Reducing Between-Cow Variation in Nutrient Intake Through Feed Bunk Management

Past research in dairy cattle nutrition has focused almost exclusively on the nutrient aspects of the diet, and has led to many discoveries and improvements in dairy cattle health and production. Despite many advances in the field of ruminant nutrition, however, we are still faced with the challenge of ensuring adequate dry matter intake (DMI) to maximize production and prevent disease, particularly with lactating dairy cows during the transition period. Many of the cows experiencing decreased DMI the pre-partum period fail to make a successful transition to the post-partum diet. Approximately 50% of cows have one or more adverse health events during transition (Ferguson, 2001), so any practices that can help reduce disease at this time are thus of broad relevance to the dairy industry.

One of the interesting aspects of transition disease is the individual variability of cow susceptibility. Despite subjecting all animals to similar management and diets, we still face a certain percentage of animals succumbing to disease while others remain healthy. An example of this would be the susceptibility of dairy cows to sub-acute ruminal acidosis, which is highest for cows in early lactation, but also highly variable among cows, despite similar cow feeding management (Penner et al., 2007).

There is some data to suggest that this may be in part due to high between-cow variability in DMI, and thus nutrient intake. Drackley (1999) reported that coefficients of variation for DMI during the 1st wk postpartum are in the range of 30 to 40%; whereas, the coefficients of variation for DMI after peak lactation typically range between 6 and 10%. Further, McGuffey et al. (1997) reported that a 1% increase in the variation of DMI in the first 21 DIM was associated with a 4% increase in post-calving incidents (dystocia-related, metabolic, or digestive disorders). There is growing evidence to suggest that much of the variability in susceptibility to disease is related to variability in nutrient consumption, both within- and between-cows. Such variability may related to whether or not cows have good access to the feed provided to them and whether or not they eat the feed as it is formulated for them. This paper will thus review this literature, and also describe feed bunk management strategies that encourage feed access, reduce feed sorting, and thus reduce variation in nutrient intake in dairy cattle.

There is recent evidence to suggest that dairy cows do not always maximize their opportunities to feed, and this can be associated with the experience of metabolic and infectious disease; these health issues not only pose immediate welfare concerns to dairy cattle, but can also affect efficiency and productivity. The transition period is the stage at which dairy cows are particularly vulnerable to metabolic and infectious diseases. Researchers have shown that cows diagnosed with acute metritis after calving spent less time feeding during the prepartum period (d –12 to –2 prior to calving; Urton et al., 2005). In a follow-up study, Huzzey et al. (2007) monitored individual feeding time using a larger sample size of cows and also monitored individual DMI. Cows diagnosed with severe metritis 7-9 d postpartum consumed less feed and spent less time at the feed bunk during the 2 wk period before calving, nearly 3 wk before the observation of clinical signs of infection. In that study, the decreases in feed intake contributed to decreased milk production; mildly and severely metritic cows produced 5.7 and 8.3 kg less milk per day compared to healthy cows during the first 3 weeks after calving. In the work described by Huzzey et al. (2007), feeding time was positively related to DMI, especially for cows with severe metritis. It follows, therefore, that management and housing practices that allow for increased feed bunk access will positively affect feeding time, and thus improve DMI and possibly reduce disease.

Recent work showed similar findings with cows that developed subclinical ketosis (SCK; Goldhawk et al., 2009). Cows diagnosed with SCK during the week after calving showed differences in feeding behavior and DMI as early as 1 wk prior to calving. Not only was DMI reduced pre partum, but SCK animals also initiated fewer displacements at the feed bunk during the week before calving. This is similar to the findings of Huzzey et al. (2007) where cows diagnosed with metritis engaged in fewer aggressive interactions at the feedbunk during peak feeding periods, resulting in lower DMI at those time periods and across the day. These results indicate that the risk of transition cow diseases, such as metritis and SCK, may be reduced by utilizing management and housing practices that allow for increased feed bunk access, particularly at times when they want to be there.

Total mixed rations (TMR) are designed as a homogenous mixture with the goal to help minimize the selective consumption of individual feed components by dairy cattle, promote a steady-state condition conducive to continuous rumen function and ingesta flow, and ensure adequate intakes of fiber (Coppock et al., 1981). It is not surprising, therefore, that providing feed as a TMR standard on most commercial dairies, particularly for the lactating animals. Unfortunately, even when providing feed as a TMR cows have been shown to preferentially select (sort) for the grain component of a TMR and discriminate against the longer forage components (Leonardi and Armentano, 2003). Sorting of the diet can lead to the cows consuming an inconsistent ration, whereby the ration actually consumed by cows is greater in fermentable carbohydrates than intended and lesser in effective fiber, and thus can increase the risk of SARA (DeVries et al., 2008). This behavior is particularly troublesome for early lactation cows, where greater sorting of a higher concentrate, lower fiber diet (DeVries et al., 2007; 2008), coupled with rapidly increasing DMI (Kertz et al., 1991), will exacerbate the intake of highly fermentable carbohydrates and refusal of physically effective fiber, and thus increase the risk of ruminal acidosis. This in turn may result in inconsistent feed intake, poor feed efficiency, reduced feed digestibility and protein synthesis, and increased incidence of diseases. Alternatively, sorting of the TMR can reduce the nutritive value of the TMR remaining in the feed bunk, particularly in the later hours past the time of feed delivery (DeVries et al., 2005; Hosseinkhani et al., 2008). For group-fed cows, this may be detrimental for those cows that do not have access to feed, at the time when it is delivered, for example when there is high competition at the feed bunk. In such cases, these cows may not be able to maintain adequate nutrient intake to maintain high levels of milk production (Krause and Oetzel, 2006). Thus, feeding management strategies are required to ensure that cows consume the feed as it is formulated for them. 

