 |
| Figure 1. DM intake for maintenance in diferent seasons |
| Livestock Research for Rural Development 26 (8) 2014 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
The effect of hot- dry, hot- humid and winter season on feed efficiency, plasma hormones and physiological responses was investigated in lactating crossbred cows. Blood and milk samples, dry matter intake, climatic variables and physiological responses were collected daily for a period of seven days in each season.
Unadjusted feed efficiency (FE) was higher in hot-dry season as compared to hot-humid and winter seasons but FE 3.5% FCM /DMI above maintenance requirement was similar. Intake of DM, total digestible nutrients and crude protein (g/d intake/kg milk production) varied in different seasons. The high ambient temperature during hot-humid season decreased feed efficiency by lowering plasma T4 and glucose levels without affecting plasma insulin and T3 levels. Plasma NEFA and T4 was more in winter season in comparison to hot dry and hot humid season. The respiration rate, pulse rate and skin temperature were higher in hot- dry and hot- humid season and lower in winter season. Milk fat, protein, lactose and SNF content varied between seasons and were more in winter than the summer. It was concluded that high temperature humidity index during hot humid decreases feed efficiency, DM intake, body weight, plasma T4, glucose and NEFA levels in comparison to winter session without affecting plasma T3 and insulin levels. Respiration rate, pulse rate and rectal temperature could be used as indicators of heat stress in lactating cows.
Key words: dry matter intake, milk composition, plasma metabolites, physiological responses
Warming of the climate system of the earth is unanimously accepted as a reality and is probably one of the most prominent challenges for scientists, development workers, policy makers and other relevant stakeholders regarding development and sustainability in international and national arena during past several years. Intergovernmental panel on climate change (IPPC 2007a,b) has described climate change as any anthropogenic or naturally occurring alteration in the climate over the time. Importance of thermal stress has increased to the dairy farmers in tropical, subtropical and even in temperate region of the world, although effects of thermal stress and cold stress at farm level can be ameliorated to an extent by altering microclimate in the farm and applying suitable nutritional management strategies (Bajagai 2011). When ambient temperature increases, animal body attempts to regulate the core body temperature by altering physiological and metabolic function, disturbance in behavior, feed efficiency and health and performance though effects of thermal stress vary according to breeds, production level, and prior experience due to decline in dry matter intake (Aggarwal and Singh 2010).
Feed efficiency, a ratio of outputs to inputs, also called dairy efficiency has been a popular topic of observation and discussion on dairy farms in the recent past (Barendse et al 2007, Nkrumah et al 2007, Moore et al 2009). Though many scientific findings have reported feed efficiency measurement and factors affecting it on a farm in cattle (Wang et al 1992; Schingoethe et al 2004; Mujibi et al 2010; Durunna et al 2011), the information on effect of different seasons on feed efficiency in relation to hormones and physiological responses in lactating crossbred cows under tropical conditions is scanty. Within a herd, changes in feed efficiency can be used by dairy managers to determine the economical impact of feeding and management changes (Britt et al 2003). An NRC publication (NRC 2001)) showed that maintenance energy requirements of milking cows were 25% higher for cows exposed to ambient temperatures of 35°C (95°F) as compared to cows kept at 20°C (68°F). The present investigation was undertaken to find out the feed efficiency of lactating cows during hot- dry, hot- humid and winter season in conjunction with hormones and metabolites. The physiological responses were measured as stress marker.
The feed efficiency of cows is directly influenced by the ambient temperature and significantly affects milk production through reduction in feed intake in tropical climate. Heat stress directly and indirectly affects feed intake, cow body temperature, maintenance requirements, metabolic processes, feed efficiency, milk yield, reproductive efficiency, cow behavior and disease incidence (Cook et al 2007; Rhoads et al 2009). In this study the effect of extreme hot- dry (38°C), hot -humid (30.2 °C, RH 95 %) and winter season (5°C) was observed on feed efficiency of cows in relation to plasma hormones and physiological responses so that extent of discomfort could be known and appropriate strategies could be worked out to alleviate the climate stress.
Six apparently healthy lactating KF crossbred cows (Holstein x Tharparkar) on average with 105 days of lactation, 3rd and 4th parity and mean body weight 385 kg, were selected from the institute livestock herd and were tied in a shelter having asbestos roof (12 feet height) and brick floor. Three sets of separate experiments were carried out for one week period during hot dry (June), hot humid (September) and winter (December) season. The experimental cows were fed as per the NRC (2001) and received green maize and wheat straw in hot dry and hot humid season and berseem with oat green fodder in winter season. The amount of feed offered and residue left was weighed daily for a period of 7 days and dry matter intake (DMI) was recorded. The concentrate mixture (21% CP, 70 % TDN) was fed to the cows based on milk yield. The experimental cows were machined milked thrice a day at 6am, 12 noon and 6pm daily and the milk yields were recorded.
