No abstract

Urea-treated whole-crop wheat harvested at growth stage (GS) 87 that was either unprocessed (U) or processed (P) by the forage harvester, and cut at one of two heights to produce a long straw (L), or short straw (S) forage, was offered to 44 Holstein-Friesian dairy cows for 14 weeks according to a 2 ✕ 2 factorial design. Whole-crop wheat (WCW) was mixed 2: 1 on a dry-matter (DM) basis with grass silage and all animals received 8·5 kg/day of concentrate and 2 kg/day of rapeseed meal. Increasing the cutting height at harvest increased the starch content in the forage from an average of 356 to 419 g/kg DM and decreased neutral-detergent fibre levels from 422 to 337 g/kg DM. Forage intake (grass silage and WCW) was higher in cows given the unprocessed compared with the processed forages (13·7 v. 12·5 kg DM per day for treatments U v. P respectively; P < 0·05) and tended (P < 0·08) to be higher in cows given the long compared with the short straw forages. Neither processing, nor alteration of cutting height, had a significant effect on milk yield (kg/day). However, milk fat content decreased (P < 0·05) with increasing cutting height (41·9 v. 37·0 g/kg for the main effects of L v. S respectively) whilst body condition score was lower (P < 0·05) in cows given the long compared with the short straw forages (2·6 v. 2·8 respectively). Plasma glucose levels were higher (P < 0·05) in animals receiving the short compared with long straw forages (3·52 v. 3·34 mmol/l respectively) whereas β-hydroxybutyrate decreased (P < 0·01) with increased cutting height. The average digestibility of starch in the total ration was higher (P < 0·001) in cows given the processed compared with the unprocessed WCW (0·96 v. 0·88 respectively). Assuming a constant apparent digestibility of starch in the other food components resulted in a WCW starch apparent digestibility of 0·87, 0·97, 0·80 and 0·96 for forages LU, LP, SU and SP respectively (P < 0·001). The results indicate that processing at harvest significantly increased the digestibility of starch in WCW and that cows responded to this higher nutrient content by decreasing forage intake. Increasing the cutting height at harvest decreased milk fat content (g/kg) and yield (kg/day) and increased body condition score.

No abstract

Previous work has shown that processing whole crop wheat (WCW) at harvest increases starch digestibility (Jackson et al., 2002). However, no effect was seen in terms of milk yield. It has been suggested that the provision of a sugar source might utilise the high rumen ammonia levels found in animals receiving urea-treated whole crop wheat (Abdalla et al., 1999). Sources such as lactose have also been shown to reduce rumen protozoa numbers, increase bacterial protein supply and result in a more stable rumen pH, particularly with high starch diets (Hussain and Miller, 1999). Additionally, to date, processed whole crop wheat has not been evaluated against other alternative forages. The objective of the current experiment was, therefore, to compare processed urea treated whole crop wheat with maize silage and determine the effects of carbohydrate supplementation of whole crop wheat on intake and milk production in dairy cows.

It has previously been demonstrated that feeding urea treated whole crop wheat to dairy cows results in a significant increase in dry matter intake but has little effect on milk yield (Sutton et al, 1997). Part of the reason behind this lack of response has been attributed to a decrease in digestibility, particularly that of starch. A forage mill has recently been developed which allow the grains to be ground prior to ensiling and potentially increase their digestibility. An alternative way to increase the energy value of whole crop wheat is to increase cutting/stubble height. Work by Weller et al, (1995) demonstrated an increase in calculated ME from 10.6 to 11.2 MJ/kg DM by increasing stubble height from 10cm to 40cm. The objective of the current experiment was therefore to determine the effects of forage processing (grinding) and cutting height at harvest of urea-treated whole crop wheat on the intake, milk production and diet digestibility in dairy cows.