Feeding Management on Animal Performance and Production Efficiency

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This entry is adapted from the peer-reviewed paper 10.3390/ani13040758

Mitigation of greenhouse gases and decreasing nutrient excretion have become increasingly important goals for the beef cattle industry. Because feed intake is a major driver of enteric CH₄ production and nutrient excretion, feeding management systems could be important mitigation tools. Programmed feeding uses net energy equations to determine the feed required to yield a specific rate of gain, whereas restricted feeding typically involves decreasing intake relative to the expected or observed ad libitum intake.

beef cattle methane prediction feeding management systems

1. Introduction

Cattle are an important source of greenhouse gases (GHG) because of their ruminant digestive system. As a result, the potential adverse effects of beef cattle operations on the environment and climate change are a concern, and ways to mitigate CH₄ emissions from cattle feeding operations are an important practical research issue for the industry. As a component of mitigation strategies, common cattle feeding practices need to be evaluated and balanced for production efficiency and environmental concerns. The primary GHG associated with animal feeding are CH₄ and N₂O, which are produced both directly from cattle (i.e., enteric emission of CH₄) and indirectly from nutrients excreted in the urine and feces for N₂O. Methane has 21 to 26 times the global warming potential (GWP) of carbon dioxide, and nitrous oxide has 296 to 310 times the GWP of carbon dioxide ^[1]. Methane emissions from feedlot cattle arise primarily from ruminal fermentation ^[2], whereas N₂O is formed during nitrification and denitrification from nitrogenous compounds present in the feces and urine of cattle ^[3]. Thus, excreted nutrients in urine and feces have an indirect effect on GHG emissions from the feedlot pen surface ^[4]^[5]^[6]. Urinary N excretion also influences ammonia emissions from the feedlot surface ^[7], which can have negative environmental consequences. Because feed intake drives both enteric emissions and nutrient excretion, precision management of feed intake could have important effects on subsequent indirect emissions of GHG and ammonia.

2. Defining Feeding Management Strategies

Based on a previous review ^[8], definitions were developed for two primary feeding management strategies—programmed feeding and restricted feeding. Programmed feeding was described as a method that uses net energy equations ^[9] to determine the quantity of feed required for a specific average daily gain (ADG; ^[8]). Multiple options within restricted feeding were described, which included any method of managing feed intake that results in restriction relative to actual or expected feed intake. Restriction could be in the form of altering the quantity of feed provided or the time of access to feed. Intensive bunk-reading and feed-delivery systems (clean or slick bunk management) are typically based on time restriction ^[8], with the potential to affect feed intake relative to ad libitum access depending on how these systems are applied in practice.

Why would producers of growing–finishing beef cattle apply these feeding management systems? Providing an alternative to pasture-based systems for growing cattle, improved feed efficiency, and decreased production of manure are key elements related to the decision to use these systems. Other aspects include avoiding the over-consumption of feed, decreasing the variation in feed intake, simplified feed bunk management and feed milling and delivery logistics, identification of sick cattle (primarily with programming at a lower ADG), and providing a system from transitioning cattle to ad libitum consumption of high-concentrate finishing diets ^[8].

3. Effects of Feeding Management on Animal Performance and Production Efficiency

Feed represents 65 to 75% of the cost in beef production ^[10]. In addition, feed is used with a relatively low efficiency ^[11], with beef cattle recovering less than 20% of gross energy consumed across most diets ^[12]^[13]^[14]^[15]^[16]. Optimized precision animal management is achieved by providing the nutrients an animal needs without over-feeding nutrients. Both restricted and programmed feeding can improve feed efficiency ^[8], which presumably relates to the observation that ADG increases at a decreasing rate as feed intake increases ^[11], but the magnitude of the effects of these feeding management strategies on efficiency has been variable in the literature.

3.1. Production Responses with Programmed Feeding

Programmed feeding, particularly with relatively high-concentrate diets, has been most frequently evaluated as an alternative to traditional growing programs based on higher-roughage diets of low-to-moderate energy concentration. The impetus for research in this area is often driven by the high cost or low availability of traditional roughage sources, but the ancillary benefits of programming gain with high-concentrate diets such as consistency in feed delivery requirements and associated logistics, as well as the potential for compensatory gain when intake is increased to ad libitum, can be important considerations that drive field application. Several experiments on programmed feeding have been conducted by researchers at the Ohio State University. In the first of two experiments ^[17], ad libitum feeding was compared with various programmed-gain strategies (different rates and patterns of gain for various periods of time), followed by ad libitum access to feed until harvest. Overall, observed programmed ADG was greater than predicted from net energy equations, and systems that decreased ADG for longer periods of time resulted in less total feed consumption to reach equivalent harvest endpoints. Similarly, Loerch and Fluharty ^[18] compared ad libitum access to feed with different programmed rates and patterns of gain followed by ad libitum access. As with the previous work ^[17], observed ADG exceeded predicted ADG, and programming for stepwise increases in ADG followed by approximately 100 d of ad libitum feeding improved feed efficiency and decreased total feed consumption by more than 100 kg/steer, with no effects on carcass weight and quality. In a third report from Ohio researchers ^[19], continuous ad libitum feeding was compared with programmed gain for the first 63 to 66 d on feed at approximately 68 to 78% of ADG achieved by ad libitum-fed cattle, followed by programming at an increased ADG for the next 60 to 70 d, with a final period of ad libitum feeding. Programmed feeding improved gain efficiency and decreased total feed consumed compared with ad libitum-fed cattle by approximately 5 to 9%, without any major effects on carcass characteristics.

