Stockpiled 'Tifton 85' Bermudagrass for Cow-Calf Production as Influenced by Nitrogen Fertilization
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A 2-yr grazing study was conducted to determine effects of rate of N fertilization on productivity and nutritive value of stockpiled 'Tifton 85' bermudagrass for lactating-cow and calf performance. On October 31, 2012 (Yr 1) and November 11, 2013 (Yr 2), 16 Angus × Simmental cows (mean initial BW for both yr, 647 ± 23 kg) and their calves (mean age, 16 ± 3 d) were assigned randomly to 0.76-ha paddocks (2 cow-calf pairs/paddock) of stockpiled ‘Tifton 85’ bermudagrass pasture that had been cut to a 10-cm stubble height in early August and fertilized with either 56 (56N), 112 (112N), or 168 (168N) kg N/ha (2 paddocks/treatment); or to replicate 0.41-ha paddocks (2 cow-calf pairs/paddock) of dormant summer pasture with free-choice access to August-cut bermudagrass hay plus 2.7 kg whole cottonseed daily (HAY). Cows were given access to strips of ungrazed forage by moving polytape every 3 to 4 d in order to maintain a target forage DM harvest efficiency of approximately 75%. In Yr 1, mean forage mass (6,113 kg DM/ha), IVDMD (60.9%) and grazing d/ha (314) were not different (P > 0.05) among the stockpile treatments over the 116-d grazing period; mean forage IVDMD (60.1%) and CP concentration (12.7%) in the stockpiled treatments were greater (P < 0.05) than the HAY treatment. Stockpiled forage CP concentration was greater (P < 0.05) for the 168N than 56N and 112N treatments, and was greater (P < 0.05) for the 56N than 112N treatment. In Yr 2, mean forage CP concentration was greater (P < 0.05) for the 168N (14.5%) than 56N (11.3%), 112N (12.0%) and HAY (9.0%) treatments; mean stockpiled forage IVDMD (59.5%) was greater (P < 0.05) than the HAY treatment (46.3%); and mean forage mass for the 168N treatment (5,017 kg DM/ha) was 378 kg and 298 kg DM/ha greater (P < 0.05) than the 112N and 56N treatments, respectively. Mean cow BW (611 ± 147 kg), BCS (5.5 ± 0.6) and milk production (9.0 ± 6.0 kg/d) were not different among treatments. Mean BUN concentrations (11.2 ml/dL) were not different among treatments, but mean BUN across treatments for the last sampling date was greater (P < 0.05) than the first and second sampling dates. Projected calving intervals and mean 205-d adjusted calf weaning weight (249 kg) were not different across treatments. An economic evaluation between each stockpiled treatment versus the HAY treatment revealed that input costs/cow were 66, 61 and 56% greater for the hay feeding system than the 56N, 112N and 168N stockpiles, respectively. Stockpiled forages were of sufficient nutritive quality to support beef cows’ lactation and reproductive performance without supplementation, and were of consistently greater quality than hay.