It is clear that, in addition to proper formulating of dairy rations, we need to also consider factors that affect both if and how the ration is consumed to ensure that all cows maximize their intake of that formulated ration. There is an increasingly growing body of literature in which the knowledge of cow behavior can be used to identify bunk management strategies to reduce variability in nutrient intake and maximize ration potential; these strategies include ensuring cows have access to their formulated ration throughout the day and minimizing feed bunk competition.

For intensively group-housed dairy cattle diurnal feeding patterns are mostly influenced by the time of feed delivery, feed push-up and milking (DeVries et al., 2003). One of the most common feeding management practices believed to stimulate feeding activity is feed push-up. When fed a TMR, dairy cows have a natural tendency to continually sort through the feed and toss it forward where it is no longer within reach. This is particularly problematic when feed is delivered via a feed alley and, thus, producers commonly push the feed closer to the cows in between feedings to ensure that cows have continuous feed access. In an observational study Menzi and Chase (1994) noted that the number of cows feeding increased after feed push up, however they concluded that feed push ups had "minor and brief effects" in comparison to milking on the feed bunk attendance. In a more recent study, we tested the stimulatory effect of feed push-up by increasing the number of push ups during the late evening and early morning (DeVries et al., 2003). In that study we found that the addition of extra feed push ups in the early morning hours did little to increase feeding activity. However, push up does play a vital role in ensuring that feed is accessible when cows want to eat.

For group-housed dairy cattle, the act of feed delivery acts as the primary stimulus by which dairy cows are attracted to the feed bunk (DeVries and von Keyserlingk, 2005). Thus, the frequency of feed delivery should influence the feeding patterns of lactating dairy cows. To test this prediction, we conducted an experiment to determine whether increasing frequency of feed delivery affects the behavior of group-housed dairy cows (DeVries et al., 2005). This objective was tested in two experiments. In the first experiment, the treatments were: 1) delivery of feed once per day (1x), and 2) delivery of feed twice per day (2x). The treatments for the second experiment were: 1) delivery of feed 2x, and 2) delivery of feed four times per day (4x). In both experiments, increased frequency of feed provision increased total daily feeding time by 10 and 14 minutes, respectively, as well as increased the distribution of feeding time throughout the day. The distribution of feeding time in both experiments indicated that cows had more equal access to feed throughout the day when provided feed more frequently. Frequency of feed delivery had no effect on the daily lying time of the cows or the total number of aggressive interactions at the feed bunk. However, we did find that subordinate cows were not displaced as frequently when fed more often, indicating that these cows would have greater access to feed, particularly fresh feed, when the frequency of feed delivery is high. In addition to these behavioral measures, we also looked at the effects of frequency of feed delivery on feed composition throughout the day. In both experiments we noted that the neutral detergent fiber (NDF) content of the TMR present in the feed bunk increased throughout the day, indicating that sorting of the feed had occurred, particularly on the 1x treatment. Corroborating this, it was recently shown in a multi-herd study (Endres and Espejo, 2010) that a greater change in ration NDF content over the course of the day was associated with lower frequency of feed delivery (i.e. 1x vs. 2x or 3x per day).

Increased sorting of a TMR when fed 1x per day may be particularly troublesome under some management situations. In two recent studies we have investigated the effects of water addition to a TMR, fed 1x per day, containing solely haylage and corn silage forage sources (Miller-Cushon and DeVries, 2009; Felton and DeVries, 2010). In the first study we reduced TMR dry matter concentration from 58 to 48% (Miller- Cushon and DeVries, 2009). In a second study we reduced TMR dry mater concentration from 56 to 50 to 44% (Felton and DeVries, 2010). In both studies we found that the addition of water to these higher moisture TMR, containing no dry forage, actually resulted in greater amounts of feed sorting. In addition to this, increased amounts of water added to the rations also resulted in lower DMI. Reduced DMI with lower dietary DM is likely due, in part, to the increased filling effect of higher moisture rations. Interestingly, in the second study we found that greater amounts of water added to the TMR resulted in greater increases in feed temperature in the hours after feed was placed in the feed bunk, particularly with higher ambient temperatures (Felton and DeVries, 2010). This increased feed temperature may be indicative of feed spoilage and, thus, may be contributing to these effects. Thus, when feeding higher moisture TMR during periods of high ambient temperatures, delivering feed 1x per day may not only increase the risk of greater amounts of sorting, but may also limit DMI.