Steers programmed to gain 1.4 kg/d for the first 62 d of a finishing period followed by ad libitum feeding did not perform better than expected from net energy calculations ^[20], but they tended to have greater gain efficiency than steers given ad libitum access to feed for the entire period. Across implanted vs. non-implanted treatments, programming gain decreased total feed intake during the feeding period by an average of 124.6 kg. Felix et al. ^[21] programmed gain at 0.9 or 1.4 kg/d for a 98-d growing period, with diets based on corn or dried distillers grains plus solubles (DDGS), followed by an ad libitum finishing period. Programmed gain was greater than expected with corn-based diets but not with DDGS diets. Gain efficiency for the overall feeding period did not differ because of programmed ADG, nor did total feed intake, and programmed ADG did not affect digestibility of dry matter, neutral detergent fiber, and ether extract.

In two experiments ^[22], steers were fed different intakes of diets that varied in energy concentration to achieve an ADG of 1.6 kg/d. As expected, the diet with the greatest energy concentration resulted in the greatest gain efficiency, but it also resulted in greater ADG, despite similar formulated intakes of net energy. In a companion study ^[23], the digestibility of the diets differing in energy concentration that were fed to yield an ADG of 1.6 kg/d was evaluated. The diet with the highest energy concentration had an increased digestibility of DM, and it increased the ruminal proportion of propionate, reflecting the greater starch and lower fiber concentrations in the diet, resulting in a lower calculated loss of CH₄ and a greater ME concentration with the higher-energy diet. Thus, diets with higher energy concentrations are likely optimal for programmed feeding, particularly if decreasing the environmental footprint of cattle feeding is a goal. As noted previously, higher-energy diets during programmed-gain periods also facilitate the transition to ad libitum feeding of a high-concentrate diet.

The physiological responses to programmed feeding have not been fully elucidated, but the effects on maintenance requirements of a relatively constant feed intake to yield a fixed ADG might explain improved feed efficiency with programmed feeding ^[24]^[25]. In addition, compensatory gain is often noted during ad libitum feeding of cattle previously programmed at low rates of gain, which presumably contributes to improved overall gain efficiency with this feeding management strategy.

3.2. Production Responses with Restricted Feeding

In research studies, restricted feeding is typically an approach in which feed intake is restricted relative to cattle with ad libitum access to feed. Obviously, intake by ad libitum-fed cattle varies from day to day and is affected by environmental and management factors, so comparisons are often made to average ad libitum intake for a previous period (e.g., the average of the previous week). Because the real-time application of restriction relative to ad libitum intake is challenging, there has been limited use of comparative restriction in practice. Thus, if implemented in feedlots, restriction is most likely applied relative to anticipated or predicted ad libitum intake. The challenge with the practical application of restricted feeding might have contributed to the development of time restriction approaches such as slick or clean bunk management, which are more easily applied in feedlots. Despite its practical challenges with application, however, comparative restricted feeding has been a useful research technique.

Hicks et al. ^[26] conducted some of the earlier research on restricted feeding. In two experiments, intake was restricted (85 or 89%) relative to ad libitum intake, whereas in a third experiment, intake was restricted to 80% of ad libitum for the first 56 d of a 138-d study followed by ad libitum access, or gain was programmed at 1.35 or 1.5 kg/d. Restriction improved feed efficiency relative to ad libitum feeding, but carcass quality grade was decreased by restricted feeding or programming gain. The digestibility of dry matter and starch was not affected by restriction or programming. The authors suggested that limiting day-to-day variation in feed intake could be a significant advantage of controlled feeding systems.

Restricted feeding of a high-grain diet at 80% of the intake achieved with ad libitum feeding of a traditional corn silage-based growing diet for 77 d, followed by ad libitum access to a high-concentrate finishing diet to harvest at 149 d, decreased intake for the overall feeding period and improved feed efficiency ^[27]. Restricting intake of an all-concentrate diet to 80 or 90% of ad libitum resulted in a linear improvement in feed efficiency but increased days on feed to achieve a similar final weight ^[28]. Moreover, carcass fat was decreased linearly with restriction vs. ad libitum feeding. In a second experiment, restricting intake of a silage-based growing diet to 80 or 90% of ad libitum for 84 d followed by ad libitum access until harvest resulted in a linear improvement in feed efficiency and a linear decrease in total feed intake for the overall feeding period (42 and 135 kg for the 90% and 80% restrictions, respectively; ^[28]). Feed restriction decreased carcass fatness and quality grade. Similarly, decreased fat cover in cattle fed barley- or corn-based diets restricted to 96% of ad libitum has been reported ^[29], but restriction did not improve feed efficiency relative to ad libitum feeding.

