The effect of season and level of concentrate on the voluntary intake and digestibility of herbage by outdoor sows

The intake and the digestibility of herbage, and the effect of level of sup plementary concentrate food, were measured in late spring and late summer i n two studies, each with eight multiparous, pregnant sows. In the spring st udy sows were nose rung to prevent rooting but only four nose-rung sows wer e available for the summer study; the remaining four were unrung. In both c ases, sows had access to a plentiful (>2.5 t organic matter IOM) per ha) ry egrass/clover sward in a paddock of 1922 m(2). After a week of adaptation t o the herbage in the experimental paddock, sows were offered 1.5 or 30kg/da y concentrate for consecutive 2-week periods in a change-over experimental design with four sows on each treatment in each period. Samples of herbage were also taken to measure the sward density, chemical composition and n-al kane content. Herbage intake and digestibility estimates were calculated us ing the n-alkanes technique, with the marker dosed on small food pellets. I n the spring study the herbage intake ranged from 0.9 to 1.8 kg OM per day in the first period (herbage neutral-detergent fibre(NDF) content 439 (s.e. 41.6)g/kg OM) and 0.2 to 1.4 kg in the second (475 (s.e. 29.3)g NDF per kg OM). The intake was affected by the level of concentrate only in the secon d period. The results obtained during the summer study with the rung and un rung sows showed an intake between 0.9 and 2.4 kg OM per day in the first p eriod (524 (s.e. 16.0)g NDF per kg OM) and between 1.3 and 4.8 kg in the se cond (526 (s.e. 22.8)g NDF per kg OM). A high intake estimation for certain unrung individuals appeared to reflect their frenzied feeding behaviour an d possible loss of some marker pellets. There were no differences between l evel of concentrate treatments in either period. Digestibility of the diet was affected by the intake of herbage and the level of fibre consumed (P < 0 01). These herbage intakes equated to proportionately 0.50 (s.e. 0.05) an d 0.66 (s.e. 0 I) (or 0.49(s.e. 0.07) excluding problem sows) of the mainte nance energy requirement in each season. Faeces of unrung sows indicated a high ingestion of soil or stones by some individuals: one of the sows produ ced a bulked faeces sample containing 450g/kg fresh weight of stones, whils t another sow had a faecal ash content of 937g/kg DM. The results indicate that the intake of nutrients from herbage by grazing sows is highly variabl e between seasons and individuals.