Brief Summary of Minutes of Annual Meeting

Objective 1 To quantify properties of feeds that determine the availability of nutrients critical to milk production. Procedures for study of rumen micro-organisms and processes were elaborated by two groups. MN researchers compared in sacco with in vitro procedures for determination of protein degradation and digestion. OH researchers discussed alterations in continuous in vitro rumen culture systems to enhance the retention of protozoa, new findings on protozoal mass that challenges older data, and issues with fecal analyses in N balance studies. Three groups investigated dietary and microbial protein metabolism. NH researchers extended prior work by VT researchers on urea supplementation, showing that microbial protein flow was increased quadratically with increasing dietary urea. LA and IL researchers presented non-linear predictions of rumen-undegradable protein. A substantial amount of research is being conducted on the use of byproducts in dairy cattle feeding. WI researchers varied dried distillers grains with solubles from 0 to 15% of intake and found that milk and milk protein yields increased while milk fat yield declined. KS researchers presented lactation performance data from cows fed wet corn gluten feed at 35-40% of intake. ND researchers examined the characteristics and feeding of canola and flaxseed. The impact of rumen carbohydrate metabolism was pursued by two groups. WI researchers presented data showing that omasal infusion of pectin resulted in an apparent stimulation of microbial growth in the hindgut, and potentially reduced rumen ammonia levels. The interactions between non-fiber carbohydrates (NFC) and rumen-degradable protein were investigated by USDA researchers. They also conducted experiments to differentiate the effects of different NFC sources. UT researchers continued their research on the enhancement of conjugated linoleic acids (CLA) in milk. Consumer acceptance of high CLA cheese was comparable to that of cheese with lower CLA content. Transition of cows to grazing requires more than 21 days to maximize CLA contents, but after returning to confinement feeding, CLA content decline to baseline within 8 days. These researchers also showed that rumen protection of fatty acids by calcium salts declines as chain length increases, with fatty acids greater than 22 carbons in length are fully dissociated. Objective 2 To quantify metabolic interactions among nutrients that alter synthesis of milk. MD researches presented data on amino acid use by the mesenteric- and portal-drained viscera that showed that use of essential amino acids occurs mostly in the fore-stomachs, pancreas, spleen, and omental fat, not the small intestine. They also presented data on urea recycling and use in the gastrointestinal tract that demonstrated that urea entry is tightly related to plasma urea concentration. Lastly, they showed results on galactose synthesis in mammary that challenges current dogma that all galactose is derived from blood glucose. VT researchers elaborated on amino acid transport in enterocytes in vitro, focusing on the transport of neutral amino acids through the L and A systems. MI researchers demonstrated that less mammary parenchyma at puberty correlates with lower subsequent milk yield in the first lactation. They also gave an update on the status of the gene expression arrays being produced through the National Bovine Functional Genomics Consortium. IA researchers presented further research on liver metabolism, showing a reduction in liver lipid accumulation with glucagon treatment. IN researchers had corroborative data on glucagon action, illustrating that the expression of specific enzymes was up-regulated following hormone treatment or treatment with monensin while others were unchanged. Further investigations from this group have shown that regulation of pyruvate carboxylase occurs by expression of different splice variants. Dietary manipulation of serum glucose, non-esterified fatty acids, and ²-hydroxybutyrate were conducted by SD researchers by feeding glycerol, drenching glycerol, or feeding lactose. Objective 3 To use these quantitative relationships to challenge and refine computer-based nutrition systems for dairy cattle. WA researchers utilized several data sets to demonstrate that understanding of adipose tissue metabolism as captured in the equations in the Molly model are correct. Thus, excess body weight gain in model is due to excess absorption of nutrients and incorrect estimates of basal energy use. Correction of energy use in viscera using observations of OH researchers (Reynolds et al.) provides partial improvement. The LOL researcher presented an update on the rumen model, identifying gaps in existing knowledge and understanding. CA researchers discussed the concept and use non-integral values for conversion of NADH and FADH to ATP. Implementing this concept resulted in dramatic changes in several metabolic functions including weight gain. Further discussion involved whether the original estimates were self-correcting.