EFFECT OF DIETARY-LIPID SUPPLEMENTATION ON PROGESTERONE CONCENTRATIONAND REPRODUCTIVE-PERFORMANCE IN SUCKLED BEEF-COWS

Using whole cottonseed as a lipid source, silage-based diets that were isocaloric and isonitrogenous yet varied in lipid level were fed to m ultiparous cows. In Experiment 1, 48 cows (n = 12 per treatment) were allotted to 1 of 4 treatments where diets were formulated to supply 3. 9, 4.3, 5.3 and 6.3% of total lipid. In Experiment 2, 66 cows (n = 22 per treatment) were allotted to 1 of 3 treatments where diets were for mulated to supply 3.1, 5.5 and 8.3% of total lipid. Length of the firs t ovarian cycle, length of the first normal estrous cycle, postpartum intervals to onset of ovarian luteal activity and to first estrus were not affected by diet (P>0.10) in either experiment. Mean progesterone (P-4) concentrations for first normal estrous cycles were not differe nt (P>0.10) in either experiment. Anestrous periods were divided into 3 phases for analyses: Phase I) parturition to onset of ovarian luteal activity, Phase II) first ovarian luteal activity and Phase III) firs t normal estrous cycle. No differences were observed in P-4 concentrat ions during any phase of the postpartum period. In conclusion, isocalo ric and isonitrogenous diets with increasing levels of lipid had no ef fect on reproductive performance in suckled beef in these experiments.