Rectal temperature (°F)
The recorded mean and standard error (mean±S.E.) values of rectal temperature (oF) during different seasons in lactating Kankrej cow were presented in the Table 1 and Fig 1. It was observed that rectal temperature was significantly (p<0.05) higher in the summer season than thermoneutral period. The mean rectal temperature determined in the present study corroborated the values of
Haque et al., (2012) and
Yadav et al., (2016); who reported higher RT during summer months in buffaloes and cattles respectively. The core body temperature of cows in thermo-neutral conditions is maintained by the thermoregulation system of the animal’s body with a range of about 1
oC (between 38 to 39.2
oC)
Ammer et al., (2016). Under these ambient conditions, the exchange of animal heat within the animal (across cellular and vascular membranes) and between the animal and its environment are kept in balance; however, it is always a dynamic equilibrium
Taylor et al., (2014). During periods of excess heat (heat stress), homeostatic mechanisms of the body are activated to re-establish the internal environment’s thermal status or regulate it within acceptable physiological limits
Werner et al., (2008). During the study, the higher rectal temperature in summer indicates that the animals could not dissipate the excess heat by usual means (conduction, convection, evaporation), which increased body temperature. A similar increase in the RT at higher temperatures/heat stress have been reported in cattle by
Marai et al., (1995); and
Nessim (2004) in buffalo,
Korde et al., (2007) and
Krishnan et al., (2009). Bewley et al., (2008) mentioned that the rectal temperature is directly affected by the ambient temperature and increasing during warmer weather. Rectal temperature is an indicator of thermal balance and may be used to assess the adversity of the thermal environment, which can affect the growth, lactation and reproduction of dairy cows
Hansen and Arechiga (1999) and
West (1999).
Respiration rate (Breaths/min)
The recorded mean and standard error of respiration rate (Breaths/min) in lactating Kankrej cow was shown in Table 1 and Fig 2. It was observed that the respiration rate was significantly (p<0.05) higher during the summer season in compared to the thermoneutral period. The mean respiration rate determined in the present study corroborates the values previously reported by
Haque et al., (2012). They reported a non-significant difference at 42
oC and 45
oC in the respiration rate in adult animals, except in the case of 45
oC, a significant higher (P<0.05) respiration rate was observed in young animals than adults. The increase in respiration rate with the increasing temperature may be due to the more demand for oxygen by the tissues in stressful conditions. A similar increase in the respiration rate at higher temperatures/heat stress have been reported by
Gaughan et al., (2000), Nonaka et al., (2008) and
Pereira et al., (2008) in cattle and
Korde et al., (2007) and
Zhang et al., (2010) in buffaloes.
The respiratory rate (RR) was highly affected by ambient air temperature changes because the respiratory rate is considered one of the major physiological reactions that can keep body temperature within the normal range
Frangiadaki et al., (2003). McLean (1963) observed the significance of the increase in respiration rate under heat stress and enables the animal to dissipate the excess of body heat by vaporizing more moisture in the expired air, which accounts for about 30% of the total dissipation. On the other hand,
McDowell (1972) and
Gaughan et al., (1999) observed contradictory results; they reported a low respiratory rate under hot weather and identified animals with lesser discomfort. This fact is evident when comparing respiration rates of
Bos taurus versus
Bos indicus under hot summer weather conditions where
Bos indicus (Zebu) cattle maintain lower respiration rates. There was a significant (p<0.05) increase in respiration rate to maintain body temperature in the present study. Still, animals could not maintain their body temperature andthere was a significant (p<0.05) increase in rectal temperature, which indicates heat stress felt by animals during the extreme summer season.
Milk composition
Fat (%)
Hot and humid environment not only affects milk yield but also effects milk quality. It was observed that the values of the fat content (%) in milk during the summer season and thermoneutral period were depicted in Table 2 and Fig 3. Results showed that the fat content of milk during the summer season was significantly (p<0.05) higher than the thermoneutral period. An increase in fat% might be due to an increase in roughage intake during the summer season, leading to higher acetate formation responsible for the increase in milk fat%. Similar result were also reported by
Bernadin (1972),
Sharma et al., (2001), Prasad (2009),
Verma et al., (2018) ,
Salim Bahashwan (2014) and
Sarkar et al., (2006) that milk composition traits were highest in hot humid season but lowest in compared to other seasons. The daily yield of fat was observed to be higher during summer (p<0.05) than winter season. Contraindication to result
Kadzere et al., (2002) and
Bouraoui et al., (2002) observed lower milk fat in the summer season. When THI value goes beyond 72, milk fat content declines.
Zheng et al., (2009) observed that the higher environmental temperature significantly reduces the percentage of milk fat in milk.
Protein (%)
The milk protein values during the summer season and thermoneutral period were presented in Table 2 and Fig 4. It was observed that milk protein was significantly (p<0.05) higher during a thermoneutral period than the summer season. The result was similar to
Zheng et al., (2009) observed that heat stress significantly reduces the production of milk and the percentage of protein in milk.
Bouraoui et al., (2002) observed lower milk protein in the summer season. When THI value goes beyond 72, milk protein content declines. Heat stress significantly reduced milk protein contents from 3.20% during the winter season to 3.07% during summer season
(Gaafar et al. 2011). While
Radhika et al., (2012) reported that, the protein content was significantly lower (p<0.05) during winter than summer season.
Lactose (%)
It was observed that the values of lactose during the summer season and thermoneutral period were shown in Table 2 and Fig 5. No significant change was found in lactose content during the summer season and thermoneutral season. The result was similar to
Zheng et al., (2009) observed that the higher environmental temperature has no significant effect on the lactose content in the milk. Contraindication to result of
Gaafar et al., (2011) reported that the heat stress significantly reduced milk lactose contents from 4.78% during the winter season to 4.59% during summer season.
Solid not fat (SNF%)
It was observed that the values of the solid not fat in milk during the summer season and thermoneutral period were presented in Table 2 and Fig 6. It was observed that solid not fat of milk was significantly (p<0.05) higher during the summer season than the thermoneutral period. The result was contraindicated to
Gaafar et al., (2011) who claims that higher temperature significantly reduced the milk SNF contents from 8.69% during the winter season to 8.34% during summer season. Similar results were also reported by
Bernadin (1972) and
Verma et al., (2018).
Density
It was observed that the values of milk density during the summer season and thermoneutral period were presented in Table 2 and Fig 7. It was observed that the density of milk was significantly (p<0.05) higher during the summer season as compared to the thermoneutral period.
In the present study, there were a significant (p<0.05) increase in fat%, concentration, solid not fat and density found during the summer season, while there was a significant (p<0.05) increase in milk protein level during the thermoneutral period.