To achieve this, heifers must be fed to grow at a high rate while not becoming overconditioned, as well as to remain healthy.
The costs of replacement dairy heifer rearing are second only to the feed costs of lactating cows, representing 15 to 20 percent of total farm operational expenses.
Of these costs, feed represents the greatest expense in heifer-rearing costs. The primary nutritional goals of a successful dairy replacement rearing program are, thus, to feed heifers for maximal production potential – at a low economic and environmental cost – without compromising health or welfare.
We have seen much advancement, particularly in the past decade, in replacement heifer nutritional research directed to these goals.
Concurrently, we have also seen a significant rise in the amount of scientific research relating behaviour to the management of dairy cattle, particularly with respect to the interaction with health.
Much of this research has been focused on using information on the natural behavioural patterns of dairy cattle to make management decisions beneficial for the health, productivity and welfare of these animals.
This article describes those primary areas where researchers have considered the interaction of behaviour and nutritional management in replacement dairy heifer rearing.
Feed delivery methods
Total mixed rations (TMR) are believed to be the optimal way to provide the balance of nutrients (including protein and structural and non-structural carbohydrates) that ruminants need to maintain a stable and efficient microbial population.
It is for this reason that providing feed as a TMR, rather than separately feeding the grain concentrate and forage components, is the most common method of feed delivery used on commercial dairy farms for nearly all classes of animals more than 6 months old.
Following milk weaning, replacement heifers are typically fed a diet consisting of grain concentrate and forage (hay or silage) until approximately 6 months old.
Under commercial management settings, the grain concentrate is provided in different ways, typically separate from the roughage, on top of the roughage (“top dressing”) or mixed in with the roughage.
Providing feed components as a TMR, as opposed to providing them separately, to replacement dairy heifers appears to increase the distribution of dry matter intake (DMI) over the course of the day, increase feeding time and reduce feeding rate.
Feeding a TMR also reduces, as compared to providing feed components separately or top-dressed, the amount of sorting against forage and for concentrate in replacement dairy heifers.
Thus, the consumption patterns of heifers consuming a TMR should, as in mature cows, result in consumption of a more balanced diet and greater rumen buffering, thus contributing to improved rumen health.
There are data to suggest feeding a TMR to heifers from a young age not only has these immediate behavioural effects, but may also have longer-term benefits to these animals.
A study found that heifers previously fed a top-dressed ration maintained similar feeding patterns after they were switched to a novel TMR (for a period of seven weeks).
Moreover, the increased competition for feed observed in heifers fed a top-dressed ration, compared to those fed a TMR, was also maintained after they were all switched to the novel TMR.
These heifers previously fed the top-dressed treatment also maintained looser fecal consistency.
Interestingly, the feeding and competitive behaviour patterns persisted throughout the seven weeks of that experiment, suggesting the animals had not only learned these behavioural patterns, but that these patterns became habitual and may be difficult to extinguish over time.
Ration composition and feeding level
To meet the objectives of rearing replacement dairy heifers, feeding strategies utilized are variable. Heifers have traditionally been provided diets that contain high-fibre, economically priced forages, which adequately meet their energy requirements.
Feeding replacement heifers a high-forage, moderate-energy diet has the potential to control caloric intake and allow producers to target the growth rate of heifers.
Researchers have also recently investigated how caloric intake can be controlled through the provision of a nutrient-dense diet fed in a limited amount.
Limit feeding allows for the effective control of average daily gain in replacement heifers and also effectively decreases fecal excretion, increases feed efficiency and reduces feed costs in some cases.
Unfortunately, limit feeding does pose behavioural concerns for dairy heifers. Limit feeding has been shown to reduce eating and lying time, resulting in animals spending more time standing while not eating.
Researchers have also found limit feeding can increase vocalization levels in heifers, as well as increased the amount of aggressive “reaching” to acquire feed.
Limit feeding dairy cattle has also been associated with increased levels of oral stereotypes, including tongue rolling, constant head nodding and bar biting or licking.
The changes in behaviour associated with limit feeding may be attributed to hunger and frustration as a result of lack of satiety.
The lack of satiety observed in limit-fed heifers results from not only having feed available in a limited amount, but also for a very short duration.
The one to two hours of feeding duration observed in limit-fed heifers is a stark contrast from the four to nine hours that dairy cattle, under natural grazing conditions, would engage in foraging behaviour throughout the day.
Moreover, there is potential for some of these behavioural effects to result in negative health implications.
For example, increased time spent standing, particularly on hard flooring surfaces, may increase the risk of hoof pathologies.
Further, the consumption of a highly-fermentable ration, when eaten rapidly and ruminated less, may cause greater within-day bouts of sub-acute ruminal acidosis, which are known to be detrimental to health and feed efficiency.
An alternative to limiting the amount of feed provided would be to limit the nutrient density of a feed offered ad libitum.
