Genetic correlations between type and test-day milk yield in small dual-purpose cattle populations: The Aosta Red Pied breed as a case study.

This study aimed at estimating the relationships between linear type traits and milk production in the dual-purpose Aosta Red Pied (ARP) cattle breed, by expressing type traits as factor scores with the same biological meaning of the individual traits. Factor analysis was applied to individual type traits for muscularity and udder of 32,275 first-parity ARP cows, obtaining 3 factor scores for individual muscularity (F1), udder side (F2), and udder conformation (F3). Data from 169,008 test-day records of milk, fat, and protein yield (kg), belonging to the first 3 lactations of 16,605 cows, were also analyzed. After obtaining genetic parameters for both morphological factors and milk production traits through a series of AIREML single-trait models, bivariate analyses were performed on a data set accounting for 201,283 records of 35,530 cows, to assess the phenotypic and genetic correlations among all factor scores and milk yield traits. The heritability estimates obtained proved to be moderate for both groups of traits, ranging from 0.132 (fat) to 0.314 (F1). Muscularity factor showed moderate and negative genetic correlations (ra) with udder size (-0.376) and udder conformation (0.214) factors. A low and negative ra was found between udder factors. Strong and positive ra were found among all the 3 milk production traits and F 0010 (ra≥0.597). Negative ra with milk traits were obtained for both F 0005 and F3, ranging from -0.417 to -0.221. Phenotypic correlations were lower than the genetic ones, and sometimes close to zero. The antagonism between milk production and meat attitude traits suggests that great attention should be paid in assigning proper weight to the traits, comprising functional traits such as udder conformation, included in selection indices for the dual-purpose breed. The ra obtained for factor scores are consistent with previous estimates for the corresponding individual type traits, and this confirms the possible use of factor analysis to improve type traits relevant to beef attitude.

Evolution of increased competitiveness in cows trades off with reduced milk yield, fertility and more masculine morphology.

In some species females compete for food, foraging territories, mating, and nesting sites. Competing females can exhibit morphological, physiological, and behavioral adaptations typical of males, which are commonly considered as secondary sexual traits. Competition and the development of traits increasing competitiveness require much energy and may exert adverse effects on fecundity and survival. From an evolutionary perspective, positive selection for increased competitiveness would then result in evolution of reduced values for traits related to fitness such as fecundity and survival. There is recent evidence for such evolutionary trade-offs involving male competition, but no study has considered competing females so far. Using data from competitions for dominance in cows (Bos taurus), we found negative genetic correlations between traits providing success in competition, that is, fighting ability and fitness traits related to milk production and with fertility (the inverse of parity-conception interval). Fighting ability also showed low but positive genetic correlations with "masculine" morphological traits, and negative correlations with "feminine" traits. A genetic change in traits over time has occurred due to selection on competitiveness, corresponding to an evolutionary process of "masculinization" counteracting the official selection for milk yield. Similar evolutionary trade-off between success in competition and fitness components may be present in various species experiencing female competition.