Performance in preweaning pure and crossbred calves in the Mato Grosso do Sul Pantanal region , Aquidauana , Mato Grosso do Sul State , Brazil

Purebred and crossbred calves (n = 3,871) were selected that were born in the sub-region of the Pantanal of Aquidauana (Brazil), derived from Nellore, Brangus, Wagyu, and 1⁄2 Brangus + 1⁄2 Nellore cows, which were artificially inseminated by bulls of the Aberdeen Angus, Red Angus, Brangus, Nellore, and Wagyubreeds. Parameters such as weaning weight, daily gain from birth to weaning, and the number of days to gain 160 kg, were assessed inthese calves and phenotypic correlations between the traits were evaluated. Data were analyzed using two statistical models. The first model included sire breed effects, the genetic group of the cow, sex, year of birth (AN), birth season (EN), and the interaction AN * EN. The second model included the genetic group of the calf, sex, AN, EN, and the interaction AN * EN. The genetic group of the cow and calf and the interaction AN * EN did not significantly affect body weight (p < 0.05). The average weaning weights of progeny were as follows: Aberdeen Angus bulls, 177.70 ± 3.28 kg; Red Angus, 180.31 ± 3.46 kg; Brangus, 181.48 ± 3.15 kg; Nellore, 175.43 ± 3.60 kg; and Wagyu, 173.16 ± 2.96 kg.

The beef cattle industry is critical for the region, with greater emphasis being placed on the calfweaning phase, as it generates the main product marketed by cattle farmers (Abreu, Lopes, Baptista, Torres & Santos, 2006;Santos, Abreu, Souza & Catto, 2009).Cattle production in this region however, is challenging because of the prevailing agro-climatic conditions.
Several breeds can adapt to the environments in which they are raised (Silva, Fraga, Espíndola Filho & Pedrosa, 2008).The Zebu, for example, is quite hardy and adaptable to tropical climates, whereas Bos taurus demonstrates high yield potential only under appropriate conditions (Ducatti et al., 2009;Prado, 2008a, b.Thus, crossing breeds can be a viable alternative to improve the production rates of cattle herds raised in the sub-region of Aquidauana Pantanal (Teixeira, Albuquerque, Alencar & Dias, 2006).
Crossbred animals can demonstrate desirable traits, because of the potential for increased genetic variation and heterosis (Pacheco et al., 2014).Teixeira & Albuquerque (2005) reported better performance in weaned crossbred calves (Bos taurus x Bos indicus) in comparison to purebred animals.The superior performance of crossbred animals could be attributed to the additive effects of heterozygous genes of the parent breeds and to heterosis (Muniz & Queiroz, 1998).
One of the techniques commonly used to verify the genetic potential of animals is to estimate the effect of the interaction between genetic and environmental factors, which can interfere with the performance of the progeny, by measuring the calf's weight at weaning (Bocchi, Teixeira & Albuquerque, 2004;Costa, Queiroz, Oliveira & Fries, 2009;Pereira & Muniz, 2013).Among the variables that can be included in this evaluation, are the daily gain from birth to weaning and the number of days to attain a given weight (Souza et al., 2011).These traits are directly related to the animal's growth rate (Malhado et al., 2005;Souza et al., 2011).
The aim of the present study was to evaluate the effects that influence the weaning weight, daily gain from birth to weaning, and the number of days to gain160 kg in pure-and cross-bred calves born in the Pantanal of Aquidauana, Mato Grosso do Sul State, Brazil.

Material and methods
Data were recorded from 3,871 calves, all sons of Nellore, Brangus, Wagyu, and ½ Brangus + ½ Nellore dams that were artificially inseminated within a fixed time frame by Aberdeen Angus, Red Angus, Brangus, Nellore, and Wagyu bulls.
Calves were raised on a farm in the sub-region of Aquidauana Pantanal (Brazil).The climate according to Köppen & Geiger (1928) is hot humid tropical, with a rainy season in the summer and a dry season in the winter.Annual rainfall varies from 1200 to 1300 mm, with an average annual temperature of 26 °C.Nutritional management systems generally consist of extensive, predominantly Brachiaria brizantha pasture, supplemented with mineral salt ad libitum.Herd health management generally follows the recommended technical standards for the region.
Performance information of calves was analyzed until weaning in the following genetic groups: Nellore; Brangus; Wagyu; ½ Aberdeen Angus + ½ Brangus; ½ Aberdeen Angus + ½ Nellore; ½ Red Angus + ½ Brangus; ½ Red Angus + ½ Nellore; ½ Brangus + ½ Nellore; ½ Wagyu + ½ Nellore; ½ Wagyu + ½ Brangus; and ½ Wagyu + ¼ Brangus + ¼ Nellore.The weight at weaning was standardized to 205 days using the following formula: WW = (GBW × 205) + BW, in which WW is adjusted weaning weight to 205, BW is the birth weight and GBW is daily gain from birth to weaning.GBW is calculated by the formula GBW = (WWo -BW)/ID, where WWo is the weaning weight observed, BW is the birth weight, and ID is the age at weaning.The number of days to gain 160 kg (D160) was calculated by the formula D160 = 160/GBW.
Statistical analysis of the data was conducted using the SAS program.The data were analyzed by two statistical models using the PROC GLM procedure.The first includes the fixed effects of bull breed, cow genetic group, sex, year of birth, birth season (dry: May to September; wet: October to April), and interaction between birth season and year of birth.The second model includes the fixed effects of genetic group of the calf, sex, year of birth, birth season (dry: May to September; and wet: October to April) and interaction between birth season and year of birth.
For both models, the interaction between birth season and year of birth was not found to be statistically significant, and was therefore eliminated from further analysis.

