Jm. Moorby et al., THE INFLUENCE OF DIETARY ENERGY-SOURCE AND DIETARY-PROTEIN LEVEL ON MILK PROTEIN-CONCENTRATION FROM DAIRY-COWS, Animal Science, 63, 1996, pp. 1-10
To investigate the effects of energy source and protein level of diets
on milk protein content, 12 multiparous Holstein-Friesian cows were u
sed in a 4 X 4 Latin square change-over experiment with 4-week periods
. Four diets were offered, with ad libitum silage as proportionately 0
.40 of the diet, and the remaining 0.60 as one of four concentrates, t
wo based on barley and two on molassed sugar-beet pulp. Two protein le
vels were achieved by altering the amounts of digestible undegraded pr
otein in the concentrates, with all diets formulated to supply equal q
uantities of rumen degradable protein. There was no effect of diet on
dry-matter intakes. Both starch and high dietary protein levels signif
icantly increased milk protein concentration (P < 0.05), but had no ef
fects on milk fat and lactose concentrations,. Mean milk yields were s
ignificantly higher (P < 0.05) with increased dietary protein. Dietary
protein significantly affected the yields of milk protein (P < 0.01)
and lactose (P < 0.05) but not that of fat Urinary allantoin excretion
was significantly greater with both high protein (P < 0.05) and starc
h-based diets (P < 0.05). No significant interaction effects were foun
d. It is concluded that dietary effects were due largely to difference
s in supply of rumen degradable protein; increases in milk protein con
centration were therefore brought about by increasing the protein supp
ly to the animal.