Does calcium propionate elicit similar growth and reproductive responses as monensin in developing heifers?

Abstract

Replacement beef heifer development is critical for the continued production of beef and for ranch success. Objectives of this research were to investigate the growth and reproductive responses of developing heifers fed similar basal diets supplemented with pellets containing different feed additives. Pellet treatments consisted of 2.27 kg x heifer -1 x d -1 of: 1) control with no feed-additive (CON), 2) 200 mg x heifer -1 x d -1 monensin (MON), or 3) 40 g x heifer -1 x d -1 calcium propionate (PRO). Experiment 1 utilized one hundred and ninety-eight heifers (254 + or = 3.8 kg) stratified by BW and randomly assigned to one of six pens (n = 2 pens per treatment). Experiment 2 utilized fifty-eight heifers (304 + or = 3.4 kg) stratified by BW and randomly assigned to one of 12 pens (4 pens per treatment). Heifers were fed a grass hay basal diet in both experiments (Exp. 1: 65% TDN and 11% CP; Exp. 2: 62% TDN and 15% CP, DM basis). Experiment 1 was 129 d and Experiment 2 was 122 d. Body weights were collected at the beginning and end of each experiment, with interim BW collected every 30 d. Serum samples were collected via coccygeal venipuncture and analyzed for progesterone to determine pubertal status. Overall pregnancy rates and pregnancy rate from AI were determined. Experiment 1 observed no differences for initial BW, final BW, overall ADG, pregnancy rate from AI, or overall pregnancy rate (P > or = 0.16). Fewer CON and PRO heifers were pubertal at experiment start than MON heifers (P < or = 0.01) in Experiment 1, which was unexpected. Differences in puberty achievement were diminished at the end of the experiment. Experiment 2 observed no differences for initial BW, final BW, overall ADG, pregnancy rate from AI, or overall pregnancy rate (P > or = 0.19). Treatment had no effect on puberty achievement at beginning or end of experiment (P > or = 0.09). A period effect was observed for ADG in both experiments (P < or = 0.01) which may be related to cold stress. Neither calcium propionate nor monensin resulted in improved performance compared to no feed additive. Further research is warranted to elucidate the impact of calcium propionate on heifer development.