LAUSR

Summer stocker calves grazing perennial warm-season grasses may benefit from protein supplementation due to the low protein content typically observed in these forages. Cottonseed meal (CSM) is an excellent protein supplement that is readily available in the south and is competitively priced per unit of protein in early summer. However, research regarding the effects of CSM supplementation level and frequency on calf gain and composition of gain is limited. It was hypothesized that supplementing CSM to grazing heifers would improve ADG and perhaps alter composition of gain when compared with non-supplemented heifers. Objectives for this experiment were to 1) compare gain and composition of gain between calves supplemented with CSM to non-supplemented calves, and 2) compare the effect of daily vs. alternating days of CSM supplementation. A total of 27 commercial Angus beef heifers weighing 234.1 ± 4.18 kg were blocked by BW (light, medium, and heavy) and allocated to 9 paddocks of W.W. B-Dahl Bluestem (Bothriochloa bladhii) for 67 d. The experimental was designed as a RCBD with 3×3 factorial arrangement of 3 treatments and 3 weight blocks. Heifers were supplemented daily with a mineral mix and either no cottonseed meal (CON), 454 g/animal of CSM daily (CSM1), or 909 g/animal of CSM every other day (CSM2). Initial and final shrunk BW was measured, and total gain, ADG, and percent of BW gained were calculated. Ultrasound of initial and final longissimus muscle area (LMA), backfat (BF), and intramuscular fat (IMF) were measured. There were no treatment by block interactions for any measured variable. Treatment significantly affected total gain and ADG (P = 0.0156), as well as percent of BW gain (P = 0.029). Heifers receiving CSM1 treatment gained 28.3% more total BW than heifers receiving CON (47.27 vs. 36.82 kg, respectively) and CSM2 was intermediate (42.73 kg). Likewise, percent of BW gained was greatest for CSM1 and least for CON (16.9 vs.3.8% of initial BW), with CSM2 not differing (15.5% of initial BW). Treatment did not affect the composition of gain (P ≥ 0.190); however, block tended (P = 0.0812) to affect LMA % gain, with light heifers being greater than medium and heavy heifers (12.00% vs. 7.35% and 5.09% increase, respectively). As expected, heifers grazing late summer W.W. B-Dahl Bluestem forage who received 454 g of CSM daily had significantly greater ADG than heifers not receiving CSM. Heifers receiving 909 g of CSM every other day tended to gain more than heifers not receiving CSM, but replication of this experiment is needed for validation of this specific supplementation strategy. In conclusion, supplementation of CSM to calves grazing low protein summer forage within a limited period may have positive measurable effects on gain.