CORRELATION BETWEEN AGE , WEIGHT AND BODY MEASURES AT FIRST PREGNANCY OF NELLORE HEIFERS ( Correlação entre idade , peso e morfometria corporal com o estabelecimento de prenhez em novilhas Nelore )

The objective of this study was to characterize and correlate weight, body condition and morphometric measurements with the beginning of the reproductive life in heifers of the Nellore breed. To determine the age of first pregnancy, 56 heifers of the Nellore breed were exposed to bulls. The females were evaluated for weight, body condition and body measurements every two months, from 16 to 32 months of age. The body measurements were: withers height, rump height, body length, head length, rump length, ear length, distance between ribs, distance from dorsal spine to belly, distance from ground to belly, head width, rump width, distance between ischiums, ear width, cannon bone perimeter, tail implantation perimeter, and thoracic perimeter. The results show that the animals had an average weight of 334±39 kg and an average age of 29±3 months at first pregnancy. The morphometric measurements of withers height, rump height, body length, rump length, head width, rump width, width between ischiums, tail implantation perimeter and thoracic perimeter were significantly greater in the pregnant animals. Can conclude from these results that a relationship between morphometric measurements and the first pregnancy in Nellore heifers.

gestação em novilhas Nelore.Palavras-chave: bovinos, medidas morfométricas, precocidade sexual INTRODUCTION Weight evaluation of performance of animals is closely related to measurements of weight, however, other measures relative to the development and structure of the body of beef cattle should also be considered.Linear or morphometric measurements, such as height and length are more accurate size parameters to determine maturity than weight, since the latter may undergo periodic fluctuations, depending on the nutritional status of the animals, whereas linear body measurements are constant (Pacheco et al., 2008).
Linear measurements are parameters of physical development of animals that are, at the same time, also related to their reproductive development (Joubert, 1954).Within this context, special mention should be made of the relationship between thoracic perimeter and the weight:height ratio with body condition (Thompson et al., 1983) and the high correlation between height, weight and age with the onset of puberty (Vargas et al., 1998).These characteristics can be measured quantitatively, and are considered to be effective tools to assess growth and body development, since they are directly related to the biological functions of the animals (Costa Júnior et al., 2006).
In addition, morphometric measures provide supplementary information used to determine genetic and phenotypic trends in the development of the animals over the years, and which may be effective to visualize and monitor the body characteristics directly associated with the reproduction and re-breeding of the animals (Gusmão Filho et al., 2009).
Considering the importance of identifying precocious animals to maximize the production cycle, the objective of this study was to characterize and establish correlations between age, weight, body condition and morphometric measurements with the onset of the reproductive life of Nellore heifers of the Mocha (polled).

