Factors that alter the growth and development of ruminants

Abstract

Growth is defined as an increase in tissue mass. Mass increases by hyperplasia early in life and hypertrophy later in life, although hyperplasia of adipose tissue continues throughout life. The growth curve, being mass or cumulative weight plotted against age, is sigmoid, consisting of a prepubertal accelerating phase plus a postpubertal decelerating phase. Mathematically, this curve can be described as a function of mature mass, fractional growth rate, and age. At a specific fraction of mature mass, body composition seems to be constant, but the degree to which nutrition can alter mature mass is not certain. If mature mass is altered, body composition at any given mass will be altered. Mature mass can be decreased by starvation or protein deficiency early in life. Alternatively, retarding the deposition of fat or the administration of estrogenic compounds may increase mature protein mass. Many of the advances in rate and efficiency of growth and in reduced fat of meat cuts can be explained by increased mature protein mass of ruminants. Animals with higher mature weight require more energy for maintenance and reach puberty later in life, so a larger mature mass is not desirable for the breeding herd. Indeed, smaller replacement heifers would prove economical if reproduction were not decreased. A period of restricted growth and fat deposition (as on pasture) can increase the slaughter weight of small cattle into a more desirable range, presumably through increasing mature protein mass. However, calves with retarded growth often make less efficient feedlot gains than do calves finished immediately after being weaned. For growing large-framed heifers, pasture alone often provides an inadequate energy supply for early puberty, but excessive amounts of supplemental feed can enhance fat deposition in the udder, which subsequently decreases milk production. By manipulating the supply of specific nutrients and hormones, it may prove feasible in the future to reduce fat deposition in specific tissues and to alter mature body protein mass.

Tamanho relativo dos órgãos internos e do trato gastrintestinal de bovinos indubrasil e mestiços leiteiros em fase de engorda

“…Em termos de prioridade de nutrientes, principalmente no decorrer do desenvolvimento corporal, os resultados têm mostrado que os órgãos coração, baço e pulmões são os componentes com maior prioridade, conforme relatos de vários autores (PERON et al, 1993;JORGE et al, 1999;VÉRAS et al, 2001). O fígado participa ativamente no metabolismo dos nutrientes, sendo considerado como de elevada taxa metabólica (OWENS et al, 1993), porém, neste trabalho, o fígado dos animais mestiços foi somente mais pesado em valores absolutos, não havendo diferença significativa.…”

“…Essa maior proporção de gordura interna tende a aumentar a exigência de mantença dos animais mestiços leiteiros. Esse fato está de acordo com OWENS et al (1993), os quais afirmam que os depósitos de gordura mesentérica e interna ocasionam maior exigência de mantença. Já PERÓN et al (1993) afirmam que os animais zebuíno apresentam menores teores dessa gordura do que os animais taurinos ou mestiços leiteiros, sendo essa gordura metabolicamente mais ativa.…”

A teleonomic model describing performance (body, milk and intake) during growth and over repeated reproductive cycles throughout the lifespan of dairy cattle. 1. Trajectories of life function priorities and genetic scaling

“…Changes in X during its lifetime are defined through the balance of a target equilibrium level of body fatness (Friggens et al, 2004) and the mobilization of body reserves. The constitution of body reserves is postponed relative to the growth of the non-labile body mass in early developmental stages (Owens et al, 1993;Vernon et al, 1999). The balancing of labile body reserves to an optimal level prevails during the developmental stages of life (constitution of body reserves) and during the transition between the lactational and gestational stages of two successive reproductive cycles (reconstitution of body reserves by mobilizing surplus or filling deficit).…”

Características de carcaças bovinas obtidas por frigoríficos na região central do Brasil, um retrato espacial e temporal

“…O crescimento contínuo, sem interrupção, é uma concepção teórica e expresso por uma curva sigmóide. A eficiência do crescimento de bovinos depende de fatores como peso, idade, tamanho adulto, raça, genética, nutrição e sexo (Koch et al, 1982;Oltjen & Garret, 1988;Owens et al, 1993).…”

“…Iniciando-se pelo tecido nervoso e seguido pelo ósseo, muscular e adiposo, esta progressão implica em diferentes exigências nutricionais conforme a fase de crescimento animal (Owens et al, 1993(Owens et al, e 1995.…”