Almost every time I visit a dairy barn, I make a point of looking at post-weaned replacement heifers as well. Raising young dairy heifers can be one of the greatest challenges even on the best-run dairies. I believe implementing a good post-weaning heifer program makes good sense and contributes to their future success as high-milk-producing dairy cows.
Sometimes it’s hard to realize that post-weaning heifers from two to six months of age are not miniature milk cows. Rather, these young replacement heifers have immature rumens, which takes up to six months of age before they are fully developed and functional; contain enough rumen microbes, digestive enzymes and volume to consume and efficiently digest all types of forages and other feedstuffs.
Keeping this in mind: a young dairy heifer diet should contain enough starch-enriched feedstuffs to promote rapid and continuous rumen development.
Don’t want them fat
Most viable dairy heifer replacement programs still target a modest growth rate for post-weaning heifers of 1.8 – two lbs. per day (increased to two – 2.2 lbs. after puberty at about nine to 10 months of age). Feeding diets with excessive energy to make them grow much faster should be strictly avoided. Overweight heifers tend to lay down fat in their developing udders, which irreversibly reduces their capacity to produce milk in their first and future lactations.
Most ruminant scientists acknowledge dairy heifers gaining more than what’s considered the “safe” limit of 2.2 lbs. per day may actually lay down more lean muscle compared to replacement heifers on a more growth-controlled program and save on overall feed and housing costs. However, they also agree chances are very good more fat heifers are produced by promoting such rapid growth.
But don’t short-change your post-weaning heifers, either!
A sound heifer grower diet for two-to-six month old animals should contain enough dietary energy of 67 to 69 per cent TDN (total digestible nutrients), 16 to 18 per cent protein, and be fortified with adequate levels of macro- and trace-minerals and vitamins. Also keep in mind young dairy calves from weaning (180 lbs.) to six months (400 lbs.) of age have a limited dry matter intake from about six to 10 lbs. per head per day.
Pick a proper diet
There are many practical diets for two-to-six month old heifers that promote good rumen development and growth performance at the same time. For example, a University of Minnesota field trial fed 90 dairy replacement heifers from three to six months of age, weighing on average 222.2 lbs. for 84 days on a balanced ration consisting of free-choice high-quality hay (16.7 per cent CP) and a 18 per cent grain ration (based on cracked corn and soybean meal) fed up to five lb./head/day.
Average daily gain was relatively consistent among the study heifers; recorded at 2.1 – 2.2 lb./head/day. Addition of some dried distillers grains to replace some of the soybean meal in the diet as an alternative protein source did not affect growth at all. Such demonstration also proves that high-quality forages and sufficient amounts of grain are required in order to achieve an acceptable level of performance.
In contrast, I am not an advocate of feeding two-month old dairy heifers a total mixed ration (TMR) containing silage, either specifically formulated for them, or producers that simply feed them lactation leftovers. In particular, I believe these young post-weaned heifers have limited rumen capacity, which is not fully developed in the first place and bulky TMRs containing silage challenges their daily intakes in order to obtain enough essential nutrients. As proof, I have on occasion seen young heifers with their “big balloon” bellies filled with silage and gas.
Another reason not to feed TMRs is some ensiled feeds such as high-grain corn silage contain excessive energy and often not enough protein, which could possibly over-condition young growing heifers. If a dairy producer wants to feed a TMR/ensiled feed, I recommend waiting until heifers become older; four to six months of age, so silage might be formulated up to 25 per cent of the total forage dry matter consumed.
Regardless of what post-weaning diet is ultimately fed, the best diet for dairy replacement heifers is also largely based upon knowing how the animals look at any given time. Dairy heifers should have a body condition score of three to 3.5 (based on a five-point scale; one = thin, five = fat). If they appear not to be growing or are thin; dry matter intake records and the entire diet should be reviewed.
Diet and management
Dairy producers should also parallel proper diet with good post-weaning heifer management. Many dairy specialists and I recommend to first wean six- to eight-week old heifers still consuming about a kilo of calf starter for a few days.
Wait a couple of weeks before removing them from hutches or individual stalls and then segregate them into small groups according to their size and weights. All of these young dairy candidates should be moved into groups of no more than five to seven heifers per pen. These pens should finally have adequate space for animals to move around and rest, be clean and well-bedded, with water provided on a free-choice basis.