Urea and short-chain fatty acids metabolism in Holstein cows fed a low-nitrogen grass-based diet

Abstract

Three ruminally cannulated and multicatheterised lactating dairy cows were used to investigate the effect of different supplement strategies to fresh clover grass on urea and short-chain fatty acid (SCFA) metabolism in a zero-grazing experiment with 24-h blood and ruminal samplings. Fresh clover grass was cut every morning and offered from 0800 to 1500 h. Maize silage was fed at 1530 h. The three treatments, arranged in a Latin square, differed by timing of feeding rolled barley and soya-bean hulls relative to fresh clover grass. All diets had the same overall composition. Treatments were soya-bean hulls fed at 0700 h and barley fed at 1530 h (SAM), barley fed at 0700 h and soya-bean hulls fed at 1530 h (BAM), and both soya-bean hulls and barley fed at 1530 h (SBPM). The grass had an unexpectedly low content of crude protein (12.7%) and the cows were severely undersupplied with rumen degradable protein. The treatment effects were numerically small; greater arterial ammonia concentration, net portal flux of ammonia and net hepatic flux of urea during part of the day were observed when no supplementary carbohydrate was fed before grass feeding. A marked diurnal variation in ruminal fermentation was observed and grass feeding increased ruminal concentrations of propionate and butyrate. The net portal fluxes of propionate, butyrate, isovalerate and valerate as well as the net hepatic uptake of propionate, butyrate, valerate and caproate increased after feeding at 0700 h. The hepatic extraction of butyrate showed a relatively large depression with grass feeding with nadir at 1200 to 1330 h. The increased net portal absorption and the decreased hepatic extraction resulted in an approximately six-fold increase in the arterial blood concentration of butyrate. The gut entry rate of urea accounted for 70 6 10% of the net hepatic production of urea. Saliva contributed to 14% of the total amount of urea recycled to the gut. Urea recycling to the gut was equivalent to 58% of the dietary nitrogen intake. Despite the severe undersupply of rumen degradable protein, the portaldrained viscera did not extract more than 4.3% of the urea supplied with arterial blood. This value is in line with the literature values for cows fed diets only moderately deficient in rumen degradable protein and indicates that cows maximise urea transfer across gut epithelia even when the diet is moderately deficient in rumen degradable protein.

Concentrate reduction and sequential roughage offer to dairy cows: effects on milk protein yield, protein efficiency and milk quality

“…This became obvious from the group effect on estimated apparent CP digestibility, which was large and to the advantage of the concentrate feeding. The values are closely comparable to data published by Røjen et al (2008) and Cantalapiedra-Hijar et al (2014) and show the expected effect of easily degradable CP in the concentrates.…”

“…Based on the apparently digested CP, the efficiency of the diet containing protein concentrates (Prot+) appeared to be even lower than that of the pure TMR and hay diets (Prot−). The finding of increased protein efficiency at low dietary protein supply is in line with earlier results (Nousiainen et al 2004;Røjen et al 2008;Kälber et al 2012) and supports the hypothesis that dairy cows of a moderate milk-type are able to compensate reduced dietary CP concentrations to some degree (Knaus, 2009;Furger et al 2013).…”

“…An important mechanism behind these results was probably lower ruminal ammonia production (Parker et al 1995) and higher urea recycling into the rumen (Røjen et al 2008). Changed rumen fermentation patterns were also indicated by the increased proportions of branched- and odd-chain FA (OBCFA) in the milk fat of group Prot− compared with Prot+, because these FA are to a large proportion of rumen microbial origin (Fievez et al 2012).…”

Propionate Affects Insulin Signaling and Progesterone Profiles in Dairy Heifers

“…Peter and Elliot (1984) demonstrated rapid propionate clearance upon delivering an IV dose to Holstein cows 20 . Previous work evaluating hepatic SCFA clearance has demonstrated variation in and ability to adapt clearance capacity 21 – 23 . This metabolic shift to utilize extra available propionate gives merit to the hypothesis that increased propionate status affects downstream processes.…”

Effect of abomasal glucose infusion on splanchnic amino acid metabolism in periparturient dairy cows

“…The ammonia concentration in whole blood was set equal to the plasma concentration, whereas the whole blood concentration of urea was obtained by dividing the plasma concentration by 1.09 (Røjen et al, 2008). The whole blood concentrations of VFA were obtained from plasma concentrations by correcting for a 45% dilution space in erythrocytes (Kristensen, 2000).…”