Effects of Dairy Cow Diet Forage Proportion on Duodenal Nutrient Supply and Urinary Purine Derivative Excretion

Abstract

Four mature Holstein-Friesian dairy cows were used in a 4 x 4 Latin square change-over design experiment made up of four 4-wk periods to investigate the relationship between microbial protein flow to the duodenum and excretion of purine derivatives (PD) in the urine. Four dietary treatments based on ad libitum access to ryegrass silage were offered, with a standard dairy concentrate included at different forage:concentrate (F:C) ratios, calculated on a dry matter basis: 80:20, 65:35, 50:50, and 35:65. Feed intakes increased as the proportion of concentrate in the diet increased, despite a concurrent decrease in silage intake. Increased feed intake led to increased nutrient flow to the duodenum. Milk yields increased as the diet F:C ratio decreased, with cows offered the 35:65 diet yielding nearly 8 kg/d more milk than cows offered the 80:20 diet; the concentrations of milk fat decreased and milk protein increased with a decreasing F:C ratio. Purine derivative excretion in the urine increased with an increasing proportion of concentrate in the diet, and there was a strong linear relationship between total PD excretion (allantoin and uric acid) and microbial N flow to the duodenum: microbial N (g/d) = 19.9 + 0.689 x total PD (mmol/d); R = 0.887. This strengthens the case for using PD excretion as a noninvasive marker of microbial protein flow from the rumen in dairy cows.

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

“…In Han et al (1992), Gonzalez-Ronquillo et al (2003) and Moorby et al (2006), lower DM intake, digestibility and milk yield could have been responsible for lower MCP production, and therefore lower AL concentrations, while very high urine volumes diluted AL concentration (mg/L) in Valadares et al (1999). 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.…”

“…However, Chizzotti et al (2008) reported that heavier animals have lower body protein content, and therefore lower urine CR outputs per unit BW. The average BW of the cows in our current study was higher (673 versus 627 and 560 kg from Moorby et al, 2006 andGonzalez-Ronquillo et al, 2003 respectively), but the BCS was relatively lower than in these studies. Since lean animals with a lower BCS may have a higher urine CR concentration per unit BW, expressing CR values as a function of metabolic BW converges the CR values among studies.…”

“…concluded that the PD to CR ratio in spot urine samples correlates well with intestinal flow of microbial purines and can be used as a qualitative indicator of rumen MCP supply, independent of urine volume, thereby obviating the need for total urine collection. Even though it is accepted that CR is excreted at a constant rate on a BW basis, daily CR excretion is related to body protein mass turnover and therefore varies among cows and studies (19-29 mg/kg BW; Valadares et al, 1999;Moorby et al, 2006). Thus our estimation of differences in MCP yield from the rumen is limited to relative measurements.…”

“…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.…”

Effects of ruminally protected methionine and/or phenylalanine on performance of high producing Holstein cows fed rations with very high levels of canola meal

“…( (( Total daily purine derivative (PD) excretion (mmol/d) is the sum of PD excreted in urine and milk of lactating dairy cows (Chen and Gomes, 1992), and was estimated assuming allantoin is 0.906 of total PD in urine (obtained from values reported by Vagnoni and Broderick, 1997;Valadares et al, 1999;Gonzalez-Ronquillo et al, 2003;Reynal & Broderick, 2005;Moorby et al, 2006) and PD excretion in milk is a constant 0.05 of urine PD excretion (Chen and Gomes, 1992).…”