Effects of crop maturity and cutting height on the nutritive value of fermented whole crop wheat and milk production in dairy cows

Abstract

Factors influencing the nutritive value of fermented whole crop wheat (WCW) and effects on milk production in dairy cows were investigated in three experiments. In experiment 1, WCW was harvested at one of two maturities: at a dry matter (DM) content of 296 g/kg, 52 g/kg DM starch (LS) or DM of 371 g/kg, 221 g/kg DM starch (HS). Ninety early lactation dairy cows were split into three groups and fed either LS, HS or a first cut grass silage (G). The WCW was mixed 2:1 on a DM basis with the grass silage. There was no significant effect of dietary treatment on milk production (kg/day) although cows fed the low starch WCW (LS) had the lowest milk protein concentration (mean values of 32.1, 30.7 and 31.6 g/kg for cows fed G, LS and HS, respectively, P<0.05). Plasma urea levels were significantly lower in cows fed the HS compared with the LS treatment ( P<0.05). In experiment 2, ninety early lactation dairy cows were fed one of three dietary treatments: WCW harvested at a long straw length and supplemented with either a starchy concentrate (LW) or a more fibrous concentrate (LF) or a short straw length and supplemented with a fibrous concentrate (SF). The WCW was mixed 1:1 on a DM basis with first cut grass silage. Increasing the cutting height increased starch concentrations from 232 to 292 g/kg DM and reduced neutral detergent fibre from 433 to 384 g/kg DM in the long and short straw WCW, respectively. There was no significant effect of dietary treatment on milk production, composition or body condition score over the experimental period. The lower plasma non-esterified fatty acid concentration in cows fed LW or SF during week 10 of lactation indicate a more positive energy balance in early lactation on these treatments. In experiment 3 the apparent digestibility of the grass silage, long straw whole crop wheat or short straw WCW fed at maintenance or the long straw WCW fed ad libitum was determined in growing lambs. Digestibility coefficients of the grass silage were significantly higher than those of any of the WCW forages, particularly for the fibre fractions. The digestibility of starch was high in all three WCW treatments and averaged 0.955 kg/kg but was not affected by straw length or feeding level. The improvement in metabolisable energy value (MJ/kg DM) by increasing the cutting height at harvest was small and not significant. Increasing the maturity at harvest and decreasing the length of straw at cutting was also observed to have a small but significant effect on decreasing the aerobic stability of the WCW forages. The results indicate that fermented whole crop wheat can provide a comparable milk production to a good quality grass silage and that harvesting at a later stage of maturity had little effect on milk production although milk protein levels tended to be higher in cows fed the higher starch material. There was little advantage to altering cutting height of fermented WCW on apparent digestibility or by altering supplement composition on milk production.