Genetic and Phenotypic Changes For Female Fertility and First Lactation Production Traits in Friesian Cattle in Egypt

This study aimed to evaluate the genetic and phenotypic trends of heifer and first-lactation cow traits using a multi-trait animal model. Data were obtained from 2,914 performance and pedigree records of Friesian heifers and first-lactation cows collected between 1979 and 2013 at the Saka and El-Karada experimental stations, Kafr El-Sheikh Governorate, under the Animal Production Research Institute, Ministry of Agriculture, Egypt. Linear regression of breeding values on year of first breeding revealed unfavorable genetic trends for age-related reproductive traits, with annual increases of 2.51, 0.18, and 0.09 days/year for age at first breeding (AFB), age at successful service (ASB), and age at first calving (AFC), respectively. In contrast, favorable improvements were observed for heifer fertility traits, including number of services per conception (NSC0; –0.01 unit/year), conception rate (CR0; +0.16%/year), and service period (SP0; –0.34 days/year). For cows, desirable genetic changes were detected for NSC1 (–0.09 unit/year), CR1 (+0.19%/year), and SP1 (–0.69 days/year), whereas unfavorable trends were noted for calving to first service interval (CFS1; +0.49 days/year) and days open (DO1; +0.44 days/year). Milk yield traits demonstrated consistent positive genetic progress, with annual increases of 2.41 kg, 14.9 kg, and 1.71 kg for 305-day milk yield (M3051), total milk yield (TMY1), and daily milk yield (DMY1), respectively. However, an unfavorable decline of –1.7 days/year was recorded for lactation period (LP1). Phenotypic trends closely paralleled the genetic results, confirming the observed patterns of change across the study period.