Published online by Cambridge University Press: 02 September 2010
The effect of ensiling grass and supplementing the resulting silage with water-soluble carbohydrate in the form of sucrose and undegradable dietary protein (UDP) in the form offish meal on forage intake and milk production and composition were evaluated in an experiment involving 63 mid-lactation Holstein-Friesian cows. Herbage from the primary growth of a predominantly perennial ryegrass sward was zero-grazed (ZG) from 19 April to 16 May 1993. The herbage was mown and picked up with a precision-chop harvester and offered as the sole diet, twice daily, to 18 cows which were on average 186 days into lactation. On 13 May, herbage from the same sward was harvested identically to the ZG herbage and ensiled, treated with formic acid at a rate of 2·85 lit grass. At 53 days after ensiling the silage was offered either as the sole diet (SO) or supplemented with sucrose at 10·3 g/kg fresh silage (SS) or supplemented with sucrose and fish meal each at 10·3 g/kg fresh silage (SSF) to 15 cows per treatment which were on average 164 days into lactation. The feeding period was 28 days for ZG and 21 days for the SO, SS and SSF treatments, and the last 7 days were the main recording interval. Prior to going on to the experimental diets all animals were offered a common silage ad libitum and supplemented with 5 kg of a 180 g/kg crude protein concentrate. Dry-matter intakes (DMI), milk yields and milk composition were recorded during the pre-experimental period and subsequently used as covariates in the statistical analysis. For diets ZG, SO, SS and SSF, forage DMI (kg/day), total DMI (kg/day), milk yields (kg/day), fat concentration (g/kg) and protein concentration (g/kg) were 14·4,14·0,13·7 and 13·9 (average s.e.d. = 0·55); 14·4,14·0,14·5 and 15·4 (average s.e.d. = 0·59); 15·4, 14·4, 14·5 and 16·7 (average s.e.d. = 0·42); 36·6, 38·6, 38·6 and 37·5 (average s.e.d. = 2·67); 33·0, 30·7, 32·2 and 32·8 (average s.e.d. = 0·75). Nitrogen (N) digestibility was higher on SO and SSF (P < 0·05) relative to ZG with SS being intermediate, otherwise treatment did not alter (P > 0·05) diet apparent digestibility. Ensilage increased the immediately soluble N fraction (a value) and degradability of N (P < 0·001) relative to ZG. It is concluded that ensilage had no effect on forage DMI but decreased milk yield and protein concentration relative to the parent herbage. The positive response in milk yield due to supplementation of the silage-based diet with sucrose and fish meal and the lack of response to sucrose supplementation alone suggests that nutrients absorbed from the digestive tract of cows offered silage-based diets are more limiting in protein or specific amino acids supplied by fish meal than in energy. The decrease in animal performance due to ensiling may be overcome by supplementation of silage-based diets with UDP at sufficient levels to equate that of the parent herbage.
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