By now, most replacement heifers are coming off their winter feeding programs and producers should be getting them ready for this year’s breeding season.
Depending how well these animals fared during the last six months should determine what we can do for them over the next two to three months until they are bred. It is a good time now to make any necessary adjustments to your feeding and management program, so heifers continue to gain enough frame size, weight, and good body condition, and therefore be ready, when the bulls are finally turned out to successfully breed them.
In retrospect, age, weight and breed influences when replacement calves will start to cycle and therefore reach puberty. Most commercial replacement heifers should have had their first heat cycle by 13 to 15 months of age in order to calve out at about two years of age. Because bodyweight, not necessarily age dictates when they’ll start to cycle, the general conscience among beef specialists and experienced producers alike recommends that replacement heifers should achieve about 65 per cent of their mature cow weight by the time the breeding season begins. This means, if a producer runs a mature herd of Simmental-Angus cross cows weighing about 600 kg (1322 lbs.) each; over wintered replacement heifers in the proper body condition should achieve a target breeding weight of about 390 to 400 kg (860 to 880 lbs.).
Just how important is this target weight for breeding replacement heifers?
A well-planned two-year field trial conducted at the University of Nevada over-wintered a group of estrus-synchronized replacement heifers on a alfalfa (and energy supplemented) diet. The researchers recorded only promising beef heifers that met the “65 per cent target weight rule” cycled and conceived within a prescribed 45-day breeding season. Heifers of similar age that did not meet this target weight failed to conceive within the same period. It was acknowledged that the quality of the forages was challenging at times during this study and may have played a significant role in whether heifers achieved a successful target heat-cycle weight.
Achieving the proper breeding weight for pre-pubertal beef heifers really boils down to feeding a well-balanced diet that meets their nutrient requirements for a calculated rate of gain. Many of these programs were often set up months ago, when these animals were newly weaned. Typically, average daily gains may vary for any group of replacement heifers, but growth performance should fall between 600 to 800 g (1.3 to 1.75 lbs.) per head per day for most of the common beef breeds.
Mainstream studies from various universities and agricultural extension agencies have consistently demonstrated that such recommended growth rates among replacement heifers do not have to be strictly adhered or be consistent for the entire time between weaning and the first breeding. The goal of good weight gains is only to help these heifers meet their absolute target weight by first breeding. Alternative flushing programs (short-term feeding of diets with an increased plane of nutrition) implemented for replacement heifers have been available to put bodyweight on thin or setback heifers, but have been met with limited success.
For the most part, keeping good growing heifers on a steady growth schedule is straightforward. To assist producers, one should keep updated records of each animal’s body condition score (BCS). A steady BCS of 2.5 –3.5 (1 = emaciated to 5 = obese) in the weaning-breeding period reflects desired steady growth and improves the likelihood of heifers achieving their target bodyweight and thus attain a strong signal of estrus for breeding.
In order to meet the above modest gains and the latter body condition scores; a typical heifer replacement diet should contain about 65 to 68 per cent TDN energy and about nine to 10 per cent protein with a suitable level of calcium (0.50 per cent) and phosphorus (0.25 per cent). In addition, a complimentary source of trace mineral-vitamins should fortify the chosen diet, along with salt and a free-choice source of water (including snow). At this point, these replacement animals (weaned last fall) during late winter (i. e.: February or March) might typically weigh anywhere from 270 –325 kg (595 to 716 lbs.) and should be consuming nutritious heifer rations on a dry matter basis at the rate of 2.3 to 2.6 percent of their bodyweight (re: 6.5 to 8.5 kg).
By no means do these pre-pubertal heifer rations need to be fancy nor complex. Consider the following common rations for starting 270 –325 kg replacement heifers with a BCS of 3.0, and gaining 600 –700 g (1.3 to 1.5 lbs.) per day. Based on current commodity prices all three rations should cost about $1 per head per day to feed:
6.5kgofmixedgrasshay 2.5 kg of barley
70 grams of 2:1 cattle mineral
15.0 kgofbarleysilage 3.0 kg of mixed alfalfa hay 70 grams of 1:1 cattle mineral
14.0kgofcornsilage 2.5 kg grass hay
1.0 kg corn distillers’ grains 70 grams of 1:1 cattle mineral
These sample rations are often post-weaning or existing overwintering rations, where slight adjustments are made to them, such as adding extra grain to increase the daily growth rate of a pen of heifers, or changing the cattle mineral to breeder type in order to facilitate estrus cycling. Complex feeding programs or drastic changes to existing replacement heifer programs are usually not warranted.
Because these rations are formulated specifically for replacement heifers, it sometimes makes sense that replacement heifers should be managed and fed as separate group away from the main cowherd. This is a good management practice that eliminates competition amongst animals of different ages and allows producers to provide a little extra care for the youngest or immature heifers during the breeding season.
Peter Vitti is an independent livestock nutritionist and consultant based in Winnipeg. To reach him call 204-254-7497 or by e-mail at [email protected]