Review of some aspects of growth and development of feedlot cattle.

Abstract

Growth in animals is defined as accretion of protein, fat and bone. Although growth typically is measured as the change in live weight, nutrient retention is estimated more precisely by measuring empty body weight and composition, whereas production economics are measured ideally through carcass weights and quality. As a percentage of live weight gain, carcass weight gain usually is a much higher percentage during the feedlot phase than during the growing phase of production because dressing percentage (ratio of carcass:live weight) increases with maturation and is greater with concentrate than with roughage diets. At a given fraction of mature body size (maximum body protein mass), body fat percentage seems to be a constant. Mature size may be altered genetically and nutritionally. Protein accretion declines to zero when cattle reach their mature body size (approximately 36% fat in empty body weight in modern cattle) even though mature animals can continue to accrete fat. Although fat accretion can be reduced by limiting the supply of net energy, rate of fat accretion by finishing steers given ad libitum access to high-concentrate diets seems to reach a plateau at approximately 550 g daily. Protein mass, in contrast, increases in proportion to empty body weight. The protein:fat ratio of the carcass can be increased through increasing mature size, by administering hormones or hormonal modifiers, by limiting energy intake during the growing period or finishing period, or by slaughtering cattle at an earlier stage of maturity. Energetically, efficiency of accretion of fat is approximately 1.7 times that of protein. But because more water is stored with deposited protein than with deposited fat, lean tissue gain is four times as efficient as accretion of fat tissue. Conversion of protein to fat is very inefficient, suggesting that excess protein is utilized inefficiently.

Ontogenesis of muscle and adipose tissues and their interactions in ruminants and other species

“…During the post-natal growth of cattle, protein and fat accretions are concomitant, with a preferential protein accretion during early growth, and of fat during later growth. The switch occurs when empty body weight reaches 300 kg in concentrate-fed steers and bulls (Owens et al, 1995). The energy level or composition of the diet have been shown to affect the lean-to-fat ratio differently according to the age and thus the respective growth rates of muscle and AT (Berge et al, 1991;Greenwood and Cafe, 2007).…”

Relationship between body composition, blood volume and maximal oxygen uptake

“…It is not well understood why fat mass increases with increasing FFM; however, it is believed that this phenomenon may be a protective mechanism (Cartwright 1991;Owens et al 1995). To this end, it has been speculated that fat deposition may accompany extreme muscle mass accumulation in order to maintain energy balance needs by retaining a larger proportion of essential fats than normal untrained populations (Owens et al 1995;Brechue and Abe 2002).…”

Associations of melanocortin 1 receptor genotype with growth and carcass traits in beef cattle

“…Although the weight differences were evident throughout this study, fat is accrued during the finish period (Owens et al 1995). More cattle of E D /E D genotype reached the finish backfat target sooner and therefore had fewer days on feed than the e/e red cattle (Table 2).…”