Hoard's Dairyman: How are those heifers doing . . . really?
How are those heifers doing . . . really?
by A. F. Kertz
The author is the principal in Adhil, LLC, a St. Louis-based consulting firm.
Some measure of calf and heifer growth is useful since they are “grown” as herd replacements. But in practice, growth often is not measured. This may seem a bit academic, but it is a very practical issue.
If a commercial calf or heifer grower is paid on the basis of gain, then a few scale weights are taken in order to establish a starting point and ending point for payment. In larger operations, this measure may be by groups of calves, being sure that calves are identified which are in the group initially so that the same calves can be measured as a group at the end point, too. On a smaller scale and with individual calves, body weight can be estimated by a calibrated tape measure.
But what about height as a measure of growth? This can be done at the withers/shoulders or at the hips. It seems more people now use hip heights than wither heights, as they may be easier to take and are less variable because young stock tends to stand more calmly for hip height than for wither height measurements.
While height curves typically have been based on wither height, these curves can be approximated for hip height by simply adding 2 inches. There also is a reasonable relationship between body weight and wither height, heart girth, hip width, and body length with correlations in the high 0.90 range (1.0 being perfect). And then there is the relationship between heart girth and body weight which was established in 1935 by Missouri scientists with an accuracy of plus or minus 7 percent of actual heifer weights.
Another element not often recognized is the rate at which height growth occurs. With heifers 30 inches tall at birth and 54 inches tall at first calving, 50 percent of that 24-inch gain in height is realized in the first 6 months of life, another 25 percent in the next 6 months, and only 25 percent during the last 12 months before first calving.
But what if the genetics and size of cows is greater than the population used to develop these thumbrules? I know no reason that this relationship would not be proportionately the same. Also, if you have measured and tracked individual calves under 6 months of age at regular intervals, you will have noted at times that height and weight go through growth spurts, just as children often are observed to do. This is another reason that experimental or field numbers must have enough observations and measured frequently over time so that these variations will not prevent measuring true differences.
There are several factors which can impact growth measurements, some especially in calves under 2 to 3 months of age. Some of these are as follows:
• Level of intake. The gut residence time of milk or milk replacer for a young calf is relatively short. These feeds have a very high digestibility and relatively fast transit. Most milk or milk replacer feeding rates are between 1 to 2 percent of body weight. By contrast, starter intake at weaning may be 1 to 2 pounds daily which is about 1.5 percent of body weight. After weaning, when starter intakes should be 4 to 6 pounds daily, rumen fill will change noticeably as starter intake alone becomes approximately 3 percent of body weight on a dry matter basis. This in itself distorts true body weight gain. This also is why there should be several postweaning body weights taken to truly measure gain as apparent daily gains of about 3 pounds or more daily can be measured if you catch calves on the upswing of rumen fill.
• Intake and outgo. Calves drink water at about four times their dry matter from starter. Therefore, water consumption associated with starter intake before weaning may be 4 to 8 pounds daily (about one-half to a full gallon) which goes up to 16 to 24 pounds after weaning. Additionally, timing of urination and defecation contribute to body weight variation.
At this stage, body weight is around 150 to 200 pounds. This is a relatively low number when intake for water or starter, along with urination and defecation, are relatively large relative to this body weight. Hence, daily gains can be quite variable and high at this time which is why more frequent weighings and with more calves are desirable, especially for research purposes which is where we get our guidelines. This variation in body weight will drop off with age as heifers grow since feed and water intake drops relative to weight.
• Rumen roughage fill. Compared to calf starter, roughage/forage has a lower digestibility, slower rate of fermentation, and a longer residence time in the rumen. This affects rumen fill and can reduce dry matter intake. You should begin feeding roughage/forage after 2 months of age. This is another transition time, like the weaning transition time, which can result in skewed body weight gains. It also can result in gains which are not representative of true overall growth.
A classic study in the United Kingdom in the 1960s illustrated how distorting rumen fill from roughage can be. These calves were fed various levels of forage and weaned at 5 weeks and sacrificed at 12 weeks.
Clearly, as roughage feeding level went up, so did rumen and digestive tract contents as a percent of body weight. It varied from 26 percent of body weight with 16 percent forage up to 36 percent at 31 percent forage.
• Estimators of BW gain.A hipometer was compared in a University of Guelph study to more traditionally available tape weights in reference to scale weights. A total of 311 Holstein heifers were used from four Canadian research herds. They ranged from 1 week old to immediately prior to calving (24 months).
Mean body weight of all heifers was 575 pounds. Correlations between hipometer and scale weights and scale and tape weights were similar, particularly for heifers aged 3 to 15 months. Authors noted this was of particular concern because groups outside this range represent ages when dairy heifers would be weaned (less than 3 months) and when breeding would normally begin (older than 15 months).
Now what was missing in all of these factors in data just reviewed? If we are measuring true growth, there should be measures of height and maybe length and width, too. But until there is a relatively more simple method of doing this, such measures are not likely to happen.
Why is this important? Calf and heifer growth affects economics of your business whether you grow them or have them raised. Eventually, it affects the kind of cows that you have along with their milk production. What are you doing on your operation to measure calf and heifer growth?