Effects of Type and Level of Energy Supplementation on Stocker Cattle Performance from Annual Ryegrass

Abstract

Previous research has indicated that supplementation of high-quality grazed forage with high-energy feedstuffs can improve animal performance and enable increased stocking rates in grazed ecosystems. However, the extent of performance improvement and direction of forage utilization response may be dependent upon supplementation level (% BW) and whether the supplement is a high-starch or highly-digestible-fiber feedstuff. For these reasons, a grazing experiment was conducted to determine the type and level of supplementation with select high-energy feedstuffs that yield optimum animal performance and forage utilization from annual ryegrass (Lolium mulitflorum). Twenty 0.81-ha pastures in Yr 1 and thirty 0.81-ha pastures in Yr 2 were each grazed by 4 crossbred steers (mean initial BW, 230 ± 16 and 242 ± 26 kg in Yr 1 and Yr 2, respectively) between February 6, and May 15, 2014 in Yr 1 and between December 18, 2014 and April 15, 2015 in Yr 2. Cracked corn, pelleted citrus pulp, or pelleted soybean hulls were fed at rates of 0.25, 0.50, and 0.75% BW daily (2 type × level replicates per treatment in Yr 1, and 3 replicates per treatment in Yr 2), including replicate pastures in which steers received no supplement. Steers were weighed every 28 d following a period of overnight shrink. Forage mass was measured every 28 d using the destructive harvest/disk meter double-sampling method. Grazing was discontinued after 98 d in Yr 1 and 119 d in Yr 2 when forage mass and quality could no longer support an ADG of 0.68 kg. Data were analyzed as completely randomized design by the PROC MIXED procedure of SAS 9.4 using pasture as the experimental unit. Main effects were supplement type, supplement level, and type × level interaction. Contrast statements were used in pre-planned comparisons of the control with individual supplement types and feeding levels. There were no type × level interactions for ADG, total gain (kg/ha), or supplement use efficiency (F:G ratio) in either yr. In Yr 1 across all supplement levels, ADG was greater (P < 0.10) for corn and soybean hull treatments than the unsupplemented control, and total gain/ha was greater (P < 0.10) for all supplement types than the unsupplemented control. Across all supplement types, ADG and total gain/ha were also greater (P < 0.10) for all supplement levels than the unsupplemented control. There were no differences (P > 0.10) in supplement F:G above the control in either yr. In Yr 2, across all supplement levels, ADG was again greater (P < 0.10) for corn and soybean hull treatments than the unsupplemented control, and total gain/ha was greater (P < 0.10) for all supplement types than the unsupplemented control. Across all supplement types, ADG was greater (P < 0.10) for all supplement levels than the unsupplemented control, and total gain was greater (P < 0.10) for the 0.25 and 0.50% BW treatments than the unsupplemented control. In Yr 1 across all levels, supplementation with corn generally resulted in greater standing forage mass throughout the grazing season than citrus pulp, soybean hull, and the unsupplemented control. However, across all supplement types, forage mass at different levels of supplementation did not differ. In Yr 2, there were generally no differences in forage mass among the supplemented treatments across both type and level; however, supplemented treatments yielded greater forage mass than the unsupplemented control late in the grazing season. Additionally, forage mass change between Dec and Jan decreased more markedly for 0.25% BW than for any of the other levels. In Yr 1, supplemented treatments displayed a decrease in forage allowance compared with the unsupplemented control on the April sampling date. Across all supplement types, there were generally no differences in standing forage mass; however, supplementation at the 0.50% BW resulted in decreased forage allowance on the April sampling date. In Yr 2, there were numerous type × level interactions observed for forage allowance; however, there did not appear to be any systematic pattern of response among the supplement types or levels. Overall, supplementation resulted in increased animal ADG and total gain/ha. However, pasture response in terms of forage mass and allowance varied greatly among supplement types and levels of feeding.