Consistent, But Not Excessive, Growth Rates for Dairy Heifers

Dr. Ronald L. Boman
USU Extension Dairy Specialist
    At the recent Western Dairy Management Conference in Las Vegas, we were privileged to hear Dr. Michael Vandehaar from Michigan State University speak on what I call the optimum growth rates for dairy replacement heifers. He did a superb job of presenting research data to back up his points. It is tempting to try to reduce the average cost of $1,200 of rearing a heifer from birth to calving at 24 months by feeding and managing for accelerated growth rates to reduce the age at first calving, but this can have adverse consequences.

    The critical time to NOT have excessive growth is from three to ten months of age. During this time period the secretory tissue of the mammary gland is growing two to four times faster than most of the other body tissues. If the heifer fattens during this time period because of excess energy intake, fat cells can replace the secretory tissue and thus reduce her ability to produce milk after she freshens and in subsequent lactations. Growth rates of 1.5 to 1.7 lbs/day are recommended during this time. At about 10 months of age the heifer should have had two estrous cycles (reached puberty) and the rate of growth of the mammary gland slows down to the same rate as the rest of the body tissues. Dr. Vandehaar presented research evidence of mammary secretory tissue reductions of 5 to 50% when accelerated growth occurred during the period of rapid mammary tissue proliferation. Reductions were greatest with corn silage based diets and less with alfalfa based diets and those diets that had higher levels of total protein and were balanced for rumen by-pass protein.

    We want Holstein heifers to weight 1,250 lbs after calving at 24 months of age. In order to achieve this the heifers need to weigh 1,400 lbs before calving. Thus they would need to average 1.8 lbs of daily gain during this time period (assuming the calf weighs 90 lbs at birth). These past few weeks I have not only seen 8 to 10 month old heifers that were too fat (over conditioned), but I have also seen heifers that were nearly 30 months of age that were too small. Sometimes dairymen forget to pay close enough attention to consistent heifer growth rate. I see too many heifers that are either put out to pasture and neglected or forced to eat low quality forages (with little or no supplemental grain). I don’t want to give the impression that heifers should not graze pasture. If pastures are fertilized and irrigated properly and if heifers are rotated and managed intensively, they do gain up to 2 lbs per day. Here again management and staying on top of things is the key.

    Let’s try harder to do a better job of raising our dairy replacement heifers during the critical period from three to ten months of age. Also let’s pay attention to them and keep them growing before and after this period so that we have well grown heifers of 1,250 lbs after they calve at 24 months of age.