The objectives of this study were to analyze body measurements of 40 crossbred bulls grazing low quality forage with different supplementation strategies, to estimate interrelationships among those measurements and carcass and body compositions, and to develop systems of equations to predict body fat using body and carcass measurements. Eight animals were slaughtered at the beginning of the experiment, and the remaining animals were slaughtered at 90 or 220 d. The biometric measures (BM) were obtained the day before the slaughter and included hook width, pin width, pelvic girdle length, rump depth, rump height, abdomen width, body length, height at withers, rib depth, girth, and body diagonal length. Other measurements included full, shrunk, and empty BW; internal physical and chemical fats; body volume; body area; carcass weight; 9th- to 11th-rib section weight and composition; fat thickness; subcutaneous fat; intermuscular fat; carcass chemical fat; and empty body physical and chemical fats. The relationships between BM and body components were evaluated, and equations to predict body area, body volume, subcutaneous fat, and carcass and body physical and chemical fat were developed. Biological interpretations of the parameter estimates of equations were similar to those found in the literature such as a ratio of 1 kg of subcutaneous fat to 1.6 kg of intermuscular fat and a deposit of 72 to 76% of body fat in the carcass. The first system used to predict carcass and empty body physical and chemical fat was devised using in vivo information, whereas the second system used BW and the 9th- to 11th-rib fat weight. Our results indicated the combination of BW, carcass traits, and BM was precise and accurate in estimating carcass and body fat composition of backgrounding bulls. The second system had better adequacy statistics [r(2) > 0.92, concordance correlation coefficient (CCC) > 0.957, and root mean square error (RMSE) < 14.4% of the average observed value] compared with the first system. The first system had acceptable adequacy statistics (r(2) > 0.767, CCC > 0.866, and RMSE varying from 15.8 to 22.3% of the average observed value). For both systems, the simultaneous F-test of the linear regression of observed on model-predicted values indicated intercepts were equal to zero, and slopes were equal to 1 (P > 0.246). We concluded that BM can improve the accuracy and precision of the predictions of body composition of grazing animals.

RESEARCHB ahiagrass (Paspalum notatum Flügge) is the main forage used for the beef cattle industry in Florida because of its reliability and persistence under adverse climatic conditions and management practices. It is the most widely planted warm-season grass in Florida, covering approximately 1 million ha. Nonetheless, overdependence on bahiagrass pastures has made the industry vulnerable to potential losses from pests and diseases. During 1996 through 2000, >150,000 ha of bahiagrass pastures were damaged by mole crickets (Scapteriscus spp.) in Florida (Adjei et al., 2001). Damage to bahiagrass pastures by mole cricket stimulated a search for other grasses adapted to the Florida environment.Brachiariagrasses are the most widely grown forages in tropical America, occupying >80 million ha (Boddey et al., 2004). Brachiaria species are popular among producers because they show rapid regrowth and good persistence under close or frequent defoliation (Rika et al., 1991). 'Mulato' is the fi rst hybrid in the Brachiaria genus and results from crossing ruzigrass (Brachiaria ruziziensis Germain & Evrard, clone 44-6) and palisadegrass [Brachiaria brizantha (A. ABSTRACTBahiagrass (Paspalum notatum Flügge) is the most used forage for beef cattle (Bos sp.) in Florida; however, damage to bahiagrass pastures by mole cricket (Scapteriscus spp.) stimulated a search for other adapted grasses. The objective of this study was to test the effect of different stocking rates (SRs) on animal performance and herbage characteristics of 'Mulato' (Brachiaria sp.) and bahiagrass pastures. The experiment was conducted in Ona, FL, from May to September, 2007 and 2008. Treatments were three SRs (4, 8, and 12 heifers ha −1 ) and two forage species (Mulato and 'Pensacola' bahiagrass). There was a linear decrease in herbage mass (from 5.9 to 3.2 Mg ha −1 ) and herbage allowance (from 2.8 to 0.6 kg dry matter kg −1 liveweight) with increasing SR. Mulato had greater in vitro digestible organic matter concentration than bahiagrass (675 vs. 534 g kg −1 ) but similar crude protein concentration (130 g kg −1 ). There was a linear decrease in average daily gain (from 0.49 to 0.22 kg d −1 ) and a quadratic response of liveweight gain ha −1 as SR increased (190, 353, and 217 kg ha −1 for SRs of 4, 8, and 12 heifers ha −1 , respectively). Mulato has potential to be an alternative forage to bahiagrass for beef cattle producers in Florida.

‘Mulato II’ (Brachiaria sp.) is a warm‐season forage hybrid with superior nutritive value introduced in Florida in 2003. The objective of this study was to evaluate the effects of harvest frequencies and stubble heights on herbage accumulation (HA), nutritive value, and persistence of Mulato II brachiariagrass. The research was conducted in Ona, FL (27°N) from August to October 2007 and 2008. Treatments were the factorial combination of 2‐ and 4‐week harvest frequencies and 1‐, 3‐, and 5‐inch stubble heights with four replicates in a randomized complete block design. Plot size was 9.8 × 6.5 ft with 3.0 ft between plots. There was a quadratic decrease in HA from 1,800 to 1,400 lb/acre with increasing stubble heights. Conversely, herbage crude protein (CP) and in vitro digestible organic matter (IVDOM) increased linearly with decreasing stubble heights (from 17% to 14% and from 67% to 66% for CP and IVDOM, respectively). There were significant season effects on responses as HA decreased and nutritive value increased from September to November for both harvest frequencies. Mulato II ground cover linearly increased from 74% to 87% as stubble height increased from 1 to 5 inches. Despite greater HA and nutritive value, short stubble heights in combination with 2‐week harvest interval decreased the persistence of Mulato II and should be avoided.

Resumo Objetivou-se avaliar as características morfogênicas e estruturais do capim-piatã submetido à lotação intermitente e adubado com fontes de fósforo de diferentes solubilidades e adubação nitrogenada. Os tratamentos foram: controle (sem aplicação de adubo fosfatado); fonte de fósforo de lenta solubilidade (FNR); fonte de fósforo de rápida solubilidade (FSS) e fonte de fósforo de solubilidade mista (FSM), associados ou não à adubação nitrogenada. Foram realizadas medições de perfilhos pré-demarcados para avaliação das características estruturais e morfogênicas das plantas. Os dados foram analisados segundo um delineamento em blocos casualizados, em arranjo fatorial 4 x 2, dentro de cada estação do ano. As médias por quadrados mínimos dos tratamentos de adubação fosfatada foram comparadas com o tratamento controle pelo teste de Dunnet, e entre si pelo teste “t” e as médias de uso ou não de adubação nitrogenada foram comparadas entre si pelo teste “t” a 5% de significância. As fontes que contém fósforo prontamente disponível, como nos tratamentos FSS e FSM, promoveram maior alongamento de folhas e colmo, bem como maior número e aparecimento de folhas, o que evidencia a importância da disponibilidade de fósforo e nitrogênio no crescimento e desenvolvimento das plantas, confirmado pelo aumento na taxa de alongamento de folhas, do aparecimento foliar e alongamento de colmo. Assim, as adubações nitrogenada e fosfatada são alternativas para a persistência e competitividade da produção animal a pasto. Em relação à fonte, o uso de fontes de fósforo com solubilidade mista fornece esse nutriente a curto, médio e longo prazo.