Despite these results, there are still potential benefits of adding water to TMR under certain circumstances. Adding water to dry TMR should help bind particles together and make it harder for dairy cattle to sort out smaller particles. Leonardi et al. (2005) demonstrated that reducing DM concentration of a TMR, containing dry forages, from 80 to 64% through water addition resulted in a reduction in the extent of feed sorting against long particles and for short particles, a tendency for increased NDF intake and greater milk fat percentage (3.41 vs. 3.31%). The effect water addition may have on reducing feed sorting may hinge on the original DM content of the ration, and whether or not dry forage was included in that ration. It would be recommended that in situations where sorting is evident, producers try adding water to their TMR, however be careful to monitor the effects that this may have. In cases where sorting increases with additional water, it would be recommended to stop this practice.

One of the specific objectives of cattle housing is to provide a comfortable environment that will allow cows to meet their behavioral and physiological needs (Phillips, 2001). There are several aspects of the feeding environment that have the potential to influence the ability of cows to access feed, including the amount of available feed bunk space per animal and the physical design of the feeding area.

Recent observations have shown that at the suggested industry standard of 24 inches of feeding space per cow not all animals can access feed at the same time (DeVries et al., 2003). As social animals, cattle tend to synchronize their behavior, including a strong desire to access the feed bunk as a group. Reduced space availability has been shown to result in increased aggressive behavior in cattle (Kondo et al., 1989). When feed bunk space is limited, increases in aggressive behavior are thought to limit the ability of some cows to access feed at times when feeding motivation is high, particularly after the delivery of fresh feed (DeVries et al., 2004; Huzzey et al., 2006). Hosseinkhani et al. (2008) recently demonstrated that competition at the feed bunk dramatically increased the feeding rate at which cows feed throughout the day. These researchers also found that competitivelyfed cows have fewer meals per day, which tend to be larger and longer. In the study by Hosseinkhani et al. (2008) it was also found that competition changed the distribution of DMI over the course of the day, resulting in higher intakes during the later hours after feed delivery after much of the feed sorting had already occurred. Thus, increased competition promotes feeding behavior that forces subordinate cows to consume more of their feed after the dominant cows have sorted the TMR. These results suggest that increased competition at the feed bunk promotes feeding behavior patterns that will likely increase the between-cow variation in composition of TMR consumed and the risk of sub-acute ruminal acidosis. Providing more space than the current industry norm has been shown to improve feed bunk access; this increases feeding times and decreases competition, with subordinate cows showing the greatest responses (DeVries et al., 2004; Huzzey et al., 2006). This change will help reduce the variation in the composition of feed cows consume as subordinate cows will be able to access the feed prior to it being sorted through by those dominant cows.

In addition to increasing the amount of available feed bunk space, competition for feed can also be reduced through design of the feeding area. Researchers have shown that a headlock system greatly reduces competition at the feed bunk compared with a postand- rail system (Endres et al., 2005; Huzzey et al., 2006). Another option to reduce competition is the use of partitions (feed stalls) between the bodies of adjacent cows at the feed bunk. DeVries and von Keyserlingk (2006) demonstrated that feed stalls resulted in increased feeding time and decreased competition, particularly for subordinate cows. Their results suggest feed stalls provide additional protection for feeding cows, and improved access to feed beyond that provided by simply increasing the amount of space per animal.

It has become increasingly evident from this research that the provision of more feed bunk space (than traditionally provided), particularly when combined with (e.g. feed stalls), will improve access to feed and reduce competition at the feed bunk, particularly for subordinate cows. This could help reduce the between-cow variation in the composition of ration consumed by preventing subordinate cows from being forced to access the bunk only after dominant cows have sorted the feed. 

This proceedings chapter summarizes a number of studies that have been undertaken that collectively provide us with a basic understanding of how various feed bunk management strategies can be used to reduce nutrient intake variability and maximize the potential of the rations provided. This can be accomplished by ensuring cows have access to their formulated ration throughout the day and minimizing feed bunk competition. Access to the formulated ration can be improved by delivering feed frequently, pushing up feed frequently, and minimizing feed sorting. Feed bunk competition may be reduced by providing more feed bunk space than traditionally recommended—particularly when combined with a physical partition at the feed barrier. 

This paper is an updated version of a proceedings paper written for, and presented at, the 2011 California Animal Nutrition Conference held in Fresno, CA in May 2011. I gratefully acknowledge Marina von Keyserlingk, Dan Weary, Karen Beauchemin, Marcia Endres, and several others for their contribution to some of the experiments cited herein. This research was funded in part by the Natural Sciences and Engineering Research Council of Canada, Dairy Farmers of Canada, Westgen Endowment Fund, Investment Agriculture Foundation of British Columbia, the Canadian Dairy Commission, Agriculture and Agri-Food Canada, the Canadian Bovine Mastitis Research Network, the Ontario Ministry of Agriculture, Food, and Rural Affairs, the University of Guelph, and the University of British Columbia Animal Welfare Program.

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