Nutritive value of parts and whole maize plant for silage differing in grain maturity

Silaža kukuruza zauzima veliki dio obroka mliječnih krava i tovnih goveda u RH, odnosno, znatno pridonosi podmirenju dnevnih potreba životinja za hranjivim tvarima i energijom. Hranjivost biljke kukuruza teško se procjenjuje zbog vrlo različitog morfološkog i kemijskog sastava glavnih dijelova, te vrlo različite razgradljivosti hranjivih tvari u buragu. Zrelost biljke kukuruza i njezina zrna, prinos zrna i dijelova biljke, te ukupni i pojedinačni sastav i struktura vlakana čimbenici su koji utječu na razgradljivost, te posljedično i na ukupnu hranjivu vrijednost silažnog kukuruza. Navedene promjene osobina kukuruza povezane su s različitim vremenom sjetve i košnje, te je cilj istraživanja utvrditi promjene u kemijskom sastavu, razgradljivosti i energetskoj vrijednosti kukuruza za silažu u različitim stadijima zrelosti, utvrditi promjene u masenom udjelu i hranjivosti dijelova biljke kukuruza, te odrediti optimalni stadij zrelosti za spremanja silaže cijele biljke kukuruza, obzirom na njen najveći potencijal za proizvodnju mlijeka. Korišten je hibrid kukuruza Bc 304 (BC Institut, Zagreb) sijan u dva perioda 01.05. i 17.05 na parceli Fakultetskog dobra Maksimir. Uzorci kukuruza su uzimani u tri stadija zrelosti, prema vizualnoj procjeni po "mliječnoj crti" (1/3, ½, 2/3). Uzgoj kukuruza različitih stadija zrelosti uzrokovao je povećanje udjela zrna sa zrenjem biljke, uz istovremeno opadanje udjela vegetativnih dijelova; stabljike i njenih dijelova (donjeg i gornjeg dijela) i listova (donjih i gornjih), dok su kod ostalih vegetativnih dijelova kukuruza promjene samo relativne (p≥0,05). Samim porastom zrna u ukupnoj masi silažnog kukuruza dolazi samo do relativnog povećanja NEL-a (p≥0,05). Starije biljke obično imaju i nešto veći sadržaj škroba, bez negativnog djelovanja na razgradljivost vlakana (NDV), te se stoga omogućava farmerima da odgode vrijeme košnje kukuruza do 2/3 (do 40% ST) mliječne linije čime dobivaju zreliji kukuruz s više škroba, ali bez štetnog utjecaja na razgradljivost vlakana, a s druge strane silažna masa je još uvijek dovoljno vlažna za odvijanje optimalne fermentacije, koja rezultira kvalitetnom silažom. Osim utjecaja na navedene parametre hranjivosti biljke kukuruza za silažu, kasnije košenog kukuruza, pri zrelosti od 2/3 mliječne linije, potencijalno osigurava i najvišu proizvodnju mlijeka hranimo li krave silažom od takvog kukuruza.The introduction points to the importance of corn silage in the diet of dairy cows and heifers, and gives a brief overview of the factors, which influence the nutritional value of whole plant silage corn. One of the main factors on which it depends nutrition and fermentation of corn silage is the stage of maturity of the crop at harvest time. Under field conditions, stage of maturity is usually determined by the development „milk line” of grain since it is robust and reliable indicator of accumulation and dry matter content in the crop of maize intended for the production of silage from the whole plant. Literature Review provide us a detailed overview of the results of domestic and foreign research on the influence of stage of maturity on the yield of silage mass and nutritional value of silage maize. From these results it is clear that the harvest at different stages of maturity of crops leads to significant changes in nutrient contents of corn silage, but the mechanism underlying these changes is relatively poorly understood. Nutritional value of the whole plant corn silage is difficult to determine because of the very different chemical compositions in major parts of the maize plant (stem, grain and cob). Furthermore, relatively well researched impact of stages of maturity on the nutritional value of the whole plant corn stalks and grain somewhat, but there are almost no data on changes in other parts of the plant such as leaf blades and leaves sleeves, cobs, husks and shank of corn cobs. Materials and Methods are appropriately selected and fully integrate the hypotheses testing. In the research are used standard and modern methods for the analysis of plant material, which makes this research repeatable and verifiable. Material and methods are described in accordance with established objectives and research hypotheses. Original research results are obtained by conducting a two factorial experiment for one year at test field Maksimir. Factors study were periods of sowing (optimal and subsequent) and stage of maturity of corn grain. Due to organizational and technical reasons, field trial instead of randomized complete block design was set up by split-plot with three replicates. For research purposes maize hybrid Bc 304 was grown under intensive cropping. Samples of corn to determine the nutritional and other studied traits were taken at three stages of maturity: at 1/3 stage of the milk line, 2/3 stage of milk line and at physiological maturity. Representative dissection samples of plants are separated into sections as follows: the lower part of the stem (part of the stem below the node from which emerges the uppermost cob), the upper part of the stem, the leaf blades of the lower leaves (leaf blades of leaves below node from which emerges cob), the leaf blades of upper leaves, sleeves of lower and upper leaves, leaf husks, cob shank, cob and grain. On these parts as well as on samples of the whole plant was determined structural fiber content, dry matter, ash, crude fat, crude fiber, crude protein and calculative soluble carbohydrates, neutral and acid detergent fiber and acid detergent lignin according to AOAC standards. Starch content in the grain and dry matter digestibility are determined of plant parts as well as the whole plant. Net energy for lactation is calculated and estimated overall nutritive value expressed in kilos of milk produced per ton of corn silage and kilos of milk per unit area. Data processing was performed by appropriate model of analysis of variance and post hoc tests to compare means after a significant F-test. The results are logically discussed in relation to the hypothesis and research goals without unnecessary repetition of results. The results are compared with the results of other domestic and foreign researchers. The author in the discussion pointed to the advantages and disadvantages of the applied methodology for sampling corn silage. The results are consistent with previous research and critically explained with those results that are in contradiction with them that is explained by the specific environmental conditions in which is performed field experiment. Finally, it is concluded that the chemical composition, digestibility and energy value of the parts and the whole plant maize were not significantly changed for silage maize grown in two planting. In contrast, in the later stages of grain maturity, there is a significant increase in the content of lignin in the stalk and cob, and increased content of fiber fractions in most parts of the maize plant, especially in the stalk and leaf sleeves, the cob and husks. With the maturing plants had a decrease ash content, crude fat and proteins in the leaf blades of the upper and lower leaves, while expected changes in fiber fraction are not statistically significant. Consequently, there was a major reduction in dry matter digestibility of leaf sleeves, husks and cob. However, this decline in digestibility of most vegetative parts did not affect the digestibility of whole plant corn due to the compensatory effect of increasing the content of highly digestible grain in the plant and starch in the grain. With maturing plants expected to increase the yield of the whole plant as a result of increased weight and grain yield. Despite the increase in weight of grain and starch accumulation in grains in the later stages of grain maturity, there was not found an increase of the energy value. This is because at the same time there was increased content of non-degradable lignin in the lower part of the stem. Significant growth of potential milk production per unit area was determined for silage maize in the later stages of maturity, but not as a result of changes in nutritional plants but due to the increased yield of whole plant corn