By W. MARK HILTON, DVM
It may seem odd to discuss the spring breeding season in the middle of the winter, but what you do now can pay huge dividends come spring.
If you have open heifers to breed to calve at 22-24 months of age, there are things to do now to set them up for success. The old recommendation was to breed heifers at 65% of mature body weight. For a 1,400 pound cow – yes, that is likely the average for the Midwest – that is 910 pounds. That figure has been reduced to 58-60 percent of mature weight or 810-840 pounds. If you own a scale, now would be a great time to see how the heifers are doing. If they weigh 600 pounds on January 1 and you will breed them on June 15, they need to gain 240 pounds or about 1.5 pounds a day.. That should be quite easy with a ration of good quality hay, DDGS and a salt-vitamin-mineral mix with Rumensin. The key is to have them gaining weight in the month before breeding.
What we do not want is for the heifers on 1/1/24 to weigh below 500 pounds or over 700 pounds. The lightweight heifers will need a much higher energy ration to make it to the target, but the heavy heifers also present a problem.
Research at Purdue University and the University of Wyoming looked at heifers that were developed on a higher plane of nutrition during the winter and then had reduced energy intake closer to breeding. The results showed a significantly reduced conception rate compared to heifers that were grown more slowly and gaining near breeding.
If these overdeveloped heifers are turned out to grass a month or so before breeding and get no supplemental feed, they can actually lose weight due to the extremely high moisture content in spring grass.
If your heifers are too heavy right now and you are not breeding for a few months, kick them out on a cornfield that has been harvested and let them ‘survive’ for a month or so. Weigh them as they come off the crop residue grazing and figure a target gain to get them to 60 percent of mature body weight at breeding. Your nutritionist, extension educator or herd heath veterinarian should be able to help you formulate a balanced ration to help you hit your target for percent pregnant.
Speaking of targets, research done in Texas showed that a heifer that conceived in the first 21 days of the breeding season had a ROI (return on investment) of 10.7 percent. Those that conceived in the second and third 21-day periods had a ROI of -0.4 and -2.8 percent respectively. This and many other studies suggest that we should breed heifers for only 30-42 days. A late calving heifer becomes a late calving cow or an open cow and neither is good for your business.
In a typical herd, the nursing 2-year-olds have the highest percent open females. The top two reasons are (1) heifers calving late in their first year which we discussed above and (2) heifers calving too thin. Bred heifers are still growing and need more energy and protein than mature cows. Having them a bit ‘fleshy’ (target is Body Condition Score 6.5-7.0 at calving) gives them a bit of reserve so they don’t have to gain as many pounds post calving. I always encourage producers to ‘find a friend’ to Body Condition Score their cows. The owner sees their own cows too often and may not see them as too thin or too fat.
Bred heifers should not be fed with mature cows for three reasons. First, they have different nutrient needs as discussed previously. Second, mature cows will dominate the heifers and cause the heifers to eat less than they need (when they actually need more than the mature cows) and lastly if heifers and cows are wintered together neonatal calf disease increases by 3 times.
A goal of 95 percent pregnant females in 65 days with 65 percent of calves born by day 21 is an achievable goal. Having heifers developed correctly is a top priority in achieving reproductive efficiency.
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