Portal Drained Visceral Flux, Hepatic Metabolism, and Mammary Uptake of Free and Peptide-Bound Amino Acids and Milk Amino Acid Output in Dairy Cows Fed Diets Containing Corn Grain Steam Flaked at 360 or Steam Rolled at 490 g/L

Abstract

Objectives were to measure net fluxes of free (FAA) and peptide bound amino acids (AA) (PBAA) across portal-drained viscera (PDV), liver, splanchnic, and mammary tissues, and of milk AA output of lactating Holstein cows (n = 6, 109 +/- 9 d in milk) as influenced by flaking density of corn grain. Cows were fed alfalfa-based total mixed ration (TMR) containing 40% steam-flaked (SFC) or steam-rolled corn (SRC) grain. The TMR were offered at 12-h intervals in a crossover design. Six sets of blood samples were obtained from indwelling catheters in portal, hepatic, and mammary veins and mesenteric or costoabdominal arteries every 2 h from each cow and diet. Intake of dry matter (18.4 +/- 0.4 kg/d), N, and net energy for lactation were not altered by corn processing. Milk and milk crude protein yields (kg/12-h sampling) were 14.2 vs. 13.5 and 0.43 vs. 0.39 for cows fed SFC or SRC, respectively. The PDV flux of total essential FAA was greater (571.2 vs. 366.4 g/12 h, SEM 51.4) in cows fed SFC. The PDV flux of total essential PBAA was 69.3 +/- 10.8 and 51.5 +/- 13.2 g/12 h for cows fed SFC and SRC, respectively, and differed from zero, but fluxes of individual PBAA rarely differed between treatments. Liver flux of essential FAA was greater in cows fed SRC, but only the PBAA flux in cows fed SRC differed from zero. Splanchnic flux of FAA and PBAA followed the pattern of PDV flux, but variation was greater. Mammary uptake (g/12 h) of total essential FAA was greater in cows fed SFC than SRC (224.6 vs. 198.3, SEM 7.03). Mammary uptake of essential PBAA was 25.0 vs. 15.1, SEM 5.2, g/12 h for cows fed SFC or SRC, respectively, and differed from zero in half of the PBAA. Milk output of EAA was 187.8 vs 175.4, SEM 4.4 g/12 h in cows fed SFC and SRC, respectively, and output of most essential AA consistently tended to be greater in cows fed SFC. It is apparent that PBAA comprise a portion of total AA flux across PDV and are affected by grain processing. Further, this pool supplies an important component of AA taken up by the mammary gland. Quantifying the contribution of PBAA may improve diet formulation with respect to intestinal absorption and mammary uptake of AA.

Protein turnover—what does it mean for animal production?

“…Thus, post-hepatic supply and mammary gland total use were again balanced. Nonetheless, under AA-limiting situations, supply to the mammary gland of leucine (Bequette et al1996a) or lysine (Guinard and Rulquin 1994;Metcalf et al 1996;Tagari et al 2000;Thieverge et al 2002) can become similar to net milk protein needs. Thus, use of these AA by the mammary gland is variable, even when milk output is unchanged, and yet post-hepatic supply matches these needs.…”

The growth performance and meat quality of goats fed diets based on maize or wheat grain

“…The portal-drained viscera (PDV) net fluxes of total free amino acids, glycine, isoleucine, leucine, phenylalanine, proline, serine, threonine, tryptophan and valine were greater in cows fed steam-flaked maize than those of cows fed steam-rolled maize (Tagari et al, 2004). The differences in PDV net fluxes of amino acids of diets based on the various starch sources may be one of main reasons for the differences in wholebody nitrogen metabolism and milk yield and composition in ruminants.…”

Net nutrient flux in visceral tissues of goats fed diets based on maize or wheat

“…In the present study, the difference in RDP between maize and wheat diets was far less than the difference in starch degradation in the rumen, the release of carbohydrate was therefore likely to be more synchronous to RDP in maize diet compared with wheat diet, and the difference in synchronization of fermentable carbohydrate and RDP between wheat and maize diets might further result in the difference in the yield of ruminal microbial protein and influence the net PDV flux of AA. Tagari et al (2004) also reported the difference in starch degradation rate of diet in the rumen of cows caused by different processing technique for maize had significant effects on the net PDV flux of free and peptide bound AAs, especially EAA of free AAs.…”

“…Complicated interrelationships between starch and protein affected ruminal fermentation products (Ørskov, 1975), microbial synthesis (Hoover and Stokes, 1991), whole-body nitrogen (N) metabolism, and milk yield and composition in ruminants (Khan et al, 2007). Tagari et al (2004) reported that portal-drained viscera (PDV) net fluxes of total free amino acid, glycine, isoleucine, leucine, phenylalanine, proline, serine, threonine, tryptophan and valine were greater in cows fed steam-flaked maize than that of cows fed steam-rolled maize.…”