Milk samples were collected daily during morning, noon and evening milking and analyzed for milk fat, protein and lactose contents by Mega lactoscan. The physiological responses: respiration rate (RR), rectal temperature (RT), pulse rate (PR) and skin temperature (ST) were recorded in the morning at 8:00 am and in evening hours at 3:00 pm. Blood samples were collected from jugular vein in heparinized vacutainer tubes before offering the feed at 8:00 am. Plasma triiodothyronine (T3), thyroxine (T4) and insulin (INS) was estimated by radioimmunoassay kits (Board of Radiation and Isotope Technology, Mumbai). Plasma glucose (PG) was measured by kit and plasma NEFA was determined by Shipe et al (1980) method. The maximum and minimum temperature, dry and wet bulb temperature were recorded and temperature humidity Index (THI) was calculated (McDowell 1972).
Statistical analysis of data was carried out using Systat programme. Mean and standard error and correlationswere calculated. The mean values were compared using Duncan Multiple Range Test.
THI score was higher in the evening than the morning in all the seasons of experiment. THI varied during hot- humid, hot- dry and winter season (Table 2). Dry matter intake, body weight, PG and NEFA varied between seasons (Table2, Figure 1). The body weights of the cows were higher during hot-dry season then the hot humid and winter season leading to higher feed efficiency. However, feed efficiency over and above maintenance was similar among the hot-dry, hot-humid and winter seasons.
|
Table 1. Proximate principle and cell wall component of feed ingredients and concentrate mixture being fed to the experimental cows (% DM basis, except for DM which is on air-dry basis). |
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|
Particulars |
Wheat straw |
Oat |
Berseem |
Concentrate mixture |
|
Dry matter |
90.2 |
20.0 |
18.6 |
90.2 |
|
Organic matter |
91.1 |
87.8 |
91.3 |
91.3 |
|
Crude protein |
4.18 |
4.74 |
16.3 |
20.3 |
|
Ether extract |
0.88 |
2.70 |
2.15 |
4.50 |
|
Crude fibre |
36.7 |
27.3 |
20.2 |
7.86 |
|
Ash |
8.8 |
12.2 |
8.90 |
8.20 |
|
Neutral detergent fibre |
73.9 |
53.9 |
58.9 |
50.3 |
|
Acid detergent fibre |
53.3 |
42.5 |
31.3 |
28.5 |
|
Table2. Mean (n=12) ±SEM of climatic variables and physiological responses of crossbred cows during different seasons. |
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|
Seasons/ Attributes |
Hot dry Season |
Hot humid Season |
WinterSeason |
SEM |
p |
|
THI Morning |
70.1ax |
74.2bx |
49.2cx |
3.61 |
0.01 |
|
THI Evening |
83.2ay |
80.9 by |
65.6cy |
2.52 |
0.01 |
|
Max.Temp. (°C) |
38.0a |
30.2 b |
21.9 c |
2.07 |
0.01 |
|
Min. Temp. (°C) |
24.0a |
21.5b |
5.34 c |
0.18 |
0.01 |
|
Parity |
3.81 |
3.42 |
3.10 |
-- |
|
|
Body wt. (kg) |
515a |
374b |
387 c |
6.29 |
0.01 |
|
Pulse rate/ min. (M) |
43.5ax |
41.4bxv |
39.2cx |
1.04 |
0.01 |
|
Pulse rate/ min. (E) |
58.9ay |
74.9by |
72.6 cy |
0.89 |
0.01 |
|
RR / min. (M) |
52.9ax |
62.2bx |
28.7cx |
1.28 |
0.01 |
|
RR/ min. (E) |
68.4ay |
63.0bx |
31.0cy |
1.94 |
0.01 |
|
RT (M) °F |
101ax |
101ax |
99.6bx |
0.44 |
0.01 |
|
RT (E) °F |
101ax |
101ax |
99.8bx |
0.48 |
0.01 |
|
ST (M) °F |
91.2ax |
95.8bx |
89.7cx |
1.03 |
0.01 |
|
ST (E) °F |
95.8ay |
96.3ax |
90.2bx |
1.09 |
0.01 |
|
M
eans with different superscript abc in the same row and xy in each column for
each parameter differ at P<0.05)
|
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The similar feed efficiency in terms of milk production in hot dry season and other seasons suggest that cows were quite adapted in all three seasons and resisted rigors of high ambient temperature of hot-dry season (Figures 2 and 3) by maintaining the DMI and lowering the energy and protein intake /kg milk production. Ludri and Singh (1987, 1989) reported no adverse effect of high ambient temperature on milk production and composition in KF crossbred cows. At the same time the cows tolerated low ambient temperature by consuming more dry matter intake. The milk protein was more in winter season than the hot dry and hot humid season due to more DMI (P<0.05) and good quality fodder like berseem which contained high crude protein (Table1). The less DMI in hot-dry condition indicated that though this season was more stressful for lactating cows, but they were quit acclimatize to the high ambient temperature and humidity as evident from high THI score and physiological responses recorded. Due to this reason the intake of TDN and CP (g)/kg for milk production was less in hot dry season. The lesser DMI was also attributed to low plasma T4 levels (P<0.05) in hot dry season than the hot humid and winter season. Plasma INS and T3 levels was not influenced by the seasons. Heat stress also resulted in a decline in plasma glucose and NEFA levels in hot- dry and hot-humid season.
