Impact of Age at First Calving on Productivity and Reproductive Performances in Crossbred Dairy Cows

Abstract

This study aimed to evaluate the impact of age at first calving (AFC) on key reproductive and productive performances of crossbred cows, including number of services per conception (NSPC), gestation length (GL), lactation milk yield (LMY), lactation length (LL), calving interval (CI), and calf birth weight (CBW). Retrospective data collected over 42 years at Haramaya University Dairy Farm were used. A total of 1093, 1131, 1043, 1031, 851, and 359 cow records for age at first (AFC) were used to evaluate NSPC, GL, LL, LMY, CI, and CBW, respectively. The AFC was categorized into six age classes (AFC1 = <26; AFC2 = 26.1-30, AFC3 = 30.1-34, AFC4 = 34.1-38, AFC5 = 38.1-42, and AFC > 42 months). Data were analyzed using the general linear model procedures of SAS 9.4 version. A simple linear regression model was employed to investigate the relationship between AFC and all response variables. The study revealed that AFC significantly influenced all the response variables except GL. The AFC was negatively correlated with LMY (r = -0.22), LL (r = -0.07), and CI (r = -0.04) while it was positively associated with NSPC (r = +00.18), GL (r = +0.03), and CBW (r = +0.05). Age at first calving was positively correlated with number of services per conception (NSPC; y = 0.71 + 0.02x), calf birth weight (CBW; y = 34.1 + 0.03x), and gestation length (GL; y = 277.07 + 0.03x), according to regression analysis, suggesting that these characteristics tended to slightly increase as age at first calving increased. Generally, cows that calved at an earlier age (<30 months), particularly those in the AFC1 and AFC2 categories, required fewer services per conception, produced higher total milk yield, and gave birth to calves with heavier birth weights.