of environmental temperature measurements, physiological responses, heat tolerance ability, and milk production of dairy cows still need to be completed in Indonesia. This information is helpful for dairy cattle development. Therefore, this research aims to study the effect of altitude on milk production, physiological responses, and heat tolerance of lactating dairy cows.

Materials and methods

Study site

The research was conducted for 46 d in June-August 2020. This timing was based on the dry season, which had the highest ambient temperature and the lowest rainfall days in the Bogor region. The research was carried out on smallholder farms located in three different altitudes: the lowlands at Kebon Pedes urban village (200 m above sea level (m asl)), the midlands at Situ Udik village, Cibungbulang (476 m asl), and the highlands at Cibeurum village, Cisarua (1,110 m asl).

Animals and feed nutrition

This research used 30 Friesian Holstein (FH) cattle with an average age of 4.21±0.53 years, 420.16±22.3 kg body weight, and 2.56±0.62 lactation period. Ten cows were assigned to each location: Kebon Pedes, Situ Udik, and Cibeurum Village. The FH cows were housed in individual pens measuring 1.8 m in length and 1.3 m in width, each equipped with feeders, drinkers, and anti-slip rubber flooring to ensure comfort and health. The pens were arranged close to each other to facilitate observations by a single observer per location. The cows were fed twice daily, at 6 am and 5 pm, with a diet comprising forage, concentrate, and supplementary feeds such as tofu and tempe dregs. Drinking water was provided ad libitum. A proximate analysis of the feed is presented in Table 1.

Variables measured

Variables observed in this study were microclimate conditions, feed intake, feed efficiency and physiological responses and heat tolerance ability of lactating dairy cows and in addition, observing the relationship of milk production parameters with THI level and heat tolerance ability of FH cows.

Microclimate condition data was measured every 2 hours from 6 am to 6 pm. Ambient temperature (Ta) and relative humidity (RH) were recorded using a thermohygrometer. The THI was calculated using the formula from Mader et al (2006):

THI= (0.8 × Ta) + (RH/100) × (Ta-14.4) + 46.4

Where Ta is in degrees Celsius (◦C) and RH in percent (%), the classification for heat stress is normal: THI ≤ 74, alert: 74 < THI < 79, danger: 79 ≤ THI < 84, emergency: THI ≥ 84.

Feed intake of lactating dairy cows was measured daily by weighing the feed given, subtracting the remaining feed and then multiplying it by the dry matter content of the feed (DMI: kg/day). Crude protein intake (CPI) and total digestible nutrients (TDN) intake were obtained from the nutrients content of each feed multiplied by DM (kg/day). DMI/BW was obtained from DMI divided by the body weight of dairy cows (%).

Milk yield was recorded daily at 5 am and 4 pm in liters. Milk density was measured with a lactodensimeter to convert milk yield to kg. Feed efficiency was calculated as the ratio of milk yield (kg/day) to DMI (kg/day) (Linn 2006).

Physiological response parameters observed included rectal temperature (RT), respiration rate (RR), and heart rate (HR). These were measured at three intervals: morning (average of 6 and 8 am), midday (average of 10, 12, and 2 pm), and afternoon (average of 4 and 6 pm). RT was recorded by inserting a rectal thermometer approximately 10 cm into the rectum for three minutes (°C). RR was determined by visually counting uninterrupted flank movements during breathing for one minute from a 2-meter distance without disturbing the cows (breaths/minute). HR was measured by placing a stethoscope near the left axilla bone for one minute (beats/minute).

Four formulas estimate the heat tolerance ability of lactating cows:

• Iberia heat tolerance test(Rhoad 1944):
  HTC= 100 – 10(RT – 101), where HTC is the Heat tolerance coefficient, RT is the average rectal temperature at midday (°F), and 101°F is the expected average rectal temperature of cattle.
• Gaalaas heat tolerance test(Gaalaas 1947):
  HTI= 100 -14(RT - 101), where HTI is the Heat tolerance index, RT is the average midday rectal temperature (°F), and 101°F is the expected average rectal temperature.
• Benezra coefficient of adaptability (BCA)(Benezra 1954) :
  BCA= RT/38.33 + RR/23, where RT is the mean midday rectal temperature (°C), 38.33 is the normal RT for cattle (°C), RR is the mean midday respiration rate (breaths/minute), and 23 is the normal RR for cattle.
• Dairy search index (DSI)(Thomas et al 1973):
  DSI= 0.5X1/X + 0.3Y1/Y + 0.2Z1/Z, where X1, Y1, and Z1 are the RT, HR, and RR after exposure, and X, Y, and Z are the same parameters before exposure, respectively.