Results and discussion
Averages of 183.1 ± 27.5 kg for WW, 0.69 ± 0.13 kg for GBW, and 238 ± 47 days for D160 were observed.The effects of sex, season, and year of birth showed were significant (p < 0.001) in both models (Table 1), indicating the need to consider these variables when comparing the performance of The observed effects of sexual dimorphism may be related to the greater weight of males, and consequently the generally higher hormonal levels and metabolic rates, which in turn leads to greater feeding capacities and faster growth, in comparison to those of females (Biffani et al., 1999).Birth-year effects can be associated with any improvements in environmental conditions (Souza et al., 2011), or fluctuating soil and weather conditions (Sarmento, Pimenta Filho, Ribeiro, & Martins Filho, 2003) over a number of years.
The effects of birth season are mainly associated with the increased availability and quality of forage for the dams, thereby facilitating a peak in milk production (McManus et al., 2002).Another factor associated with the season of birth, is low precipitation (dry season) at colder times of the year that results in a lower incidence of parasites and diseases (Menezes et al., 2013).In contrast, the warmer season associated with high humidity, facilitates an increase in parasites that can compromise normal development in the calf.
The genetic group of the dam was associated with significant differences in performance between calves in the pre weaning phase.The dam's influence decreased, however, when growth and approximate weaning weight were taken into consideration, and was insignificant at the point of weaning.Sarmento et al. (2003) found that differences in calf weight at weaning were related to maternal factors from the pre-natal phase (due to placental differences) to the postnatal period (related to maternal skills and milk production).
Genetic variability was evidenced by significant differences in the performance of calves at weaning due to breed of the bull (model 1) and genetic group of the calf (model 2).The progeny of Brangus and Red Angus bulls demonstrated higher average WW and GBW and fewer days to gain 160 kg (Table 2).Nellore and Wagyu breeds produced lighter calves and gained less weight than did other breeds.In another study in the Pantanal region, Nellore animals showed lower daily weight gains than did crossbred animals native to the region (Mariante et al., 2005).Bianchini et al. (2008) found a lower growth rate in purebred Zebu animals compared to European cattle or crossbred European x Zebu.Muniz and Queiroz (1998) reported significant differences between the performance of purebred and crossbred calves, confirming the superiority of crossbred continental breeds.In addition, Kippert, Rorato, Lopes, Weber and Boligon (2008) reported significant differences between pre-and postweaning performance in a multiracial population of Aberdeen Angus x Nellore.
The superiority of crossbred animals was observed in both models (p < 0.05) for weaning weight and gain from birth to weaning in male calves, and for animals born in the dry season, resulting in fewer days to gain 160 kg.Significant differences between traits for calves born in different years are presented in Table 3.
Males had higher weaning weights and higher gains from birth to weaning, with fewer days to reach 160 kg.These findings are consistent with those of Silveira et al. (2004), who also observed that males were, on average, 8.1% heavier than females.
The soil and climate of the Pantanal region may have influenced the birth year and season of birth.During the wet season, there was a significant increase of 22 days for the calves to gain 160 kg.According to Pott et al. (1989) of marked food restriction in the Pantanal region: one, from the height of the rainy season to its end; and the other, at the end of the dry season.Therefore, calves born in either of these two periods can have lower body weights in comparison to other animals born in times of greater food availability.Values represent average of least squares ± standard errors.Means followed by different letters in the same column are significantly different (p < 0.05).WW: the adjusted weaning weight; GBW: daily gain from birth to weaning; D160: number of days to gain 160 kg.Teixeira and Albuquerque (2005) studied the environmental effects that affect gain in pre weaning Angus, Hereford, Nellore, crossbred Angus x Nellore, and Hereford x Nellore animals and found that those born earlier in the spring (July to September) fared better.Their results are consistent with those of McManus et al. (2002).
Ideally, most animals should be sold at the same age.Crossbred animals with comparatively slower growth rates however, represent a significant cost to farmers.Slower growth rates lead to a longer maintenance period at pasture, causing subsequent delays in the breeding season, a decrease in the reproductive efficiency of females, and a longer calving interval.
The Wagyu breed demonstrated comparatively lower weaning weight (161.38 ± 10.43 kg), lower gain from birth to weaning (0.60 ± 0.05 kg), and a greater number of days to reach 160 kg (256 ± 20 days).
However, despite the relative underperformance, this breed is the focus of study in several countries (including United States, Australia, and Canada) because of desirable carcass traits such as higher levels of marbling.According to National Beef Quality audits, marbling is a major concern for suppliers, restaurant owners, and retailers, because the degree of intramuscular fat (marbling) is directly related to the juiciness and flavor of beef (Radunz, Loerch, Lowe, Fluharty & Zerby, 2009).Taninaka, Santos, Meneghini and Bernardino (2015) studied the economic viability of the full production cycle of the Wagyu breed, and reported that it can be highly profitable if the value of the final product can be differentiated.

Conclusion
Sexual dimorphism, season, and calf birth year should be considered when comparing the performance of calves.The breed of the sire caused variation in calf performance, and progenies of Brangus and Red Angus breeds, exhibited superior traits.Progeny of the Wagyu breed demonstrated comparatively lower performance for all characteristics under investigation.

Table 2 .
Performance characteristics of weaned Nellore, Brangus, Wagyu, and crossbred calves according to the breed of bull.

Table 3 .
Performance traits of weaned Nellore, Brangus, Wagyu, and crossbred calves according to the effects of sex, season, and year of birth.