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.

Early detection and prediction of infection using infrared thermography. Can. J. Anim. Sci. 84: 73-80. Early detection and/or prediction of disease in an animal is the first step towards its successful treatment. The objective of this study was to investigate the capability of infrared thermography as a non-invasive, early detection method for identifying animals with a systemic infection. A viral infection model was adopted using 15 seronegative calves whose body weight averaged 172 kg. Ten of these calves were inoculated with Type 2 bovine viral diarrhoea virus (strain 24515) and five were separately housed and served as uninfected controls. A simultaneous comparison of infrared characteristics in both infected and control animals was conducted over approximately 15 d. In addition, measures of blood and saliva cortisol, immunoglobulin A, blood haptoglobin and clinical scores were obtained. Infrared temperatures, especially for facial scans, increased by 1.5°C to over 4°C (P < 0.01) several days to 1 wk before clinical scores or serum concentrations of acute phase protein indicated illness in the infected calves. The data suggest that infrared thermal measurements can be used in developing an early prediction index for infection in calves. Le dépistage ou la prévision rapide de la maladie chez un animal est la première étape vers la guérison. La présente étude devait vérifier l'utilité de la thermographie infrarouge comme méthode de dépistage précoce non invasive en vue de l'identification des animaux atteints d'une infection systémique. Pour cela, les auteurs ont recouru à un modèle d'infection virale constitué de 15 veaux séronégatifs de 172 kg en moyenne. Ils ont inoculé le virus de type 2 de la diarrhée des bovins (souche 24515) à dix veaux et gardé les cinq autres à part comme témoins. Ensuite, ils ont simultanément comparé les paramètres infrarouges des sujets infectés et sains pendant une quinzaine de jours. Parallèlement, ils ont dosé le cortisol dans le sang et la salive, l'immunoglobine A, l'haptoglobine sérique et noté les signes cliniques. La température infrarouge, de la face surtout, passe de 1,5°C à plus de 4°C (P < 0.01) plusieurs jours à une semaine avant qu'apparaissent les signes cliniques ou que les concentrations sériques attribuables à la phase aiguë de production des protéines virales n'indiquent l'existence de la maladie chez les veaux infectés. Les résultats donnent à penser qu'on pourrait se servir des relevés thermiques infrarouges pour mettre au point un indice de prévision rapide de l'infection chez les veaux.

This study determined whether supplementing the diets of dairy cows during the peripartum period with organic trivalent Cr influenced the capacity of their peripheral blood mononuclear cells to produce activation cytokines in response to stimulation with mitogens in vitro. Nine cows were fed 0.5 ppm of Cr/d per cow from 6 wk prepartum to 16 wk postpartum; 10 other periparturient cows served as unsupplemented controls. Mononuclear leukocytes, enriched from peripheral blood during wk 0, 2, 4, and 6 of lactation, were cultured with or without the T-lymphocyte mitogen, concanavalin A. Culture supernatants, harvested at 24, 48, or 72 h, were assayed for interleukin-2, interferon-gamma, and tumor necrosis factor-alpha. The cytokines were barely detectable in the supernatants from the unstimulated cultures, but supernatants from mitogen-stimulated cultures contained higher concentrations of each cytokine. For cows fed Cr, concentrations of all three cytokines in the culture supernatants of the mitogen-stimulated mononuclear cells decreased significantly relative to values for unsupplemented cows, particularly around peak lactation for the 24- and 48-h cultures. Theses results extended our previous observations and supported the hypothesis that organic Cr is immunomodulatory in high producing cows.

No abstract

. 2006. Review: The composition and availability of straw and chaff from small grain cereals for beef cattle in western Canada. Can. J. Anim. Sci. 86: 443-455. Small cereal grain residues are heterogeneous feeds consisting of several botanical fractions: chaff, grain, leaf blade, leaf sheath, internode and node. These parts vary in composition, digestibility, resistance to comminution, intake potential and energy availability. Large differences in the nutritional quality of straw and chaff may occur from year to year and between locations due to effects of environmental conditions on botanical composition and cell anatomy. Stage of maturity, harvest method and weathering will influence composition and quality of the most nutritious parts of cereal residues, the leaf and chaff. In addition, cultivars and species differ in the proportion, anatomy and digestibility of botanical fractions. As a result, the quality of crop residues is highly variable with an economic value that is difficult to accurately assess.Cereal straw and chaff are of low economic value as they are low in nutritive value, where nutritive value is the product of nutrient intake, digestibility, and efficiency of use. However, due to availability, cereal crop residues have the potential to be a substantial feed resource for beef cows. Previous reviews have not focused on straw and chaff nutrition research relevant to use by beef cattle in western Canada. This review includes discussions on yield and nutritive value with a focus on identifying information deficiencies, including the lack of detailed production statistics for determining residue yields on a regional bases and the need for more detailed nutrient composition to update regional feed data bases for western Canada.