Effect of Dietary Level of Rumen-Degraded Protein on Production and Nitrogen Metabolism in Lactating Dairy Cows

Abstract

Twenty-eight (8 with ruminal cannulas) lactating Holstein cows were assigned to 4 × 4 Latin squares and fed diets with different levels of rumen-degraded protein (RDP) to study the effect of RDP on production and N metabolism. Diets contained [dry matter (DM) basis] 37% corn silage, 13% alfalfa silage, and 50% concentrate. The concentrate contained solvent and lignosulfonate-treated soybean meal and urea, and was adjusted to provide RDP at: 13.2, 12.3, 11.7, and 10.6% of DM in diets A to D, respectively. Intake of DM and yield of milk, fat-corrected milk, and fat were not affected by treatments. Dietary RDP had positive linear effects on milk true protein content and microbial nonammonia N (NAN) flow at the omasal canal, and a quadratic effect on true protein yield, with maximal protein production at 12.3% RDP. However, dietary RDP had a positive linear effect on total N excretion, with urinary N accounting for most of the increase, and a negative linear effect on environmental N efficiency (kg of milk produced per kg of N excreted). Therefore, a compromise between profitability and environmental quality was achieved at a dietary RDP level of 11.7% of DM. Observed microbial NAN flow and RDP supply were higher and RUP flow was lower than those predicted by the NRC ( 2001) model. The NRC ( 2001) model overpredicted production responses to RUP compared with the results in this study. Replacing default NRC degradation rates for protein supplements with rates measured in vivo resulted in similar observed and predicted values, suggesting that in situ degradation rates used by the NRC are slower than apparent rates in this study.

Determining the optimal ratio of canola meal and high protein dried distillers grain protein in diets of high producing Holstein dairy cows

“…However, when DM intake, milk yield and urine volumes similar to ours were reported (Vagnoni and Broderick, 1997;Reynal and Broderick, 2005), AL concentrations are consistent among studies. Our CR concentrations were corrected by a factor of 0.7 (based on our internal laboratory results) to adjust for loss of CR after acid treatment to stabilize urine samples, which could be one reason why it is higher than in previous studies.…”

“…Since Robinson (1996) also reported a decline in bacterial N flow when rumen ammonia concentrations fell below 90 mg/L, or exceeded 110 mg/L, either due to negative feedback mechanisms or direct bacterial toxicity, predicted rumen ammonia levels in our study (i.e., 62, 80, 100 and 113 mg/L for the 0, 65, 135 and 200 g/kg CM treatments respectively) suggest that MCP production may have been limited at the 0 g/kg CM treatment. However, rumen ammonia concentrations of 123 and 128 mg/L were reported to be optimal for rumen bacterial growth by Reynal and Broderick (2005) and Boucher et al (2007) respectively. This suggests that RDP and ammonia could have been limiting MCP production in the rumen, thereby reducing performance of cows in the all HPDDG treatments.…”

“…As it has been reported that urinary AL makes up an almost constant molar proportion of total PD, uric acid was not analyzed in our study and AL concentrations in urine samples were corrected to total PD using a factor of 0.91 (Vagnoni and Broderick, 1997;Valadares et al, 1999;Gonzalez-Ronquillo et al, 2003;Reynal and Broderick, 2005;Moorby et al, 2006), which was used to determine the purine derivative to creatinine (PDC) index as described by Chen and Ørskov (2003), thereby correcting the PD:CR ratio for metabolic BW to allow comparison among cows. The PDC index (Table 4) follows the same pattern as the AL:CR ratio, increasing linearly (P<0.01) with higher CM inclusions, strongly suggesting that MCP yield was not negatively affected by the increasing level of RDP due to increasing levels of CM in the ration.…”

Supplementing lactating dairy cows with a vitamin B12 precursor, 5,6-dimethylbenzimidazole, increases the apparent ruminal synthesis of vitamin B12

“…The following omasal digesta markers were used: indigestible NDF (Huhtanen et al, 1994) for the large particle phase (LP), YbCl 3 (modified from Siddons et al, 1985) for the small particle phase (SP) and Cr-EDTA (Udén et al, 1980) for the fluid phase (FP). A marker solution containing YbCl 3 , Cr-EDTA and 15 NH 4 SO 4 with 10 atom percentage excess 15 N (Isotec, Miamisburg, OH, USA) as a bacterial marker was prepared as described by Reynal and Broderick (2005). A sample of 500 ml of omasal digesta (background) was taken from each cow before the beginning of markers infusion on day 22 of each period to determine the natural abundance of 15 N. Cows were then pulse-dosed with 3.0 l of the same markers solution used during the continuous infusion.…”

Different true-protein sources do not modify the metabolism of crossbred Bos taurus × Bos indicus growing heifers

“…Agreeing with this result, Koenig and Beauchemin (2013) found that provision of rumen degradable and undegradable true protein sources did not affect the flow of dietary N from the rumen to the small intestine. On the other hand, Reynal and Broderick (2005) observed a linear increase in microbial N flow when the supply of rumen degradable true protein increased the dietary DM by 10.6-13.2%. , in turn, verified that higher supply of rumen-degradable protein was associated with increase in microbial N flow.…”