MATERIAL AND METHODS
A total of 56 heifers of the Mocha (polled) variety of the Nellore breed, born between August and December 2006, weaned at an average age of 7.5 months of age and weighing between 170 and 230 kg were evaluated.The heifers were placed on the experiment at an average age of 16 months and reared on cultivated (Brachiaria decumbens) pasture (Embrapa Cerrados -Planaltina-DF), with a stocking rate of 1AU/ha.The females were supplemented with mineral salt placed in covered feeding troughs during the rainy season and with protein salt in the dry season to maintain appropriate body condition throughout the year.The experimental animals were dewormed and vaccinated in accordance with the prophylactic vaccination schedule for the region.
The heifers were evaluated from 16 to 32 months of age, at intervals of two months, and assessed for the following parameters: weight, body condition, body morphometrics (16 measurements) and pregnancy diagnosis.
Two bulls (one bull per 28 heifers) were introduced into the herd to determine the beginning of the reproductive life of the females, starting from the second evaluation session, i.e. when they were about 18 months of age.Pregnancy diagnosis was performed by transrectal ultrasonography, using a 7.5 Mhz linear rectal probe from the third assessment onwards (60 days after introducing the bulls).The age interval to first pregnancy was determined considering the age of the animal at the evaluation session when pregnancy was diagnosed and the age of the animal at the preceding session.
Body condition was determined by the method proposed by Kilkenny (1978), by assigning a rating on a scale from 1 to 5, where, 1 = very thin, 2 = thin, 3 = regular, 4 = fat and 5 = very fat.
The morphometric measurements were taken using a tape measure, with a precision of one millimeter: withers height (WH), measured as the distance from the top of the shoulder blades to the elbow and from the elbow to the ground; rump height (RH), the vertical distance from the dorsal aspect of the animal's tail base to the beam; body length (BL), the distance between the humerus-scapula articulation (shoulder) and the extremity of the ischiatic tuberosity; head length (HL), the distance between the tip of the nose and the posterior end of the subopercle; rump length (RL), the distance between cranial part of the iliac tuberosity to the caudal aspect of the ischiatic tuberosity; ear length (EL), the distance between the base of the ear and the tip; distance between ribs (DR), the medial region of the space between the 12th and 13th ribs; distance from dorsal spine to belly (DDB), the distance between the top of the shoulder blades to the sternum or breastbone; the distance from ground to belly (DGB), the distance between region of the sternum or breastbone up to the extremity of the anterior member; head width (HW), the distance between the outer margins of each orbit; rump width (RW), the distance between the most posterior point of the pinbones; width between ischiums (WI), the distance between the points of the ischium bone; ear width (EW), the distance between the outer margins of the medial region of the ear; cannon bone perimeter (CP), the circumference measured just below the knee (in the medial portion of the metacarpal bone), tail implantation perimeter (TIP) the perimeter measured at the base of the tail, thoracic perimeter (TP), measurement based on the sternum or breastbone and the top of the shoulder blades.
The data obtained were analyzed by the SAS software program (Statistical Analysis System, version 9.2, 2008 update) and using the GLM (analysis of variance) and CORR (correlation) procedures.

