Ruminal IN SITU degradation as well as crude protein and carbohydrate fractions of CNCPS of forage maize depending on vegetative stage, variety, conservation and site | Ruminaler in situ - Abbau sowie Rohprotein- und Kohlenhydrat-Fraktionen des CNCPS von Vegetationsstadium, Sorte, Konservierung und Standort

The experiment investigated the effects of vegetative stage, variety, location and conservation form of forage maize on the content of carbohydrates and protein according to the Cornell Net Carbohydrate and Protein System (CNCPS) as well as on the in situ degradation of dry matter. The objective was to characterize forage maize more precisely than the Weende analysis does in order to better estimate ruminal availability. The maize samples (n = 54) were harvested in the year 2003. They differed by stage of maturity (late milk stage [ 25 % DM], early dent stage [25 - 30 % DM], late dent stage [30 - 35 % DM]); variety (Fuxxol FAO 240, Romario FAO 270, Atalante FAO 290); location (Lambach, Upper Austria; Kobenz, Styria; Gumpenstein, Styria) and conservation form (fresh maize, maize silage). The samples were analysed by different methods: Weende analysis (VDLUFA 1976), detergent analysis (Van Soest 1994), analysis according to the Cornell Net Carbohydrate and Protein System (Krishnamoorthy et al. 1982, Van Soest et al. 1991, Fox et al. 1992, Russell et al. 1992, Sniffen et al. 1992, Licitra et al. 1996) and the in situ method (Orskov & McDonald 1979, Huntington & Givens 1995, Mertens 2004). The in situ analyses to determine the ruminal degradation of dry matter were carried out with four rumen cannulated steers with an incubation time of up to 168 hours. Nutrient content was mainly influenced by conservation form and location. Stage of maturity and variety had only marginal effects. Due to fermentation processes of non-fibre carbohydrates during conservation, silages showed higher amounts of crude fibre and lower contents of N-free extracts. Van Soest detergent fibre as well as Cornell carbo-hydrate and protein fractions supported these results. With the exception of crude fat content, stage of maturity had a significant effect only on protein fractions (decrease in rapidly available fraction [A] and increase in slowly available fraction [B2] due to maturity). As expected, the factor location had significant effects on most of the chemical parameters by determining the length of vegetation period. Detergent fibre content and fiber/non-fiber ratio were mainly dependent on climatic conditions, which significantly influenced ear growth as well as aging of plants. Although variety only slightly influenced nutrient contents, it had a highly significant impact on in situ degradation characteristics of dry matter. Late maturing varieties had higher soluble fractions (a) and lower potentially degradable fractions (b), whereas the potential degradability [a + b] was equal to the other varieties. Fractions a and b were significantly affected by stage of maturity and location. Fraction a increased in early stages of maturity and locations with short vegetation periods. Those circumstances cause lower ear development but higher residual plant proportions, which lead to higher amounts of non-structural carbohydrates. Younger maize plants show lower degradation rates (c) (degradability of cellulose is lower than for starch). As the Cornell fractions showed, fermentation processes (lactate formation, partly destruction of protein matrix) increased soluble fractions (a) in feedstuffs, but reduced degradation rates (c) due to relative accumulation of fibre. Except for stage of maturity, potential degradability was not affected by the parameters investigated. Effects on effective degradability, however, differed significantly. The reason is that for calculation of effective degradability, fraction a is included as a whole, while fraction b is weighted according to rate of passage. These results show that the methods used in this investigation (Cornell System, in situ technique) lead to a more precise characterisation of nutritive value of forage maize than the classical Weende analysis.