SUMMARYTwo maize hybrid cultivars, early (Cisko FAO 300) and late maturing (Arma FAO 700), were sown on three different dates (March, April or May) and harvested at two stages of maturity (kernel milk line (ML) scores of 1/4 < ML < 1/3 or 1/2 < ML < 2/3) in the western Po plain (Italy) in 2008. Yield, chemical composition andin vitrodigestibility and fermentation kinetics of pre-ensiled whole-crop maize and of silage were measured. Cultivar and sowing date influenced the dry matter (DM) yield of whole-plant maize, with DM yield being 40% higher in Arma than in Cisko, and DM yield decreasing with later sowing dates. Later maturity increased DM concentration at harvest for both hybrids, due to differences in kernel development. The neutral detergent fibre (NDF) content declined and starch increased as plants matured. Digestibility was estimatedin vitrofollowing the Ankom procedure. Rate and extent of ruminal degradation were estimated from gas production (GP) profiles during incubation in diluted rumen fluid. Cultivar, planting date and maturity had no effect onin vitroDM digestibility of pre-ensiled whole-crop maize, but following 240 days of ensiling significant differences between cultivars in digestibility were detected. GP kinetic parameters differed between cultivars for pre-ensiled whole-crop maize, with Cisko having higher asymptotic GP but lower fractional fermentation rates and longer lag times than the Arma hybrid. GP volumes were greater as sowing or harvest dates were delayed. Energy value and milk production were estimated using the Milk2006 Model. With the pre-ensiled whole-crop maize, a 38% greater milk yield/ha was expected with Arma than with Cisko, matching the 40% greater DM yield. The same trend was observed in maize silage, where cultivar and planting date affected milk production/ha, with greater values for Arma than for Cisko and lower values for the latest planting date. Optimal management practices, including decision making on planting and harvest time and hybrid cultivar selection, can influence the yield and nutritive value of maize silage.

The aim of this study was to evaluate the effect of daily supplementation of a devitalized strain of Saccharomyces cerevisiae on milk yield and composition of Friesian-Holstein lactating cows. Average Days In Milk (DIM) and Body Weight (BW) of cows were 98+/-24 days and 619+/-13.2 kg. Prior to the experiment, the effects of the yeast culture added to the diet were investigated in 2 in vitro experiments. In the first experiment, 6 samples of rumen fluid were used to determine the DM, CP and NDF degradability (IVDMD, IVCPD, IVNDFD) of Total Mixed Ration (TMR) at 0 and 48 h with the addition of 0 g (Y(0)) and 1 g (Y(1)) of yeast culture. In the second experiment, free, total and microbial ATP production were used for the evaluation of microbial activity in rumen fluids after 0, 8, 24 and 48 h incubation. In the 4 weeks trial, 10 multiparous cows were assigned to a Control diet (C) and 10 to the experimental diet (YC = C+35 g/cow/day of yeast culture). TMR on a Dry Matter (DM) basis consisted of corn silage (42.3%), ryegrass hay (14.1%), corn meal (22.1%), soybean meal (17.9%) and a mineral/vitamins mix (3.6%). Crude Protein (CP) and ENI were 14.6% and 1.56 Mcal kg(-1) DM, respectively. Cows were individually fed once daily and milked at 7 and 19 h. In vitro experiments showed that the addition of 1 g YC to the rumen fluid increased IVCPD and IVNDFD after 48 h of incubation but did not influence IVDMD. Free, total and microbial ATP values showed a continuous decrease during the 48 h of the trial but the addition of YC proved to be effective in slowing the decrease. Milk yield (31.9 and 33.4 kg day(-1), for the C and YC group), 4% fat corrected milk (FCM: 30.3 and 31.7 kg day(-1)) and energy corrected milk (ECM: 32.9 and 34.5 kg day(-1)) were significantly different between groups. Dry Matter Intake (DIVE), milk fat and protein percentage were similar in both groups. Feed efficiency (ECM kg(-1) DMI) was higher in YC group than in C.

Near infrared reflectance spectroscopy (NIRS), in vitro digestibility and fermentation kinetics data were used to discriminate categories of forage quality, based on the method of conservation, forage species, maturity stage or harvest season of 64 forages commonly used in rumina nt production systems. Forages used in the study included 40 hay (H) and 24 silage (S) samples o f Lolium multiflorum L., Medicago sativa L., Zea mays L. and grassland herbage harvested from 20 dairy cattle farms in Pi emonte (N-W Italy). All the samples were scanned in duplicate (400 to 2500 nm) with a NIR Systems 6500 scanning monochromator, and the absorbance data were transformed by a second order derivative b efore being used in the principal com- ponent analysis (PCA). The chlorophyll absorbance in the visible re gion (650-690 nm) explained most of the variance in the spectra, so maize silage samples were classified apa

SUMMARY The effects of yeast Saccharomyces cerevisiae, either inactivated (by osmotic pressure, designated IY) or provided as a culture containing live yeast cells (YC), on ruminal fermentation of two different diets were investigated in vitro. Total mixed rations (TMR) having forage:concentrate ratios of 0·6:0·4 (medium–high forage diet) and 0·2:0·8 (low-forage diet) were incubated in batch cultures of mixed ruminal micro-organisms to which either IY (to reach concentrations of 500 and 250 mg product/l incubation medium) or YC (at a concentration of 150 mg product/l) were added directly as powder. To evaluate the effects of the additive on ruminal microbial population, sheep used as donors of rumen fluid were allocated to three experimental groups: Control (no additive), IY and YC, that received a diet with the corresponding additive for 10 days. With both diets, YC decreased ruminal pH compared to control, whereas IY had no effect. Adding yeast products to the high-fibre diet affected total volatile fatty acid (VFA) production and VFA composition, in general with a slight increase in IY and a significantly greater increase in response to the addition of YC. Ammonia nitrogen (P=0·006), total gas production (P<0·001) and in vitro dry matter disappearance (IVD) (P<0·001) showed the highest values with YC. Methane production was higher than the control when the IY inoculum was used, and increased even more with the YC inoculum (P<0·001). With the high-concentrate TMR, no effects on total VFA concentration were observed when yeast additives were used. Similar trends were shown for lactate and methane production and total gas production, where values tended to be higher when using the YC inoculum (P values of 0·055, <0·001, 0·006 and <0·001, respectively). After 144 h of incubation, differences were observed only with the high-fibre diet in the cumulative gas production at 24 h of incubation and in the average fermentation rate, which was greater with YC, although the asymptotic gas production was not affected. These results indicate that live yeasts affect ruminal fermentation slightly more than inactivated yeasts, although both products require a regular administration and some adaptation of the ruminal microbial population for the stimulatory effects to become apparent. The effects of yeasts on ruminal fermentation are diet-dependent, being more noticeable with a high-fibre substrate, and subtle with a high-concentrate diet.

3 paginas, 2 tablas.--Trabajo presentado a las XIII Jornadas sobre Produccion Animal AIDA (Zaragoza, 12 y 13 de mayo del 2009).