In all formulas, a decrease in HTC or HTI from 100 indicates that the cows are experiencing discomfort. Similarly, a BCA greater than two and a DSI greater than one indicate that the cows are in discomfort.

Statistical analysis

The THI data were analyzed descriptively. Data on feed intake, milk yield, feed efficiency, physiological responses, and heat tolerance ability were analyzed by one-way analysis of variance (ANOVA) by comparing mean values at different altitudes through SPSS version 26 (IBM 2019). The Duncan Multiple Range Test (DMRT) separated significant mean values at the 5% level. The relationship between milk production with THI and milk production with the heat tolerance ability of FH cows was analyzed using regression.

Results and Discussion

Microclimate conditions

The study was conducted at three smallholder farms with different altitudes. The effect of altitude impacts Ta, RH, and THI values. Ambient temperatures in the lowlands ranged from 23.3-33.5^oC, midlands from 22.5-30.4^oC, and the highlands from 22.1-29.9^oC (min-max, respectively). Ta is lowest in the morning and gradually peaks at 12 or 2 pm. RH observations in the lowlands range from 52-87%, in the midlands range from 48-86%, and in the highlands range from 41-73% (min-max, respectively). The RH value was highest in the morning, dropping to its lowest point at 2 pm and rising again. Combining Ta and RH values to estimate heat stress in cattle forms the THI value.

Diurnal changes in THI values at different altitudes are presented in Figure 1. THI values in the lowlands were in the range of 73.2-82, in the midlands in the range of 71.2-78.7, and in the highlands in the range of 70.2-77.2 (min-max, respectively). The mean THI value in the lowlands was 79, the midlands 76, and the highlands 74. According to Mader et al (2006), FH cows in the lowlands are in danger at midday based on the THI classification. Meanwhile, FH cows in the midlands and highlands are on alert status. In addition, Yousef (1985) also indicated that mild heat stress in cows starts at THI 72. Heat stress increases to moderate levels at THI 79 and severe levels at THI 89. THI conditions higher than 72 will begin to reduce feed intake and milk production (Dikmen and Hansen 2009, Herbut and Angrecka 2012).

Figure 1. Diurnal changes in THI at different altitude

Feed intake, milk yield, and feed efficiency

The effect of altitude on feed intake, milk production, and feed efficiency is presented in Table 2. The analysis of variance shows that altitude affects DMI, CPI, TDN intake, DMI/BW, and milk yield of lactating dairy cows (p<0.05) but does not affect feed efficiency.

Dairy cows, during lactation, require adequate nutrition to fulfil their basic needs and milk production. The primary nutrients required are DM, CP and TDN. Adi et al (2020) found that protein consumption and TDN have a positive relationship with milk production. The intake of DM, CP, and TDN at different altitudes is close to the standard feed requirements of lactating cows (NRC 2001). Dairy cows weighing 454 kg to produce 10 kg of milk in mid-lactation with feed TDN below 68% require DMI of 12.4-12.9 kg/d and CPI of 1.47-1.69 kg/d.

Variable DMI in lowlands is less than in midlands and highlands. THI levels in the lowlands reduce feed intake. A decrease in feed intake was also observed when the DMI/BW variable was less than 3% of the body weight of FH cattle. Based on the DMI/BW percentage of 2.76% in the lowlands, DMI decreased by 0.985 kg at an average THI in the lowlands of 79. This result is higher than the study of West et al (2003), that DMI decreased by 0.85 kg for every increase in^oC, and lower than the report of Bouraoui et al (2002), that DMI decreased by 1.73 kg from THI 68 to 78.

In the present study, milk production of FH cows in the lowlands was less than in the midlands and highlands. The percentage of milk production is about 14% less than in the midlands and highlands. The decrease in milk production was due to decreased dry matter consumption, the lighter body weight of FH cows, and higher THI values. There is a negative relationship between increasing THI and milk production (p<0.05). The relationship is presented in Figure 2. Regression analysis showed that each increase in THI level above 72 decreased milk production by 0.46 kg per head per day. The coefficient of determination (R²) of the relationship between milk yield and THI was relatively high at 0.643. This result is higher than that of Amamou et al (2019), who reported that an increase in THI levels above 69 decreased milk yield by 0.13 kg. THI values at different altitudes have the effect of decreasing DMI and milk yield of FH cows, resulting in an adjustment of feed efficiency from a decrease in both variables.