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Table 3. Mean values (n=12) of dry matter intake, feed efficiency, milk yield, composition, plasma metabolites and hormones in crossbred cows during different seasons. |
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|
Seasons/ Attributes |
Hot dry Season |
Hot humid Season |
Winter Season |
SEM |
p |
|
DMI, kg/d |
10.6a |
11.2a |
13.3b |
0.17 |
0.05 |
|
3.5% FCMY, kg/d |
12.1a |
9.52b |
10.4b |
0.21 |
0.01 |
|
Milk efficiency, kg milk/kg DMI |
1.14a |
1.20b |
1.24b |
0.05 |
|
|
TDN intake, kg/d |
6.57a |
8.08b |
9.07c |
0.43 |
0.05 |
|
TDN intake, g/kg milk production |
409a |
454b |
601c |
0.11 |
0.05 |
|
CP intake, kg/d |
125a |
166b |
158b |
0.04 |
0.05 |
|
CP intake, g/kg milk above maintenance |
92.1a |
120b |
114b |
0.01 |
0.05 |
|
Fat, % |
3.81a |
3.92a |
4.15a |
0.30 |
0.31 |
|
Protein, % |
3.73a |
3.83a |
3.86b |
0.28 |
0.01 |
|
Lactose, % |
3.99a |
4.25a |
4.34a |
0.35 |
0.25 |
|
SNF, % |
8.01a |
7.81a |
7.84a |
0.46 |
0.68 |
|
T3, ng/ml |
1.30a |
1.11a |
1.19a |
0.06 |
0.14 |
|
T4, ng/ml |
54.1a |
58.9b |
59.0b |
2.74 |
0.01 |
|
Insulin, uU/ml |
17.1a |
16.4a |
18.2a |
2.16 |
0.26 |
|
Plasma glucose, mg % |
68.5a |
70.5a |
79.1b |
2.86 |
0.02 |
|
NEFA, µMol/liter |
0.31a |
0.25b |
0.51c |
0.03 |
0.11 |
|
M eans with different superscript abc in the same row differ at P<0.05 |
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|
| Figure 1. DM intake for maintenance in diferent seasons |
 |
| Figure 2. Unadjusted Feed efficiency (3.5% FCM kg/DM intake) in different seasons |
 |
| Figure 3. Feed efficiency (3.5% FCM/kg DM Intake above maintenance) in different seasons |
Plasma T4 levels were lower (P<0.05) during hot- dry season in comparison to hot–humid and winter season, however plasma T3 and INS levels were not affected. Plasma glucose level was low in hot-dry season due to less DMI than the winter season (P<0.05). Plasma T4 and glucose levels decreased by 53.48 and 15.69%, respectively with increase in THI score from 72 to 84. The lower unadjusted feed efficiency in winter season was due to increased physiological demand and limited feed energy available to the cows which led to mobilization of body reserves (Mujibi et al 2010). This fact was further evident from higher plasma NEFA levels in winter season observed in this study. The body weight of cows (P<0.01) and DMI/100kg W0.75 also varied between seasons (P<0.01) of the experiment. The fat, protein and lactose content of milk varied between seasons and the values was more in winter season (P<0.05) in comparison to hot-humid season. The low DMI during hot dry and humid season could be attributed to roughage based diet, poorly digestible feed and low T4 levels. At high ambient temperature plasma T4 level declined due to reduced thyroid activity, reduced gastrointestinal tract motility and rate of passage of ingesta (Thornton et al 2009). Thermal stress induced negative energy balance condition causes lower blood insulin levels and decreased tissue sensitivity to insulin as observed in this study (Collier et al 1982).
The authors are thankful to the Director, National Dairy Research Institute, Karnal for providing the necessary facilities to conduct this study. We are also thankful to the Board of Radiation and Nuclear Science to sanction the project no. BRNS/35/13 –RTAC for providing the necessary support to carry out this study.
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Received 7 September 2013; Accepted 31 July 2014; Published 1 August 2014