Responses of lactating dairy cows to climatic conditions in Los Baños, Laguna, Philippines.

Astudy was conducted at Los Banos, Laguna to determine the degree of correlationamongproductive and physiological responses of local lactating dairy cows with climate variability. From an average of 10 lactating Holstein-Sahiwal dairy cows, the monthly average milk yield, dry matter intake, pulse rate (P), respiration rate (R) and body temperature (T) at 0700, 1100, and 1500 hfor 4 consecutive days per month were gathered from September 2011 to June 2012. Heat Index (HI) was calculated from the climatic data from PAGASA Weather Station at UPLB. Correlation analysiswas performed to determine the degreeof linear relationships betweenmilk yieldanddry matter intake, PRT values,environmental temperature, relative humidity, and HI.Milk yield was highly correlated (P<0.05) with HI (r=-0.73), environ-mental temperature (r = -0.71), dry matter intake (r = -0.64), and pulse rate (r=-0.68). The effect of increasing HI value (x) on milk yield (Y) is described by the equation: Y = 25.6 –0.189x (R2=0.535; P<0.05).This indicatesthat HI negativelyinfluencedmilk yield of lactating cows.Further studies are needed to determine the interrelationshipsof PRT, HI and milk yieldfor the formulation of adaptive mechanisms to avoid economic loss from decreased milk yield due to heat stress. Keywords:Milk yield, dry matter intake, physiological responses, heat index, dairy cows