Evaluation of the utilization of dietary nitrogen by dairy cows based on urea concentration in milk.

The objective of this study was to determine whether milk urea concentration is a valuable tool to monitor the utilization of dietary N by dairy cows. Data from 11 feed trials (n = 2828 observations of 356 cows) were used in this study. Dietary protein utilization was evaluated according to the Dutch DVE-OEB system. A close correlation (0.8) was found between rumen-degraded protein balance in the ration and urea concentration in milk. The effects of the balance of true protein digested in the small intestine and net energy on milk urea concentration were small but significant. Parity and stage of lactation did not significantly influence milk urea concentration. Because of the large variation among and within cows, the monitoring of protein utilization of an individual cow was inaccurate. However, milk urea concentration in bulk milk is a valuable tool to monitor the rumendegraded protein balance in the ration.

Estimation of variance components for somatic cell counts to determine thresholds for uninfected quarters.

The objective of this study was to determine the factors affecting somatic cell count (SCC), to estimate variance components of these factors, and to calculate and evaluate the thresholds for intramammary infection based on SCC. The infection status from 22,467 quarter milk samples from 544 cows in seven herds was determined. Infections status was the most important factor affecting SCC. The increase in SCC was more pronounced for major pathogens than for minor pathogens. Even after adjustment for infection status, the interaction between stage of lactation and parity was significant. For culture-negative samples within a lactation, the shape of the SCC curve was inversely related to the shape of the milk production curve. The shape of the SCC curve was flat for first lactation cows compared with the shape of the SCC curve for cows in subsequent lactations. The effect of clinical mastitis on SCC was significant. The use of SCC thresholds for specific parities and stages of lactation to detect intramammary infection improved quality parameters only slightly over a fixed threshold of 200,000 cells/ml.

In vitro enzymatic hydrolysis of protein and protein pattern change of soya and faba beans during germination.

In addition to technological processes like heat treatment, germination can be an alternative process for the improvement of protein quality of legumes. This was demonstrated by enzymatic protein hydrolysis of flour of germinated faba and soya beans, using a pepsin-pancreatin enzyme system. SDS-PAGE was used to study the changes in protein pattern of these legumes during germination. In addition, the effect of germination on the content of condensed tannins in flour from germinated faba beans and trypsin inhibitors in flour from germinated soya beans were studied. Germination for five days resulted in a maximum increase in enzymatic protein hydrolysis by 21.3% in flour from faba beans and by 25.7% in flour from soya beans after 12 hours of germination. Protein patterns, obtained with SDS-PAGE demonstrated a considerable protein breakdown during germination between day 2 and 3 in faba beans and between day 1 and 2 in soya beans. The tannin content in flour from faba beans decreased by 29.7% after seven days of germination, but the tannin content of the hulls of the faba beans did not change during that period of germination. The trypsin inhibitors in flour from soya beans decreased by 25.5% after seven days of germination. We conclude that the increased enzymatic hydrolysis of protein in both legumes cannot be explained by a decrease of tannins or trypsin inhibitors. The possible explanation is that through degradation of proteins during germination of the legumes, the cleaved protein fragments are more susceptible for hydrolysis by pepsin-pancreatin.