The effect of late gestation heat stress and feed restriction on nutrient digestibility and rumination behavior of Holstein dairy cows

Heat stress is one of the environmental stressors that has significant effects on the dairy cattle industry. Environmentally induced hyperthermia or heat stress (HS) during dry period has subsequent negative effects on performance of dairy cows .In utero hyperthermia can have a lasting imprint on offspring growth, behavior, and metabolism and also impairs the future HS response in a mammalian modelThe biological mechanisms by which the thermal stress effects on the livestock production performance can be somewhat explained by reduced feed intake, but it is more relevant to hormonal changes, reduced rumination and absorption of nutrients, as well as increased maintenance requirements, which reduces the amount of nutrients / energy for production purpose. The objective of this study was to identify the direct and indirect effects of acute HS during the last gestation on nutrient digestibility and rumination behavior of dairy cows.

Holstein dairy cows (n= 10/treatment) with similar parity and body weight (BW), were randomly assigned to one of the three following treatments during 45 d before calving: 1) Cooling and ad libitum feed intake (TN), 2) Cooling and pair-feeding (CLPF), and 3) HS and ad libitum feed intake (HS). Cows in all groups received individually the same diet. During the experiment, daily temperature and the relative humidity were recorded. During the 26-21 d and 10 to 5 d before calving, the feed intake behavior was record for 24 hours. Cows were housed in individual free stall barn, bedded with straw, which for CLPF and CL cows consisting of shade, sprinklers, and fans that were turned on from 0700 to 1900 h, whereas HS cows were provided only with shade. During the experiment, all cows had free access to clean drinking water. Fans were installed in waiting areas, and sprinklers were applied behind the feed bunk. Diameter of fans was 76 cm, and jet 0.47 cm3 air per fan.Nutrients digestibility in feed and fecal samples was measured on 26 - 21 d and 10 - 5 before calving.

Heat stressed and feed restricted cows had lower feed intake. Heat stressed and food restricted cows had lower eating time significantly compare to the control group. Heat stressed cows had the lowest rumination activity. Also, the heat stressed cows had significantly lower resting time than the control group. Also, heat stress significantly reduced the dry matter and NDF digestibility.

Late gestation heat stress caused decreased feed intake. Also, nutrient digestibility of the diet negatively affected by heat stress. However, feed restriction in late gestation did not have significant effect on nutrient digestibility than the control group. In addition, heat stress reduced the rumination activity and resting time of the cows.