Introduction
Past research in dairy cattle nutritional management has focused almost exclusively on the nutritive aspects of the diet, resulting in many discoveries and improvements in dairy cow health and production. Despite many advances this field we are still faced with several challenges associated with feeding dairy cattle. Recent field observations suggest that housing and management can play as large of a role as nutrition in the performance and health of dairy cows. This paper will help shed light on such findings by describing the impact of feeding management on dairy cow behavior, health, and productivity. To that end, the importance of dairy cow behavior will be emphasized, including how dairy cows eat, when they eat, and what they actually consume. The paper will then describe how we can use that knowledge to evaluate nutritional and feeding management strategies.
Importance of feeding behavior
How do cows eat?
Under natural grazing conditions dairy cattle will engage in foraging behavior from anywhere from 4 to 9 hours per day (Hafez and Bouissou, 1975). This feeding time would be split into a number of smaller meals occurring throughout the day, with the largest meals occurring in the early morning and late afternoon. Modern, intensively-housed dairy cattle fed a conserved ration typically consume their daily dry matter intake in up to 6 hours per day, spread between 7 or more meals per day (DeVries et al., 2003). Management practices that cause adult dairy cattle to eat fewer and larger meals more quickly have been associated with an increased incidence of sub-acute ruminal acidosis (Krause and Oetzel, 2006). The reason for this risk is that ruminal pH declines following meals, and the rate of pH decline increases as meal size increases and as dietary effective fiber concentration decreases (Allen, 1997). Further, as cows spend less overall time feeding, and increase their rate of feed consumption, daily salivary secretion is reduced (Beauchemin et al., 2008), decreasing the buffering capacity of the rumen and reducing rumen pH. Alternatively, when cows slow down their rate of dry matter (DM) consumption, and have more frequent, smaller meals, throughout the day, rumen buffering is maximized, large within-day depressions in pH are avoided, and the risk of sub-acute ruminal acidosis is decreased. Thus, to maximize rumen health, efficiency and productivity, it is important to utilize feeding management strategies that promote the frequent consumption of feed in small meals throughout the day.
When do cows eat?
It has typically been accepted that dairy cattle exhibit a diurnal feeding pattern where the majority of feeding activity occurs during the day, particularly around sunrise and sunset. However, this observation is almost exclusively based on the feeding patterns exhibited by grazing cattle. DeVries et al. (2003) demonstrated that the diurnal feeding patterns of free-stall housed dairy cows were mostly influenced by the time of feed delivery, feed push-up and milking. Further, these researchers noted that the most dramatic peaks in feeding activity occur around the time of feed delivery and the return from the milking parlor. In a follow-up experiment, DeVries and von Keyserlingk (2005) separated feed delivery and milking times by 6 h. When animals were fed 6 h post milking, cow shifted their feeding pattern such that the greatest bunk activity was noted after the feed delivery and not after milking. In a more recent study, we demonstrated similar results when we shifted feed delivery (2x/d) ahead of milking by 2.5 h (King et al., 2016). Initial meal size following feed delivery was similar whether or not cows were milked at that time or not. The results of these studies demonstrated that for TMR-fed dairy cattle, feed delivery acts as the primary influence on their daily feeding activity patterns; these patterns are not influenced to the same degree by feed push-up, milking activity or, as seen in grazing cattle, the time of day. As result, even though dairy cattle may still spread their meals throughout the day, the largest ones will occur right after the delivery of fresh feed.
What does the cow actually consume?
Dairy cattle as commonly fed their feed components in the form of a total mixed ration (TMR). Total mixed rations 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, dairy cattle 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; DeVries et al., 2007). The sorting of TMR by dairy cows can result in the ration actually consumed by cows being greater in fermentable carbohydrates than intended and lesser in effective fiber, thereby increasing the risk of depressed rumen pH (DeVries et al., 2008). Likely related to this, in two recent studies it has been observed that such sorting of a TMR is associated with producing milk with lower fat percentage (milk fat decreases by 0.15% for every 10% refusal of long forage particles in the ration; DeVries et al., 2011; Fish et al., 2012). Imbalanced nutrient intake and altered rumen fermentation, as result of sorting, has the potential to impact the efficiency of digestion and production. In support of this, Sova et al. (2013) recently found that efficiency of milk production decreased by 3% for every 1% of group-level selective over-consumption (sorting) of fine ration particles.