The degree of restriction could be important in terms of feed efficiency and carcass characteristics. Among groups restricted to 95%, 90%, and 85% relative to the dry matter intake (DMI) of ad libitum-fed cattle ^[30], optimal feed efficiency was observed for the 90% restriction (quadratic response). Fat thickness and marbling score were least for the 85% restriction, suggesting that carcass quality is likely to be affected negatively by more severe restrictions in feed intake.

Silva et al. ^[31] noted that the length of restriction is an important component of the potential environmental benefits of feed restriction. Restriction to 85% of ad libitum intake for 28, 42, or 84 d followed by ad libitum feeding to yield a total of 84 d on feed did not affect digestibility of dry matter, and fecal phosphorus excretion measured near the end of the feeding period was decreased only for the 84-d restriction. A 75% restriction of a grower diet based on alfalfa, sorghum silage, and modified distillers grains plus solubles decreased absolute CH₄ production (g/d), but did not affect CH₄ production per unit of DMI ^[32]. Although the environmental effects of restricted (and programmed) feeding systems can be estimated from feed intake data and assumptions about digestibility, more direct experimentation to measure the digestibility of nutrients and CH₄ emissions would be beneficial.

3.3. Production Responses with Feed Bunk Management Systems

Commercial feedlots in the U.S. and Canada frequently use intensive feed bunk management approaches during the feedlot finishing period. These systems typically involve observations of feed bunks to determine when the bunks are “slick” or “clean” (hence the terminology slick or clean bunk management). Such systems commonly have a target for a time when the feed bunk is empty, which is monitored with a bunk-scoring system. The target can range from a full 24-h cycle to several hours less than a 24-h cycle and be modified by the bunk score (e.g., completely slick vs. some small amount of feed). To avoid restricting intake relative to ad libitum, these systems also normally include a challenge approach, such that when a pen of animals meets the target for a 3-d period, the total quantity of feed is increased by a small amount (e.g., 0.1 kg/animal).

A key objective of slick bunk management is to limit the day-to-day variation in feed consumed by the pen. This is clearly an achievable goal, but whether this approach decreases intake variation by individual animals within the pen, particularly if intake is not restricted, is open to question. Even if there are no performance or animal health advantages with slick bunk management, the system clearly offers advantages in feeding logistics and milling by bringing more consistency and predictability to daily feed deliveries, which might explain its relatively high level of adoption by the U.S. feedlot industry.

Few studies have evaluated the effects of controlled bunk management systems on performance and carcass characteristics of feedlot cattle, and results have been variable. This variability could reflect how slick bunk management is applied at a given location and particularly the degree of restriction that might be imposed. In their review of feed intake variation and bunk management, Pritchard and Bruns ^[33] reported the results of an experiment in which intake was managed to eliminate extreme swings in feed intake that are frequently noted with ad libitum feeding. The managed approach decreased overall feed intake by 12% compared with ad libitum feeding, while eliminating highs and lows in intake over time. The ADG was not changed but was more variable among ad libitum-fed cattle, and gain efficiency was significantly improved by managed feeding. Carcass weight and marbling score did not differ between ad libitum and managed cattle.

In steers fed twice daily (60% at 0700 h and 40% at 1130 h), with feed bunks managed to achieve targets of 0, 0.25, or 1 kg of feed in the bunk 30 min before feed delivery ^[34], DMI decreased from 11.2 to 10.4 and 9.7 kg for the bunk targets of 1, 0.25, and 0 kg, respectively. This study was conducted as a Latin square design with 10 d adaptation and 4 d data collection periods, so the extent to which these data are applicable to long-term use of slick bunk management is open to question. Nonetheless, the results suggest the potential for at least short-term restriction of feed intake with more aggressive slick bunk management.

In contrast to the findings of ^[34], Smock et al. ^[35] found no effect of slick bunk management on ADG, DMI, and carcass characteristics in cattle fed steam-flaked corn-based diets for an average of 177 d. The slick bunk management system in this study targeted from 0 to 2% of the previous day’s feed delivery remaining in the bunk, whereas the target for ad libitum-fed cattle was 5% remaining in the bunk. For slick bunk cattle, the target was achieved 55% of the time, with the target for the ad libitum cattle achieved 59% of the time. Arguably, feed deliveries for both treatments in this study were managed, but it seems clear that slightly more intensive management of feed deliveries did not affect feed intake.

Because of the limited research that has been conducted on intensive bunk management systems, it is difficult to draw definitive conclusions about how these strategies affect feed intake and performance. Part of the challenge with research in this area is that the application of slick bunk management is very dependent on the personnel who are applying the system. Thus, the extent to which research findings can be broadly applied to the feedlot industry is a concern.

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