-Experimental data on phytate phosphorus utilisation by ruminants are scarce. The aim of this study was to estimate the phytase activity of rumen micro-organisms when phytate phosphorus supply is high. A semi-continuous culture system fermentor (RUSITEC) was used. The inoculum was obtained from eight goats fed on either high or low forage level diets. Experimental buffers only differed by the nature of phosphorus monosodium phosphate vs. corn sodium phytate. The nylon bags containing 15 g DM of substrate were removed after a 48-hour incubation period. The system was maintained for 15 days: 5 days for adaptation, in order to obtain a steady state, and 10 days for sampling and recording. No significant differences were observed for DM digestibility, gas production, pH, N-NH 3 , and SCFA for the different treatments. Bacterial efficiency of phytate phosphorus utilisation was significantly higher (p < 0.001) with organic P, but remained lower than the data usually reported in the literature. These results may be explained by the relative saturation of bacterial phytase activity when the buffer contains a high level of phytate phosphorus. phosphorus / phytate / ruminant / bacteria / in vitroRésumé -Mesure en fermenteur semi-continu (Rusitec) de l'utilisation du phosphore phytique par les bactéries du rumen chez la chèvre laitière recevant des régimes de différentes proportions fourrage-concentré. Les informations sur l'utilisation du phosphore phytique par les bactéries du rumen sont peu nombreuses. Le but de cet essai était d'évaluer in vitro (RUSITEC) l'efficacité de l'activité phytasique des micro-organismes recevant une proportion élevée de phosphore phytique. L'inoculum a été prélevé sur des chèvres recevant des régimes haut ou bas en aliment concentré. Dans les solutions nutritives, seule la nature du phosphore (phosphate monosodique vs. phytate de sodium de maïs) était différente. Les sachets nylon contenant 15 g de MS de substrat étaient maintenus 48 h Reprod. Nutr. Dev. 41 (2001) [259][260][261][262][263][264][265] 259

Ninety-nine uncastrated males were randomly distributed into four grazing groups to examine variation in growth and carcass traits, due to the implant regime [Implantation of 72 miligrams (mg) of Ralgro® at day (d) 0 followed by its reimplantation at d 90 versus implantation of Revalor® at d 0 followed by 72 mg of Ralgro® at d 90)], and suplementation type [mineral supplementation (MS) versus strategic supplementation (SS)]. With a 2 x 2 factorial arrangement, the analysis of variance included the treatments and their interaction (implant regimen x supplementation) as fixed effects, and the breed type as a random effect. The interaction was not significant; neither did the implant regimen on any growth trait (P > 0.05). Compared to MS, the SS group had a greater daily weight gain (779 vs. 541 grams; P < 0.001), required a shorter (38.3 d lesser) time of fattening to reach the end point (198.3 versus 236.6 d; P < 0.001) with a heavier liveweight (498. 2 vs. 474. 4 kilograms; P = 0.02) at an earlier age (29.4 vs. 30.­8 months; P < 0.001), with a higher carcass dressing percentage (59.13 vs 57.62 %; P = 0.03) and younger carcass bone maturity (P < 0.001). With the exception of thoracic depth, carcass traits did not vary with the implant regimen (P > 0.05). The use of aggressive implant regimens to improve growth or carcass characteristics of grazing bulls is not justified. SS is a feasible practice to improve fattening performance of grazing bulls but no beneficial impact on their carcass quality was expected.

Forty-seven Zebu calves were used to determine the effects of class (bull or steer), supplementation (SUPPL, a poultry litter-based supplement or mineral supplementation), and implant (20 mg estradiol combined with 120 mg of trenbolone acetate or no implant) on growth and carcass performance and beef eating quality. The average daily gain (ADG) of implanted cattle significantly increased for steers, but not for bulls. The SUPPL treatment increased ADG by 8.63% from day 0 to end, and shortened in 73.3 d the time to reach 480 kg BW (p < 0.01). Compared to bulls, the steer carcasses exhibited more desirable maturity and finish scores, thicker back fat (p < 0.05), and yielded greater (p < 0.01) percentages of high-value boneless subprimals (HVBLS) (+1.64%) and total cuts (1.35%). The SUPPL bulls dressed 2.63 and 1.63% greater than non-supplemented bulls and SUPPL steers, respectively (p < 0.05). Meat sensory quality was subtly affected (p < 0.05) by sex class or supplementation. The implant did not affect (p > 0.05) shear force or sensory ratings. The supplementation improved key growth performance traits while it adversely affected tenderness-related sensory traits. The implant enhanced the rate of gain of steers only, without improving cut-out yields or inducing adverse effects on palatability traits in both steers and bulls.

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