Effects of inbreeding on fighting ability measured in Aosta Chestnut and Aosta Black Pied cattle

Aosta Black Pied (ABP) and Aosta Chestnut (AC) are dual-purpose cattle indigenous to the western Alps and famous for their fighting ability in traditional Italian Batailles de Reines. The present study aimed to investigate the influence of inbreeding on breeding values for fighting ability achieved in participants. Inbreeding (F) and average relatedness (AR) were obtained from the entire pedigree information available (19,554 and 87,967 records for ABP and AC, respectively). Data (n = 23,998) relating to 8,259 cows competing in years 2001–2009 were analyzed to obtain heritability (h2) estimates and breeding values for the trait. A placement score was chosen as a phenotype for fighting ability and both a classical quantitative model (NORM) and its implementation, used to identify its indirect genetic effects (COMP), were analyzed using the expectation maximization-REML (EM-REML) method. The F and AR trends in animals born between 1990 and 2009 were generally low and were greater for ABP (+0.06%/yr) than for AC (+0.03%/yr) populations, which also presented a greater mean F (about 2.8% ± 1.7% vs. 0.8% ± 1.5% for ABP and AC, respectively) and mean AR among individuals (about 1.0% ± 0.8% vs. 0.4% ± 0.3% for ABP and AC, respectively). Heritability estimates from 0.083 ± 0.036 to 0.120 ± 0.037 were obtained using the NORM model, accounting for or not accounting for F, respectively. Similar results were obtained also for the COMP model, with h2 estimates of 0.12 ± 0.037, whether or not F was taken into consideration. Linear regression analyses carried out on the 33 major lineages to which most of participants belonged (n = 6,087) revealed an overall negative trend of EBV compared with the increase of either F (b = −21.3, P < 0.01) or AR (b = -50.1, P < 0.01). However, a great variability in the relationship between EBV and F or AR was found by analyzing data within lineages. Despite the variability, an unfavorable effect of inbreeding was detected in the fighting ability trait of both ABP and AC cattle, and this should be carefully considered in the breeding management of both breeds.