One possible method is to add a low-nutritive, low-value feedstuff to the diet that would satisfy the natural feeding behaviour patterns of limit-fed animals, as feeding duration would be increased.
In addition to achieving satiety, this feeding method may also reduce the risk of sub-acute ruminal acidosis.
A low-nutritive feedstuff will decrease passage rate and increase rumination time, thus increasing saliva production and rumen buffering.
In a recent study, straw was added (by 10 and 20 percent of DM) to a TMR fed ad libitum to replacement dairy heifers.
Researchers found that feeding rate, meal size and meal frequency decreased with increased straw in the diet, while feeding time and meal duration increased.
This would suggest that the addition of straw might help meet the natural foraging behaviour patterns of heifers. Interestingly, DMI also decreased with the addition of straw to the ration.
Based on these intakes, researchers found that all requirements for maintenance and growth of 1 kilogram per day could be sufficiently met with 10 percent straw in the diet.
Further, they found that sufficient nutrients were consumed with 20 percent straw in the diet to meet the requirements to achieve a 0.9 kilogram per day growth rate.
Overall, these findings suggest that, if a ration is balanced properly, the addition of an inexpensive, low-nutritive feedstuff may help reduce DMI and enable producers to target caloric intake for desirable weight gain and development while allowing heifers to engage in more natural foraging behaviour.
One of the drawbacks of that study was the finding that additional straw increased the amount of sorting of the ration.
This result, coupled with ad libitum intake, could potentially increase within-group variability in nutrient intake. Thus, as follow-up to this, another group of researchers conducted a study in which a low-nutritive feedstuff (straw) was provided with (either within or alongside) a limit-fed ration.
Researchers found that the provision of straw beside a limit-fed ration allowed heifers to increase their feeding time (to a similar amount of time observed for heifers fed ad libitum), increase rumination and decrease inactive standing time.
These findings suggest the provision of straw allowed heifers to express their natural foraging behaviour patterns as well as achieve satiation and promote better rumen activity.
Researchers also found the target ADG (0.9 kilogram per heifer per day) could be maintained with the provision of straw alongside the limit-fed ration.
Interestingly, they also found, as somewhat expected, the provision of straw did decrease feed efficiency and increase the cost of gain, but both not to the extent of that typically seen on a high-forage ad libitum-fed ration.
Competition for feed access
The intensification of the dairy industry, along with rapid growth in herd sizes, have resulted in housing dairy cattle, including youngstock, at higher densities (i.e. overstocking).
This management practice is often justified, as it can be argued that heifers only spend a small fraction of their day consuming feed (3 to 3.5 hours per day) and, thus, it could be assumed that the provision of a feeding place for each individual heifer within a pen is not necessary.
However, cattle tend to synchronize their behaviour; many animals in the group will feed, ruminate and rest at the same times.
When cattle are fed in groups, the initiation to feed by one animal will often stimulate the other animals regardless of whether they show signs of hunger.
Further, synchronized peaks in feeding activity occur at certain times of the day, such as when fresh feed is delivered.
As a result, provision of fewer feeding places than animals may result in high levels of competition for feed, particularly during these peak periods of feeding activity.
Alternatively, the synchrony between animals has the potential to break down in such situations of high competition and may lead to animals feeding at different times to avoid excessive aggression.
Competition for feed appears to have similar effects, across feeding strategies, on the feeding behaviour of replacement dairy heifers.
A study recently found that ad libitum-fed heifers exposed to high feedbunk competition (two heifers per feed bin) tended to have 10 percent shorter daily feeding times (192 vs. 213 minutes per day) than heifers with no feedbunk competition (one heifer per feed bin).
Similarly, decreases in feeding time have also been reported in studies on limit-fed heifers. Interestingly, despite the reduction in feeding time, researchers have not reported any effect of competition for feed on the DMI of replacement dairy heifers fed ad libitum or, less surprisingly, those that are limit-fed.
To maintain similar DMI in situations of high competition, heifers compensate by eating faster throughout the day, particularly during periods of peak feeding activity and by shifting their intake patterns such that a greater proportion of their DMI occurs in the later hours after feed delivery.
Competition for feed access also appears to change the meal patterning of heifers, resulting in consumption of fewer meals per day, which are larger and longer in duration. Given that within-day rumen pH declines increase with meal size, large and long meals may have significant negative impact on rumen fermentation.
Conclusions
There is a growing body of literature on dairy cattle behaviour and how this field of science can aid in making science-based recommendations for best management practices.
For replacement dairy heifers, much of this research has been focused on the interactions between nutritional management and behaviour, particularly how these relate to different feed delivery methods, ration composition and feeding level, and competition for feed access.
This research has provided us with a basic understanding of nutritional management practices that promote feeding behaviour patterns related to more consistent nutrient intake, improved rumen health and less variation in growth rates. PD
References omitted due to space but are available upon request.
—Excerpts from Dairy Calf & Heifer Association Conference, April 2011
- Trevor DeVries
- Assistant Professor
- University of Guelph
