Marina Vieira de Carvalho

Evaluation of corn cultivars harvested at two cutting heights for ensilage

Objetivou-se neste estudo avaliar as caracteristicas agronomicas, a composicao quimico-bromatologica e a digestibilidade de 11 cultivares de milho (Zea mays) colhido em duas alturas de corte. As cultivares D 766, D 657, D 1000, P 3021, P 3041, C 805, C 333, AG 5011, FO 01, CO 9621 e BR 205 foram avaliadas quando colhidas 5 cm acima do solo (baixa) e 5 cm abaixo da insercao da primeira espiga (alta). O experimento foi delineado como blocos casualizados, com tres repeticoes, arranjados em esquema fatorial 11 x 2. Os cultivares apresentaram producoes semelhantes de materia seca de forragem e de graos. As porcentagens das fracoes colmo, folha, palha, sabugo e grao diferiram entre os cultivares, assim como os teores de materia seca da planta inteira no momento da colheita. Considerando a planta inteira, apenas os teores de energia bruta, nitrogenio da fracao fibra em detergente neutro e a digestibilidade in vitro da fibra em detergente neutro e detergente acido nao diferiram entre os cultivares. O aumento da altura de corte melhorou a qualidade da forragem, devido a reducao das fracoes colmo e folha e dos teores dos constituintes da parede celular.

Effect of chronic infusion of leptin and nutrition on sexual maturation of zebu heifers

The amount of fat in the carcass has been proposed as a regulator of initiation of puberty in cattle. To test if changes in energy intake and in circulating leptin concentration are each capable of altering age, BW, and body composition at puberty, 36 prepubertal Nellore heifers, 18 to 20 mo old, 275.8 ± 17.2kg BW, and BCS of 5 ± 0.5 (1 to 9 scale), were randomly assigned to each of 3 treatments (n = 12): High (high energy diet), Low (low energy diet), and LL [low energy diet + ovine leptin (oLeptin)]. Diets were formulated to promote BW gain of 0.4 kg/d (groups Low and LL) or 1.2 kg/d (High group). After 14 d of adjustment to diet, heifers in LL group received subcutaneous injections of oLeptin at 4.8 μg/kg BW twice a day for 56 d. Groups High and Low received similar injections of 2 mL saline solution. Age at puberty was considered to be the age on first detection of a corpus luteum, confirmed by plasma concentrations of progesterone of >1 ng/mL. Heifers were slaughtered on the second day after first corpus luteum detection. Expression of leptin gene was quantified by real-time PCR using ribosomal protein-L19 (RP-L19) as a control gene. Leptin administration increased (P = 0.04) leptin serum concentration but had no effect (P > 0.05) on age, BW, or BCS at puberty. High energy intake increased (P < 0.01) leptin concentration, accelerated (P = 0.02) puberty, and increased (P < 0.01) BCS at puberty, without altering (P = 0.17) BW at puberty. High energy intake also accelerated (P = 0.04) follicular development. Leptin administration caused a significant (P < 0.05) but transient increase in follicular development, which was similar to the transient increase in leptin serum concentration. Results from leptin gene expression demonstrated that high energy intake increased (P < 0.01) and leptin administration decreased (P < 0.01) leptin expression in 3 adipose tissues. The observed decrease in leptin gene expression after administration of leptin could explain the reduction in leptin serum concentration after 30 d of treatment and consequently the failure of leptin to accelerate puberty. Our findings did not support the hypothesis that reduced serum concentration of leptin is an important hindrance for puberty onset in malnourished zebu heifers. Although exogenous administration of leptin temporarily enhanced rate of follicular growth, it did not accelerate puberty.

Nutritional characteristics and in vitro digestibility of silages from different corn cultivars harvested at two cutting heights

