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This study assessed the efficacy of a calcium salt of methionine hydroxy analog (MHA-Ca, 84%) relative to DL-methionine 99%) in starter pigs. In Experiment 1 (Exp. 1, N balance trial), 42 individually housed barrows (Genesus, average initial BW 19 kg) were used in two blocks of 21 pigs each with six replicates per treatment. Within each block, pigs were randomly allotted to seven diets: a methionine (Met)-deficient basal diet or the basal diet with three added levels of DL-Met (0.02%, 0.04% and 0.06%) or MHA-Ca (0.024%, 0.048% and 0.071%) on an equimolar basis. After a 7-day adaptation period, feces and urine were collected quantitatively for 5 days. Urinary and total N outputs decreased linearly (P , 0.05) with DL-Met or MHA-Ca supplementation. Nitrogen retention, expressed as g/day and as % of intake increased linearly (P , 0.01) with DL-Met and MHA-Ca supplementations. The relative efficacy of MHA-Ca to DL-Met was estimated to be 71.2% on a product-to-product basis for N retention expressed as % of intake. In Exp. 2 (performance trial), 280, 21-day-old crossbred (Pietrain 3 (Landrace 3 Large White)) pigs (eight pigs per pen, seven pens per treatment), were allocated to five diets in a completely randomized block design after a 10-day adaptation period. The Met-deficient basal diet contained 16.5% CP and 0.21% Met. Other diets were basal diet supplemented with two graded levels of DL-Met (0.04% and 0.08%) or MHA-Ca (0.062% and 0.12%) on a product basis at a DL-Met to MHA-Ca ratio of 65 : 100 at the expense of maize. BW and feed disappearance were monitored weekly for 3 weeks to determine performance. Final BW, average daily gain and average daily feed intake increased (P , 0.05) and feed to gain ratio decreased (P , 0.05) with the addition of Met to the basal diet irrespective of the source. Overall, the N retention results of Exp. 1 showed that the average relative bioavailability of MHA-Ca to DL-Met to support N retention (% of N intake) was 71% on a product-to-product basis (85% on an equimolar basis). In Exp. 2, pig performance was not different when Met was supplemented in the Met-deficient diet at a DL-Met to MHA-Ca ratio of 65 : 100 on a product basis.

The effect of the physiological state and dietary protein level on urinary excretion of creatinine (C) and purine derivatives (PD) was studied in two experiments carried out with pregnant and lactating ewes to evaluate whether the PD/C ratio in urine can he confidently used as an index of PD excretion. In both experiments ewes were given ammonia-treated straw and concentrates including different levels of fish meal and the excretion in urine and milk and the plasma concentration of C, allantoin (AL), xanthine, hypoxanthine and uric acid was measured.Creatinine excretion (in urine and milk) was higher in pregnant ewes than in those lactating (492 and 420 (s.e. 10.0) μmol/kg maternal live weight0.75) and no significant differences were found due to number of foetuses and dietary protein level. The coefficient of variation was 0·10 in both pregnancy and lactation and individual variation accounted for proportionately 0·78 and 0·93 of total variation. The AL/C ratio in urine was highly correlated with daily AL excretion (r = 0·90 and 0·78 in pregnant and lactating ewes, respectively). Changes in PD excretion with experimental treatments were mainly reflected in AL, as the main component (0-83) of total PD. Most of the variation in AL excretion was explained by differences in rumen fermentable organic matter intake (RFOMI) (R2 = 0·79) and AL excretion did not differ between treatments when expressed per kg of RFOMI. In contrast to this the ratio AL/digestible organic matter intake decreased with increasing levels of fish meal in the diet. Urinary PD excretion was better related to estimated PD kidney tubular load (r = 0·76) than to PD plasma concentration (r = 0·64).The results suggest that creatinine excretion is scarcely affected by the number of foetuses in pregnancy and dietary protein level but if the AL/С in urine is used instead of total collection as an index of purines absorbed in the duodenum, differences in urinary creatinine excretion due to physiological state must be accounted for.

The effect of carbohydrate supplementation on microbial fibre digestion was studied in vitro, by measuring the disappearance of cell wall monosaccharides, bacterial adhesion (mmol purine bases per g residue), and total (per g residue) and bacterial (per mmol purine bases) polysaccharidase activity. Straw cell walls (CW, 0.5% w/v) were cultured in medium supplemented with (0.275% w/v) or without starch, a sugar mixture, or pectin. Supplementation with these constituents did not cause a drop in pH below 6.1, and increased all parameters investigated with the exception of bacterial polysaccharidase activity, which was higher for CW cultures, suggesting a higher proportion of fibrolytic bacteria in the adherent population. By comparison with starch and sugar, pectin supplementation resulted in a lower proportion of residual sugars remaining from cell walls after 60 and 72 h (P < 0.05), which resulted in greater bacterial adhesion after 8 and 12 h (P < 0.05) and higher total cellulase activity after 8 h (P < 0.01). This was perhaps because pectin may cover particle surfaces, protecting the digestive area from external factors, or may act as a substrate for cellulolytic bacteria. The lack of differences in bacterial enzymatic activities suggests the absence of qualitative or quantitative differences in the adherent fibrolytic population.

Protein supplementation has a positive effect on milk production, particularly in ewes on negative energy balance (Gonzalez et al., 1985). The response has been associated either to an increase in the movilization of body reserves (Whitelaw et al., 1986, Hadjipanayotou et al., 1988) or to an enhanced efficiency of energy utilization for milk synthesis. On the other hand, the response has been shown to be higher with fish meal than with other protein sources (Oldham, 1984). This work aimed to study the mecanisms involved in the response to fish meal supplementation, in lactating ewes on negative energy balance.

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Protein supplementation has a positive effect on milk production, particularly in ewes on negative energy balance (Gonzalez et al., 1985). The response has been associated either to an increase in the movilization of body reserves (Whitelaw et al., 1986, Hadjipanayotou et al., 1988) or to an enhanced efficiency of energy utilization for milk synthesis. On the other hand, the response has been shown to be higher with fish meal than with other protein sources (Oldham, 1984). This work aimed to study the mecanisms involved in the response to fish meal supplementation, in lactating ewes on negative energy balance.