A study xoas carried out to examine the effects of method of grass conservation on intake and apparent digestibility by sheep and rate of degradation in the rumen of cattle. Thirty-six hoggets were arranged in a three-period partial change-over design involving nine treatments. The treatments consisted of fresh herbage or herbage from the same pasture which was ensiled for 2, 4, 7, 10, 20 and 41 days in round bales or herbage from the same pasture conserved as hay or ensiled in a bunker silo for 51 days. In addition the rate of dry-matter disappearance in the rumen for each treatment was determined using three rumen fistulated steers. The fresh and ensiled treatments had been frozen prior to feeding. Results from the study showed that the dry-matter intakes, corrected for losses of volatile compounds, of material ensiled in round bales, was increasingly depressed with period of ensiling up to 20 days after ensiling. Intakes of digestible energy followed a similar trend. Regression analysis indicated that reductions in intake with ensiling were mainly due to increases in ammonia N and n-butyric acid concentration, while changes in pH, water-soluble carbohydrate and acetic acid concentration also influenced intake. The differences in intakes of dry matter and digestible energy between fresh herbage and herbage from the bunker silo were not significant. The ensiling of herbage in round bales had little effect on organic matter apparent digestibility but led to an increase in nitrogen apparent digestibility and effective degradability when calculated at rumen outflow rates of 0-05 per h and 0-08 per h. Conservation of grass as hay led to a reduction in the intake, apparent digestibility and effective degradability of dry matter.

1998). Effect of duration of fasting period on short-term intake rates of lactating dairy cows. AbstractThe effects of duration of fasting on the short-term feeding behaviour of 12 grazing and 12 silage-fed lactating Holstein-Friesian dairy cows were examined. Four groups of three cows were rotated around fasting treatments of 1, 3, 6 or 13 h following a balanced Latin-square design. Herbage intakes for each treatment group were assessed over al-h period. As intended there were no significant differences in sward characteristics between the experimental plots grazed by cows from different treatment groups. However, total dry-matter (DM) intake, biting rate and DM intake per bite, measured over the 1-h grazing period, increased significantly when the duration of fasting was extended from 1 to 6 or 13 h (P < 0-05). There were only minor differences in grazing behaviour following fasting durations ofl and 3, or 6 and 13 h. In a parallel study, undertaken to assess the influence of fasting duration on appetite independently of grazing, four groups of three cows were housed indoors and offered 30 kg of a high quality grass silage. Silage DM intakes, measured over a 1-h period, increased significantly with extended fasting periods (P < 0-01), though silage DM intake was considerably lower than that of grazing cows for each fasting treatment. These results suggest that dairy cows grazing on good quality swards may be able to compensate for increased degree of hunger by increasing both biting rate and DM intake per bite to increase DM intake rate. Although the DM intakes of silage and grazed grass followed similar patterns of increasing intake with extended fasting duration, DM intake rates were considerably higher in grazing cows for each fasting treatment.

The effects of Na fertiliser (supplied as an NPK-Na compound) on herbage yield and composition were examined at two different sites to see if pasture responses to Na were affected by differences in K and moisture availability. At one site, pasture was grown under conditions of moisture stress and limited K availability, whereas at the other site the pasture was grown under comparatively non-stress conditions.The results were interesting in that Na fertilisation appeared to be detrimental to pasture yield and quality under conditions of moisture stress and suboptimal K supply, whereas under the non-stress conditions it actually increased herbage N offtake, marginally improved the nutritional quality of the pasture and produced appreciable (albeit non-significant) increases in DM yield. It was suggested that an important effect of Na on grass production may have been its ability to enhance the rate of NO 3 uptake by plants, thereby minimising NO 3-N losses from the soil-plant system by denitrification. However, because the amount of N fertiliser used in the experiments (i.e. 390 kg N ha -t y r -l ) was close to that normally required for maximum yield production (N max) under Northern Ireland conditions, the scope for yield increases in response to Na-elicited improvements in N offtake were thought to have been very limited at both experimental sites.On the basis of results from both the present study and previous field trials, a unifying theory is presented to explain the differential effects of Na on NO 3 uptake and herbage growth under different sets of circumstances.

A study was carried out to examine the effects of ensiling and pattern of silage fermentation on nitrogen and energy utilization, rumen fermentation and rumen degradation characteristics of forage by lactating dairy cows. Six nonfistulated dairy cows and three rumen fistulated dairy cows were offered fresh grass (G) or grass silage produced from the same sward which had undergone either an extensive (E) or restricted (R) fermentation. Animals offered extensively fermented silage had liigher urinary nitrogen (N) outputs (expressed as a proportion of N intake) than those offered fresh grass (P < 0·05). Corresponding values for animals offered restricted fermented silage were intermediate between those offered grass and extensively fermented silage. Animals offered fresh grass and restricted fermented silage also had higher methane energy losses (P < 0·05), than those offered extensively fermented silage. The ensiling of grass had little effect on metabolizable energy (ME) intake or on the efficiency of utilization of ME for lactation (k1). Animals offered extensively fermented silage had higher proportions of propionate and lower proportions of acetate than those offered fresh grass or restricted fermented silage (P < 0·001). Ensiling resulted in an increase in the soluble (a) fraction and a reduction in the potentially degradable (b) fraction of N.

A study was carried out to determine if sheep could be used as a model for predicting the intakes of silages by cattle. Fifty ewes and 45 cows were offered five grass silages unsupplemented in two parallel randomized-block experiments over a 4-week period. Each silage had been made using the same equipment over a range of cutting dates (May, July, August 1991). The silages differed in fermentation characteristics, with lactic acid concentrations varying from 15·3 to 90·7 g/kg dry matter, and ammonia-nitrogen concentrations from 77 to 198 g/kg nitrogen. When expressed on a metabolic live-weight basis, the mean intakes of silages by cows were 2·25 times those of the sheep, with the mean intakes being 35·1 and 79·1 g/kg M0·75 for the sheep and cows respectively. However, there was no significant correlation between recorded intakes during the 4th week of the study by the two species (y (cows) = 0·62× (sheep) + 58·40; r2 = 0·03). It was concluded that sheep were not a useful model system to predict the intakes of a range of grass silages of similar chop length by dairy cows.