3.1. Calving and weaning rateNo par

3.1. Calving and weaning rate
No parameterization of cow age was important for these traits
(P40.3). Year was influential for all traits and was retained in final
models for each (Po0.05). This parameterization was different from
evaluation of these breeds with Brahman in Florida (Riley et al.,
2014), in which levels of age nested within year best modeled these
2 effects. A possible reason is the absence of 2-yr-old records in the
present study; this result suggests that records from young ages are
largely responsible for age effects of reproductive rates.
The sire breed-dam breed interaction (Po0.01) was supported by
the same pattern of means for both calving and weaning rate. Angus
cows had the lowest (Po0.005) mean calving and weaning rates
(Table 2); these rates did not differ (P40.28) among the other breed
groups. The mean calving and weaning rates for Angus and Angussired
F1 cows in this study were similar to means in Florida (0.82 and 0.79 for Angus, 0.83 and 0.81 for Romosinuano, and 0.89 and 0.86 for
the Angus-sired F1 cows, respectively). However, the means for the
other groups were higher in the present study. This relative positioning
of means in both experiments may highlight the more favorable
performance of Romosinuano cows in a more temperate
region; could it conversely suggest that Angus cows were more
adapted to the conditions in Florida than in Arkansas? Such a notion,
though not well supported, is intriguing given the background of the
research Angus herd in Florida (Riley et al., 2007, 2011, 2014). In a
subset of the purebred Angus and Romosinuano cows in this study,
the Angus cows appeared to be more susceptible to the toxins in the
tall fescue and heat stress during summer months than the Romosinuano
cows (Burke et al., 2010). In addition, serum concentrations
of prolactin were greater in Romosinuano than Angus cows. This
could account for the better performance of the Romosinuano and
maybe crossbred cows compared with the Angus. Heat tolerance in
either area (Arkansas or Florida) appears to be beneficial, independent
of forage type.