At the February 20 NE Ohio Regional Dairy Conference held in the Fisher/Shisler Conference Center on the OARDC campus in Wooster, Mike Van Amburgh from the Cornell University Department of Animal Science addressed the topic of heifer management. One of the key points from Van Amburgh’s presentations is that good heifer management centers on the body weight of the animal. Heifers must continue to grow and gain weight to be productive and cost-effective. Benchmarks, based on a percentage of the animal’s mature weight, are a useful management tool.
Benchmark figures matched to heifer production stages include puberty at 45% of mature weight. Breeding and pregnancy should occur at 55 to 60% of mature weight and the heifer should weigh 82% of her mature weight at post calving as she begins her first lactation. It is important to note here that the 82% benchmark is post calving because the fetus will make up a significant percentage of the heifers weight pre calving. Looking at these benchmark figures the obvious question is, how does the manager determine what the heifer’s mature weight will be? Van Amburgh said this is where many dairy farms need to improve their management by weighing calves and heifers on a regular basis.
The projected mature body weight of heifers is based on the weight of mature cows in the milking herd with similar genetics. That mature weight is calculated based on cow weight at the middle of the third and fourth lactation of healthy cows. Van Amburgh says that one result of breeding and selecting for higher milk production is that mature cow weight has increased. He cited the Cornell University dairy herd as an example. In 1993 mature cow weight averaged 1474 lbs. and in 2016, it averaged 1777 lbs.
According to Van Amburgh, many managers are able to do a good job of growing heifers to the benchmark weight percentages for breeding through the second trimester of pregnancy but then often don’t provide enough nutrients for both fetal growth and heifer growth in the last trimester of pregnancy. It goes back to understanding the hierarchy of nutrient use and how nutrients are partitioned when limited. Once an animal has conceived, growing and nourishing the fetus then becomes a priority over growth if nutrients are limited. The nutrient requirement for fetal growth is minimal through the second trimester, but then takes a big step up in the last trimester and especially in the last 60 days before calving. A different ration is needed to meet this increased fetal growth requirement plus the heifer body growth requirement. To best accomplish this, Van Amburgh suggests that dairy farms consider having a separate third trimester feeding group for heifers.
If heifers are not fed to meet both third trimester fetal growth and continued body growth, they most likely will fail to meet the benchmark of 82% of mature weight post calving at first lactation. This is an important benchmark, with significant economic implications. Van Amburgh says this is the benchmark where many dairy herds fall short. His on-farm work indicates that in many herds first lactation heifers are peaking at 69-70% of mature cow milk yield. The goal is to peak at 80% of mature cow milk yield. Research data indicate this is directly related to and correlated with the body weight percentage benchmark. Peaking at 69-70% of mature cow milk yield instead of 80% equates to an eleven to twelve pound lower peak. Research indicates that for every pound of peak milk a total of 225 to 250 pounds of milk is produced over the entire lactation. As an example, at eleven pounds of peak milk lost, multiplied by 225 tells us that that at least 2475 pounds of milk production was lost as a consequence of the heifer not weighting enough by first lactation. Multiply that by the number of first calve heifers in the herd and the economic impact adds up quickly.
The other important benchmark in heifer management that Van Amburgh talked about was age at first calving. It affects the cost of raising a replacement dairy animal to first lactation and it is a factor in the lifetime milk production yield. Van Amburgh showed several slides with an average estimated cost of $2300 for a 25 to 25.6 month age of first calving. The most cost effective age of first calving was 22 months due to a couple of factors. First, it reduced the cost of raising the heifer from $2300 to $2000 and second, those heifers tended to have higher milk production. Research out of Wisconsin that analyzed more than 69,000 heifers showed heifers with a first calving age of 22 months had a longer herd life and produced more total lifetime milk compared to heifers entering at later ages. Keep in mind it is crucial that heifers reach this 22 to 23 month age of first calving at 82% of their mature weight so that they produce 80% of peak milk yield of mature cows.
Rory Lewandowski is an OSU Extension Agriculture & Natural Resources Educator and may be reached at 330-264-8722.
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