Objetivou-se neste estudo avaliar as caracteristicas nutricionais e a digestibilidade in vitro de silagens de diferentes cultivares de milho colhidas em duas alturas de corte. Foram avaliadas 11 cultivares (Dina 766, Dina 657, Dina 1000, P 3021, P 3041, C 805, C 333, AG 5011, FO 01, Dina co 9621 e BR 205) colhidas 5 cm acima do solo (baixa) e 5 cm abaixo da insercao da primeira espiga (alta). O experimento foi delineado em blocos casualizados (tres blocos), arranjados em esquema fatorial 11 × 2. As silagens das plantas colhidas na altura de corte alta apresentaram teor medio de materia seca significativamente superior as silagens das plantas colhidas na altura de corte baixa. As cultivares FO 01, AG 5011, Dina co 9621 e Dina 766 apresentaram maior teor de proteina bruta, que as cultivares C 805, P 3041 e P 3021, as quais apresentaram os menores teores deste nutriente. A elevacao da altura de corte aumentou os coeficientes de digestibilidade verdadeira in vitro da materia seca e digestibilidade in vitro da materia seca das silagens avaliadas. O aumento da altura de corte melhorou o valor nutritivo das silagens, diminuindo as concentracoes das fracoes fibrosas e aumentando a digestibilidade in vitro da materia seca.

Effects of BST and high energy diet on gene expression in mammary parenchyma of dairy heifers

The objective of this study was to determine the effects of dietary energy and recombinant bovine somatotropin (bST) injection to identify genes that might control mammogenesis. Total RNA was extracted from the parenchymal tissue of 32 heifers randomly assigned to one of four treatments: two diets (a standard diet and a high energy, high protein diet), each with or without bST. To perform microarray experiments, RNA samples were pooled (2 animals/pool) before reverse transcription and labeling with Cy3 or Cy5. A 4-node loop design was used to examine the differential gene expression among treatments using a bovine-specific cDNA microarray (National Bovine Functional Genomics Consortium Library, NBFGC) containing 18,263 unique expressed sequence tags (EST). Significance levels of differential gene expression among treatments were assessed using a mixed model approach. Injection of bST altered the expression of 12 % of the genes on NBFGC slide related to tissue development, whereas 6% were altered by diet. Administration of bST increases the expression of genes positively related to cell proliferation and mammary parenchyma to a greater extent than a high energy diet.

Expressão do gene da leptina e seu receptor Ob-Rb no parênquima mamário de novilhas leiteiras

The objective of this study was to examine the effects of a diet with high level of energy and protein, combined with bST injections, on leptin and leptin-receptor (Ob-Rb) gene expression profile in the mammary parenchyma of dairy heifers. Mammary parenchyma samples from 32 Holstein heifers, randomly assigned to one of four treatments (n=8), were utilized: high or low energy and protein diet, with or without bST injection. The experiment was designed in randomized blocks and arranged in a 2 × 2 factorial arrangement. Total RNA was extracted from tissue samples and gene expression profile was tested in qRT-PCR, against glucuronidase β as a control, using the 2-ΔΔCt method. Animals receiving the diet with high level of energy and protein had higher leptin mRNA expression, with an increase of 56%, and lower leptin receptor Ob-Rb mRNA expression, with a decrease of 18%. On the other hand, bST injection decreased leptin mRNA and receptor Ob-Rb mRNA expression in 74% and 23%, respectively. There was no interaction between diet and bST injection. The increase in leptin expression can explain, at least in part, the detrimental effects caused by diets rich in energy and protein, offered during the prepubertal period, in future milk production of dairy heifers.

Bromatological evaluation of eleven corn cultivars harvested at two cutting heights

The objective of this study was to evaluate the chemical composition and dry matter in vitro digestibility of stem, leaf, straw, cob and kernel fractions of eleven corn (Zea mays) cultivars, harvested at two cutting heights. The experiment was designed as randomized blocks, with three replicates, in a 2 × 11 factorial arrangement (eleven cultivars and two cutting heights). The corn cultivars evaluated were D 766, D 657, D 1000, P 3021, P 3041, C 805, C 333, AG 5011, FOR 01, CO 9621 and BR 205, harvested at a low cutting height (5 cm above ground) and a high cutting height (5 cm below the first ear insertion). Cutting height influenced the dry matter content of the stem fraction, which was lower (23.95%) in plants harvested at the low, than in plants harvested at the high cutting height (26.28%). The kernel fraction had the highest dry matter in vitro digestibility (85.13%), while cultivars did not differ between each other. Cob and straw were the fractions with the highest level of neutral detergent fiber (80.74 and 79.77%, respectively) and the lowest level of crude protein (3.84% and 3.69%, respectively). The leaf fraction had the highest crude protein content, both for plants of low and high cuttings (15.55% and 16.20%, respectively). The increase in the plant cutting height enhanced the dry matter content and dry matter in vitro digestibility of stem fraction, but did not affect the DM content of the leaf fraction.