Feeding of high yielding dairy cows. 2. The effect of ad libitum versus restricted forage feeding on milk yield and composition

Ekern, A.

Meldinger fra Norges Landbrukshoegskole 51(31): 31

1972


Accession: 000093082

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Abstract
2. In 4 experiments in Norway from 1965 to 1969, 24, 24, 18 and 18 cows were given in the declining phase of lactation grass silage to appetite; 1 feed unit (FU) hay with grass silage to appetite; grass silage 2.5 FU alone or with 1.2 FU extra from concentrates (in the last trial only). The first 2 experiments were of switchback design with 3 periods, 41 and 37 days in the respective experiments. The other experiments were of Latin square design with 3 periods of 5 weeks. All cows were offered the same amount of roots, mineral and vitamin supplements, and all got the same energy for maintenance. In the first 2 experiments 6 of the cows in each group were given 0.50 FU/kg 4% fat-corrected milk (FCM); all other cows in all experiments got 0.40 FU/kg FCM with the extra 1.2 FU/day in the last experiment. Rumen liquor at the end of each period in the last 2 experiments showed that rations low in roughage gave smaller molar proportions of acetic acid, isobutryic acid and propionic acid and a larger proportion of butyric acid than roughage to appetite. Rumen pH was lower when low roughage and high concentrate rations were given, significantly in one experiment. Restricted grass silage significantly reduced yield of FCM and milk fat in all experiments, amount of milk, milk DM, milk protein and milk energy in 3 experiments and milk sugar in 2, and also reduced energy content/kg milk DM and milk fat in one, milk sugar content in one and increased milk protein content in one experiment. With 1.8 kg hay for cows given grass silage to appetite yield of milk, FCM, milk DM, fat, protein, sugar and energy were significantly less than with silage as the only forage. Concentrate to replace silage on the basis of metabolizable energy instead of on the basis of FU gave a further decline in milk yield, the difference significant for milk fat only.