A comparison of the effects of cracked wheat and sodium hydroxide-treated wheat on food intake, milk production and rumen digestion in dairy cows given maize silage diets

To examine the effects of manipulating the amount and ruminal degradability of starch on food intake, milk production and digestion in the rumen of la ctating dairy cows, cracked wheat (CW) and sodium hydroxide-treated wheat ( SW) were compared when offered with either immature (IM) or mature (MM) mai ze silage given in a 3:1 dry matter (DM) ratio with grass silage. The total mixed ration (TMR) contained (kg/t DM basis) forage 600, wheat (CW or SW) 170, rapeseed meal 100, soya-bean meal 100, molasses/urea supplement 30 and minerals and vitamins were added at 20 kg/t diet DM. In experiments 1 and 2 respectively, 16 multiparous Holstein-Friesian cows and four similar cows with duodenal and ruminal cannulas were offered four diets (IMCW, IMSW, MM CW, MMSW) in 4 X 4 Latin-square designs. In experiment 3, the in sacco degr adability of CW and SW was measured in the rumen of three lactating fistula ted cows. In experiment 1 total DM intake was 0.7 kg/day higher and milk yi eld was 0.5 kg/day higher with MM than IM silage but the increases were not significant and type of wheat had no effect. Milk fat content was reduced by MM silage (P < 0.05) but was unaffected by type of wheat. For milk prote in content SW caused a non-significant increase with IM but a decrease (P < 0.05) with MM silage (interaction P < 0.05). There were no significant eff ects on yield of fat or protein. Neutral-detergent fibre digestibility in t he rumen was unaffected by the treatments. Starch intake increased (P < 0.0 5) with MM silage when compared with IM silage and was accompanied by an in crease (P < 0.01) in starch flow to the duodenum and in the amount (P <less than> 0.001) digested in the rumen, although there was no significant chan ge in rumen digestibility. Replacing CW with SW increased starch flow to th e duodenum (P < 0.05) and reduced rumen digestibility (P < 0.05). Although the amount of total nitrogen (TN) digested in the rumen and rumen digestibi lity decreased (P < 0.01) with crop maturity, the flow of TN and non-ammoni a nitrogen to the duodenum was unaffected. Total tract digestibility of DM was unaffected by treatments. Although the amount of starch digested in the total tract increased for MM compared with IM silage, reflecting the highe r starch intake, total tract starch digestibility was unaffected by treatme nt and averaged 0.972. There were no main treatment effects on daily mean p H, concentration of ammonia or concentration or molar proportions of volati le fatty acids in the rumen. With SW, effective degradability (outflow rate of 0.08 per h) for both DM and starch was reduced when compared with CW. I n conclusion the studies confirm that SW is more slowly fermented than CW a nd can increase the supply of starch to the duodenum. However the concept t hat increasing starch supply to the duodenum by a combination of MM silage and SW is likely to be beneficial to milk protein yield or concentration is not established under the present dietary regimen.