EFFECTS OF WORK AND DIET ON PROGESTERONE SECRETION, SHORT LUTEAL PHASES AND OVULATIONS WITHOUT ESTRUS IN POSTPARTUM F(1) CROSSBRED DAIRY-COWS

The effects of work and diet supplementation on progesterone secretion and on incidence of short luteal phases and ovulations without estrus was investigated in 40 postpartum F1 crossbred dairy cows. These cows were allocated to 1 of 4 treatment groups: Group SPNW, supplement-non working; Group SPW, supplement-working; Group NSNW, nonsupplement-nonw orking; and Group NSW, nonsupplement-working. After calving, working c ows pulled sledges with a load of 300 to 450 Newtons(N); 4 hours per d ay 4 days per week, for a total of 100 days over a 1-year period. All cows were fed natural grass hay ad libitum while the supplemented cows were fed 3 kg of concentrate per head per day. The proportion of cows which showed behavioral estrus by 1 year post partum was 100, 100, 60 . and 20% for Group SPNW, SPW, NSNW and NSW cows, respectively. Based on plasma progesterone concentrations, ovulation started 62 days earli er than onset of behavioral estrus. A total of 73 ovulations occurred by 1 year post partum. Forty-nine (67.1%) and 26 (32.9%) ovulations oc curred in the supplemented and nonsupplemented cows while 33 (45.2%) a nd 40 (54.8%) ovulations occurred in the working and nonworking cows, respectively. Of the total ovulations, 26 (35.6%) were not associated with behavioral signs of estrus and occurred in 13 (32.5%) cows. The i ncidence of ovulation without estrus was higher (P<0.05) in working (4 2.4%) than in nonworking (30%) cows and in nonsupplemented (41.7%) tha n in supplemented (32.7%) cows. Short luteal phases occurred in 32.5% of the cows before the establishment of normal estrous cycles. In work ing cows, diet supplementation off-set the negative effect of work on the onset of estrus and conception. However, a relatively higher numbe r of cows in Group SPW had ovulations without estrus before a normal e strous cycle was established. The incidence of short luteal phases or ovulations without estrus did not influence the pregnancy rate in subs equent normal estrus periods. In conclusion, in the supplemented cows, work did not influence the proportion of cows showing estrus and conc eiving, but it significantly delayed the postpartum anestrus interval. In the nonsupplemented cows, reproductive activity was impaired in bo th working and nonworking cows, but was pronounced in working cows. Ho wever, once pregnancy was established there was no effect of work on t he maintenance of pregnancy. Our study shows that with appropriate fee ding regimens lactating crossbred cows could be used for draught purpo ses without any detrimental effects on fertility, but calving interval s would be extended. Finally, the physiological mechanisms involved in anestrus and ovulations without estrus and the significance of such p henomena in affecting postpartum reproductive performance and fertilit y in working cows require further investigation.