Full Lactation Response on Restricted vs. ad Libitum Roughage Diets with Liberal Concentrate Feeding

Abstract

The effect of replacing one-half of the expected roughage consumption with equivalent TDN from concentrates was determined in full lactations with 20 pairs of high producing cows. Control cows (Group I) were fed alfalfa hay and corn silage ad libitum plus concentrates at an average ratio to FCM of 1:2.4. Paired cows restricted on roughage (Group II) were allowed roughage at the rate of 3.0kg hay and 7.5kg silage per 500kg body weight plus 3.8kg concentrates, in addition to the concentrate allowance for FCM at 1:2.4. In 294-day lactations Group I averaged 6,349kg FCM and Group II, 6,137kg, a nonsignificant difference (P>.10). Fat tests averaged 4.01 (I) and 3.89% (II), with the difference between groups from the 12th to the 22nd wk statistically significant (P<.01). Differences in body weight gain, total dry matter consumption, estimated TDN consumption, solids-not-fat tests, and milk fat yield were not significant. The average TDN/FCM ratio was significantly (P<.05) higher for Group II, 0.33, than for Group I, 0.31. Indications were that the Group II diet, which averaged 67.6% concentrate, was used less efficiently than the Group I diet, which averaged 51.1% concentrate. Restricting roughage and substituting concentrate for roughage TDN for cows fed concentrates liberally gave no benefits and resulted in lower milk fat tests and efficiency.