Information about constituents of milk and visual alterations can be used for management support in improving mastitis detection, monitoring fertility and reproduction, and adapting individual diets. Numerous sensors that gather this information are either currently available or in development. Nevertheless, there is still a need to adapt these sensors to special requirements of on-farm utilization such as robustness, calibration and maintenance, costs, operating cycle duration, and high sensitivity and specificity. This paper provides an overview of available sensors, ongoing research, and areas of application for analysis of milk constituents. Currently, the recognition of abnormal milk and the control of udder health is achieved mainly by recording electrical conductivity and changes in milk color. Further indicators of inflammation were recently investigated either to satisfy the high specificity necessary for automatic separation of milk or to create reliable alarm lists. Likewise, milk composition, especially fat:protein ratio, milk urea nitrogen content, and concentration of ketone bodies, provides suitable information about energy and protein supply, roughage fraction in the diet, and metabolic imbalances in dairy cows. In this regard, future prospects are to use frequent on-farm measurements of milk constituents for short-term automatic nutritional management. Finally, measuring progesterone concentration in milk helps farmers detect ovulation, pregnancy, and infertility. Monitoring systems for on-farm or on-line analysis of milk composition are mostly based on infrared spectroscopy, optical methods, biosensors, or sensor arrays. Their calibration and maintenance requirements have to be checked thoroughly before they can be regularly implemented on dairy farms.

SUMMARYFour lactating Friesian cows with cannulae in the rumen and in the proximal duodenum were subjected to each of four different dietary treatments. Treatments differed with respect to concentration of crude protein, supply of urea nitrogen and frequency of feeding. The rations used consisted of hay, maize silage and concentrates and were offered to the animals according to milk yield.During the last 5 days of each experimental period (5 weeks), ingesta flow at the proximal duodenum was estimated by Cr-EDTA. Samples were taken from the duodenum at 2 h intervals and were analysed for thiamin, total nitrogen and microbial nitrogen. Labelling of microbial N was achieved by continuous infusion of 16N-urea into the rumen.With treatment 2 (26% less N than with treatment 1) thiamin net synthesis in the forestomachs and total thiamin entering the duodenum were significantly reduced whereas treatment 3 (substitution of 26% plant N by urea-N) and treatment 4 (six times instead of twice feeding daily) had no effect on synthesis and flow of thiamin to the small intestines. There were significant linear regressions between flow of microbial N and flow of thiamin to the duodenum and between organic matter digested and flow of thiamin.

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Cattle (n = 995 steers and 757 heifers) were randomly selected from a commercial abattoir (Emporia, KS) to determine the relationships between USDA quality and yield grade characteristics and serum concentrations of leptin, IGF-I, and GH. Animals were randomly selected postexsanguination on the slaughter line on 4 occasions (March, May, August, and January). Blood was collected at exsanguination and transported to the University of Missouri for analysis. Sex and hide color were recorded. Carcass data included HCW, 12th-rib fat thickness, KPH, LM area, and marbling score, which were collected from each carcass approximately 24 h postmortem. Average serum leptin concentrations were greater (P = 0.008) for heifers (11.9 ng/mL) than steers (10.9 ng/mL). Heifers had lighter carcasses (331.9 vs. 352.2 kg, P < 0.001), greater 12th-rib fat measurements (1.3 vs. 1.1 cm, P < 0.001), greater KPH (2.5 vs. 2.4%, P < 0.001), and more marbling (Small(40) vs. Small(10), P < 0.001) than steers. Positive correlations (P < 0.01) existed between leptin concentration and marbling score (r = 0.28), 12th-rib fat depth (r = 0.37), KPH (r = 0.23), and USDA yield grade (r = 0.32). Negative correlations were found between leptin and IGF-I (r = -0.11; P < 0.001) and leptin and GH (r = -0.32; P < 0.001). Negative correlations (P < 0.01) were observed for IGF-I and KPH (r = -0.23) and marbling score (r = -0.20), whereas GH was most highly negatively correlated with KPH (r = -0.23; P < 0.001). Leptin concentration accounted for variation (P < 0.001) in a model separating least squares means across USDA quality grade, separating USDA standard (8.5 ng/mL), select (10.3 ng/mL), low choice (12.2 ng/mL), and upper 2/3 choice/prime (>12.9 ng/mL) carcasses. There was no difference (P = 0.31) observed in leptin concentrations between the upper 2/3 choice and prime carcasses (12.9 and 14.2 ng/mL, respectively). Relationships within endocrine profiles and between endocrine concentrations and carcass quality characteristics may prove to be a useful tool for the prediction of beef carcass composition.

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