Figure 2. Graph illustrating the effect of THI level on milk yield

Physiological responses

Figure 2 shows an R2 value of 0.64, meaning that 64% of milk production is influenced by THI level while other variables influence 36%. In addition, some authors state that dairy cows' management and individual factors are not considered in the THI formula (Brown-Brandl et al 2005, Gaughan et al 2008, Islam et al 2021). Individual dairy cows' factors include health, genotype, coat characteristics, and physiological responses. This study presents the physiological responses of FH cattle at different altitudes in Table 3.

Analysis of variance showed that different altitudes affected RT, RR, and HR values in the morning, mid-day, and afternoon (p<0.05). RT, RR, and HR variables in the lowlands had higher values than those in the midlands and highlands. This value occurs because in the lowlands, starting in the morning and continuing until the afternoon, it has a THI above 72. Meanwhile, the THI value is more than 72 in the midlands and highlands after passing the morning. In the previous variable descriptions, there was a decrease in DMI and milk yield as THI increased. Conversely, physiological responses such as RT, RR, and HR increased as THI increased. THI values have a positive linear association with the physiological traits of dairy cows (Bouraoui et al 2002, Dikmen and Hansen 2009, Amamou et al 2019). For the short term, HR variables can be used to assess the heat stress of dairy cows, but additional variables such as RR and RT are needed to assess prolonged exposure to heat stress (Islam et al 2021).

Ability of heat tolerance

RT is the primary way to describe the heat production of the cow's body (Dikmen and Hansen 2009, Godyǹ et al 2019), RR is an early indicator of heat stress (Gaughan et al 2008, Pinto et al 2020) and increased HR to maintain homeostatic conditions of the FH cow's body (Reece et al 2015). These three variables are indicators of the heat tolerance of dairy cows to heat stress. The heat tolerance ability of FH cattle at different altitudes is presented in Table 4.

The variance analysis shows that altitude affects HTI and BCA (p<0.05), while HTC and DSI variables are not different. The potential thermotolerance of FH cattle in the humid climate of Bogor can be illustrated by the formulas of Gaalaas (1947) and Benezra (1954). The HTI coefficient of FH cattle in the lowlands is smaller than in the midlands and highlands (92.0, 94.3, and 96.5, respectively). The heat tolerance ability of FH cattle in the highlands is better, with the HTI coefficient close to 100. In contrast, BCA in the lowlands was higher than in the midlands and highlands (2.78, 2.58, 2.41, respectively). However, FH cattle in the highlands still have better heat tolerance with a BCA coefficient close to 2. The BCA coefficient in this study is smaller than the results of Mariana et al (2019). The BCA coefficient differed because Mariana's study measured heat tolerance per observation time. In this study, input RT and RR were observed before and after exposure to heat stress. However, it shows the same pattern of heat tolerance in different microclimates.

The relationship between heat tolerance and milk yield of FH cows is presented in Figure 3. HTI and milk yield had a positive relationship (p<0.05). With every increase in HTI coefficient above 90, milk yield increased by 0.32 kg. The relationship between variables is shown by R² of 0.542. At the same time, the coefficient of BCA and milk yield had a negative relationship (p<0.05). With every increase in BCA above 2, milk production decreased by 4.09 with R² 0.271. The lactating cows in this study are adaptable to heat stress, including in the lowlands. Lowland lactating cows respond to increased ambient temperature by increasing RR as an action for heat loss that offsets heat production. The Benezra coefficient illustrates the action of increasing heat loss to keep the lactating cow's body homeostatic.

Figure 3. Graph illustrating the effect of heat tolerance on milk yield: a) HTI, b) BCA

Conclusion

THI levels in the lowlands exposed cows to moderate stress, while cows in the midlands and highlands experienced mild stress. Lactating cows in the lowlands experienced a decrease in DMI of 0.985 kg/d and milk yield of 0.46 kg/d, with every increase in THI above 72. The physiological response of lactating cows increased as THI level units increased. The HTI and BCA coefficients illustrate heat tolerance in humid climates where lactating cows in the highlands have better heat tolerance.

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