Studies in different countries with foals showed large body development between they born and just before the weaning principally in their height at withers and foals’ weight [1] -[4] . Also other studies had been demonstrated influence over foal’s growth by the dam, date of birth, and nutrition status [5] [6] . However, there is little information about variation of foals’ pattern of development in Brazil [3] [7] [8] and results of these researches found similar development pattern that other ones developed in different countries. However, because there is large number of horses in different countries, patterns of foal’s growth are not well understood, principally in Tropical areas.

Horse population in Pernambuco is around 150,000 plus 100,000 donkeys and mules. These animals have large economical importance in different parts of this state and in Brazil [9] [10] . Because there is little information about foals’ development in Pernambuco, it was used data from foals that were raised in seven different horse farms of Pernambuco. The aim of this study was to compare foals development between four breeds and develop regression formula to estimate foal development. This information will help the horse owners to characterize and understand their animals’ development.

The results of this study showed that Arabians foals had large mean of height at withers when compared with Quarter Horse (P < 0.05) but was similar to Campolina and Mangalarga Marchador (P > 0.05) (Table 1). During suckling period Mangalarga Marchador got large percentage of gain in height (~36%), and was followed by Arabian (~34%), Campolina (~33%) and Quater Horses (~33%) (Table 2). In other hand, Mangalarga Marchador had large mean heart girth when compared with other tree breeds (P < 0.05) (Table 1). Arabian, Campolina, Mangalarga Marchador and Quarter Horse gained 60%, 55%, 60% and 48%, respectively, between they born

Observations: different letter at same line represents P < 0.05 by Tukey test.

Observations: ARB: Arabian; CAMP: Campolina; MM: Mangalarga Marchador; QH: Quarter Horse; Different letters at same line represents P < 0.001 using Tukey test.

and weaned in their heart girth (Table 3). Campolinas presented large mean of cannon bone girth when compared with all other tree breeds (P < 0.05) (Table 1), and this body measurement was the only one that in all breeds presented different pattern of development (P < 0.05). Arabian, Campolina, Mangalarga Marchador and Quarter Horse gained 36%, 25%, 36% and 25%, respectively, between they born and weaned in their cannon bone girth (Table 4).

In this study were observed significant interactions between breed and phase of development in heart and cannon bone girths (P < 0.05) but not in height at withers (Table 5). All regression formulas obtained from these suckling foals data are very significant (P < 0.001), showing that formulas can predict height at withers in all four breeds. Regression formulas from heart and cannon bone girth have medium value for R² but they are significant (P < 0.001) (Table 6).

The body measurement average in this study detected that Arabians foals had large mean of height than Quarter Horse but similar to Campolinas and Mangalarga Marchador. However some of this result was not expected, because Campolinas horses have between 150 and 160 cm height at withers when they are adult animals [12] . This horse breed is taller than all other three breeds studied in this project. Also it is important to remember that breed also have blood lines and typical Quarter Horse bloodline in Pernambuco is working horses, and this fact may explain why Quarter horses had small average of height at withers in this research. However, Allen et al. [6] comment that foals’ linear growth is completed when their growth plates are closed and some potential plasticity in height could be achieved only before this process.

Because this potential plasticity in horse’s height some researchers work with a percentage of adults height to better understand foals development, however adult height are not well defined in some breeds. Studies with Mangalarga Marchador suckling foals showed that breed obtain more percentage of adults height than Campolinas, ~85% and 75% respectively, before weaning [7] . Also Hintz et al. [5] commented that Crossed Arabs and Quarter Horses reached ~83% of the mature height around the weaning period or six months old. Gain in height at withers was very similar between all four horses, despite of some difference observed at birth and following months, but in this actual research different values of height was not compare with final adult height.. Finally, it is important observe that the National Association of Campolina and Mangalarga Marcahdor breeds have rigid control of the adult’s height since 1950s, contributing to these measurements in both breeds, with is not common in Arabians and Quarter Horses in Brazil.

Mangalarga Marchador horses had large heart girth when compared with all other three breeds. Values of heart girth can be used to determine body mass and foals during lactation this parameter got large increase when compared with gain in height at wither. Mangalarga Marchador and Arabians gain near 60% in this parameter

Observations: ARB: Arabian; CAMP: Campolina; MM: Mangalarga Marchador; QH: Quarter Horse; Different letters at same line represents P < 0.001 using Tukey test.

Observations: ARB: Arabian; CAMP: Campolina; MM: Mangalarga Marchador; QH: Quarter Horse; Different letters at same line represents P < 0.001 using Tukey test.

Observations: Foal age in months; WH = height at withers; HG = heart girth; CBG = cannon bone girth.

between birth and weaning, differently from Campolina and Quarter Horses, but in this parameter we did not obtain the percentage from adult horse. Hintz et al. [5] showed that Thoroughbred foals with 6 months old had only 45% of adult weight and 85% of adult height at withers. Manso Filho et al. [13] ] detected in Standard bred suckling foals significant changes in fat mass only after 1 months old, but also do not inform percentage of the weight at six months old from adults horses. Interestingly, adult Mangalarga Marchador horses (~400 Kg) are lighter than Campolinas (~480 Kg) [13] , and we did not expect that suckling foals of both breed had significant difference during suckling period.

The cannon bone girths are associated to bone characteristic and the average of this parameter in this research showed significant difference between all three breeds. Interesting, Campolina, which are heavier breed developed in Brazil, had large cannon bone girth followed by Quarter Horse, Mangalarga Marchador and Arabs (P < 0.05).

Different factors are associated with modulation of the development in young horses and breeds’s of horses. All animals in this actual research were raised in pasture and are supplemented with concentrate, which follow NRC 1987 suggestions, and during dry season (summer) farm owners supplemented their animals with Tifton and Cost-Cross hay and Elephant grass. Horse can be raised on pasture with supplementation with grain have normal growth and development [14] and normal growth was expected for all animals used in this research. However the nutritional level can change some parameter used to determine foals development and Resende et al. [3] , using Mangalarga Marchador foals with different levels of supplementation of protein (18% PB versus 16% PB, but isocaloric), showed difference in height at withers but not at heart girth when these foals had near 6 months-old (202 days). In contrast, Ott et al. [5] , studying two different levels of protein supplementation (~18% PB versus ~15% PB), observed that Thoroughbred and Quarter Horses have normal growth when they received correct amount of Lysine supplementation. All these researches demonstrated that foals can growth normally if they have a good nutritional support but the genetic background have important impact in this process.

The fetal programing produces significant impact on foals’ development independently of their breed. Different research had shown the importance of fetal development and programing to postnatal development and metabolism [15] . In this actual research suckling foals where evaluated between birth and weaning, and some differences observed at height at withers may change after this period, because there is some plasticity of growth [6] . Finally, it is important to recorder that results presented here represent growth characteristic in suckling foals in tropical conditions at the Agreste region in Pernambuco, Brazil. These information can be used in different conditions but more foals’ body measurement analysis are needed to better understand equine development during its first six months of life.

In this study, there was a significant interaction between breed and development phase for heart girth and cannon bone girth measurements. Also, the regression formula obtained with the suckling foal data can be used to predict height at withers for the four studied breeds. Finally, as fetal programing may influence postnatal development, there may be some differences in after-weaning measurements. Therefore, we suggest that more measurements in this period be done in order to complete and improve the understanding of equine development.