Sorting of a TMR can also 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 cattle, this may be detrimental for those animals 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 cattle may not be able to maintain adequate nutrient intake to maintain high levels of production and growth (Krause and Oetzel, 2006). Again, there is evidence to suggest that this sorting behavior may impact production at a herd-level; Sova et al. (2013) showed that every 2 percentage point increase in selective refusal (i.e., sorting against) of long ration particles on a group level was associated with a per cow reduction of 0.9 kg/d of 4% fat-corrected milk.
Impact of nutritional management on feeding behavior
Dietary Composition
From a feed perspective, providing TMR that are high in physically-effective forage will promote a slower consumption of feed, in smaller, more frequent meals per day (DeVries et al., 2007). Such diets are also sorted to a lesser degree (DeVries et al., 2007; 2008) and, as result of greater fibre content and particle size, ruminated for longer periods of time. Despite this, the tendency in the dairy industry is not to provide higher forage diets to lactating cows, but rather diets that contain more moderate levels of forage, which in itself tends to be chopped quite moderately in length. This is done in an effort to maximize intake and digestibility, which in turn helps meet the requirements needed to optimize cow health and productivity.
Given this, other opportunities to modify the feeding behavior of cows on such rations need to be explored. There is increasing evidence that use of feed additives, which have a positive impact on the rumen environment, in turn, have concurrent benefits for feeding behavior. In recent research, we have demonstrated that supplementing lactating cows with a live strain of Saccharomyces cerevisiae yeast had beneficial impacts on meal patterning (DeVries and Chevaux, 2014). Specifically, supplementing cows with live yeast tended to result in cows having more frequent meals that were smaller and occurred closer in time together. This research supported work previously done in Spain, whereby similar effects on feeding behavior were seen (Bach et al., 2007). In that study, live yeast supplementation also had a positive impact on raising and stabilizing rumen pH. In our study (DeVries and Chevaux, 2014), cows supplemented with live yeast tended to ruminate longer and have less periods of elevated rumen temperature, which could be associated with less long bouts of depressed rumen pH. Likely, as a result of these improvements in nutrient flow, rumination, and stabilized rumen, the live yeast-supplemented cows tended to have higher milk fat content and yield.
It should be noted that this effect is not unique to live yeast. Other researchers have found similar results with other feed additives – including monensin. Lunn et al. (2005) demonstrated that providing monensin increased meal frequency in lactating cows experiencing sub-acute ruminal acidosis. Similarly, Mullins et al. (2012) found that monensin increased meal frequency and decreased the time between meals in the first few days after dairy cows were transitioned to a lactation ration. The common thread in all of these studies is an association between favorable meal patterns and a reduction in ruminal pH variation. Whereas meal patterning may, in itself, affect ruminal pH, it is likely that feed additives, such as live yeast or monensin, that have the potential to stabilize ruminal pH and fermentation, affect meal patterning as a secondary effect. Specifically, a more consistent fermentation pattern should result in less variation in volatile fatty acid production, improved fiber digestibility, and quicker return to eating.
Feed additives that promote healthy eating patterns and have a positive impact on the rumen environment and rumination may be very useful, particularly in situations where the risk of milk fat depression is high, such as with high-starch diets, or in early lactation cows, who are a greater risk of experiencing sub-acute ruminal acidosis. In these situations, the use of such additives, in addition to proper feed bunk management (as described below), will allow cows to optimize the potential of the feed provided to them and remain healthy and productive.
Feed bunk management
The delivery of fresh feed is clearly an important factor in stimulating cows to eat. Thus, increased frequency of feed delivery can greatly influence feeding behavior patterns, and thus also affect cow health and productivity. When cows are offered feed only once daily, there are significant peaks in feeding activity in the immediate time period following feed delivery compared to 2x/d feeding (DeVries et al., 2005). This behavioral response elicited by the delivery of fresh feed provided 1x/d could result in slug feeding and predispose cows to sub-acute ruminal acidosis (DeVries et al., 2005) due to large diurnal fluctuations in ruminal pH (Shabi et al., 1999). Inversely, cows fed more frequently (4x and 5x daily) tend to consume feed more evenly after each feed delivery, increasing their feeding time throughout the day (DeVries et al., 2005; Mantysaari et al., 2006). In addition, DeVries et al. (2005) found 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. Further, providing feed 2x/d or more often has also been demonstrated to reduce the amount of feed sorting as compared to feeding 1x/d (DeVries et al., 2005; Endres and Espejo, 2010; Sova et al., 2013), which would further contribute to more consistent nutrient intakes over the course of the day.
