Estimation of genetic parameters for physiological and milk production traits of Holstein Friesian crossbreds reared in Tanzania

The main objective of this study was to estimate the genetic parameters for physiological traits, milk yield, and milk composition in Holstein Friesian crossbred cattle raised at the Tanzania Livestock Research Institute's (TALIRI) Tanga dairy farm.A total of 29 lactating Holstein Friesian × Zebu crossbred cows with 50% (HF50) and 75% (HF75) Holstein Friesian gene levels in their second and third months of lactation were included.Breed composition was determined based on the animal recording system at TALIRI, Tanga.A series of univariate and bivariate repeatability (r) test-day models was used to estimate genetic parameters, genetic (rg) and phenotypic correlations (rp) for milk yield (MY), milk composition traits including fat, protein, lactose, and solids-not-fat (SNF) percentages and physiological parameters, including core body temperature (CBT), rectal temperature (RT), respiratory rate (RR), and panting score (PS) in cows during their second and third parties.A pedigree-based restricted maximum likelihood method was implemented using Wombat software.The heritability (h²) estimates (h² ± SE) for MY and composition traits ranged from 0.34 ± 0.05 to 0.41 ± 0.03.The h² ± SE for physiological traits ranged from 0.10 ± 0.08 to 0.61 ± 0.08.R estimates (r ± SE) for MY and composition ranged from 0.60 ± 0.04 to 0.62 ± 0.03 while r for physiological traits ranged from 0.58 ± 0.07 to 0.72 ± 0.08.The high h² and r estimates observed in this study indicate that genetic improvement of these traits through selective breeding may be feasible.