Investigation of Reproductive Trends and Postpartum Problems in an Industrial Dairy Farm in Yazd, Iran

Introduction
Effective reproductive management is a cornerstone of profitability in commercial dairy farming. A key challenge is the well-documented negative correlation between milk yield and reproductive efficiency, which is often exacerbated by postpartum complications.
This study aimed to conduct a systematic analysis of reproductive performance and identify critical postpartum health challenges in a large-scale industrial Holstein farm in Yazd province, Iran. The primary objectives were to evaluate the impact of specific factors calf sex and cow parity on the type of calving (normal vs. dystocia) and the incidence of postpartum disorders (uterine infection and ovarian cysts). The ultimate goal was to provide management recommendations to improve reproductive outcomes and herd profitability.
Method
A descriptive-analytical study was conducted using historical data from one of the largest industrial dairy farms in Yazd province. The dataset included 373 dairy cows and their calving records spanning a ten-year period (2005-2014, equivalent to Iranian years 1384-1393). Records from parity 1 to 5 were included, with each calving event treated as an independent observation. Data extracted from electronic and paper farm was recorded including calving type (normal, assisted, dystocia), calf sex, and diagnoses of postpartum disorders (uterine infection and ovarian cyst) confirmed by veterinary clinical examination. Incomplete or duplicate records were excluded. Statistical analysis was performed using SAS software (version 9.1). The Chi-Square test was employed to assess the significance of associations between categorical variables: calf sex and calving type, calf sex and postpartum problems, and parity number with both calving type and reproductive disorders. 
Results
The analysis significant results was as follows several:

Calving Type and Calf Sex: Normal parity were most frequent. However, male calf births were significantly associated with a higher incidence of dystocia and assisted parity compared to female calf births.
Postpartum Disorders and Calf Sex: The majority of postpartum problems were uterine infections (87.35%), and ovarian cysts comprising 12.64%. The birth of male calves was linked to a higher occurrence of both of these disorders.
Parity and Calving Type: Reproductive performance improved with higher parity. The rate of normal parity increased significantly after the third parity, while the rates of assisted calving and dystocia decreased. The lowest incidence of dystocia was observed in third to fifth parities.
Parity and Postpartum Disorders: The prevalence of ovarian cysts increased up to the third parity and then declined in fourth and fifth parities. In contrast, uterine infection was most common in heifers and decreased in subsequent parities.

Discussion: according to the findings, two primary determinants of reproductive difficulty are calf sex and cow parity. Male calves especially heavy one increase the risk of dystocia, which makes cows susceptible to secondary complications like uterine infections. The vulnerability of early-parity cows (especially first and second) is attributed to the simultaneous demands of growth and lactation, and the profound negative energy balance (NEB) in early lactation. This NEB impairs immune function and ovarian activity, explaining the higher rates of uterine infection and the initial rise in ovarian cysts. The subsequent improvement in health indicators after the third parity indicates better metabolic adaptation and energy balance in mature cows.
Conclusions
The study concludes that targeted management strategies are essential to mitigate these risks. Key recommendations include:

Strategic Sire Selection for Heifers: Using sires with proven genetic value for low birth weight and easy calving, particularly for high genetic value heifers.
Enhanced Care for Early-Parity Cows: Implementing specialized nutritional, metabolic, and health monitoring programs for cows in their first to third lactations to manage energy balance and support uterine health.
Precision Calving Management: Providing increased supervision and timely assistance during calving for cows carrying male calves.

By focusing on these factors, dairy farms can improve reproductive efficiency, reduce the calving interval, and decrease involuntary culling, thereby enhancing overall herd productivity and economic sustainability.