Previous studies have indicated that (15)N enrichment of solid-associated bacteria (SAB) may be predicted from the same value in liquid-associated bacteria (LAB). The aims of this study were to confirm this and to measure the error in the nutrient supply from SAB, when LAB are used as the reference sample. For this purpose, the chemical and amino acid (AA) compositions of both the bacterial populations were studied in four experiments carried out on different groups of three rumen cannulated wethers. Diets (one in Experiments 1 and 4 and three in Experiments 2 and 3) had forage-to-concentrate ratios (dry matter (DM) basis) between 2 : 1 and 40 : 60, and were consumed at intake levels between 40 and 75 g DM/kg (BW)(0.75). The bacteria samples were isolated after continuous infusion of ((15)NH(4))(2)SO(4) (40, 18, 30 and 25 mg (15)N/day, in Experiments 1 to 4, respectively) for at least 14 days. In all experiments, SAB had consistently higher concentrations of organic matter (826 v. 716 g/kg DM, as average) and total lipids (192 v. 95 g/kg DM, as average) than LAB. Similar CP concentrations of both populations were observed, except a higher concentration in SAB than in LAB in Experiment 3. A consistent (in Experiment 4 only as tendency) higher AA-N/total N ratio (on average 17.5%) was observed in SAB than in LAB. The (15)N enrichment in SAB was systematically lower than in LAB. On the basis of the results of all studies a close relationship was found between the (15)N enrichment in SAB and LAB, which was shown irrespective of experiments. This relationship was established from Experiments 1 and 2 and the above cited previous results (n = 20; P < 0.001; R(2) = 0.996), and then confirmed from the results of Experiments 3 and 4. These relationships between SAB and LAB demonstrate that CP supply from SAB is underevaluated by, on average, 21.2% when LAB are used as the reference. This underevaluation was higher for true protein and even higher for the lipid supply (32.5% and 59.6%, respectively, as an average of the four experiments). Large differences in AA profile were observed between SAB and LAB. The prediction equation obtained using (15)N as the marker may be used to correct the errors associated with the traditional use of LAB as the reference sample, and therefore to obtain more accurate estimates of the microbial nutrient supply to the ruminants.

Sixty New-Zealand×Californian multiparous rabbit does were used to evaluate the capability of a computerized ultrasound system to estimate changes in body condition at different physiological states: parturition, 21 st day of lactation, weaning and 28 th day of gestation. Perirenal fat weight and carcass energy concentration were significantly correlated with live weight (r = 0.58 and 0.49, respectively; P<0.001) and ultrasound measurement of perirenal fat thickness (r = 0.51 and 0.45; P<0.001). The inclusion of quadratic and cubic terms of the perirenal fat thickness as independent variables significantly increased the coefficient of determination and lowered the residual standard deviation of the models, based on the live weight of the animals, to estimate the perirenal fat weight and the carcass energy concentration (P<0.01). However, these general models tended to overestimate the perirenal fat weight and the body energy concentration of lean animals (<50 g of perirenal fat weight or 8.0 MJ kg -1 of carcass energy concentration). When specific multiple regression equations for predicting perirenal fat weight and body energy of multiparous does were developed in function of their physiological state, prediction accuracy of equations improved for rabbits at parturition (R 2 = 0.72 and 0.67), 21 days of lactation (R 2 = 0.84 and 0.67) and weaning (R 2 = 0.76 and 0.65). No model was able to predict either perirenal fat weight or carcass energy concentration of the multiparous rabbit does at 28 th day of gestation. In conclusion, excluding animals in late gestation, ultrasound measurement of perirenal fat thickness seems to be a useful technique for in vivo estimation of the body condition of reproducing multiparous rabbit does.

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