The effects of climate and herd size on reproductive traits in smallholder dairy cattle farms in Fars province

Reproductive performance of dairy cows plays an essential role in the efficiency of the herd and its economy, and indices have been defined to evaluate it. These indices can be affected by various conditions such as the climatic conditions and herd density. Although a large number of dairy cows in Fars province are kept in small farms, but information about their reproductive performance is not available. The purpose of this study was to assess reproductive traits in smallholder dairy farms in Fars province and investigate effects of climate and herd size on it. Reproductive events of 586 cows in selected farms in the cold, temperate and warm climates of Fars province which categorized base on herd size were recorded during one year (from 2017 to 2018) and using them, reproductive traits including the length of pregnancy, Voluntary waiting period (VWP), the numbers of open days (DO) calving interval (CI) and the numbers of service for each conception were calculated. Also, by calculating the number of calves per number of productive cows in herd (including pregnant heifers and dairy and dry cows) and the total number of cows in the herd, the reproductive efficiency of productive cows and the whole herd were calculated. Using analysis of variance tables, the effects of climate, herd size and their interaction on the calculated indices were investigated. The overall mean±standard deviation (SD) of the length of pregnancy, VWP, DO and CI were 278.97±4.70, 83.62±20.12, 104.35±30.04 and 383.34±30.73 days and the numbers of service for each conception was 1.56±0.71 times. The GL, VWP and CI differed significantly (p < 0.05) between warm and cold regions. The herd size alone was not influenced studied traits but in interaction with geographical regions, significant differences (p < 0.05) were observed in VWP, DO and CI between warm and cold regions in herd size 15-21 cows. Means±SD of reproductive efficacy were 54.32±21.27 and 38.20±19.30 % in productive and total cows, respectively, which were not significantly affected by climate and herd size. Unlike climate, herd size has no effect on reproductive performance indicators of small farms in Fars province and although these indicators are not ideal, but they are more desirable than the other reports from Iran.