Weekly balancing crude protein in diets for Holstein cows throughout lactation using one versus two grains

Holstein cows (n = 72, 28 primiparous) were fed for ad libitum intake a forage mixture (corn and haycrop silages, 63:37 DM) and a 71:29 ratio of two grain mixtures (13.8 and 36.2% CP, DM basis) at 1 kg/2.5 kg of the previous day's milk during 1 to 28 DIM (covariate period). Thereafter, rations were balanced and adjusted for energy and CP weekly based on monthly DHI data, forage analyses, and NRC requirements. Cows were blocked by parity (1 vs. greater than 1) and assigned randomly to receive one grain (blend of 13.8 and 36.2% CP grains, herd mean) or two grains according to individual needs. Daily yields of milk, 4% FCM, SCM, and resulting intakes of grain were higher for cows fed two grains, but the increase in daily DMI and the decreases in daily forage intake and SCM:grain ratio were not significant. Fewer pluriparous cows (3 vs. 8 out of 19) on the two-grain treatment conceived after first service, but overall services per conception (1.97) were equal. Percentage of cows with SCC below linear score 4 (91%) was equal between treatments. Means adjusted by covariate 4% FCM resulted in more modest treatment effects. Advantage of two-grain versus one-grain treatment for milk per day was 7.7% for parity 1 and only 1.6% for parities greater than 1; corresponding responses (nonsignificant) for 4% FCM were 2.8 and 4.3, respectively. Forage DMI depressions on two-grain treatment were not significant. When covariate-adjusted means were used, the advantage in income over feed cost for individualized feeding of CP was $106 and $36/yr per cow in parities 1 and greater than 1 when cows produced 8209 kg (313 DIM) and 8527 kg (320 DIM) of milk, respectively.