Effects Of Protein And Energy Balance On Associative Effects Of Feedstuffs In Ruminants

In this study, in vitro gas test and animal feeding trial were conducted to study the effects of supplementing roughage with protein and energy on associative effects (AE) of feedstuffs in ruminants, and to explore possible mechanisms in the process of both digestion and metabolism. Systemtic determination was made of fermentation characteristics, content and rate of feed degradation, microbial protein yield, fluctuation of the microbes in the rumen; and balance of energy and nitrogen supply to the rumen microbes were analyzed. Molecular biology techniques were also used in analysis of rumen microbiota and detection of gene expression of some key enzymes in metabolic process such as glycogenesis.Experiment 1 Effect of concentrate to roughage ratio and protein supplementation on the associative effects of feedstuffs in vitroIn vitro gas test was used to investigate the effect of concentrate-roughage ratio and protein supplementation level on AE. Rice straw (RS) or ammonium bicarbonate treated rice straw (ABRS) basal diet was supplemented with the mixture of rapeseed meal (RSM) and corn. Ratio of the mixture of RSM and corn to RS or ABRS was at 70:30,60:40,50:50 and 40:60, respectively, with proportion of RSM at 0,10,20, 30 and 40% in the whole diet. Gas production (GP) was recorded at 0,2,4,6,9,12, 24,36,48,72 and 96 h. The AE was defined as the difference between the observed in vitro GP and the predicted value from individual feed fermented alone. The degradation of RS was enhanced by ammonium treatment through improving potential GP. The AE values changed with the concentrate-roughage ratio and proportion of RSM. Interactions of concentrate-roughage ratio and RSM proportion significantly affected AE (P<0.01). In RS basal diet, positive AE was observed in all the mixtures after 24 h incubation and varied with concentrate-roughage ratio and proportion of RSM. When the concentrate-roughage ratio was 40:60, proportion of RSM has significantly effect on AE, and the greatest response was pronounced when proportion of RSM was 30%. When proportions of RSM were at 20,30 and 40%, the AE values were significantly affected by concentrate-roughage ratio. In ABRS basal diet, positive AE was observed in all the mixtures after 24 h incubation, which ranged between 0.1 and 12.9%. The greatest AE occurred when concentrate-roughage ratio was at 40:60 and the RSM content was 30%. The proportion of RSM has significant effect on AE when concentrate-roughage ratios were 60:40,50:50,40:60, and so does the concentrate-roughage ratio when the proportion of RSM was at 20,30 and 40% in the whole diet. It is inferred that ammonium bicarbonate treatment can improve the utilization of rice straw, but has no effect on associative effects. The associative effects are actually determined by concentrate-roughage ratio and protein supplementation level.Experiment 2 Effect of nitrogen-energy balance on the associative effects of feedstuffs in vitroThe effect of nitrogen-energy balance on associative effects of feedstuffs was investigated using in vitro gas test. The RS or ABRS basal diet was supplemented with 40% of mixture of RSM and corn in which their ratio was 0,25,50,75 and 100 %, respectively, so that different ratios of rumen degradable nitrogen (RDN) to digested organic matter (DOM) were obtained. In RS basal diet, with the increasing levels of RSM, RDN/DOM value increased from 9.7 to 44.9 g/kg, while the GP decreased at high RSM levels. Positive AE was observed in all the mixtures. With the increasing ratios of RSM to corn, the AE value was 0.6,0.7,10.8 and 6.5%, respectively. Organic matter digestibility and carboxymethyl cellulose activity did not change when the proportion of RSM was below 30%, and then decreased. The pH values were not significantly affected by ratios of RSM to corn, with all values in the normal range. Ammonia-N concentration increased with increased levels of RSM, while the opposite tendency was observed in volatile fatty acids concentration. Methane production increased with the increasing proportion of RSM up to 20%, and then decreased. Microbial protein yield showed a similar tendency to the AE. The relative population of F. succinogenes was increased with increased levels of RSM. Numbers of R. flavefaciens relative to total bacterial 16S rDNA increased with the increasing proportion of RSM up to 30%, and then decreased. The relative population of fungi was not affected (P>0.05) by the proportion of RSM. In ABRS basal diet, with the increased levels of RSM, RDN/DOM value was 11.6,18.4,24.4, 33.5,45.7 g/kg, respectively, and the AE value was 3.0,0.4,6.2,12.9,7.4%, correspondingly. The rumen fermentation parameters and rumen microbial populations showed the similar tendency to RS basal diet. It is inferred that the balance between degradable nitrogen and dietary available energy has great effects on the efficiency of microbial protein synthesis, energy utilization and AE. The increased microbial protein synthesis, rumen microbial populations and cellulolytic bacteria activity may be responsible for the positive AE.Experiment 3 Effect of supplementingrice straw with rapeseed meal on associative effects of feedstuffs in growing lambsThirty-six male Hu lambs were divided into four equal groups according to body weight. The lambs were given free access to rice straw along with 120 g/d ground corn per head. The RSM was supplemented at levels of 0 (control),80,160 or 240 g/d, respectively. Each dietary treatment involved a total of 9 lambs kept in 3 pens. The trial lasted for 60 days, the first 15 days of which were for adaptation. The RS intake was not affected (P>0.05) by RSM supplementation. The apparent digestibility of organic matter, crude protein and neutral detergent fiber were increased with RSM supplementation at 160 g/day, but no further improvement was noted at the higher levels of RSM. Total intake of digestible organic matter, crude protein and neutral detergent fiber were increased linearly with the increasing RSM (P<0.05). The ratio of degradable intake protein to digestible organic matter was estimated to be 47,111,180 and 213 g/kg at supplementary RSM levels of 0,80,160 and 240 g/d, respectively. Average daily gain of body weight for lambs supplemented with RSM was significantly higher than that of control. The highest weight gain was observed at 160g/d RSM supplementation, where positive AE in animal performance were observed. Concentration of ammonia nitrogen, microbial protein and total volatile fatty acids increased with RSM supplementation, being highest with the highest level of RSM. Rumen microbial populations were increased with increased levels of RSM. Carboxymethyl cellulase activity and the relative population of F. succinogenes and B. fibrisolvens were increased by a small quantity of RSM supplemented, and then declined when supplemental RSM reached 240g/d. Compared with the control, RSM supplementation significantly increased the relative population of R. flavefaciens and fungi, there were no significantly differences among the treatments. Serum concentrations of T3 and IGF-I were increased with increased levels of RSM. Compared with the control, concentration of insulin was increased by RSM supplementation. Expression of hepatic IGF-I was consistent with that of circulating IGF-I. Expression of hepatic PEPCK-C mRNA was increased with moderate RSM supplementation, but showed no response to overfeeding of RSM. PEPCK-M mRNA expression was not affected by RSM supplementation.In summary, ammonium bicarbonate treatment can improve the utilization of RS but it has no effect on AE. Reasonable supplementation of protein and energy in low-quality forage could improve balance between degradable nitrogen and dietary available energy, and lead to positive AE. The positive AE depend on many factors: the change of rumen rumen environment conditions; increased digestibility, microbial protein synthesis, rumen microbial populations and cellulolytic bacteria activity; improvement of growth hormone exudation and gene expression of some key enzymes in metabolic. There may also be interactions between many of these factors.