Performance of dairy cows offered isonitrogenous diets containing urea or fishmeal in early and in mid-lactation.

Sixteen Friesian cows were used in Expt 1 to measure the effect of substituting urea-N with fishmeal-N either in early lactation (Part 1) or in mid-lactation (Part 2). In Part 1 (days 15-84 of lactation) the major N constituent of the concentrate was urea (U), urea-N: fishmeal-N in the ratio 2:1 (UF) or 1:2 (FU), or fishmeal (F). In Part 2 (days 84-175 of lactation) only urea (UM) and fishmeal (FM) were used. Replacement of urea-N with fishmeal-N significantly (P less than 0.05) increased yield of milk protein both in early and in mid-lactation. At both stages of lactation the cows were, by calculation, in positive energy balance. In mid-lactation replacement of urea-N by fishmeal-N significantly depressed (P less than 0.001) the concentration of fat in milk. Blood urea concentration decreased with increasing fishmeal inclusion (P less than 0.05) from U to FU. In Expt 2 the diets used in Expt 1, Part 1, were offered at a maintenance level of feeding to non-pregnant, non-lactating heifers in a 4 X 4 Latin square design experiment. Digestibility of dry matter, organic matter and cell-wall constituents increased progressively (P less than 0.05) with the first two increments of fishmeal inclusion. A major effect of replacing urea-N with fishmeal-N was to increase digestible organic matter intake (DOMI) and differences in DOMI between treatments in Expt 1, Part 1, accounted for observed differences in performance.

Effect of teat washing on the bacteriological contamination of milk from cows kept under various housing conditions.

The effect of different methods of teat washing on bacterial contamination and sediment levels of the milk of cows kept under 3 housing conditions was studied. By use of an in line milk sampler and steam sterilized clusters the bacterial contamination from the teats after udder preparation was determined directly. The results show that, even under the same housing conditions and teat washing treatments, considerable variation in bacterial counts and sediment level occurred. Overall, washing with hypochlorite (600 mg/l available Cl) and drying with a paper towel gave total counts that were significantly lower than were obtained with the other 4 treatments. The aerobic spore count, in which thermoduric flora predominated, was greatly reduced by drying the teats, but the inclusion of hypochlorite in the wash water had little effect. Coliform contamination was very low (approximately 1/ml) even where the cows' teats were heavily soiled and were not washed. The sediment levels in the milk again showed wide variation and occasional high values (3 mg/l) were recorded for washed cows. In marked contrast to its effect on the bacteriological results, drying had little effect on reducing the sediment.

Collaborative trial of the direct epifluorescent filter technique (DEFT), a rapid method for counting bacteria in milk.

The direct epifluorescent filter technique (DEFT) is a new rapid method which uses membrane filtration and epifluorescent microscopy for counting in milk. A collaborative trial of the DEFT was conducted between six laboratories. Each laboratory obtained a highly significant relationship between the DEFT count and plate count with a correlation coefficient generally greater than 0.9 but there were significant differences between these relationships. The repeatability of the DEFT, although ca 1.5 times worse than that of the plate count, was of a level acceptable in practice. Reproducibility of the DEFT was ca 3 times that of the plate count. This poor reproducibility was probably mainly due to counting errors. Possible reasons for this and ways of reducing counting errors are discussed.

Studies on digestion and absorption in the intestines of growing pigs. Measurements of the flow of digesta and pH.

1. Thirty-five pigs were fitted with single re-entrant cannulas in either the duodenum, jejunum or ileum. A further twenty-four pigs were used in a conventional digestibility trial. 2. Methods for collecting, sampling and returning digesta were developed. 3. A 'practical-type' diet and two purfied diets were used, fed twice daily. 4. Flow and pH of digesta were measured hourly in the duodenum and jejunum, and every 6 h in the ileum. 5. In the duodenum and jejunum there were clear flow responses to feeding, while such an effect was not found in the ileum where the flow-rate was much lower and more uniform than in the former sites. 6. In the duodenum and jejunum, and within 6 h periods in the ileum, there was considerable variation in the flow-rate between different pigs within each hour but there was less variation in pH. 7. The pattern of flow in the duodenum and jejunum was similar for each of the diets but the total flow and the average pH in 24 h differed significantly between diets. There were more digesta of a lower pH from the 'practical-type' diet than the purified diets. 8. The pH in the duodenum was highest after feeding and decreased with increasing time after feeding. In the jejunum and ileum the pH-varied over a much smaller range than in the duodenum. 9. Collections for 6 h periods appeared to be insufficiently long to predict the values obtained in 24 h collections with reasonable accuracy.