1542
Estimation of histidine requirement in lactating dairy cows
Although in lactating dairy cows, His and Met show similar hepatic and mammary behaviour, with similar concentration in milk, requirement for His has been variously estimated as 2.4% (Doepel et al., 2004, JDS 87:1279), 2.7% (CPM-Dairy) and 3.2% (Rulquin et al., 2001, INRA ProdAnim 14:265) of metabolizable protein (MP) supply. Such variability may be explained by depletion or replenishment of endogenous pools of His, including intramuscular carnosine and anserine and blood hemoglobin. To test this hypothesis, 5 multiparous Holstein cows (674 ± 36 kg BW, 92 ± 18 DIM) were used in a 4×4 Latin square plus one cow, with 14-d periods. Cows were fed a diet balanced to supply 103% of NEL requirement but only 72% of MP requirement (1610 g/d) providing 34 g/d of digestible His (NRC, 2001). Treatments were abomasal infusion of His at 0, 7.6, 15.2 or 22.8 g/d in addition to a mixture of AA (595 g/d, casein profile). His represented 1.60, 1.95, 2.30 and 2.65% of MP supply, respectively. At the end of each period, 6 arterial blood samples plus muscle biopsies from the semimembranous muscle were collected
|
His supply (% of MP) |
SEM |
P Value |
||||
|
1.60 |
1.95 |
2.30 |
2.65 |
Linear |
Quadratic |
|
DMI, kg/d |
20.1 |
20.1 |
20.7 |
20.7 |
0.26 |
0.08 |
0.92 |
Yields |
|
|
|
|
|
|
|
Milk, kg/d |
32.3 |
34.0 |
36.3 |
36.8 |
0.53 |
<0.001 |
0.32 |
True protein, g/d |
875 |
1035 |
1057 |
1116 |
25.7 |
<0.001 |
0.08 |
Plasma concentrations |
|
|
|
|
|
|
|
His, µM |
14.5 |
33.4 |
51.9 |
60.1 |
3.18 |
0.001 |
0.12 |
Hemoglobin, g/100 mL |
9.2 |
9.5 |
9.7 |
9.4 |
0.21 |
0.41 |
0.17 |
Muscle concentrations |
|
|
|
|
|
|
|
Carnosine, µM |
8373 |
8478 |
9188 |
6841 |
647.9 |
0.21 |
0.09 |
Anserine, µM |
1349 |
1306 |
1422 |
993 |
101.4 |
0.07 |
0.09 |
Milk yield plateau was reached at a higher His supply (2.30%MP) than milk protein yield (1.95%MP). Between these supplies, however, milk protein yield could be sustained from depletion of endogenous pools. Observed reductions in muscle carnosine and anserine plus plasma hemoglobin could supply 3.2 g of His/d. Compared with other essential AA, the unique peculiarity that His has additional endogenous labile pools means that depletion and/or replenishment of these pools over short periods may bias estimate of true requirement.
Keywords: Histidine, carnosine, dairy cow