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 lactating dairy cows, cracked wheat (CW) and sodium hydroxide-treated wheat (SW) were compared when offered with either immature (IM) or mature (MM) maize 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, MMCW, MMSW) in 4 X 4 Latin-square designs. In experiment 3, the in sacco degradability of CW and SW was measured in the rumen of three lactating fistulated cows. In experiment 1 total DM intake was 0.7 kg/day higher and milk yield 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 protein 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 effects on yield of fat or protein. Neutral-detergent fibre digestibility in the rumen was unaffected by the treatments. Starch intake increased (P < 0.05) with MM silage when compared with IM silage and was accompanied by an increase (P < 0.01) in starch flow to the duodenum and in the amount (P < 0.001) digested in the rumen, although there was no significant change in rumen digestibility. Replacing CW with SW increased starch flow to the duodenum (P < 0.05) and reduced rumen digestibility (P < 0.05). Although the amount of total nitrogen (TN) digested in the rumen and rumen digestibility decreased (P < 0.01) with crop maturity, the flow of TN and non-ammonia 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 higher starch intake, total tract starch digestibility was unaffected by treatment and averaged 0.972. There were no main treatment effects on daily mean pH, concentration of ammonia or concentration or molar proportions of volatile 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. In conclusion the studies confirm that SW is more slowly fermented than CW and can increase the supply of starch to the duodenum. However the concept that 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.