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 was 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. These results indicate that for group-housed, 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., 2011a; 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 behaviour 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. Thus, overall, there is a large body of evidence to suggest that the way cows eat, when they eat, and what they eat, has a significant impact on rumen digestion, health, and efficiency. We can use that knowledge, therefore, to improve our feeding management strategies.
Impact of nutritional management