Glucose and urea kinetics in cows in early lactation

Abstract

I . Four mature Friesian cows were used. For 2 weeks after calving they were fed 3 kg hay (147 g crude protein (nitrogenx 6.25; CP)/kg dry matter (DM)) plus g kg concentrates (177 g CP/kg DM) per d and thereafter 4 kg hay plus 12 kg concentrates/d.2. At approximately the 2nd, 4th and 9th weeks post-partum each cow was given a single intravenous dose of ["Clurea (I mCi) and [baH]glucose (1.5 mCi). Following this, jugular venous blood samples were withdrawn up to 26 h post-injection.3. The log (specific activity) Y. time curves were not linear for either metabolite. Glucose irreversible loss rates (IRL) were calculated by a stochastic procedure. The linear part of the urea log (specific activity) Y. time curve gave the same estimate for urea IRL rate as a stochastic method of calculation, but urea pool sizes were overestimated so that stochastic analysis of results was preferred.4. Mean milk yields at the time of the three measurements were 27.1, 30.8 and 27.9 kg milk/d. 5.Urea IRL was significantly lower (P < 0.05) in the first 4 weeks of lactation than in the gth, and blood urea concentration was lower (P < 005) in the 4th than in the 2nd and 9th week, but there was no close correlation between urea IRL and concentration.6. Glucose IRL rose (P < 005) between the 2nd and 9th weeks post-partum. perhaps due to the increase in feed intake. The results were generally consistent with the relationship between milk yield and glucose IRL established by Paterson & Linzell(1974).7. Urea IRL (y) and milk protein-N (x) production values were used to calculate the dficiency of protein utilization (EPU) as x+(x+o35 y). This assumes that 035 of urea IRL was due to protein catabolism.EPU was found to be 059-0.80 (mean 0.69).8. The possible contribution of catabolized amino acids to glucose IRL was calculated by assuming that 035 of urea IRL was due to protein catabolism and 0 2 of catabolized protein-(= passed through the glucose pool. On this basis the contribution of protein4 to glucosec was < 25 g/kg glucose IRL.Quantitative aspects of protein metabolism in dairy cows have come under close scrutiny with the publication, recently, of revised systems for defining protein requirements for ruminants (Roy et al. 1977). Application of these systems to dairy cows is limited by a general lack of reliable quantitative information on metabolic processes in cows. In particular there are no published values for direct measurements of the net transfer into milk protein of amino acids absorbed from the gut, although this is a critical factor in the new proposals. Oldham (1978) called this factor the efficiency of protein utilization (EPU) and suggested that it might be measured by quantifying the partition of amino acid-N supplied to the tissues between milk-protein N and amino acid-N oxidized to form urea. This paper presents the results of studies we have carried out using this technique.Because of the particularly high glucose demand of the high-yielding cow, and the need to synthesize a large proportion of this glucose via gluconeogeni...

The effect of prepartum protein feeding on postpartum lactation performance of Ayrshire heifers and cows

“…Urea-N production attributes to includes both absorbed amino acids and those coming from protein catabolism and was assumed to be 35% of the urea-N production in dairy cows during early lactation (Bruckental et al, 1980). In the present study, though the milk urea concentration of both groups was within the recommended range of Finnish Dairies, the higher level for TH clearly reflects the abundance of rumen degradable nitrogen.…”

Influence of source and amount of dietary protein on performance, blood metabolites, and reproductive function of primiparous beef cows2

“…Glucose is an essential precursor for lactose synthesis by the mammary gland (Linzell and Peaker, 1971). Synthesis of lactose has been estimated to account for 46 to 57%' of irreversible glucose losses in lactating animals (Bruckental et al, 1980). The cows fed the highescape sources may have been shunting glucose from the bloodstream into the mammary gland for lactose synthesis.…”

Revue bibliographique : Variations quantitatives et métabolisme des lipides dans les tissus adipeux et le foie au cours du cycle gestation-lactation 2e partie : chez la brebis et la vache

“…Les réductions de l'insulinémie et de la glycémie en début de lactation contribuent probablement à l'augmentation de la néoglucogenèse hépatique (Bassett, 1978 ;Brockman, 1978 ;Baird, 1981) et à la diminution du prélèvement et de l'oxydation du glucose par les tissus extra-mammaires (Kronfeld et Raggi, 1964 ;Benninck et al, 1972 ;Bruckental et al, 1980 ;Thilsted, 1985a). Par contre, le prélèvement mammaire n'est pas affecté car il est moins dépendant de l'insuline (Hove, 1978b ;Bauman et al, 1973 ;Laarveld et al, 1981) et de la glycémie, lorsqu'elle reste supérieure à environ 0,4 g/1 (Kronfeld et al, 1963 ;Rook, 1979 ;Baldwin et al, 1980).…”