Nitrogen partitioning and microbial protein synthesis in lactating dairy cows with different phenotypic residual feed intake

Table 2 Productivity of lactating cows selected for phenotypic divergence in residual feed intake (RFI)

Items	Low RFI	High RFI	SEM	P value^a
Items	Low RFI	High RFI	SEM	RFI	Day	RFI × Day
Number, head	10	8
Lactation performance^b
DMI, kg/d	24.2	26.6	0.68	0.02	< 0.01	0.32
Milk yield, kg/d	34.0	33.1	1.39	0.65	< 0.01	0.96
Milk protein yield, kg/d	1.11	1.10	0.05	0.90	0.03	0.91
ECM, kg/d	35.7	36.4	1.35	0.72	< 0.01	0.85
ECM/DMI, kg/kg	1.48	1.36	0.03	< 0.01	< 0.01	0.77
Milk/DMI, kg/kg	1.41	1.24	0.04	< 0.01	< 0.01	0.64
RFI, kg/d	−0.96	1.18	0.22	< 0.01	–	–
Milk composition^c
Milk fat, %	3.83	4.23	0.12	0.01	0.05	0.87
Milk protein, %	3.26	3.33	0.06	0.40	< 0.01	0.64
Lactose, %	4.97	4.90	0.03	0.21	< 0.01	0.15
Total solids, %	12.7	13.0	0.14	0.12	0.12	0.90
MUN, mg/dL	12.7	13.9	0.39	0.05	< 0.01	0.62
SCC, × 10³/mL	50.5	38.7	9.46	0.39	0.33	0.46
Days in milk	193	182	6.30	0.22	–	–
Parity	2.70	2.50	0.22	0.56	–	–
Body weight, kg	739	737	16.7	0.96	< 0.01	0.24
Average dairy gain, kg	0.17	0.26	0.18	0.66	0.08	0.68

^aP value associated with RFI, time, and the interaction of RFI and time
^bDMI, dry matter intake; ECM (kg) = 0.3246 × milk yield (kg) + 13.86 × milk fat (kg) + 7.04 × milk protein (kg) [44]. All cows remained pregnant during the trial
^cMUN milk urea nitrogen, SCC somatic cell counts

ISSN: 2049-1891