RESULTS AND DISCUSSION
Thirty-seven heifers (66%) became pregnant during the experiment and, at the beginning of their reproductive life, had an average weight of 333 ± 39 kg, heavier than found by Restle et al. (1999) andOliveira et al. (2009) who reported weights at first pregnancy of 299 ± 20kg and 292 ± 3.8kg, respectively.The weight difference between the animals in this experiment and the weight values described by the abovementioned authors is probably due to the different handling techniques used on each farm, with the animals assessed by Oliveira et al. (2009) pertaining to a herd that participated in a breed improvement program, which would account for the lower weight values reported in their study.
When becoming pregnant for the first time, the weight of the heifers represented about 73% of the adult weight, considering the average weight of 456 kg of the females of the same herd.This value is, at the same time, greater than that reported by Montanholi et al. (2004), who found a percentage of 65% of the adult weight (460 kg), but lower than the value reported by Freneau et al. (2008) who found that heifers of the herd they evaluated weighed on average 85% of the mean adult weight (450 kg) when they became pregnant for the first time.These variations may be explained by differences in nutrition and genetic variations between the herds.Animals raised on farms using nutritional strategies or treatments to promote faster weight gain tend to begin their reproductive life at an earlier age, since animals with greater initial development tend to reach their sexual maturity at a young age and at a proportionally lighter weight compared to the adult weight.
The approximate age of first pregnancy of the heifers in this experiment was between 26 and 33 months, values that are close to those reported by Restle et al. (1999), who reported an age interval between 24 and 28 months; however, with a pregnancy rate of 53%, lower than the rate of 66% found in this study.Silva et al. (2005) observed a pregnancy rate of 42% when the experimental animals were 24 months of age.Oliveira et al. ( 2009), working with 19-to-24-month-old heifers obtained a pregnancy rate of 25% when the females were not stimulated by the presence of bulls during re-breeding and a pregnancy rate of 66% for the females stimulated by bulls.According to Vaz & Lobato et al. (2010) and Gojjam et al. (2011) another reason for the variations in the rate of pregnancy may be attributed to the effect(s) of the weight or weight gain of the animals.
Another factor related to changes in the pregnancy rates may be associated with increased body condition scores (Santos et al., 2009).This situation was observed in this study, in which most of the pregnant heifers had body condition scores (P>0.05%)greater than those of nonpregnant animals (Figure 1).As a rule, the animals exhibiting the best body condition also have a better nutritional status, present better muscle development and greater fat deposition values, thereby promoting higher pregnancy rates.The use of the body condition score was found to be useful in the selection of animals most suited and in the best conditions to begin their reproductive cycle.Table 1 shows the mean values of morphometric measurements of animals pregnant and not pregnant group.The characteristics Withers height, Rump height, Body length, Rump length, Rump width, Width between ischiums, Tail implantation perimeter and Thoracic perimeter were body traits that were found to show significant differences (P<0.05).Body length, Rump width and Width between ischiums are traits associated with reproduction, since animals that exhibit larger measures of these traits have greater ease to giving birth due to their wider pelvic opening.According to Barreto et al. (2004) 2008) who, studying cattle, reported that measurements of height are less susceptible to environmental variations and to the availability of feed resources than life weight.These authors further observed that the upper and lower limits of morphometric measures are reached at an earlier stage of life than the adult weight, since the latter may undergo a series of variations throughout the lifespan of the animal.For that reason, measuring the height is an alternative to determine the point in time when the reproductive life of heifers begins.
Table 2 depicts   In this study, high correlations were observed between weight, height and thoracic perimeter, since all the animals investigated were in the growing stage (Table 1).These parameters are of utmost importance for the characterization of the development of the animals.However, these correlations become less important with the development of the animals due to stabilization of the growth process (Montanholi et al., 2008).
The Ear length, Distance from ground to belly, Body Score, Head width, Width between ischiums, Ear width present low correlations (<0.30) with age, that is, they are little influenced by the increase in age.The Distance between ribs trait showed negative correlation.
Table 3 shows the regression equations for the determination of the growth rate of all the characteristics investigated.The growth rates of the Withers height, Rump height, Body length, Head length, Rump length, Distance from dorsal spine to belly, Rump width, Width between ischiums Weight, Cannon bone perimeter, Tail implantation perimeter and Thoracic perimeter characteristics of the pregnant animals are lower than those of the nonpregnant animals, in spite of the fact that the actual measures of the pregnant animals are larger.These differences in the growth rates and measures may be explained by a greater or more intense initial development of the pregnant heifers.
Table 3 -Regression equations to determine the growth rate of the morphometric characteristics of pregnant and non-pregnant heifers of the Nellore breed.Traits such as Ear length, Head length and Ear width exhibit low growth rates and little variation between the animals throughout the experiment, since these are characteristics closely linked to the characterization of the Nellore breed.
Distance between ribs shows negative regression values.This can be justified by the position of the animal tied in the containment pen when the measurements were taken.In addition, the increase in body mass of the animals makes it more difficult to get access to the space between the ribs.This fact was also observed by Cyrillo et al. (2000), who encountered difficulties during the taking of measurements because of the restless behaviour of the animals.

CONCLUSION
The measurements of weight, body condition score and morphometric measures showed positive correlations among each other and provide very useful tools for the selection of precociously developing animals, with the additional advantage of being characteristics that are easy to be obtained and applied by farmers.Studies on animal handling, feeding and reproduction should be conducted with the objective of enhancing the effectiveness and impact of the measured parameters, so as to develop animals of the Nelore breed raised in the open that begin their reproductive life earlier., v.76, n.10, p.2536-2541, 1998.VAZ, R. Z.; LOBATO, J. F. P. Efeito da idade de desmame no desempenho reprodutivo de novilhas de corte exposta à reprodução aos 13/15 meses de idade.

Figure 1 -
Figure 1 -Description of the number of heifers distributed across the different body condition scores (BCS) and the groups (Pregnant -P and non-pregnant -NP) during each information evaluation session performed during the experiment.

Table 1 -
Mean and standard deviation of morphometric characteristics of Nellore breed heifers pregnant and not pregnant, raised at Embrapa Cerrados in Planaltina -DF.Different lowercase letters, in the same row, indicate significant difference (P<0,05).
all the correlations between the characteristics investigated.The Withers height, Rump height, Body length, Head length, Rump length, Distance from dorsal spine to belly, Rump width, Cannon bone perimeter, Tail implantation perimeter, Thoracic perimeter traits show high correlations (>0.60) with age and weight.Positive correlations were also found by Costa Júnior et al. (2006) and Pinheiro & Jorge (2010) between morphometric measures and body weight.
a,b Different lowercase letters, in the same row, indicate significant difference (P<0,05).