Growth of yearling fillies fed alfalfa or soybean meal

Abstract

Sixteen Quarter Horse yearling fillies were used in a 112-d randomized, block experiment to determine the efficacy of alfalfa hay protein to support growth in young horses. The yearlings were paired according to weight and age then randomly allotted to each diet. Group I was fed a diet of coastal bermudagrass hay and concentrate supplemented with soybean meal such that their total diet contained 13% CP. Group 2 was fed a diet of alfalfa hay and a similar concentrate without soybean meal so that their total diet also contained 13% CP. Intakes between pairs were equalized and fed at 60:40 grain-to-hay ratios. Physical measurements and rump fat were collected every 28 d. Radiographs of the left Mc3 were taken on d 0 and d II 2. Blood samples were taken every 14 d to determine blood urea nitrogen, Ca, P and osteocalcin. Calcium, P and nitrogen balances were determined during the last 4 d of the trial. Average feed intake was 6.2 kg/d/filly for both diets. Average energy digestibilities, Ca and P absorptions as percent of intake, daily gains and all RBAE values were not affected (P>0.05) by diet. The SBM-supplemented fillies gained more forearm and heart girth circumference and more rump fat (P<0.05). than did the ALF-fed fillies. The ALF-fed fillies had higher (P<0.05) mean serum osteocalcin concentrations on d 0, 70, 84; however, normalized concentrations indicated that osteocalcin in the SBM-fed fillies went up or remained at zero, while concentrations in the ALF-fed fillies dropped and remained below zero throughout the trial. Blood urea nitrogen concentrations were higher in the ALF-fed fillies on d 70 (P<0.05) and d 84 (P<O. 1). but normalized for the entire trial. Results indicated a moderate rate of growth by both groups, with physical measures being inconclusive in regard to the use of either protein source; however, growth differences may occur at the tissue level when physical measures are not affected. Whether these observations would be applicable to horses growing at a faster rate is not clear.