By Jerad Jaborek
Bunk management refers to matching the amount of feed delivered to the amount of feed cattle can consume without causing digestive upsets. The simplest form of bunk management is to provide cattle with ad libitum feed, which means to ensure feed is always available. More refined bunk management strategies such as slick bunk management closely matches the amount of feed offered with maximal feed intake of the cattle resulting in a ‘slick’ or empty feed bunk just before the next feeding time. Programming feed intakes uses a bunk management strategy known as limit-feeding or restricted-feeding. The amount of feed offered with limit-feeding is less than what cattle could eat ad libitum or if feed is supplied free choice.
An Ohio State University study conducted by Murphy and Loerch that was published in the Journal of Animal Science investigated the effects of limit-feeding cattle in two experimental trials. In trial 1, crossbred beef steers were offered an all-concentrate diet (without forage) at either ad libitum intake, 90%, or 80% of ad libitum intake. By design, average daily dry matter intake decreased with increasing feed restriction. Likewise, average daily gain, final weight, backfat thickness, and USDA quality grade decreased linearly with increasing feed restriction. However, increasing feed restriction was thought to increase the energy use available to fulfill maintenance and gain requirements for the animal.
In trial 2, crossbred beef steers were offered an 80% corn silage growing diet for 84 days before being switched to a finishing ration with 18% corn silage at either ad libitum intake, 90%, or 80% ad libitum intake. During the growing period average daily gain decreased with increasing feed restriction and feed efficiency was similar. During the finishing period average daily gain decreased with increasing feed restriction and steers with restricted intakes required more days on feed to reach similar final body weights. However, feed efficiency increased with increasing feed restriction. This resulted in a linear increase in feed efficiency for steers with increasingly greater feed restrictions over the entire feeding period. The improvement in feed efficiency by steers that were feed restricted may have been due to reduced maintenance requirements from the visceral organs and digestive tract. Greater intakes of a high-forage growing diet likely produced a larger digestive tract and visceral organs which would require more time, energy, and protein to maintain once switched to a high-concentrate finishing diet. In trial 2, no carcass composition differences were observed, possibly due to an additional 14 and 27 days on feed by the 90% and 80% restricted steers, respectively.
Programmed-feeding strategies often include limit-feeding to attain a prescribed constant daily weight gain for cattle throughout the feeding period. In a Journal of Animal Science publication, Loerch and Fluharty from The Ohio State University investigated the effects of various programmed-feeding strategies on cattle performance and carcass characteristics while offering a high-moisture corn diet. In trial 1, from 600-820 pounds, crossbred beef steers were offered enough feed to achieve a target rate of gain of either 2.0, 2.5, 3.0 lb./d, or offered feed ad libitum to achieve maximum gain. All steers in trial 1 were then allowed ad libitum feed for the remainder of the finishing period until reaching a final weight of 1175 pounds. With extra days on feed, steers with programmed feed intakes were able to catch up with steers offered ad libitum feed resulting in no differences in average daily gain, total feed consumed, feed efficiency, or carcass composition during the feeding period.
In trial 2, crossbred beef steers were programmed to achieve either increasing gains (2.5, 3.0 lb./d, max), decreasing gains (max, 3.0, 2.5 lb./d), constant gains (3.0, 3.0, 3.0 lb./d), or maximum gains (max, max, max) over three periods from 660 to 873, 873 to 1073, and 1073 to 1188 pounds. Steers raised to achieve increasing gains consumed the least amount of total feed and were the most feed efficient, while producing a similar carcass composition to steers in the other treatments. The authors determined that steers programmed for increasing gains consumed 240 pounds less dry matter compared to steers consuming ad libitum feed. At the time of the trial, feed was priced at $0.099/lb. of dry matter, resulting in a savings in feed costs of $23.65 per steer.
In a Journal of Animal Science article, Rossi and Loerch from The Ohio State University investigated the use of corn silage when using programmed-feeding strategies. In experiment 1, crossbred beef steers were offered either a 15% corn silage diet at ad libitum intake for the entire feeding period (AL), a 85, 50, and 15% corn silage diet at ad libitum intake (CS; step-wise increases in concentrate), or a 15% corn silage diet offered to achieve a target rate of gain of 2.5, 3.0 lb./d, followed by ad libitum intake (PI). Average daily gain was similar across treatments, but CS steers consumed a greater total amount of feed and were less feed efficient compared with AL and PI steers.
In experiment 2, crossbred beef steers were offered either a 15% corn silage diet offered ad libitum for the entire feeding period (AL), a 15% corn silage diet offered to achieve a target rate of gain of 2.5, 3.0 lb./d, followed by ad libitum intake (PI-H), a 85, 50, and 15% corn silage diet offered to achieve a target rate of gain of 2.5, 3.0 lb./d, followed by ad libitum intake, respectively (PI-I), or a 85, 50, and 15% corn silage diet offered to achieve a target rate of gain of 2.5, 3.0 lb./d, followed by ad libitum intake, respectively (PI-L). Overall, AL and PI-H steers had the greatest average daily gains. AL steers had the greatest daily dry matter intake (18.96 pounds) followed by PI-L steers (18.26 pounds), then PI-I (17.36 pounds) and PI-H steers (17.16 pounds). However, total dry matter intake was greatest for PI-L steers because they required the most days on feed to reach the targeted harvest weight of 1250 pounds. PI-H steers were the most feed efficient (4.83 lb. feed/lb. gain), followed by AL (5.15 lb./lb.) and PI-I steers (5.24 lb./lb.), and lastly PI-L steers (5.65 lb./lb.). There were no carcass differences between steers in both experiments 1 and 2.
In summary, limit-feeding cattle can improve feed efficiency, particularly during the growing period when feeding corn silage, as compared to a high-concentrate diet due to reduced maintenance requirements of the animal. Limit-feeding also extends the growth curve of cattle, resulting in leaner cattle with less backfat when compared with ad libitum fed counterparts. Programming cattle intakes to achieve increasingly greater average daily gains during the feeding period can result in a similar average daily gain, reduced feed intake, and improved feed efficiency compared with cattle offered feed ad libitum. Cattle started on a corn silage-based diet, where concentrates are stepped-up to replace roughage over the feeding period, consume a greater amount of feed and are less feed efficient when compared with cattle that have a programmed feed intake with a high-concentrate diet. Additionally, cattle fed using programmed feeding strategies for high corn silage diets were outperformed by cattle with programmed intakes on a high-concentrate diet.
Source : msu.edu