| Heat stress can affect the performance of dairy cows and threaten their health,reduce economic benefits.Summer lasts for a long time in Guanzhong area of Shaanxi Province,with the high temperature reaching 38 C(Fengxiang Weather Forecast,2017).At present,cows are troubled by heat stress in Guanzhong area,and there is few report on the study of this area.Therefore,it is worthwhile to study and relieve the heat stress of dairy cows in Guanzhong area.This trial used Delikang Dairy Farm as a project with the advantage of geographical location,using temperature and humidity sensors MX2301 record the enviornmetal temperature and humidity,using SCR collars and HOBO?loggers record the information of dairy cow behaviors.The main objection of this experiment was to study the effects of heat stress on performance,rumination and lying behavior of dairy cows.To provide theoretical basis for further understand the influence mechanism of heat stress on the health of dairy cows under natural conditions in Guanzhong area.Thirty-five high-yield and thirty-five low-yield dairy cows with similar parity and lactating period were selected in the experiment.The trial period began from May and ended in August.The results are as follows:1.Accuracy evaluation of automatic monitoring system HR-Tag and HOBO?logger.The results showed that rumination time(RT)recorded by HR-Tag was highly correlated with RT directly recorded by human beings(R~2,95%).There was no significant difference between HR-Tag recording and RT recording using LoA method obtained,the upper and lower limits of the difference were 3.9 and-2.6 minutes,respectively.The time of lying down recorded by direct observation was highly correlated with the time of lying down recorded by HOBO~?logger(R~2,0.92 to 0.99).The above results showed that HR-Tag and HOBO~?logger could replace the direct observation method to measure RT and lying behavior of dairy cows in large-scale dairy farms.2.Measurement of heat stress and its effect on performance of dairy cows.The results showed that the dairy Cows Suffered from mild to moderate heat stress during the experiment period according to the size and duration of THI.Milk yield of high-and low-yielding dairy cows in comfort period respectively was 33.10+0.71 kg,24.62+1.25 kg,respectively.After heat shock,milk yield was decreased to 27.56+0.47 kg,21.37+0.05 kg,respectively.Milk yield of high-yielding dairy cows was significantly changed before and after heat stress(P<0.05),while milk yield of low-yielding dairy cows was slight changed and the changed difference was not significant(P>0.05).3.Effects of heat stress on physiological indexes and rumination behavior of dairy cows.Compared with the daily maximum THI<80,rectal temperature and respiratory frequency of high and low yield cows had significant difference(P<0.05)when the daily maximum THI>85,and respiratory frequency had significant difference(P<0.05)in the daily maximum THI between 80 and 85.Meanwhile,when the daily maximum THI>85,the average rectal temperature was higher than 39℃and the respiratory frequency was higher than 70 times/min.RT of high and low yield cows had significant difference(P<0.05)when the daily maximum THI>85,and RT had not significant difference(P>0.05)in the daily maximum THI between 80 and 85.The average daily and night RT of high yield cows was from 545.69 min/d to 500.76 min/d,the average daily and night RT of low yield cows was from 549.65 min/d to 509.94 min/d.The average daily and night RT of high and low cows group was 537.53 min/d,there was no significant difference between high-yielding and low-yielding cattle(P>0.05).4.The effect of heat stress on lying behavior of dairy cows.The results showed that the proportion of high and low yield cows nighttime lying behavior was 62.40%&64.50%and that of daytime lying behavior was 39.18%&42.56%in comfortable period,respectively.Under mild heat stress,the proportion of nighttime lying behavior was 55.18%&59.12%and that of daily lying behavior was 37.60%&39.24%,respectively.However,compared with the former two,the nighttime lying behavior of high and low yield cows under moderate heat stress decreased to 48.79%&51.33%and the proportion of daily lying behavior decreased significantly(P<0.05)to 25.09%&28.12%,respectively.With the increase of THI,the lying time of high and low yield cows was significantly shortened(P<0.01).The average daily lying time of cows in comfort period had little change with mild heat stress(12.05 h/d&11.96 h/d and 10.46 h/d&10.96 h/d,respectively),while the average lying time of cows in moderate heat stress decreased significantly(P<0.05)to 8.42 h/d&8.63 h/d,respectively.Between 8:00 p.m.and 6:00 a.m.,the lying time of dairy cows in comfortable period was similar that in mild heat stress,37.44min/h and 33.11 min/h,respectively.There was a significant difference(P<0.05)in comfortable period and moderate heat stress(29.27 min/h)for the lying time of dairy cows.In conclusion,when THI>72,cows can appear heat stress.Heat stress significantly increased the rectum temperature and respiratory rate of dairy cows,and led to a decline in performance of dairy cows,and significantly reduced the rumination and lying behavior of dairy cows. |
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