Effect of different levels of casein, with or without formaldehyde treatment, on carbohydrate metabolism between mouth and duodenum of steers

Rumen fluid metabolomics of beef steers differing in feed efficiency

INTRODUCTION

Beef is the most consumed red meat in the United States, and the US is the largest producer and consumer of beef cattle globally. Feed is one of the largest input costs for the beef cattle industry, accounting for 40-60% of the total input costs. Identifying methods for improving feed efficiency in beef cattle herds could result in decreased cost to both producers and consumers, as well as increased animal protein available for global consumption.

METHODS

In this study, rumen fluid was collected from low- (n = 14) and high-RFI (n = 15) steers. Rumen fluid was filtered through a 0.22 µM syringe filter, extracted using 0.1% formic acid in acetonitrile:water:methanol (2:2:1) and injected into the Dionex UltiMate 3000 UHPLC system with an Exactive Plus Orbitrap MS. Peaks were identified using MAVEN and analyzed using MetaboAnalyst 4.0 and SAS. Significance was determined using an α ≤ 0.05.

RESULTS

Eight metabolites were greater in low-RFI steers compared to high-RFI steers, including 3,4-dihydroxyphenylacetate, 4-pyridoxate, citraconate, hypoxanthine, succinate/methylmalonate, thymine, uracil, and xylose (P ≤ 0.05). These metabolites were predominantly involved in amino acid and lipid metabolism.

CONCLUSIONS

Rumen fluid metabolomes differ in steers of varying feed efficiencies. These metabolites may be used as biomarkers of feed efficiency, and may provide insight as to factors contributing to differences in feed efficiency that may be exploited to improve feed efficiency in beef cattle herds.

Factors influencing the digestion of dietary carbohydrates between the mouth and abomasum of steers

Six protozoa-free steers with simple rumen and abomasal cannulas were given basal diets consisting of a concentrate mixture of flaked maize and tapioca with either barley straw (BS) or alkali-treated barley straw (BSA). Other diets used were supplemented with urea (BSU and BSAU respectively) or contained fish meal in place of tapioca BSF and BSAF respectively). The diets were given in a 6 X 6 Latin square design. Diets were isoenergetic and provided sufficient metabolizable energy (ME) to support a growth rate of approximately 0.5 kg/d. Basal diets, urea- and fish-meal-supplemented diets had estimated rumen-degradable nitrogen (RDN):ME values (g/MJ) of 0.5, 1.2 and 0.8 respectively. 103Ruthenium and polyethylene glycol were given as flow markers, and flows (g/24 h) at the abomasum of organic matter (OM) and carbohydrate components were calculated. True digestibility coefficients of OM between mouth and abomasum were significantly greater for diets containing alkali-treated straw (approximately 0.63) than for those containing untreated straw (approximately 0.55) but were not significantly affected by N supplementation. Digestibility coefficients of the neutral-sugar components of dietary polysaccharides between mouth and abomasum were 0.28, 0.34, 0.31, 0.23, 0.31 and 0.87 for mannose, galactose arabinose, xylose, cellulose-glucose and starch-glucose respectively for diet BS. Corresponding values were 0.37, 0.42, 0.56, 0.51, 0.40 and 0.88 for diet BSA. All but the mannose and starch-glucose values were significantly greater for the latter diet. N supplementation also led to increases in digestibility of all neutral sugars except mannose and starch-glucose. Fish meal produced a markedly greater effect than urea but only significantly so for cellulose-glucose. Thus, the highest digestibilities were seen for diet BSAF and were 0.68, 0.67, 0.74 and 0.64 for galactose, arabinose, xylose and cellulose-glucose respectively. Of all these sugars xylose consistently showed the greatest response in digestibility to sodium hydroxide treatment or N supplementation.

Effects of level of dietary intake and physical form of protein supplement on the digestibilities of different dietary carbohydrates between mouth and abomasum of young steers

Steers fitted with simple rumen and abomasal cannulas were given isoenergetic diets of rolled barley and chopped straw, pelleted together with some tapioca alone (B) or with some tapioca replaced by coarse soyabean meal (M) or finely ground soyabean flour (F). The diets were given at two levels to support 0.5 (L) and 1.0 (H) kg/d live weight gain. Chromic oxide and PEG were given as digesta flow markers. Mouth to abomasum digestibilities of different dietary sugars at the low level of intake (LB) were 0.65, 0.68, 0.59, 0.56 and 0.94 for arabinose, galactose, xylose, cellulose-glucose and starch-glucose respectively. Corresponding values at the higher level of intake (HB) were 0.55, 0.66, 0.55, 0.44 and 0.93 respectively. Supplementation with either soya bean meal or flour had no significant effects on the mouth to abomasum of dietary carbohydrate digestibilities at either level of feeding.