Effect of concentrate type and distribution method on milk fat content and milk production in dairy cows

Twenty-one Holstein dairy cows in mid lactation were included in a 3 x 3 Latin square design study over three successive 4-week periods. Throughout the trial, the animals were fed an isoenergetic diet composed of 55% grass silage and 45% concentrate. Silage was offered twice a day (9:00 and 16:00). In the first treatment (GW) the concentrate was ground wheat given in two meals per day 1 h before silage distribution. In the second treatment (RW), the concentrate was rolled wheat given three times a day 2 h after silage distribution. In the third treatment (PHM), the concentrate was a mixture of beet pulp (40%). soybean hulls (40%) and maize (20%) given under the same conditions as treatment RW. Milk yield was higher (+ 2 kg/day) for PHM treatment than for the GW and RW treatments (P < 0.01). In the PHM treatment milk contained more fat (+2 g/kg, P < 0.01) and less protein (-1.7 g/kg, P < 0.01) than in the GW and RW treatments. These results were associated with changes in rumen fluid parameters (higher pH and higher proportions of acetic acid for PHM treatment). There was little difference between the GW and RW treatment groups, probably because of slower intake and marked concentrate refusal in the GW group, which may have affected the effects of that treatment on rumen fermentation.