The effect of daily milk yield and ambient temperature on reproduction performance in Holstein cows

The aim of this study was to identify the effect of ambient temperature and daily milk yield on reproduction efficiency in Holstein cattle. Data was consisted test-day records of first-parity Holstein cows together with their reproduction performance belonged to a dairy cattle herd in Isfahan. Daily of meteorological data, maximum and minimum temperature, relative humidity and rainfall were also used. Dairy cows were grouped according to the average of daily milk yield to four groups: low (average of 21.68 Kg), medium downward (average of 26.54), medium upward (average of 29.91) and high (average of 34.89). Data were grouped according to the daily average temperature to four groups: 4.30°c, 11.84°c, 20.06°c and 27.42°c; in average for the group 1 to 4 respectively. Results showed that insemination year and month, daily milk yield, age at insemination, interaction between milk yield and age at insemination and interaction between age at insemination and daily temperature, significantly affect the number of artificial insemination (AI) for successful pregnancy (p<0.0001). The months January, February and March had maximum number of AI and April and September had minimum of AI. Pregnancy rate for the cows with the age of first insemination under 30 months, with high daily milk production (average 34.89 kg) and under high daily temperature (27°c) is more desirable rather than others. Better reproductive performance of cows with high milk production, possibly related to considering of better conditions such as management, nutrition, healthy cares, housing and etc to this group of dairy cattle in the farms.