PROTEIN FEEDING FOR DAIRY COWS

Khaled  M. HECHEIMI

1. The critical period for a dairy cow regarding the supply of protein is believed to be from calving until peak milk production. Dairy cows are unable to consume sufficient dry matter of food in their early lactation to support maximal milk production. It has been suggested that cows must be fed concentrates to maximize their nutrient concentration at the peak level of milk production to maximize total output. A series of experiments was conducted with the principle objective of investigating the effects of allocating protein supplements to dairy cows at different stages of the lactation.
2. The literature concerning methods of measuring protein value of feed and feeding and its effect on milk yield, milk constituents, live weight and condition score was reviewed.
3. In experiment one a comparison between soyabean meal and fishmeal as a protein supplement was made. There was no significant difference between fishmeal and soyabean meal on milk production or live weight. A supplement of sodium bicarbonate tended to increase dry matter intake.
4. In experiment two a comparison was made between extruded and ground barley fed as a supplement to dairy cows. In one treatment urea was given with extruded barley at a rate of 100g/cow/day. Extrusion of the barley did not affect the milk yield or composition. The inclusion of the urea increased the protein content of the milk.
5. Experiment three was designed to compare feeding a high quality protein supplement according to the predicted requirements of dairy cows with a simplified system based on feeding the UDP at a flat rate to all cows. There was no significant effect of treatment on dry matter intake, mild yield and constituents except for the fat content which were higher for the group fed according to requirements. Body weight change and condition score change were not affected by treatment.
6. Experiment four investigated the response of cows to a fish meal supplement given at different stages of lactation. Supplementation of fishmeal significantly increased dry matter intake. Milk yield and constituents were not significantly affected by the supplementation but it was slightly higher for supplemented cows except fat content, which was significantly higher (p<0.001) for unsupplemented cows.
7. Experiment five was designed to compare supplementing a high quality protein source to lactation cows in an increasing or decreasing pattern of allocation during the first 24 weeks of lactation. Feeding the high UDP supplement at the beginning of lactation has significantly increased dry matter intake, milk yield and constituents, no significant effect has been observed for body weight change and condition score change.
8. The metabolisable protein system was published after these experiments were completed. The results of these were applied to the new system and a comparison was done between the ARC, (1980,1984) and the ARFC, (1993) systems.
9. The findings of the series of experiments are discussed in relation to high quality protein supplementation  strategy and the effect on dry matter intake and milk production.