The effect of stage of maturity and inclusion rate of processed, whole-crop wheat on the metabolism and performance of dairy cows

Abstract

A series of experiments were undertaken to determine the effects of stage of maturity and inclusion rate of processed whole-crop wheat (WCW) on crop production, dairy cow performance and metabolism. In experiment one, WCW was harvested at four stages of maturity. Harvesting WCW at approximately 700 g dry matter (DM)/kg significantly increased grain DM yield. Inclusion of processed WCW harvested at 700 g DM/kg and urea-treated resulted in a higher milk yield and lower DM intake compared with animals offered a lower DM, fermented forage or a high DM processed untreated forage. In experiment two, WCW was harvested at 800 g/kg and urea-treated. Processed, urea-treated WCW was included in the ration of dairy cows at differing inclusion rates and the effect on dairy cow performance and apparent digestibility determined. Inclusion of WCW at 0.25 of the forage DM resulted in increased milk yield and protein yield compared with feeding grass silage alone, whilst there was little benefit in feeding WCW at higher inclusion rates. In the third experiment, the effect of rate of inclusion of processed, urea-treated WCW on ruminal fermentation, microbial growth and ruminal digestibility was determined using continuous culture fermentors. The inclusion of processed, urea-treated WCW had no effect on pH, total volatile fatty acid concentration or the proportion of acetate and butyrate. However, the ratio of acetate to propionate increased with rate of inclusion of processed, urea-treated WCW from 2.5 in vessels receiving 0.25 whole-crop wheat to 3.2 in those receiving 0.75 whole-crop wheat. Dry matter, organic matter and neutral detergent fibre digestibilities were not affected by WCW inclusion whilst starch digestibility increased. There was no effect of inclusion on microbial protein synthesis, although numerically diets containing 0.25 WCW had higher values. It is therefore recommended that processed, urea-treated WCW be harvested at a minimum of 700 g DM/kg or as soon thereafter as practically possible and urea-treated and that it should replace 0.25 of the silage in the ration