Search

The effect of a biosynthetic bacterial 6-phytase (PhyG) on the digestibility and excretion of crude protein (CP), phosphorus (P), and phytate-P (PP) in midlactating dairy cows was investigated. Thirty Holstein-Friesians were assigned to three treatments with 10 cows per treatment in a randomized block design. Cows were fed forage (grass and corn silage) provided ad libitum, and a concentrate (without added inorganic phosphate) administered separately in amounts individualized per cow according to milk production, supplemented with phytase according to treatment. The formulated forage-to-concentrate-ratio was ~65%:35%. Dietary treatments comprised the control diet (CON) and CON supplemented with 2,000 (PhyG2,000) or 5,000 (PhyG5,000) phytase units (FTU)/kg DM in the total diet. The experiment comprised an 18-d preperiod for the collection of data to facilitate the allocation of cows to the treatments, followed by a 19-d experimental period comprising a 14-d diet adaptation period and 5 d of twice daily feces collection. Fecal samples were analyzed for the determination of apparent total tract digestibility (ATTD) of chemical constituents in the diet. The ATTD of PP was 92.6% in CON suggesting a high but incomplete degradation of phytate by ruminal microbial phytases. Cows fed PhyG2,000 exhibited increased ATTD of CP and PP [68.4% (2.7% points above CON) and 95.1% (2.5% points above CON), respectively] whilst PhyG5,000 further increased ATTD PP and also increased ATTD P [54.1% (7.8% points above CON)]; ATTD of Ca tended to be increased in PhyG5,000 vs. CON. Linear dose-response relationships were observed for ATTD of DM, CP, P, Ca, and PP. In addition, fecal excretion of P, and PP linearly reduced and that of Ca and CP tended to linearly reduce with increasing PhyG dose level. No difference was observed for DM intake and milk composition was unaffected except for milk protein which tended to be higher in cows fed PhyG5,000 than CON. In summary, the addition of exogenous phytase at 2,000 FTU/kg or higher to diets of lactating dairy cows improved P, PP, Ca, and CP digestibility and reduced fecal excretion of P, PP, and CP in a dose-dependent manner., (© The Author(s) 2023. Published by Oxford University Press on behalf of the American Society of Animal Science.)

The aim of the present study was to study the effect of exogenous amylase on postruminal disappearance of increasing amounts of corn starch being infused into the abomasum of heifers, and to detect a possible limitation of starch digestion in the small intestine. Four rumen-fistulated heifers (2 German Black Pied and 2 Jersey × German Black Pied) with an initial BW of 565 ± 6 kg were fed 5.6 kg DM/d of a diet targeted to contain only a negligible amount of starch. Animals were assigned randomly to a crossover trial with 2 experimental periods lasting 35 d each with 10 d of diet adaption followed by 25 d of sample collection. During the sampling period, each animal was abomasally infused with native corn starch at 5 levels (953, 1,213, 1,425, 1,733, and 1,993 g DM/d) each for a 5-d period with and without exogenous amylase, respectively. At days 6 to 10 the heifers received an abomasal infusion of starch in amounts of 724 g/d. Feces were sampled 4 times a day during the collection periods. Titanium dioxide was ruminally administered (10 g/d) to estimate fecal excretion. Purine bases in feces were determined and used as a marker for microbial N excretion. Fecal excretion of microbial N increased linearly with increasing level of starch infusion (P < 0.001), indicating a constant proportion of the infused starch being fermented in the hindgut. In contrast, the apparent digestibility of starch from the total postruminal tract decreased linearly from 90% to 80% (P < 0.001) when the intestinal starch supply increased from 1 to 2 kg/d. There is strong evidence based on the increasing starch excretion with feces and the indication of a constant proportion of infused starch being fermented in the hindgut for a decreasing efficiency of starch digestion in the small intestine with increasing intestinal supply. Amylase administration increased fecal excretion of butyrate (P = 0.04) and tended to increase isovalerate excretion (P = 0.06). However, amylase did not affect fecal excretion of microbial N or starch, suggesting that pancreatic amylase activity may not be the primarily limiting factor of postruminal starch digestion in heifers when corn starch is abomasally infused in amounts up to 2 kg/d., (© The Author(s) 2019. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The effect of an exogenous amylase on postruminal digestion of starch infused into the abomasum of cattle was studied. Four rumen-cannulated heifers were fed 5.5 kg DM/d of a diet without starch, and assigned randomly to a crossover design. The experiment consisted of 2 periods lasting 23 d each with 10 d for adaptation to the diet followed by 13 d of abomasal infusion and sample collection. During the first 3 d of each infusion phase, isotonic saline solution was infused (1 liter/h) for measurement of baseline values in feces, followed by daily infusions of 880 g DM corn starch (1 kg/10 liters of water) without or with the addition of 2% of amylase. Titanium dioxide (10 g/d) was ruminally administered for estimation of fecal excretion. Digestion of starch in small intestine was calculated as the difference between the amounts of infused starch, disappeared from hindgut and fecal excretion. The apparent disappearance of starch from the hindgut was estimated based on the increment of microbial nitrogen (N) excretion due to starch infusion (1 g microbial N/100 g fermented starch) compared to baseline values. The concentration of purine bases in feces was used to estimate excretion of microbial N. Microbial N excretion increased with starch infusion (P < 0.05) but was not influenced by amylase (P = 0.81). Starch disappearance from the small intestine was not improved by amylase (P = 0.78) and averaged 85%. Amylase affected neither blood concentration of glucose (P = 0.80) nor of insulin (P = 0.26), but glucagon was lower without (P < 0.0001) than with amylase. The infusion of starch increased fecal excretion of total VFA (acetate, propionate, and butyrate) by 53% (P < 0.05), which indicates increased carbohydrate fermentation in the hindgut and incomplete digestion of starch in the small intestine. However, the excretion of total VFA was not affected by amylase (P = 0.66). Lactate excretion was higher at the second day of starch infusion (P < 0.05) without than with amylase, which suggests lower flow of starch from the small intestine to the hindgut due to a possible effect of amylase addition in animals not adapted to starch digestion. However, lactate excretion returned near to baseline values within 2 d, which was probably due to increase of lactate-utilizing bacteria and the adaptation of the microbial population in the hindgut. Further studies with higher starch levels and addition of amylase are recommended.