Relationships of Efficiency to Reproductive Disorders in Danish Milk Production: A Stochastic Frontier Analysis

Relationships of various reproductive disorders and milk production performance of Danish dairy farms were investigated. A stochastic frontier production function was estimated using data collected in 1998 from 514 Danish dairy farms. Measures of farm-level milk production efficiency relative to this production frontier were obtained, and relationships between milk production efficiency and the incidence risk of reproductive disorders were examined. There were moderate positive relationships between milk production efficiency and retained placenta, induction of estrus, uterine infections, ovarian cysts, and induction of birth. Inclusion of reproductive management variables showed that these moderate relationships disappeared, but directions of coefficients for almost all those variables remained the same. Dystocia showed a weak negative correlation with milk production efficiency. Farms that were mainly managed by young farmers had the highest average efficiency scores. The estimated milk losses due to inefficiency averaged 1142, 488, and 256 kg of energy-corrected milk per cow, respectively, for low-, medium-, and high-efficiency herds. It is concluded that the availability of younger cows, which enabled farmers to replace cows with reproductive disorders, contributed to high cow productivity in efficient farms. Thus, a high replacement rate more than compensates for the possible negative effect of reproductive disorders. The use of frontier production and efficiency/ inefficiency functions to analyze herd data may enable dairy advisors to identify inefficient herds and to simulate the effect of alternative management procedures on the individual herd's efficiency.

Milk thistle and indinavir: a randomized controlled pharmacokinetics study and meta-analysis

Objectives: To determine whether ingestion of milk thistle affects the pharmacokinetics of indinavir. Methods: We conducted a three-period, randomized controlled trial with 16 healthy participants. We randomized participants to milk thistle or control. All participants received initial dosing of indinavir, and baseline indinavir levels were obtained (AUC(0-8)) (phase I). The active group were then given 450 mg milk-thistle extract capsules to be taken t.i.d. from day 2 to day 30. The control group received no plant extract. On day 29 and day 30, indinavir dosing and sampling was repeated in both groups as before (phase II). After a wash-out period of 7 days, indinavir dosing and sampling were repeated as before (phase III). Results: All participants completed the trial, but two were excluded from analysis due to protocol violation. There were no significant between-group differences. Active group mean AUC(0-8) indinavir decreased by 4.4% (90% CI, -27.5% to -26%, P=0.78) from phase I to phase II in the active group, and by 17.3% (90% CI, -37.3% to +9%, P=0.25) in phase III. Control group mean AUC(0-8) decreased by 21.5% (90% CI, -43% to +8%, P=0.2) from phase I to phase II and by 38.5% (90% CI, -55.3% to -15.3%, P=0.01) of baseline at phase III. To place our findings in context, milk thistle-oindinavir trials were identified through systematic searches of the literature. A meta-analysis of three milk thistle-indinavir trials revealed a non-significant pooled mean difference of 1% in AUC(0-8) (95% CI, -53% to 55%, P=0.97). Conclusions: Indinavir levels were not reduced significantly in the presence of milk thistle.

Proteomic analysis of k-casein micro-heterogeneity

The proteome of bovine milk is dominated by just six gene products that constitute approximately 95% of milk protein. Nonetheless, over 150 protein spots can be readily detected following two-dimensional electrophoresis of whole milk. Many of these represent isoforms of the major gene products produced through extensive posttranslational modification. Peptide mass fingerprinting of in-gel tryptic digests (using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) in reflectron mode with alpha-cyano-4-hydroxycinnamic acid as the matrix) identified 10 forms of K-casein with isoelectric point (pl) values from 4.47 to 5.81, but could not distinguish between them. MALDI-TOF MS in linear mode, using sinapinic acid as the matrix, revealed a large tryptic peptide (mass > 5990 Da) derived from the C-terminus that contained all the known sites of genetic variance, phosphorylation and glycosylation. Two genetic variants present as singly or doubly phosphorylated forms could be distinguished using mass data alone. Glycoforms containing a single acidic tetrasaccharide were also identified. The differences in electrophoretic mobility of these isoforms were consistent with the addition of the acidic groups. While more extensively glycosylated forms were also observed, substantial loss of N-acetylneuraminic acid from the glycosyl group was evident in the MALDI spectra such that ions corresponding to the intact glycopeptide were not observed and assignment of the glycoforms was not possible. However, by analysing the pl shifts observed on the two-dimensional gels in conjunction with the MS data, the number of N-acetylneuraminic acid residues, and hence the glycoforms present, could be determined.

Milk Proteomics

Milk proteins have been studied continuously for over 50 years. Knowledge of this complex protein system has evolved incrementally in recent decades, largely coinciding with advances in technology. Proteomics and associated technologies have the potential to facilitate further advances in our knowledge of milk proteins. Proteomics allows for the detection, identification and characterization of milk proteins. More importantly, proteomics facilitates the analysis of large numbers of milk proteins simultaneously. In the first part of this review we provide a description of the key techniques used within proteomic methodologies, with an emphasis on their general uses within proteomics. In the second part we summarize recent applications of proteomics to milk proteins and highlight the potential for new and rapid advances in the analysis of milk proteins. In particular, we emphasise the effectiveness of two-dimensional gel electrophoresis in combination with various mass spectrometry techniques for the detailed characterization of milk proteins. (C) 2004 Elsevier Ltd. All rights reserved.

Analysis of O-glycosylation site occupancy in bovine kappa-casein glycoforms separated by two-dimensional gel electrophoresis

The ability of two-dimensional gel electrophoresis (2-DE) to separate glycoproteins was exploited to separate distinct glycoforms of kappa-casein that differed only in the number of O-glycans that were attached. To determine where the glycans were attached, the individual glycoforms were digested in-gel with pepsin and the released glycopeptides were identified from characteristic sugar ions in the tandem mass spectrometry (MS) spectra. The O-glycosylation sites were identified by tandem MS after replacement of the glycans with ammonia/aminoethanethiol. The results showed that glycans were not randomly distributed among the five potential glycosylation sites in kappa-casein. Rather, glycosylation of the monoglycoform could only be detected at a single site, T-152. Similarly the diglycoform appeared to be modified exclusively at T-152 and T-163, while the triglycoform was modified at T-152, T-163 and T-154. While low levels of glycosylation at other sites cannot be excluded the hierarchy of site occupation between glycoforms was clearly evident and argues for an ordered addition of glycans to the protein. Since all five potential O-glycosylation sites can be glycosylated in vivo, it would appear that certain sites remain latent until other sites are occupied. The determination of glycosylation site occupancy in individual glycoforms separated by 2-DE revealed a distinct pattern of in vivo glycosylation that has not been recognized previously.

A sensitive HPLC method for measuring bacterial proteolysis and proteinase activity in UHT milk

A sensitive quantitative reversed-phase HPLC method is described for measuring bacterial proteolysis and proteinase activity in UHT milk. The analysis is performed on a TCA filtrate of the milk. The optimum concentration of TCA was found to be 4%; at lower concentrations, non-precipitated protein blocked the HPLC while higher concentrations yielded lower amounts of peptides. The method showed greater sensitivity and reproducibility than a fluorescamine-based method. Quantification of the HPLC method was achieved by use of an external dipeptide standard or a standard proteinase. (c) 2006 Elsevier Ltd. All rights reserved.