EVALUATION OF THE REPRODUCTIVE EFFICIENCY OF SIMMENTAL AND FRIESIAN DAIRY-COWS FARMED IN FRIULI (NORTHEAST ITALY) BY THE ANALYSIS OF PROGESTERONE LEVELS

The present research was conducted 1) to investigate the usefulness of progesterone profiles for the study of reproductive efficiency, 2) to identify new reproductive indexes and 3) to examine the possibility o f modelling changes in the biological status of animals. Two groups of dairy cows were chosen for this investigation: Italian Simmental and Italian Friesian cows. Milk samples were taken from each cow every 3 t o 4 d between Day 10 and Day 240 after calving, and whey progesterone was determined by RIA. The cows were classified into the following 4 c ategories on the basis of their luteinic activity: 1) Acyclic cows wit h P4 values <100 pg/ml; 2) Cyclic cows with a normal cycle (1 or 2 sam ples <100 pg/ml, followed by 1 sample greater than or equal to 120 pg/ ml, followed by at least 3 samples greater than or equal to 200 pg/ml, followed by 1 sample <100 pg/ml) or a short cycle (1 or 2 samples <10 0 pg/ml, followed by 1 sample greater than or equal to 120 pg/ml, foll owed by 2 samples greater than or equal to 200 pg/ml, followed by 1 sa mple <100 pg/ml followed by a normal cycle); 3) pregnant cows with P4 values >120 pg/ml at 21 to 24 d from AI; and 4) cows with atypical lut einic activity and P4 values >120 pg/ml in a single sample. Analysis o f the P4 frequency distribution indicated that ovarian activity resume d from Day 15 and Day 18 after calving in the Italian Friesian and Ita lian Simmental cows, respectively, and the highest percentage of cycli c cows was observed on Day 60 for Italian Friesian cows (45%) and Day 70 for Italian Simmental cows (55%). The acyclic phase was considered to be concluded by Day 164 and Day 120 for Italian Friesian and Italia n Simmental cows, respectively. By Day 240, 66% of Italian Friesian co ws and 79% of Italian Simmental cows were pregnant. The percentage of cows with atypical luteinic activity was almost constant throughout th e experiment (Italian Friesian=5 to 10%, Italian Simmental=10 to 15%). The calving-conception interval was 104 d for Italian Friesian cows a nd 94 d for Italian Simmental cows. In both groups, the area on the P4 frequency diagram representing the acyclic cows was not very differen t from that representing the cyclic cows, while the area occupied on t he diagram by pregnant animals was larger. These results are derived f rom an accurate mathematical analysis. The average number of times in the acyclic status for both groups of cows was about 3-fold smaller th an the average number in the cyclic status.