Such desirable feeding patterns are conducive to more consistent rumen pH (French and Kennelly, 1990), which likely contributes to improved milk fat (Rottman et al., 2014); fiber digestibility (Dhiman et al., 2002); and possibly production efficiency (Mantysaari et al., 2006) observed when cows are fed more frequently than 1x/d. Delivering TMR more frequently does also have the potential to impact DMI and milk yield. Hart et al. (2014) recently demonstrated that under 3x/d milking schedules, DMI was greatest in cows fed 3x/d (27.8 kg/d) compared to when fed 2x/d (27.0 kg/d) or 1x/d (27.4 kg/d). This increase in DMI came as a result of increased DMI following the return from milking and the delivery of feed. Interestingly, in a recent field study of free-stall herds in Canada, feed delivery of 2x/d compared to 1x/d was demonstrated to be associated with less feed sorting, greater DMI (+1.4 kg/d), and greater milk yield (+2.0 kg/d; Sova et al., 2013).
It is also interesting to note that in our recent study where we shifted feed delivery (2x/d) ahead of milking by 2.5 h (King et al., 2016), we found that this increase feed stimulation across the day resulted in cows consuming their feed more slowly in smaller, more frequent meals across the day. This change in feeding pattern contributed to an improvement in the efficiency of milk production. Collectively, the results of these studies all suggest that gains in intake, production, and efficiency may be had by having greater opportunities for cows to access fresh TMR across the day, either by increasing the frequency of feed delivery or by altering the timing of feed delivery to create multiple stimulation points for feeding across the day.
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. Research suggests that feed push-up does not have the same stimulatory impact on feeding activity as does fresh feed delivery (DeVries et al., 2003); nonetheless, push-up does play a vital role in ensuring that feed is accessible when cows want to eat.
There is evidence to suggest that the timing of feed delivery is also important for lactating dairy cows. Availability of fresh feed following the return from milking has typically been used to encourage cows to remain standing (while feeding) rather than to lie down. Researchers have shown that the presence of fresh feed in the bunk encourages longer post-milking standing times (DeVries and von Keyserlingk, 2005; King et al., 2016). DeVries et al. (2010) also found that the provision of feed around milking time resulted in the longest post-milking standing times. Further, this was the first study to document how post-milking standing time relates to the risk of intramammary infection; cows that lay down, on average, for the first time 40 to 60 min after milking tended to have lower odds of a new intramammary infection caused by environmental bacteria compared to cows that lay down within 40 min after milking. These results suggest that management practices that discourage cows from lying down immediately after milking, such as providing fresh feed frequently through the day (near the time of milking) may help decrease the risk of intramammary infection.
Conclusions
The feeding behavior of dairy cows is important for keeping cows healthy, efficient, and productive. Dietary rations provided to lactating cows need to be designed not only to encourage high intake and discourage feed sorting but also to be consumed in small, frequent meals. Feeding management strategies may then be implemented that allow cows to have good access to that feed and consume it in a manner which is conducive to good health, productivity, and efficiency.
ACKNOWLEDGEMENTS
This paper is an updated version of a proceedings paper written for, and presented at, the 2014 Mid-South Ruminant Nutrition Conference, held in Grapevine, Texas in April 2014. Much of the research presented in this manuscript was funded by the Natural Sciences and Engineering Research Council of Canada, Dairy Farmers of Canada, Agriculture and Agri-Food Canada, the Canadian Dairy Commission, Dairy Farmers of Ontario, the Canadian Bovine Mastitis Research Network, the Ontario Ministry of Agriculture, Food, and Rural Affairs, the Canadian Foundation for Innovation, the Ontario Research Fund, Westgen Endowment Fund, Investment Agriculture Foundation of British Columbia, the University of Guelph, and the University of British Columbia Animal Welfare Program.
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