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Le Producteur de Lait Québécois MagazineVolume Number January/February, 2020January 21, 2020

The importance of the feed bunk in free-stall housing

L’importance de la mangeoire en stabulation libre
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Feed bunk design plays a crucial role in the welfare of farm animals of all ages. The repercussions of a poorly designed feed bunk include, among other things, neck injuries, lameness, and substandard body condition among animals. 

When it comes to the question of a building's feed bunk, everyone has their own experience, their own opinion. No one escapes from the day-to-day reality of working with the feed bunk. Indeed, it is a key element, and one that must be taken seriously to avoid it becoming a limiting factor for animal welfare and for the productivity and cost-effectiveness of an operation.

Understanding the feeding behaviour of cows and the impact of inadequate bunk space can help producers make informed decisions. 

Behaviour

Feed intake

Dairy cows generally consume their TMRs in 7 to 12 meals a day, with a total feeding time between 3 and 5 hours. When feed bunk design and feeding management are inadequate, cows may eat large portions less frequently, thus increasing the risk of ruminal acidosis. Cows are more motivated to visit the feed bunk when fresh feed is offered rather than when the feed is pushed or when they eat to satisfy their hunger after milking.

Competition

Like all herd animals, dairy cows prefer to eat as a group. Insufficient space at the feed bunk generates competition, which may compromise the health and well-being of individual cows. Competition can be direct or indirect. Indirect competition arises when cows modify their behaviour to access the feed bunk, either by visiting during non-peak times of the day or by eating faster. The few studies that have focussed on the subject have shown that an overstocked feed bunk in an automated milking system leads to a reduction in the number of times subordinate cows visit the robotic milker. Likewise, having access to the feed bunk when fresh feed is served increases the cows’ motivation to visit the milker, even among subordinate cows.

Direct competition occurs through altercations or aggressive behaviour between individual cows. Some subordinate cows will even begin to distance themselves from dominant cows when feeding. They may even prefer a less palatable ration (e.g., leftovers) that is farther away from dominant cows to a more palatable ration in the presence of a dominant cow.

Impact on health and production

Foot health

Limited bunk space at peak times will also increase the amount of time that subordinate cows spend standing while they wait for bunk access. Inactive standing on a hard and damp surface increases the risk of developing foot health problems and the incidence of lameness in the herd.

Metabolic diseases

Cows that are struggling to secure a place at the feed bunk have higher peaks in insulin response (similar to insulin resistance), and first-calf heifers have more difficulty managing competition than mature animals do. 

Fatty acid profile

A study conducted by Woolpert in 2017 showed that the greater the bunk space, the greater the production of de novo fatty acids, which are synthesized in the mammary gland from precursors that derive from ruminal fermentation. This suggests that when cows have more room at the feed bunk, their stress level decreases, their feeding behaviour is more natural, and ruminal fermentation is better. Lactanet data shows that promoting the production of de novo fatty acids is advantageous, as these acids are associated with increased milk fat levels.

Reproduction

The probability of pregnancy at 150 days increases as bunk space increases.

Components and milk quality

In 2013, Sova reported that for every 10 cm of additional space at the feed bunk (between 36 and 99 cm), cows increased their fat levels by 0.06 per cent. Furthermore, somatic cell counts dropped by an average of 13 per cent, suggesting that the cows were eating after milking rather than returning immediately to their stalls to lie down while the teat sphincters were likely still open.

Transition cows

The transition period is probably the most documented in literature with respect to bunk space for dairy cattle. A number of studies show that overpopulation at the feed bunk leads to a decrease in dry matter intake. Cows are therefore more likely to develop subclinical ketosis and metritis when feed bunk space is limited.  

What are the recommendations?

Space

An experiment done by Lactanet at McGill University’s Macdonald Campus Farm determined that the overall width of a Holstein cow exceeds 76 cm (30 in.) (Figure 1).

Hence, lactating cows should be allowed at least 60 cm (24 in.) of linear bunk space per cow (Table 1), under the assumption that one in four cows does not have access to the feed bunk. For dry and fresh cows, the recommended space allowance is at least 76 cm (30 in.) per animal, and the optimal allowance for close-up cows would be 90 cm (36 in.).

Feed bunk design

The bottom of the feed bunk should be 10 to 15 cm (4 to 6 in.) higher than the height of the cows’ feet. It is recommended that the surface of the feed bunk be acid-resistant and smooth to facilitate cleaning. Producers who are not equipped with automatic feed pushers may use shallower feed bunks (1 to 3 in.) to keep the feed close to the animals. It is also important to clean the feed bunk regularly to remove any feed trapped in the corners.

Feed bunk design

Height of the manger curb

The recommended curb height depends on whether or not headlocks are used. It is also based on the clearance that cows require to avoid brisket injuries and comfortably access feed. Barriers higher than 20-22 in. (51-56 cm), i.e., roughly 1/3 of hip height (HH), should be avoided. This formula is useful when it comes to determining the appropriate curb height for replacement animals or for dairy breeds other than the Holstein. For replacement animals, the height of the curb should accommodate the smallest animals in the group. In practical terms, when pouring the concrete for the curb, it is important to take into account the thickness of the horizontal bar if headlocks or slant bars are to be installed. The edges of the curb should also be rounded to avoid injury.

Feed barriers

Studies have found no differences in feed intake or milk production between the different types of restraints (rails versus headlocks). Nonetheless, subordinate cows seems to benefit from a physical barrier separating them from dominant cows. Cow displacements were reduced by 21 per cent less when headlocks were used as opposed to a post-and-rail barrier. Cows also spent less time standing inactively in the feed alley, which may decrease the risk of lameness.

A headlock inclination of 15 to 20% will facilitate access to food.When installing headlocks, ensure that the top bar is higher than the height of the cow’s back to avoid neck injuries. For replacement animals, the bar should be adjusted for the tallest animals in the group. Likewise, a slope of at least 15 to 20 per cent (20 cm or 8 in.) will ensure easier access to feed (Photo2).  Standard commercial headlocks are generally 60 or 76 cm wide (24 or 30 in.). When using 60-cm (24 in.) headlocks, it is normal that some spaces remain vacant (1 out of 5) because the cows are wider than the openings. The important thing is to make sure the feed bunk is long enough for the number of animals present.

The height of a rail barrier should be around 110-125 cm (45-50 in.). To avoid neck injuries, the rail should be offset over the manger by 20 to 35 cm (8 to 14 in.) from the inside of the curb on the cow side. Pushing feed up frequently also reduces the pressure on the cows’ necks.

Conclusion

There are many aspects to consider when designing a feed bunk for dairy cattle. Different groups of animals have different requirements. A well-designed feed bunk can make a big difference in ensuring healthy and productive cows.

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