Being aware of some of the major risks that can result from overcrowding heifers is essential to managing them effectively. Implementing mitigation strategies early on can help prevent the situation from taking a negative toll that will ripple into future lactations.
So how many heifers are too many? There are multiple ways heifers can be overcrowded; the feedbunk and available waterers probably comes to mind for most, but also for things like shade or shelter. While not a lot of research exists on this topic specific to heifers, there is quite a bit of lactating cow research that demonstrates negative impacts starting at 120 percent of stocking density.
At this level of overcrowding, cows begin to sacrifice eating time for resting time and experience negative effects to health and productivity. Therefore, it’s reasonable to conclude heifers would begin to feel the strain of overcrowding at the same density.
Risk No. 1: Poor body condition scores
I see many dairies compensate for overcrowding by offering more feed. For example, a producer may put out extra bales of hay. The rationale: Animals will stop eating when their energy requirement has been met, and all animals will be able to meet their requirements. However, with social dynamics in an overcrowding situation, this simply isn’t the case.
With overcrowding, there is more competition to get to the feedbunk. The dominant boss heifers will always be sure to get their fill. Just like humans, some bovines will overeat, so their diet must be regulated. Overcrowding at the feedbunk can also allow dominant animals to sort for more palatable feed, leaving leftover, picked-through feed for the subordinate animals.
This can lead to differences in nutrient intake and dominant heifers may become overconditioned. The more timid, subordinate heifers will have to pick through the left-behind feed, often falling short of their nutrient needs. While underweight heifers can be a challenge to breed, overweight heifers can be just as problematic.
When dairy heifers become too fat, there is a point where the fat pad in the mammary gland starts to impede the secretion cells, forever limiting her future milk production. For this reason, overfeeding is not a good solution to overcrowding.
Mitigation strategies
It’s important to feed these developing heifers appropriately and provide the right amount of energy to meet their needs. Providing a more nutrient-dense diet can help make every bite of feed count. Utilizing headlocks can help limit dominant animals from taking over and give timid animals more time at the feedbunk.
Be sure to push up feed routinely. Often times, heifer barn feedbunk management can be forgotten compared to the lactating barn, but increasing feed push-up ensures greater access to feed for subdominant animals and can reduce nutrient intake variability.
Finally, be sure to monitor body condition scores (BCS) for this group on a routine basis, monthly at a minimum. If you move heifers to the pen and don’t look at them until breeding time, you might not like what you see. By routinely checking heifer body scores, you can spot issues before they become major problems and take corrective action before breeding.
At 3 months of age, BCS should be around 2.2, and by 12 months, BCS should be about 3 to achieve a 3.5 BCS at calving.
Risk No. 2: Ongoing subacute rumen acidosis (SARA)
SARA is a condition that sets in when volatile fatty acids accumulate in the rumen and the pH falls below 5.5 for more than three hours. Excessive intake of rapidly fermentable carbohydrates is one of the major causes of SARA.
Research from the Miner Institute has shown that overcrowding can alter rumination patterns, increase aggressive behavior at the feedbunk and reduce total feeding time. As a result, animals have greater risk for SARA due to overstocking than because of changes in diet.
In 2008, work out of the Lethbridge Research Centre showed repeated exposure to SARA resulted in increased severity for subsequent SARA attacks. If heifers are overstocked and experience SARA during the growth stage, it may pre-expose them to greater severity of SARA during lactation, which can adversely impact dry matter intake, feed efficiency and ultimately milk production.
Mitigation strategies
Working with a nutritionist on the heifer ration can help ensure the ration meets the nutritional requirements of these developing animals, while also balancing for volatile fatty acid load.
The physical makeup of the ration can be just as important as the nutrient content. Failure to present a diet with adequately processed mixed fiber is another common cause of SARA. Providing adequate to extra physically effective fiber (peNDF) in the diet can help stimulate chewing, which in turn helps to buffer the rumen, counteracting SARA observed during overcrowded conditions.
It’s important that the peNDF is adequately processed (cut to the ideal length), as some work has shown inadequately processed straw can exacerbate the negative responses of overstocking. Your nutritionist can help you determine the ideal particle length for each forage type ahead of harvest.
Risk No. 3: Increased health challenges
When you stock facilities past their capacity, it can be more challenging to maintain sanitation and health. More heifers means more manure, urine, flies, etc. Therefore, it should be no surprise that one of the biggest risks of overcrowding is an increase in lameness and disease outbreak. Overstocking serves as a subclinical stressor, so any additional stress on heifers during overstocked conditions will only worsen the negative effects and weaken the immune system.
Overcrowding often results in heifers standing longer in the alley, waiting for water or freestalls for resting. If bedding and stalls aren’t maintained, heifers are less likely to use them when they become available, resulting in increased stress and more standing time, further increasing the likelihood of lameness. Furthermore, if the animals are standing in manure, there is a greater risk for hairy heel wart development. Heavy fly populations can also increase the chance of heifers freshening in with mastitis.
Mitigation strategies
If you have to overcrowd heifers, try to make them as comfortable as possible by maintaining facilities and sanitation. This means you can’t keep the same chore schedule; you need to adjust frequency of chores appropriately for the increase in stocking density.
For example, if you scrape alleys and change bedding every five days when heifers are stocked at 100 percent, you would want to increase these activities to every four days if stocking density increases to 120 percent.
Also, take precautions to manage additional environmental stressors, such as flies, to help prevent common outbreaks of pinkeye and other highly contagious diseases that spread quickly in overcrowded settings.
By managing heifers with careful attention, the risks of overcrowding can be mitigated. Know the challenges and plan accordingly. 
PHOTO: If you have to overcrowd heifers, try to make them as comfortable as possible by maintaining facilities and sanitation. Staff photo.
Kate Cowles is a nutritionist with Cargill Animal Nutrition. Email Kate Cowles.
