2014 Volume 2 Issue 1 Pages 51-62
An accumulated data set from digestion trials with lactating dairy cows (n = 170) was used to determine the effects of a proportion of herbage dry matter (DM) intake and crude protein (CP) content of herbage on nitrogen and energy utilization. The data set was divided into 2 groups based on the proportion of herbage DM intake in total diet (LI: < 35%, HI: > 35%). Moreover, the data set within HI was divided into 3 groups based on herbage CP content (LP: < 15%, MP: 15-18.5%, HP: > 18.5% of DM). Total dietary nitrogen intake and urinary nitrogen excretion increased as the proportion of herbage DM intake and herbage CP content increased. Milk nitrogen as a proportion of total nitrogen intake increased with herbage DM intake and decreased with an increase of herbage CP contents in HI. Digestible energy and metabolizable energy (ME) intakes were greater for HI than for LI (P < 0.01). In HI, DE and ME intake did not differ among groups. Milk energy yield for HI was greater than that for LI (P < 0.05), but was similar across herbage CP concentrations within HI. Simple regression analysis of milk energy against ME for production (ME intake - ME for maintenance) revealed that the conversation rate of ME for production was smaller for LI than for HI (P < 0.05), and tended to decrease as herbage CP content increased within HI.
